| Message ID | 20230603145244.1538-2-demi@invisiblethingslab.com (mailing list archive) |
|---|---|
| State | Accepted, archived |
| Delegated to: | Mike Snitzer |
| Headers | show |
| Series | Several device-mapper fixes | expand |
On Sat, Jun 03 2023 at 10:52P -0400, Demi Marie Obenour <demi@invisiblethingslab.com> wrote: > Otherwise subsequent code will dereference a misaligned > `struct dm_target_spec *`, which is undefined behavior. > > Signed-off-by: Demi Marie Obenour <demi@invisiblethingslab.com> > Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") > Cc: stable@vger.kernel.org > --- > drivers/md/dm-ioctl.c | 7 +++++++ > 1 file changed, 7 insertions(+) > > diff --git a/drivers/md/dm-ioctl.c b/drivers/md/dm-ioctl.c > index cc77cf3d410921432eb0c62cdede7d55b9aa674a..34fa74c6a70db8aa67aaba3f6a2fc4f38ef736bc 100644 > --- a/drivers/md/dm-ioctl.c > +++ b/drivers/md/dm-ioctl.c > @@ -1394,6 +1394,13 @@ static inline fmode_t get_mode(struct dm_ioctl *param) > static int next_target(struct dm_target_spec *last, uint32_t next, void *end, > struct dm_target_spec **spec, char **target_params) > { > + static_assert(_Alignof(struct dm_target_spec) <= 8, > + "struct dm_target_spec has excessive alignment requirements"); Really not sure what you mean by "has excessive alignment requirements"... > + if (next % 8) { > + DMERR("Next target spec (offset %u) is not 8-byte aligned", next); > + return -EINVAL; > + } > + > *spec = (struct dm_target_spec *) ((unsigned char *) last + next); > *target_params = (char *) (*spec + 1); > But this patch and patches 2 and 3 need more review. I'd like Mikulas to review. I did pick up patches 4-6 for the upcoming 6.5 merge window. Note, please prefix with "dm ioctl" instead of "device-mapper". (I just switched my "dm" prefix to "dm ioctl" and forced update on the dm-6.5 branch, so the commit I referenced earlier for your version copy patch is now here: https://git.kernel.org/pub/scm/linux/kernel/git/device-mapper/linux-dm.git/commit/?h=dm-6.5&id=a5a3de762b3ae8959347928843c12502b1b23163 ) Mike -- dm-devel mailing list dm-devel@redhat.com https://listman.redhat.com/mailman/listinfo/dm-devel
On Sat, 3 Jun 2023, Demi Marie Obenour wrote: > Otherwise subsequent code will dereference a misaligned > `struct dm_target_spec *`, which is undefined behavior. > > Signed-off-by: Demi Marie Obenour <demi@invisiblethingslab.com> > Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") > Cc: stable@vger.kernel.org > --- > drivers/md/dm-ioctl.c | 7 +++++++ > 1 file changed, 7 insertions(+) > > diff --git a/drivers/md/dm-ioctl.c b/drivers/md/dm-ioctl.c > index cc77cf3d410921432eb0c62cdede7d55b9aa674a..34fa74c6a70db8aa67aaba3f6a2fc4f38ef736bc 100644 > --- a/drivers/md/dm-ioctl.c > +++ b/drivers/md/dm-ioctl.c > @@ -1394,6 +1394,13 @@ static inline fmode_t get_mode(struct dm_ioctl *param) > static int next_target(struct dm_target_spec *last, uint32_t next, void *end, > struct dm_target_spec **spec, char **target_params) > { > + static_assert(_Alignof(struct dm_target_spec) <= 8, > + "struct dm_target_spec has excessive alignment requirements"); > + if (next % 8) { > + DMERR("Next target spec (offset %u) is not 8-byte aligned", next); > + return -EINVAL; > + } > + > *spec = (struct dm_target_spec *) ((unsigned char *) last + next); > *target_params = (char *) (*spec + 1); > > -- > Sincerely, > Demi Marie Obenour (she/her/hers) > Invisible Things Lab Hi Some architectures (such as 32-bit x86) specify that the alignment of 64-bit integers is only 4-byte. This could in theory break old userspace code that only uses 4-byte alignment. I would change "next % 8" to "next % __alignof__(struct dm_target_spec)". I think that there is no need to backport this patch series to the stable kernels because the bugs that it fixes may only be exploited by the user with CAP_SYS_ADMIN privilege. So, there is no security or reliability problem being fixed. Mikulas -- dm-devel mailing list dm-devel@redhat.com https://listman.redhat.com/mailman/listinfo/dm-devel
