[v7,8/9] ALSA: add new 32-bit layout for snd_pcm_mmap_status/control

Commit Message

Arnd Bergmann Dec. 11, 2019, 9:20 p.m. UTC

The snd_pcm_mmap_status and snd_pcm_mmap_control interfaces are one of the
trickiest areas to get right when moving to 64-bit time_t in user space.

The snd_pcm_mmap_status structure layout is incompatible with user space
that uses a 64-bit time_t, so we need a new layout for it. Since the
SNDRV_PCM_IOCTL_SYNC_PTR ioctl combines it with snd_pcm_mmap_control
into snd_pcm_sync_ptr, we need to change those two as well.

Both structures are also exported via an mmap() operation on certain
architectures, and this suffers from incompatibility between 32-bit
and 64-bit user space. As we have to change both structures anyway,
this is a good opportunity to fix the mmap() problem as well, so let's
standardize on the existing 64-bit layout of the structure where possible.

The downside is that we lose mmap() support for existing 32-bit x86 and
powerpc applications, adding that would introduce very noticeable runtime
overhead and complexity. My assumption here is that not too many people
will miss the removed feature, given that:

- Almost all x86 and powerpc users these days are on 64-bit kernels,
the majority of today's 32-bit users are on architectures that never
supported mmap (ARM, MIPS, ...).
- It never worked in compat mode (it was intentionally disabled there)
- The application already needs to work with a fallback to
SNDRV_PCM_IOCTL_SYNC_PTR, which will keep working with both the old
and new structure layout.

Both the ioctl() and mmap() based interfaces are changed at the same
time, as they are based on the same structures. Unlike other interfaces,
we change the uapi header to export both the traditional structure and
a version that is portable between 32-bit and 64-bit user space code
and that corresponds to the existing 64-bit layout. We further check the
__USE_TIME_BITS64 macro that will be defined by future C library versions
whenever we use the new time_t definition, so any existing user space
source code will not see any changes until it gets rebuilt against a new
C library. However, the new structures are all visible in addition to the
old ones, allowing applications to explicitly request the new structures.

In order to detect the difference between the old snd_pcm_mmap_status and
the new __snd_pcm_mmap_status64 structure from the ioctl command number,
we rely on one quirk in the structure definition: snd_pcm_mmap_status
must be aligned to alignof(time_t), which leads the compiler to insert
four bytes of padding in struct snd_pcm_sync_ptr after 'flags' and a
corresponding change in the size of snd_pcm_sync_ptr itself. On x86-32
(and only there), the compiler doesn't use 64-bit alignment in structure,
so I'm adding an explicit pad in the structure that has no effect on the
existing 64-bit architectures but ensures that the layout matches for x86.

The snd_pcm_uframes_t type compatibility requires another hack: we can't
easily make that 64 bit wide, so I leave the type as 'unsigned long',
but add padding before and after it, to ensure that the data is properly
aligned to the respective 64-bit field in the in-kernel structure.

For the SNDRV_PCM_MMAP_OFFSET_STATUS/CONTROL constants that are used
as the virtual file offset in the mmap() function, we also have to
introduce new constants that depend on hte __USE_TIME_BITS64 macro:
The existing macros are renamed to SNDRV_PCM_MMAP_OFFSET_STATUS_OLD
and SNDRV_PCM_MMAP_OFFSET_CONTROL_OLD, they continue to work fine on
64-bit architectures, but stop working on native 32-bit user space.
The replacement _NEW constants are now used by default for user space
built with __USE_TIME_BITS64, those now work on all new kernels for x86,
ppc and alpha (32 and 64 bit, native and compat). It might be a good idea
for a future alsa-lib to support both the _OLD and _NEW macros and use
the corresponding structures directly. Unmodified alsa-lib source code
will retain the current behavior, so it will no longer be able to use
mmap() for the status/control structures on 32-bit systems, until either
the C library gets updated to 64-bit time_t or alsa-lib gets updated to
support both mmap() layouts.

Co-developed-with: Baolin Wang <[e-mail]>
Signed-off-by: Baolin Wang <[e-mail]>
Signed-off-by: Arnd Bergmann <[e-mail]>
---
 include/uapi/sound/asound.h | 110 ++++++++++++++++++++++++++++++++----
 sound/core/pcm_compat.c     |  30 +++++-----
 sound/core/pcm_lib.c        |  10 ++--
 sound/core/pcm_native.c     |  38 ++++++++-----
 4 files changed, 147 insertions(+), 41 deletions(-)

Comments

Michael Forney Oct. 6, 2021, 5:49 p.m. UTC | #1

Arnd Bergmann <[e-mail]> wrote:
> +#if defined(__BYTE_ORDER) ? __BYTE_ORDER == __BIG_ENDIAN : defined(__BIG_ENDIAN)
> +typedef char __pad_before_uframe[sizeof(__u64) - sizeof(snd_pcm_uframes_t)];
> +typedef char __pad_after_uframe[0];
> +#endif
> +
> +#if defined(__BYTE_ORDER) ? __BYTE_ORDER == __LITTLE_ENDIAN : defined(__LITTLE_ENDIAN)
> +typedef char __pad_before_uframe[0];
> +typedef char __pad_after_uframe[sizeof(__u64) - sizeof(snd_pcm_uframes_t)];
> +#endif
> +
> +struct __snd_pcm_mmap_status64 {
> +	__s32 state;			/* RO: state - SNDRV_PCM_STATE_XXXX */
> +	__u32 pad1;			/* Needed for 64 bit alignment */
> +	__pad_before_uframe __pad1;
> +	snd_pcm_uframes_t hw_ptr;	/* RO: hw ptr (0...boundary-1) */
> +	__pad_after_uframe __pad2;
> +	struct __snd_timespec64 tstamp;	/* Timestamp */
> +	__s32 suspended_state;		/* RO: suspended stream state */
> +	__u32 pad3;			/* Needed for 64 bit alignment */
> +	struct __snd_timespec64 audio_tstamp; /* sample counter or wall clock */
> +};
> +
> +struct __snd_pcm_mmap_control64 {
> +	__pad_before_uframe __pad1;
> +	snd_pcm_uframes_t appl_ptr;	 /* RW: appl ptr (0...boundary-1) */
> +	__pad_before_uframe __pad2;

I was looking through this header and happened to notice that this
padding is wrong. I believe it should be __pad_after_uframe here.

I'm not sure of the implications of this typo, but I suspect it
breaks something on 32-bit systems with 64-bit time (regardless of
the endianness, since it changes the offset of avail_min).

> +
> +	__pad_before_uframe __pad3;
> +	snd_pcm_uframes_t  avail_min;	 /* RW: min available frames for wakeup */
> +	__pad_after_uframe __pad4;
> +};

Takashi Iwai Oct. 7, 2021, 10:52 a.m. UTC | #2

On Wed, 06 Oct 2021 19:49:17 +0200,
Michael Forney wrote:
> 
> Arnd Bergmann <[e-mail]> wrote:
> > +#if defined(__BYTE_ORDER) ? __BYTE_ORDER == __BIG_ENDIAN : defined(__BIG_ENDIAN)
> > +typedef char __pad_before_uframe[sizeof(__u64) - sizeof(snd_pcm_uframes_t)];
> > +typedef char __pad_after_uframe[0];
> > +#endif
> > +
> > +#if defined(__BYTE_ORDER) ? __BYTE_ORDER == __LITTLE_ENDIAN : defined(__LITTLE_ENDIAN)
> > +typedef char __pad_before_uframe[0];
> > +typedef char __pad_after_uframe[sizeof(__u64) - sizeof(snd_pcm_uframes_t)];
> > +#endif
> > +
> > +struct __snd_pcm_mmap_status64 {
> > +	__s32 state;			/* RO: state - SNDRV_PCM_STATE_XXXX */
> > +	__u32 pad1;			/* Needed for 64 bit alignment */
> > +	__pad_before_uframe __pad1;
> > +	snd_pcm_uframes_t hw_ptr;	/* RO: hw ptr (0...boundary-1) */
> > +	__pad_after_uframe __pad2;
> > +	struct __snd_timespec64 tstamp;	/* Timestamp */
> > +	__s32 suspended_state;		/* RO: suspended stream state */
> > +	__u32 pad3;			/* Needed for 64 bit alignment */
> > +	struct __snd_timespec64 audio_tstamp; /* sample counter or wall clock */
> > +};
> > +
> > +struct __snd_pcm_mmap_control64 {
> > +	__pad_before_uframe __pad1;
> > +	snd_pcm_uframes_t appl_ptr;	 /* RW: appl ptr (0...boundary-1) */
> > +	__pad_before_uframe __pad2;
> 
> I was looking through this header and happened to notice that this
> padding is wrong. I believe it should be __pad_after_uframe here.
> 
> I'm not sure of the implications of this typo, but I suspect it
> breaks something on 32-bit systems with 64-bit time (regardless of
> the endianness, since it changes the offset of avail_min).

Right, that's the expected breakage.  It seems that the 64bit time on
32bit arch is still rare, so we haven't heard a regression by that, so
far...

In anyway, care to send a formal fix patch?

Thanks for catching this!


Takashi

Arnd Bergmann Oct. 7, 2021, 11:48 a.m. UTC | #3

On Thu, Oct 7, 2021 at 12:53 PM Takashi Iwai <[e-mail]> wrote:
> On Wed, 06 Oct 2021 19:49:17 +0200, Michael Forney wrote:
> >
> > Arnd Bergmann <[e-mail]> wrote:
> > > +#if defined(__BYTE_ORDER) ? __BYTE_ORDER == __BIG_ENDIAN : defined(__BIG_ENDIAN)
> > > +typedef char __pad_before_uframe[sizeof(__u64) - sizeof(snd_pcm_uframes_t)];
> > > +typedef char __pad_after_uframe[0];
> > > +#endif
> > > +
> > > +#if defined(__BYTE_ORDER) ? __BYTE_ORDER == __LITTLE_ENDIAN : defined(__LITTLE_ENDIAN)
> > > +typedef char __pad_before_uframe[0];
> > > +typedef char __pad_after_uframe[sizeof(__u64) - sizeof(snd_pcm_uframes_t)];
> > > +#endif
> > > +
> > > +struct __snd_pcm_mmap_status64 {
> > > +   __s32 state;                    /* RO: state - SNDRV_PCM_STATE_XXXX */
> > > +   __u32 pad1;                     /* Needed for 64 bit alignment */
> > > +   __pad_before_uframe __pad1;
> > > +   snd_pcm_uframes_t hw_ptr;       /* RO: hw ptr (0...boundary-1) */
> > > +   __pad_after_uframe __pad2;
> > > +   struct __snd_timespec64 tstamp; /* Timestamp */
> > > +   __s32 suspended_state;          /* RO: suspended stream state */
> > > +   __u32 pad3;                     /* Needed for 64 bit alignment */
> > > +   struct __snd_timespec64 audio_tstamp; /* sample counter or wall clock */
> > > +};
> > > +
> > > +struct __snd_pcm_mmap_control64 {
> > > +   __pad_before_uframe __pad1;
> > > +   snd_pcm_uframes_t appl_ptr;      /* RW: appl ptr (0...boundary-1) */
> > > +   __pad_before_uframe __pad2;
> >
> > I was looking through this header and happened to notice that this
> > padding is wrong. I believe it should be __pad_after_uframe here.
> >
> > I'm not sure of the implications of this typo, but I suspect it
> > breaks something on 32-bit systems with 64-bit time (regardless of
> > the endianness, since it changes the offset of avail_min).

Thanks a lot for the report! Yes, this is definitely broken in some ways.

> Right, that's the expected breakage.  It seems that the 64bit time on
> 32bit arch is still rare, so we haven't heard a regression by that, so
> far...

It might actually be worse: on a native 32-bit kernel, both user space
and kernel see the same broken definition with a 64-bit time_t, which
would end up actually making it work as expected. However, in
compat mode, the layout seen on the 32-bit user space is now
different from what the 64-bit kernel has, which would in turn not
work, in both the SNDRV_PCM_IOCTL_SYNC_PTR ioctl and in
the mmap() interface.

Fixing the layout to look like the way we had intended would make
newly compiled applications work in compat mode, but would break
applications built against the old header on new kernels and also
newly built applications on old kernels.

I still hope I missed something and it's not quite that bad, but I
fear the best we can do in this case make the broken interface
the normative one and fixing compat mode to write
mmap_control64->avail_min in the wrong location for
SNDRV_PCM_IOCTL_SYNC_PTR, as well as disabling
the mmap() interface again for compat tasks.

As far as I can tell, the broken interface will always result in
user space seeing a zero value for "avail_min". Can you
make a prediction what that would mean for actual
applications? Will they have no audio output, run into
a crash, or be able to use recover and appear to work normally
here?

       Arnd

Takashi Iwai Oct. 7, 2021, 12:43 p.m. UTC | #4

On Thu, 07 Oct 2021 13:48:44 +0200,
Arnd Bergmann wrote:
> 
> On Thu, Oct 7, 2021 at 12:53 PM Takashi Iwai <[e-mail]> wrote:
> > On Wed, 06 Oct 2021 19:49:17 +0200, Michael Forney wrote:
> > >
> > > Arnd Bergmann <[e-mail]> wrote:
> > > > +#if defined(__BYTE_ORDER) ? __BYTE_ORDER == __BIG_ENDIAN : defined(__BIG_ENDIAN)
> > > > +typedef char __pad_before_uframe[sizeof(__u64) - sizeof(snd_pcm_uframes_t)];
> > > > +typedef char __pad_after_uframe[0];
> > > > +#endif
> > > > +
> > > > +#if defined(__BYTE_ORDER) ? __BYTE_ORDER == __LITTLE_ENDIAN : defined(__LITTLE_ENDIAN)
> > > > +typedef char __pad_before_uframe[0];
> > > > +typedef char __pad_after_uframe[sizeof(__u64) - sizeof(snd_pcm_uframes_t)];
> > > > +#endif
> > > > +
> > > > +struct __snd_pcm_mmap_status64 {
> > > > +   __s32 state;                    /* RO: state - SNDRV_PCM_STATE_XXXX */
> > > > +   __u32 pad1;                     /* Needed for 64 bit alignment */
> > > > +   __pad_before_uframe __pad1;
> > > > +   snd_pcm_uframes_t hw_ptr;       /* RO: hw ptr (0...boundary-1) */
> > > > +   __pad_after_uframe __pad2;
> > > > +   struct __snd_timespec64 tstamp; /* Timestamp */
> > > > +   __s32 suspended_state;          /* RO: suspended stream state */
> > > > +   __u32 pad3;                     /* Needed for 64 bit alignment */
> > > > +   struct __snd_timespec64 audio_tstamp; /* sample counter or wall clock */
> > > > +};
> > > > +
> > > > +struct __snd_pcm_mmap_control64 {
> > > > +   __pad_before_uframe __pad1;
> > > > +   snd_pcm_uframes_t appl_ptr;      /* RW: appl ptr (0...boundary-1) */
> > > > +   __pad_before_uframe __pad2;
> > >
> > > I was looking through this header and happened to notice that this
> > > padding is wrong. I believe it should be __pad_after_uframe here.
> > >
> > > I'm not sure of the implications of this typo, but I suspect it
> > > breaks something on 32-bit systems with 64-bit time (regardless of
> > > the endianness, since it changes the offset of avail_min).
> 
> Thanks a lot for the report! Yes, this is definitely broken in some ways.
> 
> > Right, that's the expected breakage.  It seems that the 64bit time on
> > 32bit arch is still rare, so we haven't heard a regression by that, so
> > far...
> 
> It might actually be worse: on a native 32-bit kernel, both user space
> and kernel see the same broken definition with a 64-bit time_t, which
> would end up actually making it work as expected. However, in
> compat mode, the layout seen on the 32-bit user space is now
> different from what the 64-bit kernel has, which would in turn not
> work, in both the SNDRV_PCM_IOCTL_SYNC_PTR ioctl and in
> the mmap() interface.
> 
> Fixing the layout to look like the way we had intended would make
> newly compiled applications work in compat mode, but would break
> applications built against the old header on new kernels and also
> newly built applications on old kernels.
> 
> I still hope I missed something and it's not quite that bad, but I
> fear the best we can do in this case make the broken interface
> the normative one and fixing compat mode to write
> mmap_control64->avail_min in the wrong location for
> SNDRV_PCM_IOCTL_SYNC_PTR, as well as disabling
> the mmap() interface again for compat tasks.
>
> As far as I can tell, the broken interface will always result in
> user space seeing a zero value for "avail_min". Can you
> make a prediction what that would mean for actual
> applications? Will they have no audio output, run into
> a crash, or be able to use recover and appear to work normally
> here?

No, fortunately it's only about control->avail_min, and fiddling this
value can't break severely (otherwise it'd be a security problem ;)

In the buggy condition, it's always zero, and the kernel treated as if
1, i.e. wake up as soon as data is available, which is OK-ish for most
applications.   Apps usually don't care about the wake-up condition so
much.  There are subtle difference and may influence on the stability
of stream processing, but the stability usually depends more strongly
on the hardware and software configurations.

That being said, the impact by this bug (from the application behavior
POV) is likely quite small, but the contamination is large; as you
pointed out, it's much larger than I thought.

The definition in uapi/sound/asound.h is a bit cryptic, but IIUC,
__snd_pcm_mmap_control64 is used for 64bit archs, right?  If so, the
problem rather hits more widely on 64bit archs silently.  Then, the
influence by this bug must be almost negligible, as we've had no bug
report about the behavior change.

