diff mbox series

[4.4,2/3] ALSA: control: Fix memory corruption risk in snd_ctl_elem_read

Message ID 20230324171812.221086-3-theflamefire89@gmail.com (mailing list archive)
State New
Headers show
Series ALSA: control: Fix locking around snd_ctl_elem_read/write | expand

Commit Message

Alexander Grund March 24, 2023, 5:18 p.m. UTC 
From: Richard Fitzgerald <rf@opensource.cirrus.com>

commit 5a23699a39abc5328921a81b89383d088f6ba9cc upstream.

The patch "ALSA: control: code refactoring for ELEM_READ/ELEM_WRITE
operations" introduced a potential for kernel memory corruption due
to an incorrect if statement allowing non-readable controls to fall
through and call the get function. For TLV controls a driver can omit
SNDRV_CTL_ELEM_ACCESS_READ to ensure that only the TLV get function
can be called. Instead the normal get() can be invoked unexpectedly
and as the driver expects that this will only be called for controls
<= 512 bytes, potentially try to copy >512 bytes into the 512 byte
return array, so corrupting kernel memory.

The problem is an attempt to refactor the snd_ctl_elem_read function
to invert the logic so that it conditionally aborted if the control
is unreadable instead of conditionally executing. But the if statement
wasn't inverted correctly.

The correct inversion of

    if (a && !b)

is
    if (!a || b)

Fixes: becf9e5d553c2 ("ALSA: control: code refactoring for ELEM_READ/ELEM_WRITE operations")
Signed-off-by: Richard Fitzgerald <rf@opensource.cirrus.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Signed-off-by: Alexander Grund <theflamefire89@gmail.com>
---
 sound/core/control.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Comments

Nobuhiro Iwamatsu March 29, 2023, 10:33 p.m. UTC | #1 
Hi,

Thanks for your patch!

> -----Original Message-----
> From: cip-dev@lists.cip-project.org <cip-dev@lists.cip-project.org> On
> Behalf Of Alexander Grund
> Sent: Saturday, March 25, 2023 2:18 AM
> To: cip-dev@lists.cip-project.org
> Cc: uli+cip@fpond.eu
> Subject: [cip-dev] [PATCH 4.4 2/3] ALSA: control: Fix memory corruption risk in
> snd_ctl_elem_read
> 
> From: Richard Fitzgerald <rf@opensource.cirrus.com>
> 
> commit 5a23699a39abc5328921a81b89383d088f6ba9cc upstream.
> 
> The patch "ALSA: control: code refactoring for ELEM_READ/ELEM_WRITE
> operations" introduced a potential for kernel memory corruption due to an
> incorrect if statement allowing non-readable controls to fall through and call
> the get function. For TLV controls a driver can omit
> SNDRV_CTL_ELEM_ACCESS_READ to ensure that only the TLV get function
> can be called. Instead the normal get() can be invoked unexpectedly and as the
> driver expects that this will only be called for controls <= 512 bytes, potentially
> try to copy >512 bytes into the 512 byte return array, so corrupting kernel
> memory.
> 
> The problem is an attempt to refactor the snd_ctl_elem_read function to invert
> the logic so that it conditionally aborted if the control is unreadable instead of
> conditionally executing. But the if statement wasn't inverted correctly.
> 
> The correct inversion of
> 
>     if (a && !b)
> 
> is
>     if (!a || b)
> 
> Fixes: becf9e5d553c2 ("ALSA: control: code refactoring for
> ELEM_READ/ELEM_WRITE operations")
> Signed-off-by: Richard Fitzgerald <rf@opensource.cirrus.com>
> Cc: <stable@vger.kernel.org>
> Signed-off-by: Takashi Iwai <tiwai@suse.de>
> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> 

Space here is not required.

> Signed-off-by: Alexander Grund <theflamefire89@gmail.com>
> ---
>  sound/core/control.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/sound/core/control.c b/sound/core/control.c index
> a042a30d6a728..3ca81e85a1492 100644
> --- a/sound/core/control.c
> +++ b/sound/core/control.c
> @@ -884,7 +884,7 @@ static int snd_ctl_elem_read(struct snd_card *card,
> 
>  	index_offset = snd_ctl_get_ioff(kctl, &control->id);
>  	vd = &kctl->vd[index_offset];
> -	if (!(vd->access & SNDRV_CTL_ELEM_ACCESS_READ) && kctl->get
> == NULL)
> +	if (!(vd->access & SNDRV_CTL_ELEM_ACCESS_READ) || kctl->get
> == NULL)
>  		return -EPERM;
> 
>  	snd_ctl_build_ioff(&control->id, kctl, index_offset);
> --
> 2.40.0

Best regards,
  Nobuhiro
Alexander Grund March 31, 2023, 3:52 p.m. UTC | #2 
> 
> Space here is not required.

I agree. Can this be just ignored when applying this or do I need to resend the patch?
diff mbox series

Patch

diff --git a/sound/core/control.c b/sound/core/control.c
index a042a30d6a728..3ca81e85a1492 100644
--- a/sound/core/control.c
+++ b/sound/core/control.c
@@ -884,7 +884,7 @@  static int snd_ctl_elem_read(struct snd_card *card,
 
 	index_offset = snd_ctl_get_ioff(kctl, &control->id);
 	vd = &kctl->vd[index_offset];
-	if (!(vd->access & SNDRV_CTL_ELEM_ACCESS_READ) && kctl->get == NULL)
+	if (!(vd->access & SNDRV_CTL_ELEM_ACCESS_READ) || kctl->get == NULL)
 		return -EPERM;
 
 	snd_ctl_build_ioff(&control->id, kctl, index_offset);