On Thu, Jun 22, 2023 at 12:28:28PM -0400, Mike Snitzer wrote: > On Sat, Jun 03 2023 at 10:52P -0400, > Demi Marie Obenour <demi@invisiblethingslab.com> wrote: > > > Otherwise subsequent code will dereference a misaligned > > `struct dm_target_spec *`, which is undefined behavior. > > > > Signed-off-by: Demi Marie Obenour <demi@invisiblethingslab.com> > > Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") > > Cc: stable@vger.kernel.org > > --- > > drivers/md/dm-ioctl.c | 7 +++++++ > > 1 file changed, 7 insertions(+) > > > > diff --git a/drivers/md/dm-ioctl.c b/drivers/md/dm-ioctl.c > > index cc77cf3d410921432eb0c62cdede7d55b9aa674a..34fa74c6a70db8aa67aaba3f6a2fc4f38ef736bc 100644 > > --- a/drivers/md/dm-ioctl.c > > +++ b/drivers/md/dm-ioctl.c > > @@ -1394,6 +1394,13 @@ static inline fmode_t get_mode(struct dm_ioctl *param) > > static int next_target(struct dm_target_spec *last, uint32_t next, void *end, > > struct dm_target_spec **spec, char **target_params) > > { > > + static_assert(_Alignof(struct dm_target_spec) <= 8, > > + "struct dm_target_spec has excessive alignment requirements"); > > Really not sure what you mean by "has excessive alignment requirements"... This patch checks that struct dm_target_spec is 8-byte aligned. That is okay if its alignment is 8 or less, but not if is 16 or more, so I added a static assert to check that struct dm_target_spec indeed requires at most 8-byte alignment. That said, “excessive alignment requirements” is (as shown by you having to ask this question) a bad error message. Would “must not require more than 8-byte alignment” be better? > > + if (next % 8) { > > + DMERR("Next target spec (offset %u) is not 8-byte aligned", next); > > + return -EINVAL; > > + } > > + > > *spec = (struct dm_target_spec *) ((unsigned char *) last + next); > > *target_params = (char *) (*spec + 1); > > > > But this patch and patches 2 and 3 need more review. I'd like Mikulas to review. > > I did pick up patches 4-6 for the upcoming 6.5 merge window. Thanks! > Note, please prefix with "dm ioctl" instead of "device-mapper". Good to know, thanks! I have several additional patches written that require patch 4. Should I send patches 1 through 3 in the same series as well?
On Thu, Jun 22, 2023 at 07:29:52PM +0200, Mikulas Patocka wrote: > > > On Sat, 3 Jun 2023, Demi Marie Obenour wrote: > > > Otherwise subsequent code will dereference a misaligned > > `struct dm_target_spec *`, which is undefined behavior. > > > > Signed-off-by: Demi Marie Obenour <demi@invisiblethingslab.com> > > Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") > > Cc: stable@vger.kernel.org > > --- > > drivers/md/dm-ioctl.c | 7 +++++++ > > 1 file changed, 7 insertions(+) > > > > diff --git a/drivers/md/dm-ioctl.c b/drivers/md/dm-ioctl.c > > index cc77cf3d410921432eb0c62cdede7d55b9aa674a..34fa74c6a70db8aa67aaba3f6a2fc4f38ef736bc 100644 > > --- a/drivers/md/dm-ioctl.c > > +++ b/drivers/md/dm-ioctl.c > > @@ -1394,6 +1394,13 @@ static inline fmode_t get_mode(struct dm_ioctl *param) > > static int next_target(struct dm_target_spec *last, uint32_t next, void *end, > > struct dm_target_spec **spec, char **target_params) > > { > > + static_assert(_Alignof(struct dm_target_spec) <= 8, > > + "struct dm_target_spec has excessive alignment requirements"); > > + if (next % 8) { > > + DMERR("Next target spec (offset %u) is not 8-byte aligned", next); > > + return -EINVAL; > > + } > > + > > *spec = (struct dm_target_spec *) ((unsigned char *) last + next); > > *target_params = (char *) (*spec + 1); > > > > -- > > Sincerely, > > Demi Marie Obenour (she/her/hers) > > Invisible Things Lab > > Hi > > Some architectures (such as 32-bit x86) specify that the alignment of > 64-bit integers is only 4-byte. This could in theory break old userspace > code that only uses 4-byte alignment. I would change "next % 8" to "next % > __alignof__(struct dm_target_spec)". That’s fine, provided that the rest of the code is okay with 4-byte alignment. > I think that there is no need to backport this patch series to the stable > kernels because the bugs that it fixes may only be exploited by the user > with CAP_SYS_ADMIN privilege. So, there is no security or reliability > problem being fixed. I agree that there is no reliability problem, but with kernel lockdown root → kernel is a security boundary, so fixes for memory unsafety problems should still be backported IMO.