We may just fix it in kernel and for new library with hoping that no
one sees the actual problem.  Or, we may provide a complete new set of
mmap offsets and ioctl to cover both broken and fixed interfaces...
The decision depends on how perfectly we'd like to address the bug.
As of now, I'm inclined to go for the former, but I'm open for more
opinions.


thanks,

Takashi

Takashi Iwai Oct. 7, 2021, 1:02 p.m. UTC | #5

On Thu, 07 Oct 2021 14:43:53 +0200,
Takashi Iwai wrote:
> 
> On Thu, 07 Oct 2021 13:48:44 +0200,
> Arnd Bergmann wrote:
> > 
> > On Thu, Oct 7, 2021 at 12:53 PM Takashi Iwai <[e-mail]> wrote:
> > > On Wed, 06 Oct 2021 19:49:17 +0200, Michael Forney wrote:
> > > >
> > > > Arnd Bergmann <[e-mail]> wrote:
> > > > > +#if defined(__BYTE_ORDER) ? __BYTE_ORDER == __BIG_ENDIAN : defined(__BIG_ENDIAN)
> > > > > +typedef char __pad_before_uframe[sizeof(__u64) - sizeof(snd_pcm_uframes_t)];
> > > > > +typedef char __pad_after_uframe[0];
> > > > > +#endif
> > > > > +
> > > > > +#if defined(__BYTE_ORDER) ? __BYTE_ORDER == __LITTLE_ENDIAN : defined(__LITTLE_ENDIAN)
> > > > > +typedef char __pad_before_uframe[0];
> > > > > +typedef char __pad_after_uframe[sizeof(__u64) - sizeof(snd_pcm_uframes_t)];
> > > > > +#endif
> > > > > +
> > > > > +struct __snd_pcm_mmap_status64 {
> > > > > +   __s32 state;                    /* RO: state - SNDRV_PCM_STATE_XXXX */
> > > > > +   __u32 pad1;                     /* Needed for 64 bit alignment */
> > > > > +   __pad_before_uframe __pad1;
> > > > > +   snd_pcm_uframes_t hw_ptr;       /* RO: hw ptr (0...boundary-1) */
> > > > > +   __pad_after_uframe __pad2;
> > > > > +   struct __snd_timespec64 tstamp; /* Timestamp */
> > > > > +   __s32 suspended_state;          /* RO: suspended stream state */
> > > > > +   __u32 pad3;                     /* Needed for 64 bit alignment */
> > > > > +   struct __snd_timespec64 audio_tstamp; /* sample counter or wall clock */
> > > > > +};
> > > > > +
> > > > > +struct __snd_pcm_mmap_control64 {
> > > > > +   __pad_before_uframe __pad1;
> > > > > +   snd_pcm_uframes_t appl_ptr;      /* RW: appl ptr (0...boundary-1) */
> > > > > +   __pad_before_uframe __pad2;
> > > >
> > > > I was looking through this header and happened to notice that this
> > > > padding is wrong. I believe it should be __pad_after_uframe here.
> > > >
> > > > I'm not sure of the implications of this typo, but I suspect it
> > > > breaks something on 32-bit systems with 64-bit time (regardless of
> > > > the endianness, since it changes the offset of avail_min).
> > 
> > Thanks a lot for the report! Yes, this is definitely broken in some ways.
> > 
> > > Right, that's the expected breakage.  It seems that the 64bit time on
> > > 32bit arch is still rare, so we haven't heard a regression by that, so
> > > far...
> > 
> > It might actually be worse: on a native 32-bit kernel, both user space
> > and kernel see the same broken definition with a 64-bit time_t, which
> > would end up actually making it work as expected. However, in
> > compat mode, the layout seen on the 32-bit user space is now
> > different from what the 64-bit kernel has, which would in turn not
> > work, in both the SNDRV_PCM_IOCTL_SYNC_PTR ioctl and in
> > the mmap() interface.
> > 
> > Fixing the layout to look like the way we had intended would make
> > newly compiled applications work in compat mode, but would break
> > applications built against the old header on new kernels and also
> > newly built applications on old kernels.
> > 
> > I still hope I missed something and it's not quite that bad, but I
> > fear the best we can do in this case make the broken interface
> > the normative one and fixing compat mode to write
> > mmap_control64->avail_min in the wrong location for
> > SNDRV_PCM_IOCTL_SYNC_PTR, as well as disabling
> > the mmap() interface again for compat tasks.
> >
> > As far as I can tell, the broken interface will always result in
> > user space seeing a zero value for "avail_min". Can you
> > make a prediction what that would mean for actual
> > applications? Will they have no audio output, run into
> > a crash, or be able to use recover and appear to work normally
> > here?
> 
> No, fortunately it's only about control->avail_min, and fiddling this
> value can't break severely (otherwise it'd be a security problem ;)
> 
> In the buggy condition, it's always zero, and the kernel treated as if
> 1, i.e. wake up as soon as data is available, which is OK-ish for most
> applications.   Apps usually don't care about the wake-up condition so
> much.  There are subtle difference and may influence on the stability
> of stream processing, but the stability usually depends more strongly
> on the hardware and software configurations.
> 
> That being said, the impact by this bug (from the application behavior
> POV) is likely quite small, but the contamination is large; as you
> pointed out, it's much larger than I thought.
> 
> The definition in uapi/sound/asound.h is a bit cryptic, but IIUC,
> __snd_pcm_mmap_control64 is used for 64bit archs, right?  If so, the
> problem rather hits more widely on 64bit archs silently.  Then, the
> influence by this bug must be almost negligible, as we've had no bug
> report about the behavior change.

Erm, scratch this part: on 64bit arch, both __pad_before_uframe and
__pad_after_uframe is 0-size, so the bug doesn't hit.  It's only about
32bit arch.

> We may just fix it in kernel and for new library with hoping that no
> one sees the actual problem.  Or, we may provide a complete new set of
> mmap offsets and ioctl to cover both broken and fixed interfaces...
> The decision depends on how perfectly we'd like to address the bug.
> As of now, I'm inclined to go for the former, but I'm open for more
> opinions.


Takashi

Arnd Bergmann Oct. 7, 2021, 1:11 p.m. UTC | #6

On Thu, Oct 7, 2021 at 2:43 PM Takashi Iwai <[e-mail]> wrote:
> On Thu, 07 Oct 2021 13:48:44 +0200, Arnd Bergmann wrote:
> > On Thu, Oct 7, 2021 at 12:53 PM Takashi Iwai <[e-mail]> wrote:
> > > On Wed, 06 Oct 2021 19:49:17 +0200, Michael Forney wrote:
> >
> > As far as I can tell, the broken interface will always result in
> > user space seeing a zero value for "avail_min". Can you
> > make a prediction what that would mean for actual
> > applications? Will they have no audio output, run into
> > a crash, or be able to use recover and appear to work normally
> > here?
>
> No, fortunately it's only about control->avail_min, and fiddling this
> value can't break severely (otherwise it'd be a security problem ;)
>
> In the buggy condition, it's always zero, and the kernel treated as if
> 1, i.e. wake up as soon as data is available, which is OK-ish for most
> applications.   Apps usually don't care about the wake-up condition so
> much.  There are subtle difference and may influence on the stability
> of stream processing, but the stability usually depends more strongly
> on the hardware and software configurations.
>
> That being said, the impact by this bug (from the application behavior
> POV) is likely quite small, but the contamination is large; as you
> pointed out, it's much larger than I thought.

Ok, got it.

> The definition in uapi/sound/asound.h is a bit cryptic, but IIUC,
> __snd_pcm_mmap_control64 is used for 64bit archs, right?  If so, the
> problem rather hits more widely on 64bit archs silently.  Then, the
> influence by this bug must be almost negligible, as we've had no bug
> report about the behavior change.

While __snd_pcm_mmap_control64 is only used on 32-bit
architectures when 64-bit time_t is used. At the moment, this
means all users of musl-1.2.x libc, but not glibc.

On 64-bit architectures, __snd_pcm_mmap_control and
__snd_pcm_mmap_control64 are meant to be identical,
and this is actually true regardless of the bug, since
__pad_before_uframe and __pad_after_uframe both
end up as zero-length arrays here.

> We may just fix it in kernel and for new library with hoping that no
> one sees the actual problem.  Or, we may provide a complete new set of
> mmap offsets and ioctl to cover both broken and fixed interfaces...
> The decision depends on how perfectly we'd like to address the bug.
> As of now, I'm inclined to go for the former, but I'm open for more
> opinions.

Adding the musl list to Cc for additional testers, anyone interested
please see [1] for the original report.

It would be good to hear from musl users that are already using
audio support with 32-bit applications on 64-bit kernels, which
is the case that has the problem today. Have you noticed any
problems with audio support here? If not, we can probably
"fix" the kernel here and make the existing binaries behave
the same way on 32-bit kernels. If there are applications that
don't work in that environment today, I think we need to instead
change the kernel to accept the currently broken format on
both 32-bit and 64-bit kernels, possibly introducing yet another
format that works as originally intended but requires a newly
built kernel.

      Arnd

[1] https://lore.kernel.org/all/[e-mail]/

Takashi Iwai Oct. 7, 2021, 3:33 p.m. UTC | #7

On Thu, 07 Oct 2021 15:11:00 +0200,
Arnd Bergmann wrote:
> 
>  On Thu, Oct 7, 2021 at 2:43 PM Takashi Iwai <[e-mail]> wrote:
> > On Thu, 07 Oct 2021 13:48:44 +0200, Arnd Bergmann wrote:
> > > On Thu, Oct 7, 2021 at 12:53 PM Takashi Iwai <[e-mail]> wrote:
> > > > On Wed, 06 Oct 2021 19:49:17 +0200, Michael Forney wrote:
> > >
> > > As far as I can tell, the broken interface will always result in
> > > user space seeing a zero value for "avail_min". Can you
> > > make a prediction what that would mean for actual
> > > applications? Will they have no audio output, run into
> > > a crash, or be able to use recover and appear to work normally
> > > here?
> >
> > No, fortunately it's only about control->avail_min, and fiddling this
> > value can't break severely (otherwise it'd be a security problem ;)
> >
> > In the buggy condition, it's always zero, and the kernel treated as if
> > 1, i.e. wake up as soon as data is available, which is OK-ish for most
> > applications.   Apps usually don't care about the wake-up condition so
> > much.  There are subtle difference and may influence on the stability
> > of stream processing, but the stability usually depends more strongly
> > on the hardware and software configurations.
> >
> > That being said, the impact by this bug (from the application behavior
> > POV) is likely quite small, but the contamination is large; as you
> > pointed out, it's much larger than I thought.
> 
> Ok, got it.
> 
> > The definition in uapi/sound/asound.h is a bit cryptic, but IIUC,
> > __snd_pcm_mmap_control64 is used for 64bit archs, right?  If so, the
> > problem rather hits more widely on 64bit archs silently.  Then, the
> > influence by this bug must be almost negligible, as we've had no bug
> > report about the behavior change.
> 
> While __snd_pcm_mmap_control64 is only used on 32-bit
> architectures when 64-bit time_t is used. At the moment, this
> means all users of musl-1.2.x libc, but not glibc.
> 
> On 64-bit architectures, __snd_pcm_mmap_control and
> __snd_pcm_mmap_control64 are meant to be identical,
> and this is actually true regardless of the bug, since
> __pad_before_uframe and __pad_after_uframe both
> end up as zero-length arrays here.
> 
> > We may just fix it in kernel and for new library with hoping that no
> > one sees the actual problem.  Or, we may provide a complete new set of
> > mmap offsets and ioctl to cover both broken and fixed interfaces...
> > The decision depends on how perfectly we'd like to address the bug.
> > As of now, I'm inclined to go for the former, but I'm open for more
> > opinions.
> 
> Adding the musl list to Cc for additional testers, anyone interested
> please see [1] for the original report.
> 
> It would be good to hear from musl users that are already using
> audio support with 32-bit applications on 64-bit kernels, which
> is the case that has the problem today. Have you noticed any
> problems with audio support here? If not, we can probably
> "fix" the kernel here and make the existing binaries behave
> the same way on 32-bit kernels. If there are applications that
> don't work in that environment today, I think we need to instead
> change the kernel to accept the currently broken format on
> both 32-bit and 64-bit kernels, possibly introducing yet another
> format that works as originally intended but requires a newly
> built kernel.

Thanks!

And now, looking more deeply, I feel more desperate.

This bug makes the expected padding gone on little-endian.
On LE 32bit, the buggy definition is:

	char __pad1[0];
	u32 appl_ptr;
	char __pad2[0]; // this should have been [4]
	char __pad3[0];
	u32 avail_min;
	char __pad4[4];
	
When an application issues SYNC_PTR64 ioctl to submit appl_ptr and
avail_min updates, 64bit kernel (in compat mode) reads directly as:

	u64 appl_ptr;
	u64 avail_min;

Hence a bogus appl_ptr would be passed if avail_min != 0.
And usually application sets non-zero avail_min.
That is, the bug must hit more severely if the new API were really
used.  It wouldn't crash, but some weird streaming behavior can
happen like noise, jumping or underruns.

(Reading back avail_min=0 to user-space is rather harmless.  Ditto for
 the case of BE, then at least there is no appl_ptr corruption.)

This made me wonder which way to go:
it's certainly possible to fix the new kernel to treat both buggy and
sane formats (disabling compat mmap and re-define ioctls, having the
code for old APIs).  The problem is, however, in the case where the
application needs to run on the older kernel that expects the buggy
format.  Then apps would still have to send in the old buggy format --
or maybe better in the older 32bit format that won't hit the bug
above.  It makes situation more complicated.

Do we know how widely the __USE_TIME_BITS64 is deployed nowadays?


Takashi

Rich Felker Oct. 7, 2021, 4:06 p.m. UTC | #8

On Thu, Oct 07, 2021 at 05:33:19PM +0200, Takashi Iwai wrote:
> On Thu, 07 Oct 2021 15:11:00 +0200,
> Arnd Bergmann wrote:
> > 
> >  On Thu, Oct 7, 2021 at 2:43 PM Takashi Iwai <[e-mail]> wrote:
> > > On Thu, 07 Oct 2021 13:48:44 +0200, Arnd Bergmann wrote:
> > > > On Thu, Oct 7, 2021 at 12:53 PM Takashi Iwai <[e-mail]> wrote:
> > > > > On Wed, 06 Oct 2021 19:49:17 +0200, Michael Forney wrote:
> > > >
> > > > As far as I can tell, the broken interface will always result in
> > > > user space seeing a zero value for "avail_min". Can you
> > > > make a prediction what that would mean for actual
> > > > applications? Will they have no audio output, run into
> > > > a crash, or be able to use recover and appear to work normally
> > > > here?
> > >
> > > No, fortunately it's only about control->avail_min, and fiddling this
> > > value can't break severely (otherwise it'd be a security problem ;)
> > >
> > > In the buggy condition, it's always zero, and the kernel treated as if
> > > 1, i.e. wake up as soon as data is available, which is OK-ish for most
> > > applications.   Apps usually don't care about the wake-up condition so
> > > much.  There are subtle difference and may influence on the stability
> > > of stream processing, but the stability usually depends more strongly
> > > on the hardware and software configurations.
> > >
> > > That being said, the impact by this bug (from the application behavior
> > > POV) is likely quite small, but the contamination is large; as you
> > > pointed out, it's much larger than I thought.
> > 
> > Ok, got it.
> > 
> > > The definition in uapi/sound/asound.h is a bit cryptic, but IIUC,
> > > __snd_pcm_mmap_control64 is used for 64bit archs, right?  If so, the
> > > problem rather hits more widely on 64bit archs silently.  Then, the
> > > influence by this bug must be almost negligible, as we've had no bug
> > > report about the behavior change.
> > 
> > While __snd_pcm_mmap_control64 is only used on 32-bit
> > architectures when 64-bit time_t is used. At the moment, this
> > means all users of musl-1.2.x libc, but not glibc.
> > 
> > On 64-bit architectures, __snd_pcm_mmap_control and
> > __snd_pcm_mmap_control64 are meant to be identical,
> > and this is actually true regardless of the bug, since
> > __pad_before_uframe and __pad_after_uframe both
> > end up as zero-length arrays here.
> > 
> > > We may just fix it in kernel and for new library with hoping that no
> > > one sees the actual problem.  Or, we may provide a complete new set of
> > > mmap offsets and ioctl to cover both broken and fixed interfaces...
> > > The decision depends on how perfectly we'd like to address the bug.
> > > As of now, I'm inclined to go for the former, but I'm open for more
> > > opinions.
> > 
> > Adding the musl list to Cc for additional testers, anyone interested
> > please see [1] for the original report.
> > 
> > It would be good to hear from musl users that are already using
> > audio support with 32-bit applications on 64-bit kernels, which
> > is the case that has the problem today. Have you noticed any
> > problems with audio support here? If not, we can probably
> > "fix" the kernel here and make the existing binaries behave
> > the same way on 32-bit kernels. If there are applications that
> > don't work in that environment today, I think we need to instead
> > change the kernel to accept the currently broken format on
> > both 32-bit and 64-bit kernels, possibly introducing yet another
> > format that works as originally intended but requires a newly
> > built kernel.
> 
> Thanks!
> 
> And now, looking more deeply, I feel more desperate.
> 
> This bug makes the expected padding gone on little-endian.
> On LE 32bit, the buggy definition is:
> 
> 	char __pad1[0];
> 	u32 appl_ptr;
> 	char __pad2[0]; // this should have been [4]
> 	char __pad3[0];
> 	u32 avail_min;
> 	char __pad4[4];
> 	
> When an application issues SYNC_PTR64 ioctl to submit appl_ptr and
> avail_min updates, 64bit kernel (in compat mode) reads directly as:
> 
> 	u64 appl_ptr;
> 	u64 avail_min;
> 
> Hence a bogus appl_ptr would be passed if avail_min != 0.
> And usually application sets non-zero avail_min.
> That is, the bug must hit more severely if the new API were really
> used.  It wouldn't crash, but some weird streaming behavior can
> happen like noise, jumping or underruns.
> 
> (Reading back avail_min=0 to user-space is rather harmless.  Ditto for
>  the case of BE, then at least there is no appl_ptr corruption.)
> 
> This made me wonder which way to go:
> it's certainly possible to fix the new kernel to treat both buggy and
> sane formats (disabling compat mmap and re-define ioctls, having the
> code for old APIs).  The problem is, however, in the case where the
> application needs to run on the older kernel that expects the buggy
> format.  Then apps would still have to send in the old buggy format --
> or maybe better in the older 32bit format that won't hit the bug
> above.  It makes situation more complicated.

Can't an ioctl number just be redefined so that, on old kernels with
the buggy one, newly built applications get told that mmap is not
available and use the unaffected non-mmap fallback?

> Do we know how widely the __USE_TIME_BITS64 is deployed nowadays?

Anyone using musl on 32-bit archs who's not >=2 years behind current.

Rich

Takashi Iwai Oct. 7, 2021, 4:18 p.m. UTC | #9

On Thu, 07 Oct 2021 18:06:36 +0200,
Rich Felker wrote:
> 
> On Thu, Oct 07, 2021 at 05:33:19PM +0200, Takashi Iwai wrote:
> > On Thu, 07 Oct 2021 15:11:00 +0200,
> > Arnd Bergmann wrote:
> > > 
> > >  On Thu, Oct 7, 2021 at 2:43 PM Takashi Iwai <[e-mail]> wrote:
> > > > On Thu, 07 Oct 2021 13:48:44 +0200, Arnd Bergmann wrote:
> > > > > On Thu, Oct 7, 2021 at 12:53 PM Takashi Iwai <[e-mail]> wrote:
> > > > > > On Wed, 06 Oct 2021 19:49:17 +0200, Michael Forney wrote:
> > > > >
> > > > > As far as I can tell, the broken interface will always result in
> > > > > user space seeing a zero value for "avail_min". Can you
> > > > > make a prediction what that would mean for actual
> > > > > applications? Will they have no audio output, run into
> > > > > a crash, or be able to use recover and appear to work normally
> > > > > here?
> > > >
> > > > No, fortunately it's only about control->avail_min, and fiddling this
> > > > value can't break severely (otherwise it'd be a security problem ;)
> > > >
> > > > In the buggy condition, it's always zero, and the kernel treated as if
> > > > 1, i.e. wake up as soon as data is available, which is OK-ish for most
> > > > applications.   Apps usually don't care about the wake-up condition so
> > > > much.  There are subtle difference and may influence on the stability
> > > > of stream processing, but the stability usually depends more strongly
> > > > on the hardware and software configurations.
> > > >
> > > > That being said, the impact by this bug (from the application behavior
> > > > POV) is likely quite small, but the contamination is large; as you
> > > > pointed out, it's much larger than I thought.
> > > 
> > > Ok, got it.
> > > 
> > > > The definition in uapi/sound/asound.h is a bit cryptic, but IIUC,
> > > > __snd_pcm_mmap_control64 is used for 64bit archs, right?  If so, the
> > > > problem rather hits more widely on 64bit archs silently.  Then, the
> > > > influence by this bug must be almost negligible, as we've had no bug
> > > > report about the behavior change.
> > > 
> > > While __snd_pcm_mmap_control64 is only used on 32-bit
> > > architectures when 64-bit time_t is used. At the moment, this
> > > means all users of musl-1.2.x libc, but not glibc.
> > > 
> > > On 64-bit architectures, __snd_pcm_mmap_control and
> > > __snd_pcm_mmap_control64 are meant to be identical,
> > > and this is actually true regardless of the bug, since
> > > __pad_before_uframe and __pad_after_uframe both
> > > end up as zero-length arrays here.
> > > 
> > > > We may just fix it in kernel and for new library with hoping that no
> > > > one sees the actual problem.  Or, we may provide a complete new set of
> > > > mmap offsets and ioctl to cover both broken and fixed interfaces...
> > > > The decision depends on how perfectly we'd like to address the bug.
> > > > As of now, I'm inclined to go for the former, but I'm open for more
> > > > opinions.
> > > 
> > > Adding the musl list to Cc for additional testers, anyone interested
> > > please see [1] for the original report.
> > > 
> > > It would be good to hear from musl users that are already using
> > > audio support with 32-bit applications on 64-bit kernels, which
> > > is the case that has the problem today. Have you noticed any
> > > problems with audio support here? If not, we can probably
> > > "fix" the kernel here and make the existing binaries behave
> > > the same way on 32-bit kernels. If there are applications that
> > > don't work in that environment today, I think we need to instead
> > > change the kernel to accept the currently broken format on
> > > both 32-bit and 64-bit kernels, possibly introducing yet another
> > > format that works as originally intended but requires a newly
> > > built kernel.
> > 
> > Thanks!
> > 
> > And now, looking more deeply, I feel more desperate.
> > 
> > This bug makes the expected padding gone on little-endian.
> > On LE 32bit, the buggy definition is:
> > 
> > 	char __pad1[0];
> > 	u32 appl_ptr;
> > 	char __pad2[0]; // this should have been [4]
> > 	char __pad3[0];
> > 	u32 avail_min;
> > 	char __pad4[4];
> > 	
> > When an application issues SYNC_PTR64 ioctl to submit appl_ptr and
> > avail_min updates, 64bit kernel (in compat mode) reads directly as:
> > 
> > 	u64 appl_ptr;
> > 	u64 avail_min;
> > 
> > Hence a bogus appl_ptr would be passed if avail_min != 0.
> > And usually application sets non-zero avail_min.
> > That is, the bug must hit more severely if the new API were really
> > used.  It wouldn't crash, but some weird streaming behavior can
> > happen like noise, jumping or underruns.
> > 
> > (Reading back avail_min=0 to user-space is rather harmless.  Ditto for
> >  the case of BE, then at least there is no appl_ptr corruption.)
> > 
> > This made me wonder which way to go:
> > it's certainly possible to fix the new kernel to treat both buggy and
> > sane formats (disabling compat mmap and re-define ioctls, having the
> > code for old APIs).  The problem is, however, in the case where the
> > application needs to run on the older kernel that expects the buggy
> > format.  Then apps would still have to send in the old buggy format --
> > or maybe better in the older 32bit format that won't hit the bug
> > above.  It makes situation more complicated.
> 
> Can't an ioctl number just be redefined so that, on old kernels with
> the buggy one, newly built applications get told that mmap is not
> available and use the unaffected non-mmap fallback?

