[PATCH v2 01/16] device-mapper: Check that target specs are sufficiently aligned

[Demi Marie Obenour <demi@xxxxxxxxxxxxxxxxxxxxxx>]

Otherwise subsequent code will dereference a misaligned
`struct dm_target_spec *`, which is undefined behavior.

Signed-off-by: Demi Marie Obenour <demi@xxxxxxxxxxxxxxxxxxxxxx>
Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Cc: stable@xxxxxxxxxxxxxxx
---
 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