On Thu, Jun 22 2023 at 3:51P -0400, Demi Marie Obenour <demi@invisiblethingslab.com> wrote: > On Thu, Jun 22, 2023 at 12:28:28PM -0400, Mike Snitzer wrote: > > On Sat, Jun 03 2023 at 10:52P -0400, > > Demi Marie Obenour <demi@invisiblethingslab.com> wrote: > > > > > Otherwise subsequent code will dereference a misaligned > > > `struct dm_target_spec *`, which is undefined behavior. > > > > > > Signed-off-by: Demi Marie Obenour <demi@invisiblethingslab.com> > > > Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") > > > Cc: stable@vger.kernel.org > > > --- > > > drivers/md/dm-ioctl.c | 7 +++++++ > > > 1 file changed, 7 insertions(+) > > > > > > diff --git a/drivers/md/dm-ioctl.c b/drivers/md/dm-ioctl.c > > > index cc77cf3d410921432eb0c62cdede7d55b9aa674a..34fa74c6a70db8aa67aaba3f6a2fc4f38ef736bc 100644 > > > --- a/drivers/md/dm-ioctl.c > > > +++ b/drivers/md/dm-ioctl.c > > > @@ -1394,6 +1394,13 @@ static inline fmode_t get_mode(struct dm_ioctl *param) > > > static int next_target(struct dm_target_spec *last, uint32_t next, void *end, > > > struct dm_target_spec **spec, char **target_params) > > > { > > > + static_assert(_Alignof(struct dm_target_spec) <= 8, > > > + "struct dm_target_spec has excessive alignment requirements"); > > > > Really not sure what you mean by "has excessive alignment requirements"... > > This patch checks that struct dm_target_spec is 8-byte aligned. That is > okay if its alignment is 8 or less, but not if is 16 or more, so I added > a static assert to check that struct dm_target_spec indeed requires at > most 8-byte alignment. That said, “excessive alignment requirements” is > (as shown by you having to ask this question) a bad error message. > Would “must not require more than 8-byte alignment” be better? Yes, that's better, I've updated it to use that. > > > + if (next % 8) { > > > + DMERR("Next target spec (offset %u) is not 8-byte aligned", next); > > > + return -EINVAL; > > > + } > > > + > > > *spec = (struct dm_target_spec *) ((unsigned char *) last + next); > > > *target_params = (char *) (*spec + 1); > > > > > > > But this patch and patches 2 and 3 need more review. I'd like Mikulas to review. > > > > I did pick up patches 4-6 for the upcoming 6.5 merge window. > > Thanks! > > > Note, please prefix with "dm ioctl" instead of "device-mapper". > > Good to know, thanks! I have several additional patches written that > require patch 4. Should I send patches 1 through 3 in the same series > as well? I did end up picking up patches 1-3 and rebased so they are in front of your patches 4-6 like you intended. But I agree with Mikulas, I'm not seeing the point in tagging any of these for stable@. All commits are currently at the tip of dm-6.5, see: https://git.kernel.org/pub/scm/linux/kernel/git/device-mapper/linux-dm.git/log/?h=dm-6.5 Mike -- dm-devel mailing list dm-devel@redhat.com https://listman.redhat.com/mailman/listinfo/dm-devel
diff --git a/drivers/md/dm-ioctl.c b/drivers/md/dm-ioctl.c index cc77cf3d410921432eb0c62cdede7d55b9aa674a..34fa74c6a70db8aa67aaba3f6a2fc4f38ef736bc 100644 --- a/drivers/md/dm-ioctl.c +++ b/drivers/md/dm-ioctl.c @@ -1394,6 +1394,13 @@ static inline fmode_t get_mode(struct dm_ioctl *param) static int next_target(struct dm_target_spec *last, uint32_t next, void *end, struct dm_target_spec **spec, char **target_params) { + static_assert(_Alignof(struct dm_target_spec) <= 8, + "struct dm_target_spec has excessive alignment requirements"); + if (next % 8) { + DMERR("Next target spec (offset %u) is not 8-byte aligned", next); + return -EINVAL; + } + *spec = (struct dm_target_spec *) ((unsigned char *) last + next); *target_params = (char *) (*spec + 1);
Otherwise subsequent code will dereference a misaligned `struct dm_target_spec *`, which is undefined behavior. Signed-off-by: Demi Marie Obenour <demi@invisiblethingslab.com> Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Cc: stable@vger.kernel.org --- drivers/md/dm-ioctl.c | 7 +++++++ 1 file changed, 7 insertions(+)