The problem is that the SYNC_PTR64 ioctl itself for non-mmap fallback
is equally buggy due to this bug, too.  So disabling mmap doesn't help
alone.

And, yes, we can redefine ioctl numbers.  But, then, application would
have to be bilingual, as well as the kernel; it'll have to switch back
to old API when running on older kernel, while the same binary would
need to run in a new API for a newer kernel.

Maybe we can implement it in alsa-lib, if it really worth for it.

> > Do we know how widely the __USE_TIME_BITS64 is deployed nowadays?
> 
> Anyone using musl on 32-bit archs who's not >=2 years behind current.

OK.


Takashi

Rich Felker Oct. 7, 2021, 4:51 p.m. UTC | #10

On Thu, Oct 07, 2021 at 06:18:52PM +0200, Takashi Iwai wrote:
> On Thu, 07 Oct 2021 18:06:36 +0200,
> Rich Felker wrote:
> > 
> > On Thu, Oct 07, 2021 at 05:33:19PM +0200, Takashi Iwai wrote:
> > > On Thu, 07 Oct 2021 15:11:00 +0200,
> > > Arnd Bergmann wrote:
> > > > 
> > > >  On Thu, Oct 7, 2021 at 2:43 PM Takashi Iwai <[e-mail]> wrote:
> > > > > On Thu, 07 Oct 2021 13:48:44 +0200, Arnd Bergmann wrote:
> > > > > > On Thu, Oct 7, 2021 at 12:53 PM Takashi Iwai <[e-mail]> wrote:
> > > > > > > On Wed, 06 Oct 2021 19:49:17 +0200, Michael Forney wrote:
> > > > > >
> > > > > > As far as I can tell, the broken interface will always result in
> > > > > > user space seeing a zero value for "avail_min". Can you
> > > > > > make a prediction what that would mean for actual
> > > > > > applications? Will they have no audio output, run into
> > > > > > a crash, or be able to use recover and appear to work normally
> > > > > > here?
> > > > >
> > > > > No, fortunately it's only about control->avail_min, and fiddling this
> > > > > value can't break severely (otherwise it'd be a security problem ;)
> > > > >
> > > > > In the buggy condition, it's always zero, and the kernel treated as if
> > > > > 1, i.e. wake up as soon as data is available, which is OK-ish for most
> > > > > applications.   Apps usually don't care about the wake-up condition so
> > > > > much.  There are subtle difference and may influence on the stability
> > > > > of stream processing, but the stability usually depends more strongly
> > > > > on the hardware and software configurations.
> > > > >
> > > > > That being said, the impact by this bug (from the application behavior
> > > > > POV) is likely quite small, but the contamination is large; as you
> > > > > pointed out, it's much larger than I thought.
> > > > 
> > > > Ok, got it.
> > > > 
> > > > > The definition in uapi/sound/asound.h is a bit cryptic, but IIUC,
> > > > > __snd_pcm_mmap_control64 is used for 64bit archs, right?  If so, the
> > > > > problem rather hits more widely on 64bit archs silently.  Then, the
> > > > > influence by this bug must be almost negligible, as we've had no bug
> > > > > report about the behavior change.
> > > > 
> > > > While __snd_pcm_mmap_control64 is only used on 32-bit
> > > > architectures when 64-bit time_t is used. At the moment, this
> > > > means all users of musl-1.2.x libc, but not glibc.
> > > > 
> > > > On 64-bit architectures, __snd_pcm_mmap_control and
> > > > __snd_pcm_mmap_control64 are meant to be identical,
> > > > and this is actually true regardless of the bug, since
> > > > __pad_before_uframe and __pad_after_uframe both
> > > > end up as zero-length arrays here.
> > > > 
> > > > > We may just fix it in kernel and for new library with hoping that no
> > > > > one sees the actual problem.  Or, we may provide a complete new set of
> > > > > mmap offsets and ioctl to cover both broken and fixed interfaces...
> > > > > The decision depends on how perfectly we'd like to address the bug.
> > > > > As of now, I'm inclined to go for the former, but I'm open for more
> > > > > opinions.
> > > > 
> > > > Adding the musl list to Cc for additional testers, anyone interested
> > > > please see [1] for the original report.
> > > > 
> > > > It would be good to hear from musl users that are already using
> > > > audio support with 32-bit applications on 64-bit kernels, which
> > > > is the case that has the problem today. Have you noticed any
> > > > problems with audio support here? If not, we can probably
> > > > "fix" the kernel here and make the existing binaries behave
> > > > the same way on 32-bit kernels. If there are applications that
> > > > don't work in that environment today, I think we need to instead
> > > > change the kernel to accept the currently broken format on
> > > > both 32-bit and 64-bit kernels, possibly introducing yet another
> > > > format that works as originally intended but requires a newly
> > > > built kernel.
> > > 
> > > Thanks!
> > > 
> > > And now, looking more deeply, I feel more desperate.
> > > 
> > > This bug makes the expected padding gone on little-endian.
> > > On LE 32bit, the buggy definition is:
> > > 
> > > 	char __pad1[0];
> > > 	u32 appl_ptr;
> > > 	char __pad2[0]; // this should have been [4]
> > > 	char __pad3[0];
> > > 	u32 avail_min;
> > > 	char __pad4[4];
> > > 	
> > > When an application issues SYNC_PTR64 ioctl to submit appl_ptr and
> > > avail_min updates, 64bit kernel (in compat mode) reads directly as:
> > > 
> > > 	u64 appl_ptr;
> > > 	u64 avail_min;
> > > 
> > > Hence a bogus appl_ptr would be passed if avail_min != 0.
> > > And usually application sets non-zero avail_min.
> > > That is, the bug must hit more severely if the new API were really
> > > used.  It wouldn't crash, but some weird streaming behavior can
> > > happen like noise, jumping or underruns.
> > > 
> > > (Reading back avail_min=0 to user-space is rather harmless.  Ditto for
> > >  the case of BE, then at least there is no appl_ptr corruption.)
> > > 
> > > This made me wonder which way to go:
> > > it's certainly possible to fix the new kernel to treat both buggy and
> > > sane formats (disabling compat mmap and re-define ioctls, having the
> > > code for old APIs).  The problem is, however, in the case where the
> > > application needs to run on the older kernel that expects the buggy
> > > format.  Then apps would still have to send in the old buggy format --
> > > or maybe better in the older 32bit format that won't hit the bug
> > > above.  It makes situation more complicated.
> > 
> > Can't an ioctl number just be redefined so that, on old kernels with
> > the buggy one, newly built applications get told that mmap is not
> > available and use the unaffected non-mmap fallback?
> 
> The problem is that the SYNC_PTR64 ioctl itself for non-mmap fallback
> is equally buggy due to this bug, too.  So disabling mmap doesn't help
> alone.
> 
> And, yes, we can redefine ioctl numbers.  But, then, application would
> have to be bilingual, as well as the kernel; it'll have to switch back
> to old API when running on older kernel, while the same binary would
> need to run in a new API for a newer kernel.
> 
> Maybe we can implement it in alsa-lib, if it really worth for it.

In musl we already have ioctl struct conversion for running on
time32-only kernels. So it may be practical to convert this too if
needed.

Rich

Takashi Iwai Oct. 8, 2021, 8:43 a.m. UTC | #11

On Thu, 07 Oct 2021 18:51:58 +0200,
Rich Felker wrote:
> 
> On Thu, Oct 07, 2021 at 06:18:52PM +0200, Takashi Iwai wrote:
> > On Thu, 07 Oct 2021 18:06:36 +0200,
> > Rich Felker wrote:
> > > 
> > > On Thu, Oct 07, 2021 at 05:33:19PM +0200, Takashi Iwai wrote:
> > > > On Thu, 07 Oct 2021 15:11:00 +0200,
> > > > Arnd Bergmann wrote:
> > > > > 
> > > > >  On Thu, Oct 7, 2021 at 2:43 PM Takashi Iwai <[e-mail]> wrote:
> > > > > > On Thu, 07 Oct 2021 13:48:44 +0200, Arnd Bergmann wrote:
> > > > > > > On Thu, Oct 7, 2021 at 12:53 PM Takashi Iwai <[e-mail]> wrote:
> > > > > > > > On Wed, 06 Oct 2021 19:49:17 +0200, Michael Forney wrote:
> > > > > > >
> > > > > > > As far as I can tell, the broken interface will always result in
> > > > > > > user space seeing a zero value for "avail_min". Can you
> > > > > > > make a prediction what that would mean for actual
> > > > > > > applications? Will they have no audio output, run into
> > > > > > > a crash, or be able to use recover and appear to work normally
> > > > > > > here?
> > > > > >
> > > > > > No, fortunately it's only about control->avail_min, and fiddling this
> > > > > > value can't break severely (otherwise it'd be a security problem ;)
> > > > > >
> > > > > > In the buggy condition, it's always zero, and the kernel treated as if
> > > > > > 1, i.e. wake up as soon as data is available, which is OK-ish for most
> > > > > > applications.   Apps usually don't care about the wake-up condition so
> > > > > > much.  There are subtle difference and may influence on the stability
> > > > > > of stream processing, but the stability usually depends more strongly
> > > > > > on the hardware and software configurations.
> > > > > >
> > > > > > That being said, the impact by this bug (from the application behavior
> > > > > > POV) is likely quite small, but the contamination is large; as you
> > > > > > pointed out, it's much larger than I thought.
> > > > > 
> > > > > Ok, got it.
> > > > > 
> > > > > > The definition in uapi/sound/asound.h is a bit cryptic, but IIUC,
> > > > > > __snd_pcm_mmap_control64 is used for 64bit archs, right?  If so, the
> > > > > > problem rather hits more widely on 64bit archs silently.  Then, the
> > > > > > influence by this bug must be almost negligible, as we've had no bug
> > > > > > report about the behavior change.
> > > > > 
> > > > > While __snd_pcm_mmap_control64 is only used on 32-bit
> > > > > architectures when 64-bit time_t is used. At the moment, this
> > > > > means all users of musl-1.2.x libc, but not glibc.
> > > > > 
> > > > > On 64-bit architectures, __snd_pcm_mmap_control and
> > > > > __snd_pcm_mmap_control64 are meant to be identical,
> > > > > and this is actually true regardless of the bug, since
> > > > > __pad_before_uframe and __pad_after_uframe both
> > > > > end up as zero-length arrays here.
> > > > > 
> > > > > > We may just fix it in kernel and for new library with hoping that no
> > > > > > one sees the actual problem.  Or, we may provide a complete new set of
> > > > > > mmap offsets and ioctl to cover both broken and fixed interfaces...
> > > > > > The decision depends on how perfectly we'd like to address the bug.
> > > > > > As of now, I'm inclined to go for the former, but I'm open for more
> > > > > > opinions.
> > > > > 
> > > > > Adding the musl list to Cc for additional testers, anyone interested
> > > > > please see [1] for the original report.
> > > > > 
> > > > > It would be good to hear from musl users that are already using
> > > > > audio support with 32-bit applications on 64-bit kernels, which
> > > > > is the case that has the problem today. Have you noticed any
> > > > > problems with audio support here? If not, we can probably
> > > > > "fix" the kernel here and make the existing binaries behave
> > > > > the same way on 32-bit kernels. If there are applications that
> > > > > don't work in that environment today, I think we need to instead
> > > > > change the kernel to accept the currently broken format on
> > > > > both 32-bit and 64-bit kernels, possibly introducing yet another
> > > > > format that works as originally intended but requires a newly
> > > > > built kernel.
> > > > 
> > > > Thanks!
> > > > 
> > > > And now, looking more deeply, I feel more desperate.
> > > > 
> > > > This bug makes the expected padding gone on little-endian.
> > > > On LE 32bit, the buggy definition is:
> > > > 
> > > > 	char __pad1[0];
> > > > 	u32 appl_ptr;
> > > > 	char __pad2[0]; // this should have been [4]
> > > > 	char __pad3[0];
> > > > 	u32 avail_min;
> > > > 	char __pad4[4];
> > > > 	
> > > > When an application issues SYNC_PTR64 ioctl to submit appl_ptr and
> > > > avail_min updates, 64bit kernel (in compat mode) reads directly as:
> > > > 
> > > > 	u64 appl_ptr;
> > > > 	u64 avail_min;
> > > > 
> > > > Hence a bogus appl_ptr would be passed if avail_min != 0.
> > > > And usually application sets non-zero avail_min.
> > > > That is, the bug must hit more severely if the new API were really
> > > > used.  It wouldn't crash, but some weird streaming behavior can
> > > > happen like noise, jumping or underruns.
> > > > 
> > > > (Reading back avail_min=0 to user-space is rather harmless.  Ditto for
> > > >  the case of BE, then at least there is no appl_ptr corruption.)
> > > > 
> > > > This made me wonder which way to go:
> > > > it's certainly possible to fix the new kernel to treat both buggy and
> > > > sane formats (disabling compat mmap and re-define ioctls, having the
> > > > code for old APIs).  The problem is, however, in the case where the
> > > > application needs to run on the older kernel that expects the buggy
> > > > format.  Then apps would still have to send in the old buggy format --
> > > > or maybe better in the older 32bit format that won't hit the bug
> > > > above.  It makes situation more complicated.
> > > 
> > > Can't an ioctl number just be redefined so that, on old kernels with
> > > the buggy one, newly built applications get told that mmap is not
> > > available and use the unaffected non-mmap fallback?
> > 
> > The problem is that the SYNC_PTR64 ioctl itself for non-mmap fallback
> > is equally buggy due to this bug, too.  So disabling mmap doesn't help
> > alone.
> > 
> > And, yes, we can redefine ioctl numbers.  But, then, application would
> > have to be bilingual, as well as the kernel; it'll have to switch back
> > to old API when running on older kernel, while the same binary would
> > need to run in a new API for a newer kernel.
> > 
> > Maybe we can implement it in alsa-lib, if it really worth for it.
> 
> In musl we already have ioctl struct conversion for running on
> time32-only kernels. So it may be practical to convert this too if
> needed.

I guess we can work around without ioctl renumbering.  The PCM API has
a protocol version handshaking, and user-space is supposed to tell its
API version to kernel.  So the kernel can know in what version
user-space is talking with.

Below is the PoC fix in the kernel side (totally untested).
The fix for alsa-lib will follow.


thanks,

Takashi

---
diff --git a/include/uapi/sound/asound.h b/include/uapi/sound/asound.h
index 5859ca0a1439..dbdbf0c794d8 100644
--- a/include/uapi/sound/asound.h
+++ b/include/uapi/sound/asound.h
@@ -156,7 +156,7 @@ struct snd_hwdep_dsp_image {
  *                                                                           *
  *****************************************************************************/
 
-#define SNDRV_PCM_VERSION		SNDRV_PROTOCOL_VERSION(2, 0, 15)
+#define SNDRV_PCM_VERSION		SNDRV_PROTOCOL_VERSION(2, 0, 16)
 
 typedef unsigned long snd_pcm_uframes_t;
 typedef signed long snd_pcm_sframes_t;
@@ -550,6 +550,7 @@ struct __snd_pcm_sync_ptr {
 	} s;
 	union {
 		struct __snd_pcm_mmap_control control;
+		struct __snd_pcm_mmap_control control_api_2_0_15; /* no bug in 32bit mode */
 		unsigned char reserved[64];
 	} c;
 };
@@ -557,11 +558,15 @@ struct __snd_pcm_sync_ptr {
 #if defined(__BYTE_ORDER) ? __BYTE_ORDER == __BIG_ENDIAN : defined(__BIG_ENDIAN)
 typedef char __pad_before_uframe[sizeof(__u64) - sizeof(snd_pcm_uframes_t)];
 typedef char __pad_after_uframe[0];
+typedef char __pad_before_u32[4];
+typedef char __pad_after_u32[0];
 #endif
 
 #if defined(__BYTE_ORDER) ? __BYTE_ORDER == __LITTLE_ENDIAN : defined(__LITTLE_ENDIAN)
 typedef char __pad_before_uframe[0];
 typedef char __pad_after_uframe[sizeof(__u64) - sizeof(snd_pcm_uframes_t)];
+typedef char __pad_before_u32[0];
+typedef char __pad_after_u32[4];
 #endif
 
 struct __snd_pcm_mmap_status64 {
@@ -579,13 +584,23 @@ struct __snd_pcm_mmap_status64 {
 struct __snd_pcm_mmap_control64 {
 	__pad_before_uframe __pad1;
 	snd_pcm_uframes_t appl_ptr;	 /* RW: appl ptr (0...boundary-1) */
-	__pad_before_uframe __pad2;
+	__pad_after_uframe __pad2;
 
 	__pad_before_uframe __pad3;
 	snd_pcm_uframes_t  avail_min;	 /* RW: min available frames for wakeup */
 	__pad_after_uframe __pad4;
 };
 
+/* buggy mmap control definition for 2.0.15 PCM API on 32bit mode */
+struct __snd_pcm_mmap_control64_api_2_0_15 {
+	__pad_before_u32 __pad1;
+	__u32 appl_ptr;
+	__pad_before_u32 __pad2;	/* SiC! here is the bug */
+	__pad_before_u32 __pad3;
+	__u32 avail_min;
+	__pad_after_uframe __pad4;
+};
+
 struct __snd_pcm_sync_ptr64 {
 	__u32 flags;
 	__u32 pad1;
@@ -595,6 +610,7 @@ struct __snd_pcm_sync_ptr64 {
 	} s;
 	union {
 		struct __snd_pcm_mmap_control64 control;
+		struct __snd_pcm_mmap_control64_api_2_0_15 control_api_2_0_15;
 		unsigned char reserved[64];
 	} c;
 };
diff --git a/sound/core/pcm_native.c b/sound/core/pcm_native.c
index 46c643db18eb..1f26dd2a2525 100644
--- a/sound/core/pcm_native.c
+++ b/sound/core/pcm_native.c
@@ -2958,8 +2958,19 @@ static int snd_pcm_delay(struct snd_pcm_substream *substream,
 	return err;
 }
 		
