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