+/* PCM 2.0.15 API definition had a bug in mmap control; it puts the avail_min
+ * at the wrong offset due to a typo in padding type.
+ * The bug hits only on 32bit, either on 32bit arch or in 32bit compat mode.
+ */
+static bool is_buggy_control(struct snd_pcm_file *pcm_file)
+{
+	return pcm_file->user_pversion == SNDRV_PROTOCOL_VERSION(2, 0, 15) &&
+		(in_compat_syscall() || !IS_ENABLED(CONFIG_64BIT));
+}
+
 static int snd_pcm_sync_ptr(struct snd_pcm_substream *substream,
-			    struct snd_pcm_sync_ptr __user *_sync_ptr)
+			    struct snd_pcm_sync_ptr __user *_sync_ptr,
+			    bool buggy_control)
 {
 	struct snd_pcm_runtime *runtime = substream->runtime;
 	struct snd_pcm_sync_ptr sync_ptr;
@@ -2970,8 +2981,17 @@ static int snd_pcm_sync_ptr(struct snd_pcm_substream *substream,
 	memset(&sync_ptr, 0, sizeof(sync_ptr));
 	if (get_user(sync_ptr.flags, (unsigned __user *)&(_sync_ptr->flags)))
 		return -EFAULT;
-	if (copy_from_user(&sync_ptr.c.control, &(_sync_ptr->c.control), sizeof(struct snd_pcm_mmap_control)))
-		return -EFAULT;	
+	if (buggy_control) {
+		if (copy_from_user(&sync_ptr.c.control_api_2_0_15,
+				   &(_sync_ptr->c.control_api_2_0_15),
+				   sizeof(sync_ptr.c.control_api_2_0_15)))
+			return -EFAULT;
+	} else {
+		if (copy_from_user(&sync_ptr.c.control,
+				   &(_sync_ptr->c.control),
+				   sizeof(sync_ptr.c.control)))
+			return -EFAULT;
+	}
 	status = runtime->status;
 	control = runtime->control;
 	if (sync_ptr.flags & SNDRV_PCM_SYNC_PTR_HWSYNC) {
@@ -2981,19 +3001,34 @@ static int snd_pcm_sync_ptr(struct snd_pcm_substream *substream,
 	}
 	snd_pcm_stream_lock_irq(substream);
 	if (!(sync_ptr.flags & SNDRV_PCM_SYNC_PTR_APPL)) {
-		err = pcm_lib_apply_appl_ptr(substream,
-					     sync_ptr.c.control.appl_ptr);
+		if (buggy_control) {
+			err = pcm_lib_apply_appl_ptr(substream,
+						     sync_ptr.c.control_api_2_0_15.appl_ptr);
+		} else {
+			err = pcm_lib_apply_appl_ptr(substream,
+						     sync_ptr.c.control.appl_ptr);
+		}
 		if (err < 0) {
 			snd_pcm_stream_unlock_irq(substream);
 			return err;
 		}
 	} else {
-		sync_ptr.c.control.appl_ptr = control->appl_ptr;
+		if (buggy_control)
+			sync_ptr.c.control_api_2_0_15.appl_ptr = control->appl_ptr;
+		else
+			sync_ptr.c.control.appl_ptr = control->appl_ptr;
+	}
+	if (!(sync_ptr.flags & SNDRV_PCM_SYNC_PTR_AVAIL_MIN)) {
+		if (buggy_control)
+			control->avail_min = sync_ptr.c.control_api_2_0_15.avail_min;
+		else
+			control->avail_min = sync_ptr.c.control.avail_min;
+	} else {
+		if (buggy_control)
+			sync_ptr.c.control_api_2_0_15.avail_min = control->avail_min;
+		else
+			sync_ptr.c.control.avail_min = control->avail_min;
 	}
-	if (!(sync_ptr.flags & SNDRV_PCM_SYNC_PTR_AVAIL_MIN))
-		control->avail_min = sync_ptr.c.control.avail_min;
-	else
-		sync_ptr.c.control.avail_min = control->avail_min;
 	sync_ptr.s.status.state = status->state;
 	sync_ptr.s.status.hw_ptr = status->hw_ptr;
 	sync_ptr.s.status.tstamp = status->tstamp;
@@ -3289,7 +3324,8 @@ static int snd_pcm_common_ioctl(struct file *file,
 	case __SNDRV_PCM_IOCTL_SYNC_PTR32:
 		return snd_pcm_ioctl_sync_ptr_compat(substream, arg);
 	case __SNDRV_PCM_IOCTL_SYNC_PTR64:
-		return snd_pcm_sync_ptr(substream, arg);
+		return snd_pcm_sync_ptr(substream, arg,
+					is_buggy_control(pcm_file));
 #ifdef CONFIG_SND_SUPPORT_OLD_API
 	case SNDRV_PCM_IOCTL_HW_REFINE_OLD:
 		return snd_pcm_hw_refine_old_user(substream, arg);
@@ -3851,6 +3887,8 @@ static int snd_pcm_mmap(struct file *file, struct vm_area_struct *area)
 			return -ENXIO;
 		fallthrough;
 	case SNDRV_PCM_MMAP_OFFSET_CONTROL_NEW:
+		if (is_buggy_control(pcm_file))
+			return -ENXIO;
 		if (!pcm_control_mmap_allowed(pcm_file))
 			return -ENXIO;
 		return snd_pcm_mmap_control(substream, file, area);

Takashi Iwai Oct. 8, 2021, 8:44 a.m. UTC | #12

On Fri, 08 Oct 2021 10:43:24 +0200,
Takashi Iwai wrote:
> 
> On Thu, 07 Oct 2021 18:51:58 +0200,
> Rich Felker wrote:
> > 
> > On Thu, Oct 07, 2021 at 06:18:52PM +0200, Takashi Iwai wrote:
> > > On Thu, 07 Oct 2021 18:06:36 +0200,
> > > Rich Felker wrote:
> > > > 
> > > > On Thu, Oct 07, 2021 at 05:33:19PM +0200, Takashi Iwai wrote:
> > > > > On Thu, 07 Oct 2021 15:11:00 +0200,
> > > > > Arnd Bergmann wrote:
> > > > > > 
> > > > > >  On Thu, Oct 7, 2021 at 2:43 PM Takashi Iwai <[e-mail]> wrote:
> > > > > > > On Thu, 07 Oct 2021 13:48:44 +0200, Arnd Bergmann wrote:
> > > > > > > > On Thu, Oct 7, 2021 at 12:53 PM Takashi Iwai <[e-mail]> wrote:
> > > > > > > > > On Wed, 06 Oct 2021 19:49:17 +0200, Michael Forney wrote:
> > > > > > > >
> > > > > > > > As far as I can tell, the broken interface will always result in
> > > > > > > > user space seeing a zero value for "avail_min". Can you
> > > > > > > > make a prediction what that would mean for actual
> > > > > > > > applications? Will they have no audio output, run into
> > > > > > > > a crash, or be able to use recover and appear to work normally
> > > > > > > > here?
> > > > > > >
> > > > > > > No, fortunately it's only about control->avail_min, and fiddling this
> > > > > > > value can't break severely (otherwise it'd be a security problem ;)
> > > > > > >
> > > > > > > In the buggy condition, it's always zero, and the kernel treated as if
> > > > > > > 1, i.e. wake up as soon as data is available, which is OK-ish for most
> > > > > > > applications.   Apps usually don't care about the wake-up condition so
> > > > > > > much.  There are subtle difference and may influence on the stability
> > > > > > > of stream processing, but the stability usually depends more strongly
> > > > > > > on the hardware and software configurations.
> > > > > > >
> > > > > > > That being said, the impact by this bug (from the application behavior
> > > > > > > POV) is likely quite small, but the contamination is large; as you
> > > > > > > pointed out, it's much larger than I thought.
> > > > > > 
> > > > > > Ok, got it.
> > > > > > 
> > > > > > > The definition in uapi/sound/asound.h is a bit cryptic, but IIUC,
> > > > > > > __snd_pcm_mmap_control64 is used for 64bit archs, right?  If so, the
> > > > > > > problem rather hits more widely on 64bit archs silently.  Then, the
> > > > > > > influence by this bug must be almost negligible, as we've had no bug
> > > > > > > report about the behavior change.
> > > > > > 
> > > > > > While __snd_pcm_mmap_control64 is only used on 32-bit
> > > > > > architectures when 64-bit time_t is used. At the moment, this
> > > > > > means all users of musl-1.2.x libc, but not glibc.
> > > > > > 
> > > > > > On 64-bit architectures, __snd_pcm_mmap_control and
> > > > > > __snd_pcm_mmap_control64 are meant to be identical,
> > > > > > and this is actually true regardless of the bug, since
> > > > > > __pad_before_uframe and __pad_after_uframe both
> > > > > > end up as zero-length arrays here.
> > > > > > 
> > > > > > > We may just fix it in kernel and for new library with hoping that no
> > > > > > > one sees the actual problem.  Or, we may provide a complete new set of
> > > > > > > mmap offsets and ioctl to cover both broken and fixed interfaces...
> > > > > > > The decision depends on how perfectly we'd like to address the bug.
> > > > > > > As of now, I'm inclined to go for the former, but I'm open for more
> > > > > > > opinions.
> > > > > > 
> > > > > > Adding the musl list to Cc for additional testers, anyone interested
> > > > > > please see [1] for the original report.
> > > > > > 
> > > > > > It would be good to hear from musl users that are already using
> > > > > > audio support with 32-bit applications on 64-bit kernels, which
> > > > > > is the case that has the problem today. Have you noticed any
> > > > > > problems with audio support here? If not, we can probably
> > > > > > "fix" the kernel here and make the existing binaries behave
> > > > > > the same way on 32-bit kernels. If there are applications that
> > > > > > don't work in that environment today, I think we need to instead
> > > > > > change the kernel to accept the currently broken format on
> > > > > > both 32-bit and 64-bit kernels, possibly introducing yet another
> > > > > > format that works as originally intended but requires a newly
> > > > > > built kernel.
> > > > > 
> > > > > Thanks!
> > > > > 
> > > > > And now, looking more deeply, I feel more desperate.
> > > > > 
> > > > > This bug makes the expected padding gone on little-endian.
> > > > > On LE 32bit, the buggy definition is:
> > > > > 
> > > > > 	char __pad1[0];
> > > > > 	u32 appl_ptr;
> > > > > 	char __pad2[0]; // this should have been [4]
> > > > > 	char __pad3[0];
> > > > > 	u32 avail_min;
> > > > > 	char __pad4[4];
> > > > > 	
> > > > > When an application issues SYNC_PTR64 ioctl to submit appl_ptr and
> > > > > avail_min updates, 64bit kernel (in compat mode) reads directly as:
> > > > > 
> > > > > 	u64 appl_ptr;
> > > > > 	u64 avail_min;
> > > > > 
> > > > > Hence a bogus appl_ptr would be passed if avail_min != 0.
> > > > > And usually application sets non-zero avail_min.
> > > > > That is, the bug must hit more severely if the new API were really
> > > > > used.  It wouldn't crash, but some weird streaming behavior can
> > > > > happen like noise, jumping or underruns.
> > > > > 
> > > > > (Reading back avail_min=0 to user-space is rather harmless.  Ditto for
> > > > >  the case of BE, then at least there is no appl_ptr corruption.)
> > > > > 
> > > > > This made me wonder which way to go:
> > > > > it's certainly possible to fix the new kernel to treat both buggy and
> > > > > sane formats (disabling compat mmap and re-define ioctls, having the
> > > > > code for old APIs).  The problem is, however, in the case where the
> > > > > application needs to run on the older kernel that expects the buggy
> > > > > format.  Then apps would still have to send in the old buggy format --
> > > > > or maybe better in the older 32bit format that won't hit the bug
> > > > > above.  It makes situation more complicated.
> > > > 
> > > > Can't an ioctl number just be redefined so that, on old kernels with
> > > > the buggy one, newly built applications get told that mmap is not
> > > > available and use the unaffected non-mmap fallback?
> > > 
> > > The problem is that the SYNC_PTR64 ioctl itself for non-mmap fallback
> > > is equally buggy due to this bug, too.  So disabling mmap doesn't help
> > > alone.
> > > 
> > > And, yes, we can redefine ioctl numbers.  But, then, application would
> > > have to be bilingual, as well as the kernel; it'll have to switch back
> > > to old API when running on older kernel, while the same binary would
> > > need to run in a new API for a newer kernel.
> > > 
> > > Maybe we can implement it in alsa-lib, if it really worth for it.
> > 
> > In musl we already have ioctl struct conversion for running on
> > time32-only kernels. So it may be practical to convert this too if
> > needed.
> 
> I guess we can work around without ioctl renumbering.  The PCM API has
> a protocol version handshaking, and user-space is supposed to tell its
> API version to kernel.  So the kernel can know in what version
> user-space is talking with.
> 
> Below is the PoC fix in the kernel side (totally untested).
> The fix for alsa-lib will follow.

And below is the PoC fix for alsa-lib.


Takashi

---
diff --git a/include/sound/uapi/asound.h b/include/sound/uapi/asound.h
index 9fe3943f5fbb..ee91fe1f881f 100644
--- a/include/sound/uapi/asound.h
+++ b/include/sound/uapi/asound.h
@@ -154,7 +154,7 @@ struct snd_hwdep_dsp_image {
  *                                                                           *
  *****************************************************************************/
 
-#define SNDRV_PCM_VERSION		SNDRV_PROTOCOL_VERSION(2, 0, 15)
+#define SNDRV_PCM_VERSION		SNDRV_PROTOCOL_VERSION(2, 0, 16)
 
 typedef unsigned long snd_pcm_uframes_t;
 typedef signed long snd_pcm_sframes_t;
@@ -541,6 +541,7 @@ struct __snd_pcm_sync_ptr {
 	} s;
 	union {
 		struct __snd_pcm_mmap_control control;
+		struct __snd_pcm_mmap_control control_api_2_0_15; /* no bug in 32bit mode */
 		unsigned char reserved[64];
 	} c;
 };
@@ -548,11 +549,15 @@ struct __snd_pcm_sync_ptr {
 #if defined(__BYTE_ORDER) ? __BYTE_ORDER == __BIG_ENDIAN : defined(__BIG_ENDIAN)
 typedef char __pad_before_uframe[sizeof(__u64) - sizeof(snd_pcm_uframes_t)];
 typedef char __pad_after_uframe[0];
+typedef char __pad_before_u32[4];
+typedef char __pad_after_u32[0];
 #endif
 
 #if defined(__BYTE_ORDER) ? __BYTE_ORDER == __LITTLE_ENDIAN : defined(__LITTLE_ENDIAN)
 typedef char __pad_before_uframe[0];
 typedef char __pad_after_uframe[sizeof(__u64) - sizeof(snd_pcm_uframes_t)];
+typedef char __pad_before_u32[0];
+typedef char __pad_after_u32[4];
 #endif
 
 struct __snd_pcm_mmap_status64 {
@@ -570,13 +575,23 @@ struct __snd_pcm_mmap_status64 {
 struct __snd_pcm_mmap_control64 {
 	__pad_before_uframe __pad1;
 	snd_pcm_uframes_t appl_ptr;	 /* RW: appl ptr (0...boundary-1) */
-	__pad_before_uframe __pad2;
+	__pad_after_uframe __pad2;
 
 	__pad_before_uframe __pad3;
 	snd_pcm_uframes_t  avail_min;	 /* RW: min available frames for wakeup */
 	__pad_after_uframe __pad4;
 };
 
+/* buggy mmap control definition for 2.0.15 PCM API on 32bit mode */
+struct __snd_pcm_mmap_control64_api_2_0_15 {
+	__pad_before_u32 __pad1;
+	__u32 appl_ptr;
+	__pad_before_u32 __pad2;	/* SiC! here is the bug */
+	__pad_before_u32 __pad3;
+	__u32 avail_min;
+	__pad_after_uframe __pad4;
+};
+
 struct __snd_pcm_sync_ptr64 {
 	__u32 flags;
 	__u32 pad1;
@@ -586,6 +601,7 @@ struct __snd_pcm_sync_ptr64 {
 	} s;
 	union {
 		struct __snd_pcm_mmap_control64 control;
+		struct __snd_pcm_mmap_control64_api_2_0_15 control_api_2_0_15;
 		unsigned char reserved[64];
 	} c;
 };
diff --git a/src/pcm/pcm_hw.c b/src/pcm/pcm_hw.c
index b3f9d1579d29..bb97b7ecf5ca 100644
--- a/src/pcm/pcm_hw.c
+++ b/src/pcm/pcm_hw.c
@@ -94,6 +94,7 @@ typedef struct {
 
 	volatile struct snd_pcm_mmap_status * mmap_status;
 	struct snd_pcm_mmap_control *mmap_control;
+	snd_pcm_uframes_t *avail_min_p;
 	bool mmap_status_fallbacked;
 	bool mmap_control_fallbacked;
 	struct snd_pcm_sync_ptr *sync_ptr;
@@ -507,7 +508,7 @@ static int snd_pcm_hw_sw_params(snd_pcm_t *pcm, snd_pcm_sw_params_t * params)
 	    params->silence_threshold == pcm->silence_threshold &&
 	    params->silence_size == pcm->silence_size &&
 	    old_period_event == hw->period_event) {
-		hw->mmap_control->avail_min = params->avail_min;
+		*hw->avail_min_p = params->avail_min;
 		err = issue_avail_min(hw);
 		goto out;
 	}
@@ -540,7 +541,7 @@ static int snd_pcm_hw_sw_params(snd_pcm_t *pcm, snd_pcm_sw_params_t * params)
 		}
 		pcm->tstamp_type = params->tstamp_type;
 	}
-	hw->mmap_control->avail_min = params->avail_min;
+	*hw->avail_min_p = params->avail_min;
 	if (hw->period_event != old_period_event) {
 		err = snd_pcm_hw_change_timer(pcm, old_period_event);
 		if (err < 0)
@@ -980,6 +981,14 @@ static bool map_control_data(snd_pcm_hw_t *hw,
 	}
 
 	hw->mmap_control = mmap_control;
+	hw->avail_min_p = &mmap_control->avail_min;
+#ifdef __SND_STRUCT_TIME64
+	if (hw->version == SNDRV_PROTOCOL_VERSION(2, 0, 15)) {
+		struct __snd_pcm_mmap_control64_api_2_0_15 *buggy_control =
+			(struct __snd_pcm_mmap_control64_api_2_0_15 *)mmap_control;
+		hw->avail_min_p = &buggy_control->avail_min;
+	}
+#endif
 
 	return fallbacked;
 }
@@ -1015,7 +1024,7 @@ static int map_status_and_control_data(snd_pcm_t *pcm, bool force_fallback)
 	if (!(pcm->mode & SND_PCM_APPEND)) {
 		/* Initialize the data. */
 		hw->mmap_control->appl_ptr = 0;
-		hw->mmap_control->avail_min = 1;
+		*hw->avail_min_p = 1;
 	}
 	snd_pcm_set_hw_ptr(pcm, &hw->mmap_status->hw_ptr, hw->fd,
 			   SNDRV_PCM_MMAP_OFFSET_STATUS +

Arnd Bergmann Oct. 8, 2021, 9:24 a.m. UTC | #13

On Fri, Oct 8, 2021 at 10:43 AM Takashi Iwai <[e-mail]> wrote:
> On Thu, 07 Oct 2021 18:51:58 +0200, Rich Felker wrote:
> > On Thu, Oct 07, 2021 at 06:18:52PM +0200, Takashi Iwai wrote:
>
> @@ -557,11 +558,15 @@ struct __snd_pcm_sync_ptr {
>  #if defined(__BYTE_ORDER) ? __BYTE_ORDER == __BIG_ENDIAN : defined(__BIG_ENDIAN)
>  typedef char __pad_before_uframe[sizeof(__u64) - sizeof(snd_pcm_uframes_t)];
>  typedef char __pad_after_uframe[0];
> +typedef char __pad_before_u32[4];
> +typedef char __pad_after_u32[0];
>  #endif
>
>  #if defined(__BYTE_ORDER) ? __BYTE_ORDER == __LITTLE_ENDIAN : defined(__LITTLE_ENDIAN)
>  typedef char __pad_before_uframe[0];
>  typedef char __pad_after_uframe[sizeof(__u64) - sizeof(snd_pcm_uframes_t)];
> +typedef char __pad_before_u32[0];
> +typedef char __pad_after_u32[4];
>  #endif

I think these should remain unchanged, the complex expression was intentionally
done so the structures are laid out the same way on 64-bit
architectures, so that
the kernel can use the __SND_STRUCT_TIME64 path internally on both 32-bit
and 64-bit architectures.

> @@ -2970,8 +2981,17 @@ static int snd_pcm_sync_ptr(struct snd_pcm_substream *substream,
>         memset(&sync_ptr, 0, sizeof(sync_ptr));
>         if (get_user(sync_ptr.flags, (unsigned __user *)&(_sync_ptr->flags)))
>                 return -EFAULT;
> -       if (copy_from_user(&sync_ptr.c.control, &(_sync_ptr->c.control), sizeof(struct snd_pcm_mmap_control)))
> -               return -EFAULT;
> +       if (buggy_control) {
> +               if (copy_from_user(&sync_ptr.c.control_api_2_0_15,
> +                                  &(_sync_ptr->c.control_api_2_0_15),
> +                                  sizeof(sync_ptr.c.control_api_2_0_15)))
> +                       return -EFAULT;
> +       } else {
> +               if (copy_from_user(&sync_ptr.c.control,
> +                                  &(_sync_ptr->c.control),
> +                                  sizeof(sync_ptr.c.control)))
> +                       return -EFAULT;
> +       }

The problem I see with this is that it might break musl's ability to
emulate the new
interface on top of the old (time32) one for linux-4.x and older
kernels, as the conversion
function is no longer stateless but has to know the negotiated
interface version.

It's probably fine as long as we can be sure that the 2.0.16+ API
version only gets
negotiated if both the kernel and user sides support it, and musl only emulates
the 2.0.15 API version from the current kernels.

I've tried to understand this part of musl's convert_ioctl_struct(), but I just
can't figure out whether it does the conversion based the on the layout that
is currently used in the kernel, or based on the layout we should have been
using, and would use with the above fix. Rich, can you help me here?

       Arnd

Takashi Iwai Oct. 8, 2021, 11:11 a.m. UTC | #14

On Fri, 08 Oct 2021 11:24:39 +0200,
Arnd Bergmann wrote:
> 
> On Fri, Oct 8, 2021 at 10:43 AM Takashi Iwai <[e-mail]> wrote:
> > On Thu, 07 Oct 2021 18:51:58 +0200, Rich Felker wrote:
> > > On Thu, Oct 07, 2021 at 06:18:52PM +0200, Takashi Iwai wrote:
> >
> > @@ -557,11 +558,15 @@ struct __snd_pcm_sync_ptr {
> >  #if defined(__BYTE_ORDER) ? __BYTE_ORDER == __BIG_ENDIAN : defined(__BIG_ENDIAN)
> >  typedef char __pad_before_uframe[sizeof(__u64) - sizeof(snd_pcm_uframes_t)];
> >  typedef char __pad_after_uframe[0];
> > +typedef char __pad_before_u32[4];
> > +typedef char __pad_after_u32[0];
> >  #endif
> >
> >  #if defined(__BYTE_ORDER) ? __BYTE_ORDER == __LITTLE_ENDIAN : defined(__LITTLE_ENDIAN)
> >  typedef char __pad_before_uframe[0];
> >  typedef char __pad_after_uframe[sizeof(__u64) - sizeof(snd_pcm_uframes_t)];
> > +typedef char __pad_before_u32[0];
> > +typedef char __pad_after_u32[4];
> >  #endif
> 
> I think these should remain unchanged, the complex expression was intentionally
> done so the structures are laid out the same way on 64-bit
> architectures, so that
> the kernel can use the __SND_STRUCT_TIME64 path internally on both 32-bit
> and 64-bit architectures.

That was explicitly defined, but OK, this isn't necessarily defined
here.

> > @@ -2970,8 +2981,17 @@ static int snd_pcm_sync_ptr(struct snd_pcm_substream *substream,
> >         memset(&sync_ptr, 0, sizeof(sync_ptr));
> >         if (get_user(sync_ptr.flags, (unsigned __user *)&(_sync_ptr->flags)))
> >                 return -EFAULT;
> > -       if (copy_from_user(&sync_ptr.c.control, &(_sync_ptr->c.control), sizeof(struct snd_pcm_mmap_control)))
> > -               return -EFAULT;
> > +       if (buggy_control) {
> > +               if (copy_from_user(&sync_ptr.c.control_api_2_0_15,
> > +                                  &(_sync_ptr->c.control_api_2_0_15),
> > +                                  sizeof(sync_ptr.c.control_api_2_0_15)))
> > +                       return -EFAULT;
> > +       } else {
> > +               if (copy_from_user(&sync_ptr.c.control,
> > +                                  &(_sync_ptr->c.control),
> > +                                  sizeof(sync_ptr.c.control)))
> > +                       return -EFAULT;
> > +       }
> 
> The problem I see with this is that it might break musl's ability to
> emulate the new
> interface on top of the old (time32) one for linux-4.x and older
> kernels, as the conversion
> function is no longer stateless but has to know the negotiated
> interface version.
> 
> It's probably fine as long as we can be sure that the 2.0.16+ API
> version only gets
> negotiated if both the kernel and user sides support it, and musl only emulates
> the 2.0.15 API version from the current kernels.
> 
> I've tried to understand this part of musl's convert_ioctl_struct(), but I just
> can't figure out whether it does the conversion based the on the layout that
> is currently used in the kernel, or based on the layout we should have been
> using, and would use with the above fix. Rich, can you help me here?

So, at this moment, I'm not sure whether we should correct the struct
at all.  This will lead to yet more breakage, and basically the struct
itself *works* -- the only bug is in 32bit compat handling in the
kernel (again).

The below is a revised kernel patch (again untested), just correcting
the behavior of 32bit compat mode.  32bit apps on 32bit kernel work
fine as is, as well as 64bit apps on 64bit kernel.


Takashi

--- a/sound/core/pcm_compat.c
+++ b/sound/core/pcm_compat.c
@@ -468,6 +468,75 @@ static int snd_pcm_ioctl_sync_ptr_x32(struct snd_pcm_substream *substream,
 }
 #endif /* CONFIG_X86_X32 */
 
+#ifdef __BIG_ENDIAN
+typedef char __pad_before_u32[4];
+typedef char __pad_after_u32[0];
+#else
+typedef char __pad_before_u32[0];
+typedef char __pad_after_u32[4];
+#endif
+
+/* PCM 2.0.15 API definition had a bug in mmap control; it puts the avail_min
+ * at the wrong offset due to a typo in padding type, hitting only on 32bit.
+ * Workaround for incorrect read/write is needed only in 32bit compat mode.
+ */
+struct __snd_pcm_mmap_control64_buggy {
+	__pad_before_u32 __pad1;
+	__u32 appl_ptr;
+	__pad_before_u32 __pad2;	/* SiC! here is the bug */
+	__pad_before_u32 __pad3;
+	__u32 avail_min;
+	__pad_after_uframe __pad4;
+};
+
+static int snd_pcm_ioctl_sync_ptr_buggy(struct snd_pcm_substream *substream,
+					struct snd_pcm_sync_ptr __user *_sync_ptr)
+{
+	struct snd_pcm_runtime *runtime = substream->runtime;
+	struct snd_pcm_sync_ptr sync_ptr;
+	struct __snd_pcm_mmap_control64_buggy *sync_cp;
+	volatile struct snd_pcm_mmap_status *status;
+	volatile struct snd_pcm_mmap_control *control;
+	int err;
+
+	memset(&sync_ptr, 0, sizeof(sync_ptr));
+	sync_cp = (struct __snd_pcm_mmap_control64_buggy *)&sync_ptr.c.control;
+	if (get_user(sync_ptr.flags, (unsigned __user *)&(_sync_ptr->flags)))
+		return -EFAULT;
+	if (copy_from_user(sync_cp, &(_sync_ptr->c.control), sizeof(*sync_cp)))
+		return -EFAULT;
+	status = runtime->status;
+	control = runtime->control;
+	if (sync_ptr.flags & SNDRV_PCM_SYNC_PTR_HWSYNC) {
+		err = snd_pcm_hwsync(substream);
+		if (err < 0)
+			return err;
+	}
+	snd_pcm_stream_lock_irq(substream);
+	if (!(sync_ptr.flags & SNDRV_PCM_SYNC_PTR_APPL)) {
+		err = pcm_lib_apply_appl_ptr(substream, sync_cp->appl_ptr);
+		if (err < 0) {
+			snd_pcm_stream_unlock_irq(substream);
+			return err;
+		}
+	} else {
+		sync_cp->appl_ptr = control->appl_ptr;
+	}
+	if (!(sync_ptr.flags & SNDRV_PCM_SYNC_PTR_AVAIL_MIN))
+		control->avail_min = sync_cp->avail_min;
+	else
+		sync_cp->avail_min = control->avail_min;
+	sync_ptr.s.status.state = status->state;
+	sync_ptr.s.status.hw_ptr = status->hw_ptr;
+	sync_ptr.s.status.tstamp = status->tstamp;
+	sync_ptr.s.status.suspended_state = status->suspended_state;
+	sync_ptr.s.status.audio_tstamp = status->audio_tstamp;
+	snd_pcm_stream_unlock_irq(substream);
+	if (copy_to_user(_sync_ptr, &sync_ptr, sizeof(sync_ptr)))
+		return -EFAULT;
+	return 0;
+}
+
 /*
  */
 enum {
@@ -537,7 +606,7 @@ static long snd_pcm_ioctl_compat(struct file *file, unsigned int cmd, unsigned l
 		if (in_x32_syscall())
 			return snd_pcm_ioctl_sync_ptr_x32(substream, argp);
 #endif /* CONFIG_X86_X32 */
-		return snd_pcm_common_ioctl(file, substream, cmd, argp);
+		return snd_pcm_ioctl_sync_ptr_buggy(substream, argp);
 	case SNDRV_PCM_IOCTL_HW_REFINE32:
 		return snd_pcm_ioctl_hw_params_compat(substream, 1, argp);
 	case SNDRV_PCM_IOCTL_HW_PARAMS32:

Arnd Bergmann Oct. 8, 2021, 11:45 a.m. UTC | #15

On Fri, Oct 8, 2021 at 1:11 PM Takashi Iwai <[e-mail]> wrote:
> On Fri, 08 Oct 2021 11:24:39 +0200, Arnd Bergmann wrote:

> >
> > I've tried to understand this part of musl's convert_ioctl_struct(), but I just
> > can't figure out whether it does the conversion based the on the layout that
> > is currently used in the kernel, or based on the layout we should have been
> > using, and would use with the above fix. Rich, can you help me here?
>
> So, at this moment, I'm not sure whether we should correct the struct
> at all.  This will lead to yet more breakage, and basically the struct
> itself *works* -- the only bug is in 32bit compat handling in the
> kernel (again).

I'm still unsure if the musl fallback code is correct or not.

> The below is a revised kernel patch (again untested), just correcting
> the behavior of 32bit compat mode.  32bit apps on 32bit kernel work
> fine as is, as well as 64bit apps on 64bit kernel.

Right, this should cover all cases of the ioctl itself misbehaving.
In addition, we still need to disallow the mmap() interface on compat
kernels then. Strictly speaking, we could allow the snd_pcm_mmap_status
but not snd_pcm_mmap_control to be mapped, but I'm not sure if
that's better than disallowing both.

       Arnd

Takashi Iwai Oct. 8, 2021, 11:53 a.m. UTC | #16

On Fri, 08 Oct 2021 13:45:45 +0200,
Arnd Bergmann wrote:
> 
> On Fri, Oct 8, 2021 at 1:11 PM Takashi Iwai <[e-mail]> wrote:
> > On Fri, 08 Oct 2021 11:24:39 +0200, Arnd Bergmann wrote:
> 
> > >
> > > I've tried to understand this part of musl's convert_ioctl_struct(), but I just
> > > can't figure out whether it does the conversion based the on the layout that
> > > is currently used in the kernel, or based on the layout we should have been
> > > using, and would use with the above fix. Rich, can you help me here?
> >
> > So, at this moment, I'm not sure whether we should correct the struct
> > at all.  This will lead to yet more breakage, and basically the struct
> > itself *works* -- the only bug is in 32bit compat handling in the
> > kernel (again).
> 
> I'm still unsure if the musl fallback code is correct or not.

We need to verify the current behavior in anyway...

> > The below is a revised kernel patch (again untested), just correcting
> > the behavior of 32bit compat mode.  32bit apps on 32bit kernel work
> > fine as is, as well as 64bit apps on 64bit kernel.
> 
> Right, this should cover all cases of the ioctl itself misbehaving.
> In addition, we still need to disallow the mmap() interface on compat
> kernels then. Strictly speaking, we could allow the snd_pcm_mmap_status
> but not snd_pcm_mmap_control to be mapped, but I'm not sure if
> that's better than disallowing both.

IIRC, the compat mmap is already disallowed even for the
SNDRV_PCM_MMAP_OFFSET_CONTROL_NEW (in pcm_control_mmap_allowed()), so
no need to change around that.


thanks,

Takashi

Rich Felker Oct. 8, 2021, 12:06 p.m. UTC | #17

On Fri, Oct 08, 2021 at 11:24:39AM +0200, Arnd Bergmann wrote:
> On Fri, Oct 8, 2021 at 10:43 AM Takashi Iwai <[e-mail]> wrote:
> > On Thu, 07 Oct 2021 18:51:58 +0200, Rich Felker wrote:
> > > On Thu, Oct 07, 2021 at 06:18:52PM +0200, Takashi Iwai wrote:
> >
> > @@ -557,11 +558,15 @@ struct __snd_pcm_sync_ptr {
> >  #if defined(__BYTE_ORDER) ? __BYTE_ORDER == __BIG_ENDIAN : defined(__BIG_ENDIAN)
> >  typedef char __pad_before_uframe[sizeof(__u64) - sizeof(snd_pcm_uframes_t)];
> >  typedef char __pad_after_uframe[0];
> > +typedef char __pad_before_u32[4];
> > +typedef char __pad_after_u32[0];
> >  #endif
> >
> >  #if defined(__BYTE_ORDER) ? __BYTE_ORDER == __LITTLE_ENDIAN : defined(__LITTLE_ENDIAN)
> >  typedef char __pad_before_uframe[0];
> >  typedef char __pad_after_uframe[sizeof(__u64) - sizeof(snd_pcm_uframes_t)];
> > +typedef char __pad_before_u32[0];
> > +typedef char __pad_after_u32[4];
> >  #endif
> 
> I think these should remain unchanged, the complex expression was intentionally
> done so the structures are laid out the same way on 64-bit
> architectures, so that
> the kernel can use the __SND_STRUCT_TIME64 path internally on both 32-bit
> and 64-bit architectures.
> 
> > @@ -2970,8 +2981,17 @@ static int snd_pcm_sync_ptr(struct snd_pcm_substream *substream,
> >         memset(&sync_ptr, 0, sizeof(sync_ptr));
> >         if (get_user(sync_ptr.flags, (unsigned __user *)&(_sync_ptr->flags)))
> >                 return -EFAULT;
> > -       if (copy_from_user(&sync_ptr.c.control, &(_sync_ptr->c.control), sizeof(struct snd_pcm_mmap_control)))
> > -               return -EFAULT;
> > +       if (buggy_control) {
> > +               if (copy_from_user(&sync_ptr.c.control_api_2_0_15,
> > +                                  &(_sync_ptr->c.control_api_2_0_15),
> > +                                  sizeof(sync_ptr.c.control_api_2_0_15)))
> > +                       return -EFAULT;
> > +       } else {
> > +               if (copy_from_user(&sync_ptr.c.control,
> > +                                  &(_sync_ptr->c.control),
> > +                                  sizeof(sync_ptr.c.control)))
> > +                       return -EFAULT;
> > +       }
> 
> The problem I see with this is that it might break musl's ability to
> emulate the new
> interface on top of the old (time32) one for linux-4.x and older
> kernels, as the conversion
> function is no longer stateless but has to know the negotiated
> interface version.
> 
> It's probably fine as long as we can be sure that the 2.0.16+ API
> version only gets
> negotiated if both the kernel and user sides support it, and musl only emulates
> the 2.0.15 API version from the current kernels.
> 
> I've tried to understand this part of musl's convert_ioctl_struct(), but I just
> can't figure out whether it does the conversion based the on the layout that
> is currently used in the kernel, or based on the layout we should have been
> using, and would use with the above fix. Rich, can you help me here?

If the attempted 64-bit ioctl is missing (ENOTTY), it does the
conversion to the legacy 32-bit one and retries with that, then
converts the results back to the 64-bit form.

Not only do I fail to see how the proposed fix is workable with this
framework; I also don't see how the proposed fix would let new
applications (compiled without the buggy type) run on old kernels. I'm
pretty sure there really should be a new ioctl number for this...

Rich

Rich Felker Oct. 8, 2021, 12:07 p.m. UTC | #18

On Fri, Oct 08, 2021 at 01:11:34PM +0200, Takashi Iwai wrote:
> On Fri, 08 Oct 2021 11:24:39 +0200,
> Arnd Bergmann wrote:
> > 
> > On Fri, Oct 8, 2021 at 10:43 AM Takashi Iwai <[e-mail]> wrote:
> > > On Thu, 07 Oct 2021 18:51:58 +0200, Rich Felker wrote:
> > > > On Thu, Oct 07, 2021 at 06:18:52PM +0200, Takashi Iwai wrote:
> > >
> > > @@ -557,11 +558,15 @@ struct __snd_pcm_sync_ptr {
> > >  #if defined(__BYTE_ORDER) ? __BYTE_ORDER == __BIG_ENDIAN : defined(__BIG_ENDIAN)
> > >  typedef char __pad_before_uframe[sizeof(__u64) - sizeof(snd_pcm_uframes_t)];
> > >  typedef char __pad_after_uframe[0];
> > > +typedef char __pad_before_u32[4];
> > > +typedef char __pad_after_u32[0];
> > >  #endif
> > >
> > >  #if defined(__BYTE_ORDER) ? __BYTE_ORDER == __LITTLE_ENDIAN : defined(__LITTLE_ENDIAN)
> > >  typedef char __pad_before_uframe[0];
> > >  typedef char __pad_after_uframe[sizeof(__u64) - sizeof(snd_pcm_uframes_t)];
> > > +typedef char __pad_before_u32[0];
> > > +typedef char __pad_after_u32[4];
> > >  #endif
> > 
> > I think these should remain unchanged, the complex expression was intentionally
> > done so the structures are laid out the same way on 64-bit
> > architectures, so that
> > the kernel can use the __SND_STRUCT_TIME64 path internally on both 32-bit
> > and 64-bit architectures.
> 
> That was explicitly defined, but OK, this isn't necessarily defined
> here.
> 
> > > @@ -2970,8 +2981,17 @@ static int snd_pcm_sync_ptr(struct snd_pcm_substream *substream,
> > >         memset(&sync_ptr, 0, sizeof(sync_ptr));
> > >         if (get_user(sync_ptr.flags, (unsigned __user *)&(_sync_ptr->flags)))
> > >                 return -EFAULT;
> > > -       if (copy_from_user(&sync_ptr.c.control, &(_sync_ptr->c.control), sizeof(struct snd_pcm_mmap_control)))
> > > -               return -EFAULT;
> > > +       if (buggy_control) {
> > > +               if (copy_from_user(&sync_ptr.c.control_api_2_0_15,
> > > +                                  &(_sync_ptr->c.control_api_2_0_15),
> > > +                                  sizeof(sync_ptr.c.control_api_2_0_15)))
> > > +                       return -EFAULT;
> > > +       } else {
> > > +               if (copy_from_user(&sync_ptr.c.control,
> > > +                                  &(_sync_ptr->c.control),
> > > +                                  sizeof(sync_ptr.c.control)))
> > > +                       return -EFAULT;
> > > +       }
> > 
> > The problem I see with this is that it might break musl's ability to
> > emulate the new
> > interface on top of the old (time32) one for linux-4.x and older
> > kernels, as the conversion
> > function is no longer stateless but has to know the negotiated
> > interface version.
> > 
> > It's probably fine as long as we can be sure that the 2.0.16+ API
> > version only gets
> > negotiated if both the kernel and user sides support it, and musl only emulates
> > the 2.0.15 API version from the current kernels.
> > 
> > I've tried to understand this part of musl's convert_ioctl_struct(), but I just
> > can't figure out whether it does the conversion based the on the layout that
> > is currently used in the kernel, or based on the layout we should have been
> > using, and would use with the above fix. Rich, can you help me here?
> 
> So, at this moment, I'm not sure whether we should correct the struct
> at all.  This will lead to yet more breakage, and basically the struct
> itself *works* -- the only bug is in 32bit compat handling in the
> kernel (again).
> 
> The below is a revised kernel patch (again untested), just correcting
> the behavior of 32bit compat mode.  32bit apps on 32bit kernel work
> fine as is, as well as 64bit apps on 64bit kernel.

I'm perfectly okay with this if Arnd is! It's probably the least
invasive and has the least long-term maintenance cost and fallout on
other projects.

Rich

Arnd Bergmann Oct. 8, 2021, 12:13 p.m. UTC | #19

On Fri, Oct 8, 2021 at 1:53 PM Takashi Iwai <[e-mail]> wrote:
> On Fri, 08 Oct 2021 13:45:45 +0200, Arnd Bergmann wrote:
> > On Fri, Oct 8, 2021 at 1:11 PM Takashi Iwai <[e-mail]> wrote:
> > > On Fri, 08 Oct 2021 11:24:39 +0200, Arnd Bergmann wrote:
> > > The below is a revised kernel patch (again untested), just correcting
> > > the behavior of 32bit compat mode.  32bit apps on 32bit kernel work
> > > fine as is, as well as 64bit apps on 64bit kernel.
> >
> > Right, this should cover all cases of the ioctl itself misbehaving.
> > In addition, we still need to disallow the mmap() interface on compat
> > kernels then. Strictly speaking, we could allow the snd_pcm_mmap_status
> > but not snd_pcm_mmap_control to be mapped, but I'm not sure if
> > that's better than disallowing both.
>
> IIRC, the compat mmap is already disallowed even for the
> SNDRV_PCM_MMAP_OFFSET_CONTROL_NEW (in pcm_control_mmap_allowed()), so
> no need to change around that.

Ah, right. I think it was meant to become allowed as part of commit
80fe7430c708 ("ALSA: add new 32-bit layout for snd_pcm_mmap_status/control"),
which did allow the snd_pcm_mmap_status to be mmap()ed, but it appears
to be the rare case where two mistakes cancel out and we don't have to
change the mmap code.

         Arnd

Arnd Bergmann Oct. 8, 2021, 12:37 p.m. UTC | #20

On Fri, Oct 8, 2021 at 2:06 PM Rich Felker <[e-mail]> wrote:
> On Fri, Oct 08, 2021 at 11:24:39AM +0200, Arnd Bergmann wrote:
> >
> > I've tried to understand this part of musl's convert_ioctl_struct(), but I just
> > can't figure out whether it does the conversion based the on the layout that
> > is currently used in the kernel, or based on the layout we should have been
> > using, and would use with the above fix. Rich, can you help me here?
>
> If the attempted 64-bit ioctl is missing (ENOTTY), it does the
> conversion to the legacy 32-bit one and retries with that, then
> converts the results back to the 64-bit form.

I understand that it tries to do that.

The part that I'm not sure about is which of the two possible
64-bit forms it's using -- the broken one we have defined in the
kernel headers, or the one we were trying to define but failed.

      Arnd

Rich Felker Oct. 8, 2021, 5:20 p.m. UTC | #21

On Fri, Oct 08, 2021 at 02:37:12PM +0200, Arnd Bergmann wrote:
> On Fri, Oct 8, 2021 at 2:06 PM Rich Felker <[e-mail]> wrote:
> > On Fri, Oct 08, 2021 at 11:24:39AM +0200, Arnd Bergmann wrote:
> > >
> > > I've tried to understand this part of musl's convert_ioctl_struct(), but I just
> > > can't figure out whether it does the conversion based the on the layout that
> > > is currently used in the kernel, or based on the layout we should have been
> > > using, and would use with the above fix. Rich, can you help me here?
> >
> > If the attempted 64-bit ioctl is missing (ENOTTY), it does the
> > conversion to the legacy 32-bit one and retries with that, then
> > converts the results back to the 64-bit form.
> 
> I understand that it tries to do that.
> 
> The part that I'm not sure about is which of the two possible
> 64-bit forms it's using -- the broken one we have defined in the
> kernel headers, or the one we were trying to define but failed.

It's attempting to convert the intended format, not the one that the
uapi headers defined. That is, it's taking padded-to-64-bit values at
offsets 0 and 8 in __snd_pcm_mmap_control64, putting them at offsets 0
and 4 in the 32-bit struct, and padding them back to 64-bit in the
result.

Since applications would have been compiled with the buggy
(unintended) version of the uapi headers, this will not match the
application's layout of the struct. I haven't worked through what all
the consequences of that are, but I think some fix is needed here in
musl regardless of what happens on the kernel side.

Rich

Takashi Iwai Oct. 10, 2021, 7:53 a.m. UTC | #22

On Fri, 08 Oct 2021 14:07:39 +0200,
Rich Felker wrote:
> 
> On Fri, Oct 08, 2021 at 01:11:34PM +0200, Takashi Iwai wrote:
> > On Fri, 08 Oct 2021 11:24:39 +0200,
> > Arnd Bergmann wrote:
> > > 
> > > On Fri, Oct 8, 2021 at 10:43 AM Takashi Iwai <[e-mail]> wrote:
> > > > On Thu, 07 Oct 2021 18:51:58 +0200, Rich Felker wrote:
> > > > > On Thu, Oct 07, 2021 at 06:18:52PM +0200, Takashi Iwai wrote:
> > > >
> > > > @@ -557,11 +558,15 @@ struct __snd_pcm_sync_ptr {
> > > >  #if defined(__BYTE_ORDER) ? __BYTE_ORDER == __BIG_ENDIAN : defined(__BIG_ENDIAN)
> > > >  typedef char __pad_before_uframe[sizeof(__u64) - sizeof(snd_pcm_uframes_t)];
> > > >  typedef char __pad_after_uframe[0];
> > > > +typedef char __pad_before_u32[4];
> > > > +typedef char __pad_after_u32[0];
> > > >  #endif
> > > >
> > > >  #if defined(__BYTE_ORDER) ? __BYTE_ORDER == __LITTLE_ENDIAN : defined(__LITTLE_ENDIAN)
> > > >  typedef char __pad_before_uframe[0];
> > > >  typedef char __pad_after_uframe[sizeof(__u64) - sizeof(snd_pcm_uframes_t)];
> > > > +typedef char __pad_before_u32[0];
> > > > +typedef char __pad_after_u32[4];
> > > >  #endif
> > > 
> > > I think these should remain unchanged, the complex expression was intentionally
> > > done so the structures are laid out the same way on 64-bit
> > > architectures, so that
> > > the kernel can use the __SND_STRUCT_TIME64 path internally on both 32-bit
> > > and 64-bit architectures.
> > 
> > That was explicitly defined, but OK, this isn't necessarily defined
> > here.
> > 
> > > > @@ -2970,8 +2981,17 @@ static int snd_pcm_sync_ptr(struct snd_pcm_substream *substream,
> > > >         memset(&sync_ptr, 0, sizeof(sync_ptr));
> > > >         if (get_user(sync_ptr.flags, (unsigned __user *)&(_sync_ptr->flags)))
> > > >                 return -EFAULT;
> > > > -       if (copy_from_user(&sync_ptr.c.control, &(_sync_ptr->c.control), sizeof(struct snd_pcm_mmap_control)))
> > > > -               return -EFAULT;
> > > > +       if (buggy_control) {
> > > > +               if (copy_from_user(&sync_ptr.c.control_api_2_0_15,
> > > > +                                  &(_sync_ptr->c.control_api_2_0_15),
> > > > +                                  sizeof(sync_ptr.c.control_api_2_0_15)))
> > > > +                       return -EFAULT;
> > > > +       } else {
> > > > +               if (copy_from_user(&sync_ptr.c.control,
> > > > +                                  &(_sync_ptr->c.control),
> > > > +                                  sizeof(sync_ptr.c.control)))
> > > > +                       return -EFAULT;
> > > > +       }
> > > 
> > > The problem I see with this is that it might break musl's ability to
> > > emulate the new
> > > interface on top of the old (time32) one for linux-4.x and older
> > > kernels, as the conversion
> > > function is no longer stateless but has to know the negotiated
> > > interface version.
> > > 
> > > It's probably fine as long as we can be sure that the 2.0.16+ API
> > > version only gets
> > > negotiated if both the kernel and user sides support it, and musl only emulates
> > > the 2.0.15 API version from the current kernels.
> > > 
> > > I've tried to understand this part of musl's convert_ioctl_struct(), but I just
> > > can't figure out whether it does the conversion based the on the layout that
> > > is currently used in the kernel, or based on the layout we should have been
> > > using, and would use with the above fix. Rich, can you help me here?
> > 
> > So, at this moment, I'm not sure whether we should correct the struct
> > at all.  This will lead to yet more breakage, and basically the struct
> > itself *works* -- the only bug is in 32bit compat handling in the
> > kernel (again).
> > 
> > The below is a revised kernel patch (again untested), just correcting
> > the behavior of 32bit compat mode.  32bit apps on 32bit kernel work
> > fine as is, as well as 64bit apps on 64bit kernel.
> 
> I'm perfectly okay with this if Arnd is! It's probably the least
> invasive and has the least long-term maintenance cost and fallout on
> other projects.

OK, I'll submit a proper patch now, to be included in the next PR for
5.15-rc.  For further fixes, let's think carefully.


thanks,

Takashi

Rich Felker Oct. 18, 2021, 2:43 p.m. UTC | #23

On Sun, Oct 10, 2021 at 09:53:38AM +0200, Takashi Iwai wrote:
> On Fri, 08 Oct 2021 14:07:39 +0200,
> Rich Felker wrote:
> > 
> > On Fri, Oct 08, 2021 at 01:11:34PM +0200, Takashi Iwai wrote:
> > > On Fri, 08 Oct 2021 11:24:39 +0200,
> > > Arnd Bergmann wrote:
> > > > 
> > > > On Fri, Oct 8, 2021 at 10:43 AM Takashi Iwai <[e-mail]> wrote:
> > > > > On Thu, 07 Oct 2021 18:51:58 +0200, Rich Felker wrote:
> > > > > > On Thu, Oct 07, 2021 at 06:18:52PM +0200, Takashi Iwai wrote:
> > > > >
> > > > > @@ -557,11 +558,15 @@ struct __snd_pcm_sync_ptr {
> > > > >  #if defined(__BYTE_ORDER) ? __BYTE_ORDER == __BIG_ENDIAN : defined(__BIG_ENDIAN)
> > > > >  typedef char __pad_before_uframe[sizeof(__u64) - sizeof(snd_pcm_uframes_t)];
> > > > >  typedef char __pad_after_uframe[0];
> > > > > +typedef char __pad_before_u32[4];
> > > > > +typedef char __pad_after_u32[0];
> > > > >  #endif
> > > > >
> > > > >  #if defined(__BYTE_ORDER) ? __BYTE_ORDER == __LITTLE_ENDIAN : defined(__LITTLE_ENDIAN)
> > > > >  typedef char __pad_before_uframe[0];
> > > > >  typedef char __pad_after_uframe[sizeof(__u64) - sizeof(snd_pcm_uframes_t)];
> > > > > +typedef char __pad_before_u32[0];
> > > > > +typedef char __pad_after_u32[4];
> > > > >  #endif
> > > > 
> > > > I think these should remain unchanged, the complex expression was intentionally
> > > > done so the structures are laid out the same way on 64-bit
> > > > architectures, so that
> > > > the kernel can use the __SND_STRUCT_TIME64 path internally on both 32-bit
> > > > and 64-bit architectures.
> > > 
> > > That was explicitly defined, but OK, this isn't necessarily defined
> > > here.
> > > 
> > > > > @@ -2970,8 +2981,17 @@ static int snd_pcm_sync_ptr(struct snd_pcm_substream *substream,
> > > > >         memset(&sync_ptr, 0, sizeof(sync_ptr));
> > > > >         if (get_user(sync_ptr.flags, (unsigned __user *)&(_sync_ptr->flags)))
> > > > >                 return -EFAULT;
> > > > > -       if (copy_from_user(&sync_ptr.c.control, &(_sync_ptr->c.control), sizeof(struct snd_pcm_mmap_control)))
> > > > > -               return -EFAULT;
> > > > > +       if (buggy_control) {
> > > > > +               if (copy_from_user(&sync_ptr.c.control_api_2_0_15,
> > > > > +                                  &(_sync_ptr->c.control_api_2_0_15),
> > > > > +                                  sizeof(sync_ptr.c.control_api_2_0_15)))
> > > > > +                       return -EFAULT;
> > > > > +       } else {
> > > > > +               if (copy_from_user(&sync_ptr.c.control,
> > > > > +                                  &(_sync_ptr->c.control),
> > > > > +                                  sizeof(sync_ptr.c.control)))
> > > > > +                       return -EFAULT;
> > > > > +       }
> > > > 
> > > > The problem I see with this is that it might break musl's ability to
> > > > emulate the new
> > > > interface on top of the old (time32) one for linux-4.x and older
> > > > kernels, as the conversion
> > > > function is no longer stateless but has to know the negotiated
> > > > interface version.
> > > > 
> > > > It's probably fine as long as we can be sure that the 2.0.16+ API
> > > > version only gets
> > > > negotiated if both the kernel and user sides support it, and musl only emulates
> > > > the 2.0.15 API version from the current kernels.
> > > > 
> > > > I've tried to understand this part of musl's convert_ioctl_struct(), but I just
> > > > can't figure out whether it does the conversion based the on the layout that
> > > > is currently used in the kernel, or based on the layout we should have been
> > > > using, and would use with the above fix. Rich, can you help me here?
> > > 
> > > So, at this moment, I'm not sure whether we should correct the struct
> > > at all.  This will lead to yet more breakage, and basically the struct
> > > itself *works* -- the only bug is in 32bit compat handling in the
> > > kernel (again).
> > > 
> > > The below is a revised kernel patch (again untested), just correcting
> > > the behavior of 32bit compat mode.  32bit apps on 32bit kernel work
> > > fine as is, as well as 64bit apps on 64bit kernel.
> > 
> > I'm perfectly okay with this if Arnd is! It's probably the least
> > invasive and has the least long-term maintenance cost and fallout on
> > other projects.
> 
> OK, I'll submit a proper patch now, to be included in the next PR for
> 5.15-rc.  For further fixes, let's think carefully.

Am I correct in my understanding that the fix of keeping the "broken"
definition (and having the 64-bit kernel honor it for 32-bit binaries)
has been accepted? Since musl's translation for pre-time64 kernels
seems to have been using the "non-broken" definition, I think
completing the fix requires a change in musl too.

Rich

Takashi Iwai Oct. 18, 2021, 2:58 p.m. UTC | #24

On Mon, 18 Oct 2021 16:43:00 +0200,
Rich Felker wrote:
> 
> On Sun, Oct 10, 2021 at 09:53:38AM +0200, Takashi Iwai wrote:
> > On Fri, 08 Oct 2021 14:07:39 +0200,
> > Rich Felker wrote:
> > > 
> > > On Fri, Oct 08, 2021 at 01:11:34PM +0200, Takashi Iwai wrote:
> > > > On Fri, 08 Oct 2021 11:24:39 +0200,
> > > > Arnd Bergmann wrote:
> > > > > 
> > > > > On Fri, Oct 8, 2021 at 10:43 AM Takashi Iwai <[e-mail]> wrote:
> > > > > > On Thu, 07 Oct 2021 18:51:58 +0200, Rich Felker wrote:
> > > > > > > On Thu, Oct 07, 2021 at 06:18:52PM +0200, Takashi Iwai wrote:
> > > > > >
> > > > > > @@ -557,11 +558,15 @@ struct __snd_pcm_sync_ptr {
> > > > > >  #if defined(__BYTE_ORDER) ? __BYTE_ORDER == __BIG_ENDIAN : defined(__BIG_ENDIAN)
> > > > > >  typedef char __pad_before_uframe[sizeof(__u64) - sizeof(snd_pcm_uframes_t)];
> > > > > >  typedef char __pad_after_uframe[0];
> > > > > > +typedef char __pad_before_u32[4];
> > > > > > +typedef char __pad_after_u32[0];
> > > > > >  #endif
> > > > > >
> > > > > >  #if defined(__BYTE_ORDER) ? __BYTE_ORDER == __LITTLE_ENDIAN : defined(__LITTLE_ENDIAN)
> > > > > >  typedef char __pad_before_uframe[0];
> > > > > >  typedef char __pad_after_uframe[sizeof(__u64) - sizeof(snd_pcm_uframes_t)];
> > > > > > +typedef char __pad_before_u32[0];
> > > > > > +typedef char __pad_after_u32[4];
> > > > > >  #endif
> > > > > 
> > > > > I think these should remain unchanged, the complex expression was intentionally
> > > > > done so the structures are laid out the same way on 64-bit
> > > > > architectures, so that
> > > > > the kernel can use the __SND_STRUCT_TIME64 path internally on both 32-bit
> > > > > and 64-bit architectures.
> > > > 
> > > > That was explicitly defined, but OK, this isn't necessarily defined
> > > > here.
> > > > 
> > > > > > @@ -2970,8 +2981,17 @@ static int snd_pcm_sync_ptr(struct snd_pcm_substream *substream,
> > > > > >         memset(&sync_ptr, 0, sizeof(sync_ptr));
> > > > > >         if (get_user(sync_ptr.flags, (unsigned __user *)&(_sync_ptr->flags)))
> > > > > >                 return -EFAULT;
> > > > > > -       if (copy_from_user(&sync_ptr.c.control, &(_sync_ptr->c.control), sizeof(struct snd_pcm_mmap_control)))
> > > > > > -               return -EFAULT;
> > > > > > +       if (buggy_control) {
> > > > > > +               if (copy_from_user(&sync_ptr.c.control_api_2_0_15,
> > > > > > +                                  &(_sync_ptr->c.control_api_2_0_15),
> > > > > > +                                  sizeof(sync_ptr.c.control_api_2_0_15)))
> > > > > > +                       return -EFAULT;
> > > > > > +       } else {
> > > > > > +               if (copy_from_user(&sync_ptr.c.control,
> > > > > > +                                  &(_sync_ptr->c.control),
> > > > > > +                                  sizeof(sync_ptr.c.control)))
> > > > > > +                       return -EFAULT;
> > > > > > +       }
> > > > > 
> > > > > The problem I see with this is that it might break musl's ability to
> > > > > emulate the new
> > > > > interface on top of the old (time32) one for linux-4.x and older
> > > > > kernels, as the conversion
> > > > > function is no longer stateless but has to know the negotiated
> > > > > interface version.
> > > > > 
> > > > > It's probably fine as long as we can be sure that the 2.0.16+ API
> > > > > version only gets
> > > > > negotiated if both the kernel and user sides support it, and musl only emulates
> > > > > the 2.0.15 API version from the current kernels.
> > > > > 
> > > > > I've tried to understand this part of musl's convert_ioctl_struct(), but I just
> > > > > can't figure out whether it does the conversion based the on the layout that
> > > > > is currently used in the kernel, or based on the layout we should have been
> > > > > using, and would use with the above fix. Rich, can you help me here?
> > > > 
> > > > So, at this moment, I'm not sure whether we should correct the struct
> > > > at all.  This will lead to yet more breakage, and basically the struct
> > > > itself *works* -- the only bug is in 32bit compat handling in the
> > > > kernel (again).
> > > > 
> > > > The below is a revised kernel patch (again untested), just correcting
> > > > the behavior of 32bit compat mode.  32bit apps on 32bit kernel work
> > > > fine as is, as well as 64bit apps on 64bit kernel.
> > > 
> > > I'm perfectly okay with this if Arnd is! It's probably the least
> > > invasive and has the least long-term maintenance cost and fallout on
> > > other projects.
> > 
> > OK, I'll submit a proper patch now, to be included in the next PR for
> > 5.15-rc.  For further fixes, let's think carefully.
> 
> Am I correct in my understanding that the fix of keeping the "broken"
> definition (and having the 64-bit kernel honor it for 32-bit binaries)
> has been accepted?

Yes, as it was already set in stone, we accept the broken definition
as is.

> Since musl's translation for pre-time64 kernels
> seems to have been using the "non-broken" definition, I think
> completing the fix requires a change in musl too.

Hm, musl translator contains the own definition of ioctl?

If so, we may reconsider about renumbering ioctls altogether.
Suppose musl having a fallback to the old ioctl, the possible breakage
by old kernels (that don't support renewed ioctls) would be minimal,
right?


Takashi

Rich Felker Oct. 18, 2021, 3:08 p.m. UTC | #25

On Mon, Oct 18, 2021 at 04:58:03PM +0200, Takashi Iwai wrote:
> On Mon, 18 Oct 2021 16:43:00 +0200,
> Rich Felker wrote:
> > 
> > On Sun, Oct 10, 2021 at 09:53:38AM +0200, Takashi Iwai wrote:
> > > On Fri, 08 Oct 2021 14:07:39 +0200,
> > > Rich Felker wrote:
> > > > 
> > > > On Fri, Oct 08, 2021 at 01:11:34PM +0200, Takashi Iwai wrote:
> > > > > On Fri, 08 Oct 2021 11:24:39 +0200,
> > > > > Arnd Bergmann wrote:
> > > > > > 
> > > > > > On Fri, Oct 8, 2021 at 10:43 AM Takashi Iwai <[e-mail]> wrote:
> > > > > > > On Thu, 07 Oct 2021 18:51:58 +0200, Rich Felker wrote:
> > > > > > > > On Thu, Oct 07, 2021 at 06:18:52PM +0200, Takashi Iwai wrote:
> > > > > > >
> > > > > > > @@ -557,11 +558,15 @@ struct __snd_pcm_sync_ptr {
> > > > > > >  #if defined(__BYTE_ORDER) ? __BYTE_ORDER == __BIG_ENDIAN : defined(__BIG_ENDIAN)
> > > > > > >  typedef char __pad_before_uframe[sizeof(__u64) - sizeof(snd_pcm_uframes_t)];
> > > > > > >  typedef char __pad_after_uframe[0];
> > > > > > > +typedef char __pad_before_u32[4];
> > > > > > > +typedef char __pad_after_u32[0];
> > > > > > >  #endif
> > > > > > >
> > > > > > >  #if defined(__BYTE_ORDER) ? __BYTE_ORDER == __LITTLE_ENDIAN : defined(__LITTLE_ENDIAN)
> > > > > > >  typedef char __pad_before_uframe[0];
> > > > > > >  typedef char __pad_after_uframe[sizeof(__u64) - sizeof(snd_pcm_uframes_t)];
> > > > > > > +typedef char __pad_before_u32[0];
> > > > > > > +typedef char __pad_after_u32[4];
> > > > > > >  #endif
> > > > > > 
> > > > > > I think these should remain unchanged, the complex expression was intentionally
> > > > > > done so the structures are laid out the same way on 64-bit
> > > > > > architectures, so that
> > > > > > the kernel can use the __SND_STRUCT_TIME64 path internally on both 32-bit
> > > > > > and 64-bit architectures.
> > > > > 
> > > > > That was explicitly defined, but OK, this isn't necessarily defined
> > > > > here.
> > > > > 
> > > > > > > @@ -2970,8 +2981,17 @@ static int snd_pcm_sync_ptr(struct snd_pcm_substream *substream,
> > > > > > >         memset(&sync_ptr, 0, sizeof(sync_ptr));
> > > > > > >         if (get_user(sync_ptr.flags, (unsigned __user *)&(_sync_ptr->flags)))
> > > > > > >                 return -EFAULT;
> > > > > > > -       if (copy_from_user(&sync_ptr.c.control, &(_sync_ptr->c.control), sizeof(struct snd_pcm_mmap_control)))
> > > > > > > -               return -EFAULT;
> > > > > > > +       if (buggy_control) {
> > > > > > > +               if (copy_from_user(&sync_ptr.c.control_api_2_0_15,
> > > > > > > +                                  &(_sync_ptr->c.control_api_2_0_15),
> > > > > > > +                                  sizeof(sync_ptr.c.control_api_2_0_15)))
> > > > > > > +                       return -EFAULT;
> > > > > > > +       } else {
> > > > > > > +               if (copy_from_user(&sync_ptr.c.control,
> > > > > > > +                                  &(_sync_ptr->c.control),
> > > > > > > +                                  sizeof(sync_ptr.c.control)))
> > > > > > > +                       return -EFAULT;
> > > > > > > +       }
> > > > > > 
> > > > > > The problem I see with this is that it might break musl's ability to
> > > > > > emulate the new
> > > > > > interface on top of the old (time32) one for linux-4.x and older
> > > > > > kernels, as the conversion
> > > > > > function is no longer stateless but has to know the negotiated
> > > > > > interface version.
> > > > > > 
> > > > > > It's probably fine as long as we can be sure that the 2.0.16+ API
> > > > > > version only gets
> > > > > > negotiated if both the kernel and user sides support it, and musl only emulates
> > > > > > the 2.0.15 API version from the current kernels.
> > > > > > 
> > > > > > I've tried to understand this part of musl's convert_ioctl_struct(), but I just
> > > > > > can't figure out whether it does the conversion based the on the layout that
> > > > > > is currently used in the kernel, or based on the layout we should have been
> > > > > > using, and would use with the above fix. Rich, can you help me here?
> > > > > 
> > > > > So, at this moment, I'm not sure whether we should correct the struct
> > > > > at all.  This will lead to yet more breakage, and basically the struct
> > > > > itself *works* -- the only bug is in 32bit compat handling in the
> > > > > kernel (again).
> > > > > 
> > > > > The below is a revised kernel patch (again untested), just correcting
> > > > > the behavior of 32bit compat mode.  32bit apps on 32bit kernel work
> > > > > fine as is, as well as 64bit apps on 64bit kernel.
> > > > 
> > > > I'm perfectly okay with this if Arnd is! It's probably the least
> > > > invasive and has the least long-term maintenance cost and fallout on
> > > > other projects.
> > > 
> > > OK, I'll submit a proper patch now, to be included in the next PR for
> > > 5.15-rc.  For further fixes, let's think carefully.
> > 
> > Am I correct in my understanding that the fix of keeping the "broken"
> > definition (and having the 64-bit kernel honor it for 32-bit binaries)
> > has been accepted?
> 
> Yes, as it was already set in stone, we accept the broken definition
> as is.
> 
> > Since musl's translation for pre-time64 kernels
> > seems to have been using the "non-broken" definition, I think
> > completing the fix requires a change in musl too.
> 
> Hm, musl translator contains the own definition of ioctl?
> 
> If so, we may reconsider about renumbering ioctls altogether.

No, I don't think so. The musl translator is to translate between the
time64 ioctl structures and the old time32 ones for the sake of
executing on an old kernel. Up til now, it has been broken comparably
to how 32-bit binaries running in compat mode on a 64-bit kernel were
broken: the code in musl translated the time64 structure to (and back
from) the time32 one assuming the intended padding. But the
application was using the actual kernel uapi struct where the padding
was (and still is) illogical. Thus, nothing was built with the wrong
ABI; it's only the musl-internal translation logic that was wrong (and
only pre-time64 kernels are affected).

The attached patch should fix it, I think.

Rich
diff --git a/src/misc/ioctl.c b/src/misc/ioctl.c
index 49282811..6d3e5095 100644
--- a/src/misc/ioctl.c
+++ b/src/misc/ioctl.c
@@ -6,6 +6,7 @@
 #include <stddef.h>
 #include <stdint.h>
 #include <string.h>
+#include <endian.h>
 #include "syscall.h"
 
 #define alignof(t) offsetof(struct { char c; t x; }, x)
@@ -90,7 +91,14 @@ static void convert_ioctl_struct(const struct ioctl_compat_map *map, char *old,
 		 * if another exception appears this needs changing. */
 		convert_ioctl_struct(map+1, old, new, dir);
 		convert_ioctl_struct(map+2, old+4, new+8, dir);
-		convert_ioctl_struct(map+3, old+68, new+72, dir);
+		int adj = BYTE_ORDER==BIG_ENDIAN ? 4 : 0;
+		if (dir==W) {
+			memcpy(old+68, new+72+adj, 4);
+			memcpy(old+72, new+72+4+2*adj, 4);
+		} else {
+			memcpy(new+72+adj, old+68, 4);
+			memcpy(new+72+4+2*adj, old+72, 4);
+		}
 		return;
 	}
 	for (int i=0; i < map->noffs; i++) {

Arnd Bergmann Oct. 18, 2021, 3:26 p.m. UTC | #26

On Mon, Oct 18, 2021 at 5:08 PM Rich Felker <[e-mail]> wrote:
> On Mon, Oct 18, 2021 at 04:58:03PM +0200, Takashi Iwai wrote:
> > On Mon, 18 Oct 2021 16:43:00 +0200, Rich Felker wrote:
>
> No, I don't think so. The musl translator is to translate between the
> time64 ioctl structures and the old time32 ones for the sake of
> executing on an old kernel. Up til now, it has been broken comparably
> to how 32-bit binaries running in compat mode on a 64-bit kernel were
> broken: the code in musl translated the time64 structure to (and back
> from) the time32 one assuming the intended padding. But the
> application was using the actual kernel uapi struct where the padding
> was (and still is) illogical. Thus, nothing was built with the wrong
> ABI; it's only the musl-internal translation logic that was wrong (and
> only pre-time64 kernels are affected).
>
> The attached patch should fix it, I think.
>
> + int adj = BYTE_ORDER==BIG_ENDIAN ? 4 : 0;
> + if (dir==W) {
> +     memcpy(old+68, new+72+adj, 4);
> +     memcpy(old+72, new+72+4+2*adj, 4);

I think that should be "new+72+4+3*adj": the "2*adj" would
be what the code does already for the originally intended
format.

        Arnd

Rich Felker Oct. 18, 2021, 8:42 p.m. UTC | #27

On Mon, Oct 18, 2021 at 05:26:35PM +0200, Arnd Bergmann wrote:
> On Mon, Oct 18, 2021 at 5:08 PM Rich Felker <[e-mail]> wrote:
> > On Mon, Oct 18, 2021 at 04:58:03PM +0200, Takashi Iwai wrote:
> > > On Mon, 18 Oct 2021 16:43:00 +0200, Rich Felker wrote:
> >
> > No, I don't think so. The musl translator is to translate between the
> > time64 ioctl structures and the old time32 ones for the sake of
> > executing on an old kernel. Up til now, it has been broken comparably
> > to how 32-bit binaries running in compat mode on a 64-bit kernel were
> > broken: the code in musl translated the time64 structure to (and back
> > from) the time32 one assuming the intended padding. But the
> > application was using the actual kernel uapi struct where the padding
> > was (and still is) illogical. Thus, nothing was built with the wrong
> > ABI; it's only the musl-internal translation logic that was wrong (and
> > only pre-time64 kernels are affected).
> >
> > The attached patch should fix it, I think.
> >
> > + int adj = BYTE_ORDER==BIG_ENDIAN ? 4 : 0;
> > + if (dir==W) {
> > +     memcpy(old+68, new+72+adj, 4);
> > +     memcpy(old+72, new+72+4+2*adj, 4);
> 
> I think that should be "new+72+4+3*adj": the "2*adj" would
> be what the code does already for the originally intended
> format.

Well for little endian either would work (because adj is 0 :) but yes
there are 3 such paddings before the second member on big endian, so
it should be 3.

Rich

Rich Felker Oct. 19, 2021, 2:16 p.m. UTC | #28

On Mon, Oct 18, 2021 at 04:42:04PM -0400, Rich Felker wrote:
> On Mon, Oct 18, 2021 at 05:26:35PM +0200, Arnd Bergmann wrote:
> > On Mon, Oct 18, 2021 at 5:08 PM Rich Felker <[e-mail]> wrote:
> > > On Mon, Oct 18, 2021 at 04:58:03PM +0200, Takashi Iwai wrote:
> > > > On Mon, 18 Oct 2021 16:43:00 +0200, Rich Felker wrote:
> > >
> > > No, I don't think so. The musl translator is to translate between the
> > > time64 ioctl structures and the old time32 ones for the sake of
> > > executing on an old kernel. Up til now, it has been broken comparably
> > > to how 32-bit binaries running in compat mode on a 64-bit kernel were
> > > broken: the code in musl translated the time64 structure to (and back
> > > from) the time32 one assuming the intended padding. But the
> > > application was using the actual kernel uapi struct where the padding
> > > was (and still is) illogical. Thus, nothing was built with the wrong
> > > ABI; it's only the musl-internal translation logic that was wrong (and
> > > only pre-time64 kernels are affected).
> > >
> > > The attached patch should fix it, I think.
> > >
> > > + int adj = BYTE_ORDER==BIG_ENDIAN ? 4 : 0;
> > > + if (dir==W) {
> > > +     memcpy(old+68, new+72+adj, 4);
> > > +     memcpy(old+72, new+72+4+2*adj, 4);
> > 
> > I think that should be "new+72+4+3*adj": the "2*adj" would
> > be what the code does already for the originally intended
> > format.
> 
> Well for little endian either would work (because adj is 0 :) but yes
> there are 3 such paddings before the second member on big endian, so
> it should be 3.

How about this? It avoids open coding the logic and handles it as 2
4-byte substructures with endian-specific offsets.

Rich
diff --git a/src/misc/ioctl.c b/src/misc/ioctl.c
index 49282811..35804f02 100644
--- a/src/misc/ioctl.c
+++ b/src/misc/ioctl.c
@@ -6,6 +6,7 @@
 #include <stddef.h>
 #include <stdint.h>
 #include <string.h>
+#include <endian.h>
 #include "syscall.h"
 
 #define alignof(t) offsetof(struct { char c; t x; }, x)
@@ -53,7 +54,7 @@ static const struct ioctl_compat_map compat_map[] = {
 	{ _IOWR('A', 0x23, char[136]), _IOWR('A', 0x23, char[132]), 0, WR, 1, 0 },
 	{ 0, 0, 4, WR, 1, 0 }, /* snd_pcm_sync_ptr (flags only) */
 	{ 0, 0, 32, WR, 1, OFFS(8,12,16,24,28) }, /* snd_pcm_mmap_status */
-	{ 0, 0, 8, WR, 1, OFFS(0,4) }, /* snd_pcm_mmap_control */
+	{ 0, 0, 4, WR, 1, 0 }, /* snd_pcm_mmap_control (each member) */
 
 	/* VIDIOC_QUERYBUF, VIDIOC_QBUF, VIDIOC_DQBUF, VIDIOC_PREPARE_BUF */
 	{ _IOWR('V',  9, new_misaligned(68)), _IOWR('V',  9, char[68]), 68, WR, 1, OFFS(20, 24) },
@@ -90,7 +91,11 @@ static void convert_ioctl_struct(const struct ioctl_compat_map *map, char *old,
 		 * if another exception appears this needs changing. */
 		convert_ioctl_struct(map+1, old, new, dir);
 		convert_ioctl_struct(map+2, old+4, new+8, dir);
-		convert_ioctl_struct(map+3, old+68, new+72, dir);
+		/* snd_pcm_mmap_control, special-cased due to kernel
+		 * type definition having been botched. */
+		int adj = BYTE_ORDER==BIG_ENDIAN ? 4 : 0;
+		convert_ioctl_struct(map+3, old+68, new+72+adj, dir);
+		convert_ioctl_struct(map+3, old+72, new+76+3*adj, dir);
 		return;
 	}
 	for (int i=0; i < map->noffs; i++) {

Arnd Bergmann Oct. 19, 2021, 2:23 p.m. UTC | #29

On Tue, Oct 19, 2021 at 4:16 PM Rich Felker <[e-mail]> wrote:
> On Mon, Oct 18, 2021 at 04:42:04PM -0400, Rich Felker wrote:
> >
> > Well for little endian either would work (because adj is 0 :) but yes
> > there are 3 such paddings before the second member on big endian, so
> > it should be 3.
>
> How about this? It avoids open coding the logic and handles it as 2
> 4-byte substructures with endian-specific offsets.

Looks good to me.

      Arnd

Patch

diff --git a/include/uapi/sound/asound.h b/include/uapi/sound/asound.h
index ad86c5a7a1e2..df9983e7ead5 100644
--- a/include/uapi/sound/asound.h
+++ b/include/uapi/sound/asound.h
@@ -35,6 +35,8 @@ 
 #include <time.h>
 #endif
 
+#include <asm/byteorder.h>
+
 /*
  *  protocol version
  */
@@ -301,7 +303,9 @@  typedef int __bitwise snd_pcm_subformat_t;
 #define SNDRV_PCM_INFO_DRAIN_TRIGGER	0x40000000		/* internal kernel flag - trigger in drain */
 #define SNDRV_PCM_INFO_FIFO_IN_FRAMES	0x80000000	/* internal kernel flag - FIFO size is in frames */
 
-
+#if (__BITS_PER_LONG == 32 && defined(__USE_TIME_BITS64)) || defined __KERNEL__
+#define __SND_STRUCT_TIME64
+#endif
 
 typedef int __bitwise snd_pcm_state_t;
 #define	SNDRV_PCM_STATE_OPEN		((__force snd_pcm_state_t) 0) /* stream is open */
@@ -317,8 +321,17 @@  typedef int __bitwise snd_pcm_state_t;
 
 enum {
 	SNDRV_PCM_MMAP_OFFSET_DATA = 0x00000000,
-	SNDRV_PCM_MMAP_OFFSET_STATUS = 0x80000000,
-	SNDRV_PCM_MMAP_OFFSET_CONTROL = 0x81000000,
+	SNDRV_PCM_MMAP_OFFSET_STATUS_OLD = 0x80000000,
+	SNDRV_PCM_MMAP_OFFSET_CONTROL_OLD = 0x81000000,
+	SNDRV_PCM_MMAP_OFFSET_STATUS_NEW = 0x82000000,
+	SNDRV_PCM_MMAP_OFFSET_CONTROL_NEW = 0x83000000,
+#ifdef __SND_STRUCT_TIME64
+	SNDRV_PCM_MMAP_OFFSET_STATUS = SNDRV_PCM_MMAP_OFFSET_STATUS_NEW,
+	SNDRV_PCM_MMAP_OFFSET_CONTROL = SNDRV_PCM_MMAP_OFFSET_CONTROL_NEW,
+#else
+	SNDRV_PCM_MMAP_OFFSET_STATUS = SNDRV_PCM_MMAP_OFFSET_STATUS_OLD,
+	SNDRV_PCM_MMAP_OFFSET_CONTROL = SNDRV_PCM_MMAP_OFFSET_CONTROL_OLD,
+#endif
 };
 
 union snd_pcm_sync_id {
@@ -480,16 +493,46 @@  struct snd_pcm_status {
 };
 #endif
 
-struct snd_pcm_mmap_status {
+/*
+ * For mmap operations, we need the 64-bit layout, both for compat mode,
+ * and for y2038 compatibility. For 64-bit applications, the two definitions
+ * are identical, so we keep the traditional version.
+ */
+#ifdef __SND_STRUCT_TIME64
+#define __snd_pcm_mmap_status64		snd_pcm_mmap_status
+#define __snd_pcm_mmap_control64	snd_pcm_mmap_control
+#define __snd_pcm_sync_ptr64		snd_pcm_sync_ptr
+#ifdef __KERNEL__
+#define __snd_timespec64		__kernel_timespec
+#else
+#define __snd_timespec64		timespec
+#endif
+struct __snd_timespec {
+	__s32 tv_sec;
+	__s32 tv_nsec;
+};
+#else
+#define __snd_pcm_mmap_status		snd_pcm_mmap_status
+#define __snd_pcm_mmap_control		snd_pcm_mmap_control
+#define __snd_pcm_sync_ptr		snd_pcm_sync_ptr
+#define __snd_timespec			timespec
+struct __snd_timespec64 {
+	__s64 tv_sec;
+	__s64 tv_nsec;
+};
+
+#endif
+
+struct __snd_pcm_mmap_status {
 	snd_pcm_state_t state;		/* RO: state - SNDRV_PCM_STATE_XXXX */
 	int pad1;			/* Needed for 64 bit alignment */
 	snd_pcm_uframes_t hw_ptr;	/* RO: hw ptr (0...boundary-1) */
-	struct timespec tstamp;		/* Timestamp */
+	struct __snd_timespec tstamp;	/* Timestamp */
 	snd_pcm_state_t suspended_state; /* RO: suspended stream state */
-	struct timespec audio_tstamp;	/* from sample counter or wall clock */
+	struct __snd_timespec audio_tstamp; /* from sample counter or wall clock */
 };
 
-struct snd_pcm_mmap_control {
+struct __snd_pcm_mmap_control {
 	snd_pcm_uframes_t appl_ptr;	/* RW: appl ptr (0...boundary-1) */
 	snd_pcm_uframes_t avail_min;	/* RW: min available frames for wakeup */
 };
@@ -498,14 +541,59 @@  struct snd_pcm_mmap_control {
 #define SNDRV_PCM_SYNC_PTR_APPL		(1<<1)	/* get appl_ptr from driver (r/w op) */
 #define SNDRV_PCM_SYNC_PTR_AVAIL_MIN	(1<<2)	/* get avail_min from driver */
 
-struct snd_pcm_sync_ptr {
+struct __snd_pcm_sync_ptr {
 	unsigned int flags;
 	union {
-		struct snd_pcm_mmap_status status;
+		struct __snd_pcm_mmap_status status;
+		unsigned char reserved[64];
+	} s;
+	union {
+		struct __snd_pcm_mmap_control control;
+		unsigned char reserved[64];
+	} c;
+};
+
+#if defined(__BYTE_ORDER) ? __BYTE_ORDER == __BIG_ENDIAN : defined(__BIG_ENDIAN)
+typedef char __pad_before_uframe[sizeof(__u64) - sizeof(snd_pcm_uframes_t)];
+typedef char __pad_after_uframe[0];
+#endif
+
+#if defined(__BYTE_ORDER) ? __BYTE_ORDER == __LITTLE_ENDIAN : defined(__LITTLE_ENDIAN)
+typedef char __pad_before_uframe[0];
+typedef char __pad_after_uframe[sizeof(__u64) - sizeof(snd_pcm_uframes_t)];
+#endif
+
+struct __snd_pcm_mmap_status64 {
+	__s32 state;			/* RO: state - SNDRV_PCM_STATE_XXXX */
+	__u32 pad1;			/* Needed for 64 bit alignment */
+	__pad_before_uframe __pad1;
+	snd_pcm_uframes_t hw_ptr;	/* RO: hw ptr (0...boundary-1) */
+	__pad_after_uframe __pad2;
+	struct __snd_timespec64 tstamp;	/* Timestamp */
+	__s32 suspended_state;		/* RO: suspended stream state */
+	__u32 pad3;			/* Needed for 64 bit alignment */
+	struct __snd_timespec64 audio_tstamp; /* sample counter or wall clock */
+};
+
+struct __snd_pcm_mmap_control64 {
+	__pad_before_uframe __pad1;
+	snd_pcm_uframes_t appl_ptr;	 /* RW: appl ptr (0...boundary-1) */
+	__pad_before_uframe __pad2;
+
+	__pad_before_uframe __pad3;
+	snd_pcm_uframes_t  avail_min;	 /* RW: min available frames for wakeup */
+	__pad_after_uframe __pad4;
+};
+
+struct __snd_pcm_sync_ptr64 {
+	__u32 flags;
+	__u32 pad1;
+	union {
+		struct __snd_pcm_mmap_status64 status;
 		unsigned char reserved[64];
 	} s;
 	union {
-		struct snd_pcm_mmap_control control;
+		struct __snd_pcm_mmap_control64 control;
 		unsigned char reserved[64];
 	} c;
 };
@@ -590,6 +678,8 @@  enum {
 #define SNDRV_PCM_IOCTL_STATUS		_IOR('A', 0x20, struct snd_pcm_status)
 #define SNDRV_PCM_IOCTL_DELAY		_IOR('A', 0x21, snd_pcm_sframes_t)
 #define SNDRV_PCM_IOCTL_HWSYNC		_IO('A', 0x22)
+#define __SNDRV_PCM_IOCTL_SYNC_PTR	_IOWR('A', 0x23, struct __snd_pcm_sync_ptr)
+#define __SNDRV_PCM_IOCTL_SYNC_PTR64	_IOWR('A', 0x23, struct __snd_pcm_sync_ptr64)
 #define SNDRV_PCM_IOCTL_SYNC_PTR	_IOWR('A', 0x23, struct snd_pcm_sync_ptr)
 #define SNDRV_PCM_IOCTL_STATUS_EXT	_IOWR('A', 0x24, struct snd_pcm_status)
 #define SNDRV_PCM_IOCTL_CHANNEL_INFO	_IOR('A', 0x32, struct snd_pcm_channel_info)
diff --git a/sound/core/pcm_compat.c b/sound/core/pcm_compat.c
index 6a2e5ea145e6..967c689fb8da 100644
--- a/sound/core/pcm_compat.c
+++ b/sound/core/pcm_compat.c
@@ -178,8 +178,6 @@  struct compat_snd_pcm_status64 {
 	unsigned char reserved[52-4*sizeof(s64)];
 } __packed;
 
-#define put_timespec(src, dst) copy_to_user(dst, src, sizeof(*dst))
-
 static int snd_pcm_status_user_compat64(struct snd_pcm_substream *substream,
 					struct compat_snd_pcm_status64 __user *src,
 					bool ext)
@@ -382,10 +380,12 @@  struct snd_pcm_mmap_status_x32 {
 	s32 pad1;
 	u32 hw_ptr;
 	u32 pad2; /* alignment */
-	struct timespec tstamp;
+	s64 tstamp_sec;
+	s64 tstamp_nsec;
 	s32 suspended_state;
 	s32 pad3;
-	struct timespec audio_tstamp;
+	s64 audio_tstamp_sec;
+	s64 audio_tstamp_nsec;
 } __packed;
 
 struct snd_pcm_mmap_control_x32 {
@@ -453,9 +453,11 @@  static int snd_pcm_ioctl_sync_ptr_x32(struct snd_pcm_substream *substream,
 	snd_pcm_stream_unlock_irq(substream);
 	if (put_user(sstatus.state, &src->s.status.state) ||
 	    put_user(sstatus.hw_ptr, &src->s.status.hw_ptr) ||
-	    put_timespec(&sstatus.tstamp, &src->s.status.tstamp) ||
+	    put_user(sstatus.tstamp.tv_sec, &src->s.status.tstamp_sec) ||
+	    put_user(sstatus.tstamp.tv_nsec, &src->s.status.tstamp_nsec) ||
 	    put_user(sstatus.suspended_state, &src->s.status.suspended_state) ||
-	    put_timespec(&sstatus.audio_tstamp, &src->s.status.audio_tstamp) ||
+	    put_user(sstatus.audio_tstamp.tv_sec, &src->s.status.audio_tstamp_sec) ||
+	    put_user(sstatus.audio_tstamp.tv_nsec, &src->s.status.audio_tstamp_nsec) ||
 	    put_user(scontrol.appl_ptr, &src->c.control.appl_ptr) ||
 	    put_user(scontrol.avail_min, &src->c.control.avail_min))
 		return -EFAULT;
@@ -480,7 +482,6 @@  enum {
 	SNDRV_PCM_IOCTL_READI_FRAMES32 = _IOR('A', 0x51, struct snd_xferi32),
 	SNDRV_PCM_IOCTL_WRITEN_FRAMES32 = _IOW('A', 0x52, struct snd_xfern32),
 	SNDRV_PCM_IOCTL_READN_FRAMES32 = _IOR('A', 0x53, struct snd_xfern32),
-	SNDRV_PCM_IOCTL_SYNC_PTR32 = _IOWR('A', 0x23, struct snd_pcm_sync_ptr32),
 	SNDRV_PCM_IOCTL_STATUS_COMPAT64 = _IOR('A', 0x20, struct compat_snd_pcm_status64),
 	SNDRV_PCM_IOCTL_STATUS_EXT_COMPAT64 = _IOWR('A', 0x24, struct compat_snd_pcm_status64),
 #ifdef CONFIG_X86_X32
@@ -504,8 +505,8 @@  static long snd_pcm_ioctl_compat(struct file *file, unsigned int cmd, unsigned l
 
 	/*
 	 * When PCM is used on 32bit mode, we need to disable
-	 * mmap of PCM status/control records because of the size
-	 * incompatibility.
+	 * mmap of the old PCM status/control records because
+	 * of the size incompatibility.
 	 */
 	pcm_file->no_compat_mmap = 1;
 
@@ -527,6 +528,13 @@  static long snd_pcm_ioctl_compat(struct file *file, unsigned int cmd, unsigned l
 	case SNDRV_PCM_IOCTL_XRUN:
 	case SNDRV_PCM_IOCTL_LINK:
 	case SNDRV_PCM_IOCTL_UNLINK:
+	case __SNDRV_PCM_IOCTL_SYNC_PTR32:
+		return snd_pcm_common_ioctl(file, substream, cmd, argp);
+	case __SNDRV_PCM_IOCTL_SYNC_PTR64:
+#ifdef CONFIG_X86_X32
+		if (in_x32_syscall())
+			return snd_pcm_ioctl_sync_ptr_x32(substream, argp);
+#endif /* CONFIG_X86_X32 */
 		return snd_pcm_common_ioctl(file, substream, cmd, argp);
 	case SNDRV_PCM_IOCTL_HW_REFINE32:
 		return snd_pcm_ioctl_hw_params_compat(substream, 1, argp);
@@ -538,8 +546,6 @@  static long snd_pcm_ioctl_compat(struct file *file, unsigned int cmd, unsigned l
 		return snd_pcm_status_user32(substream, argp, false);
 	case SNDRV_PCM_IOCTL_STATUS_EXT_COMPAT32:
 		return snd_pcm_status_user32(substream, argp, true);
-	case SNDRV_PCM_IOCTL_SYNC_PTR32:
-		return snd_pcm_ioctl_sync_ptr_compat(substream, argp);
 	case SNDRV_PCM_IOCTL_CHANNEL_INFO32:
 		return snd_pcm_ioctl_channel_info_compat(substream, argp);
 	case SNDRV_PCM_IOCTL_WRITEI_FRAMES32:
@@ -561,8 +567,6 @@  static long snd_pcm_ioctl_compat(struct file *file, unsigned int cmd, unsigned l
 	case SNDRV_PCM_IOCTL_STATUS_EXT_COMPAT64:
 		return snd_pcm_status_user_compat64(substream, argp, true);
 #ifdef CONFIG_X86_X32
-	case SNDRV_PCM_IOCTL_SYNC_PTR_X32:
-		return snd_pcm_ioctl_sync_ptr_x32(substream, argp);
 	case SNDRV_PCM_IOCTL_CHANNEL_INFO_X32:
 		return snd_pcm_ioctl_channel_info_x32(substream, argp);
 #endif /* CONFIG_X86_X32 */
diff --git a/sound/core/pcm_lib.c b/sound/core/pcm_lib.c
index ea5518d44e66..0271802bfba9 100644
--- a/sound/core/pcm_lib.c
+++ b/sound/core/pcm_lib.c
@@ -148,7 +148,8 @@  void __snd_pcm_xrun(struct snd_pcm_substream *substream)
 		struct timespec64 tstamp;
 
 		snd_pcm_gettime(runtime, &tstamp);
-		runtime->status->tstamp = timespec64_to_timespec(tstamp);
+		runtime->status->tstamp.tv_sec = tstamp.tv_sec;
+		runtime->status->tstamp.tv_nsec = tstamp.tv_nsec;
 	}
 	snd_pcm_stop(substream, SNDRV_PCM_STATE_XRUN);
 	if (xrun_debug(substream, XRUN_DEBUG_BASIC)) {
@@ -238,9 +239,10 @@  static void update_audio_tstamp(struct snd_pcm_substream *substream,
 
 	if (runtime->status->audio_tstamp.tv_sec != audio_tstamp->tv_sec ||
 	    runtime->status->audio_tstamp.tv_nsec != audio_tstamp->tv_nsec) {
-		runtime->status->audio_tstamp =
-			timespec64_to_timespec(*audio_tstamp);
-		runtime->status->tstamp = timespec64_to_timespec(*curr_tstamp);
+		runtime->status->audio_tstamp.tv_sec = audio_tstamp->tv_sec;
+		runtime->status->audio_tstamp.tv_nsec = audio_tstamp->tv_nsec;
+		runtime->status->tstamp.tv_sec = curr_tstamp->tv_sec;
+		runtime->status->tstamp.tv_nsec = curr_tstamp->tv_nsec;
 	}
 
 
diff --git a/sound/core/pcm_native.c b/sound/core/pcm_native.c
index ba0636a2b437..5a1245509eac 100644
--- a/sound/core/pcm_native.c
+++ b/sound/core/pcm_native.c
@@ -2889,14 +2889,15 @@  static int snd_pcm_sync_ptr(struct snd_pcm_substream *substream,
 	return 0;
 }
 
-#ifdef CONFIG_COMPAT
 struct snd_pcm_mmap_status32 {
 	s32 state;
 	s32 pad1;
 	u32 hw_ptr;
-	struct compat_timespec tstamp;
+	s32 tstamp_sec;
+	s32 tstamp_nsec;
 	s32 suspended_state;
-	struct compat_timespec audio_tstamp;
+	s32 audio_tstamp_sec;
+	s32 audio_tstamp_nsec;
 } __attribute__((packed));
 
 struct snd_pcm_mmap_control32 {
@@ -2976,17 +2977,18 @@  static int snd_pcm_ioctl_sync_ptr_compat(struct snd_pcm_substream *substream,
 	snd_pcm_stream_unlock_irq(substream);
 	if (put_user(sstatus.state, &src->s.status.state) ||
 	    put_user(sstatus.hw_ptr, &src->s.status.hw_ptr) ||
-	    compat_put_timespec(&sstatus.tstamp, &src->s.status.tstamp) ||
+	    put_user(sstatus.tstamp.tv_sec, &src->s.status.tstamp_sec) ||
+	    put_user(sstatus.tstamp.tv_nsec, &src->s.status.tstamp_nsec) ||
 	    put_user(sstatus.suspended_state, &src->s.status.suspended_state) ||
-	    compat_put_timespec(&sstatus.audio_tstamp,
-				&src->s.status.audio_tstamp) ||
+	    put_user(sstatus.audio_tstamp.tv_sec, &src->s.status.audio_tstamp_sec) ||
+	    put_user(sstatus.audio_tstamp.tv_nsec, &src->s.status.audio_tstamp_nsec) ||
 	    put_user(scontrol.appl_ptr, &src->c.control.appl_ptr) ||
 	    put_user(scontrol.avail_min, &src->c.control.avail_min))
 		return -EFAULT;
 
 	return 0;
 }
-#endif
+#define __SNDRV_PCM_IOCTL_SYNC_PTR32 _IOWR('A', 0x23, struct snd_pcm_sync_ptr32)
 
 static int snd_pcm_tstamp(struct snd_pcm_substream *substream, int __user *_arg)
 {
@@ -3156,7 +3158,9 @@  static int snd_pcm_common_ioctl(struct file *file,
 			return -EFAULT;
 		return 0;
 	}
-	case SNDRV_PCM_IOCTL_SYNC_PTR:
+	case __SNDRV_PCM_IOCTL_SYNC_PTR32:
+		return snd_pcm_ioctl_sync_ptr_compat(substream, arg);
+	case __SNDRV_PCM_IOCTL_SYNC_PTR64:
 		return snd_pcm_sync_ptr(substream, arg);
 #ifdef CONFIG_SND_SUPPORT_OLD_API
 	case SNDRV_PCM_IOCTL_HW_REFINE_OLD:
@@ -3494,8 +3498,6 @@  static int snd_pcm_mmap_control(struct snd_pcm_substream *substream, struct file
 
 static bool pcm_status_mmap_allowed(struct snd_pcm_file *pcm_file)
 {
-	if (pcm_file->no_compat_mmap)
-		return false;
 	/* See pcm_control_mmap_allowed() below.
 	 * Since older alsa-lib requires both status and control mmaps to be
 	 * coupled, we have to disable the status mmap for old alsa-lib, too.
@@ -3720,11 +3722,19 @@  static int snd_pcm_mmap(struct file *file, struct vm_area_struct *area)
 
 	offset = area->vm_pgoff << PAGE_SHIFT;
 	switch (offset) {
-	case SNDRV_PCM_MMAP_OFFSET_STATUS:
+	case SNDRV_PCM_MMAP_OFFSET_STATUS_OLD:
+		if (pcm_file->no_compat_mmap || !IS_ENABLED(CONFIG_64BIT))
+			return -ENXIO;
+		/* fallthrough */
+	case SNDRV_PCM_MMAP_OFFSET_STATUS_NEW:
 		if (!pcm_status_mmap_allowed(pcm_file))
 			return -ENXIO;
 		return snd_pcm_mmap_status(substream, file, area);
-	case SNDRV_PCM_MMAP_OFFSET_CONTROL:
+	case SNDRV_PCM_MMAP_OFFSET_CONTROL_OLD:
+		if (pcm_file->no_compat_mmap || !IS_ENABLED(CONFIG_64BIT))
+			return -ENXIO;
+		/* fallthrough */
+	case SNDRV_PCM_MMAP_OFFSET_CONTROL_NEW:
 		if (!pcm_control_mmap_allowed(pcm_file))
 			return -ENXIO;
 		return snd_pcm_mmap_control(substream, file, area);
@@ -3884,9 +3894,9 @@  static unsigned long snd_pcm_get_unmapped_area(struct file *file,
 	unsigned long offset = pgoff << PAGE_SHIFT;
 
 	switch (offset) {
-	case SNDRV_PCM_MMAP_OFFSET_STATUS:
+	case SNDRV_PCM_MMAP_OFFSET_STATUS_NEW:
 		return (unsigned long)runtime->status;
-	case SNDRV_PCM_MMAP_OFFSET_CONTROL:
+	case SNDRV_PCM_MMAP_OFFSET_CONTROL_NEW:
 		return (unsigned long)runtime->control;
 	default:
 		return (unsigned long)runtime->dma_area + offset;