dm ioctl: Check dm_target_spec is sufficiently aligned

Otherwise subsequent code, if given malformed input, could dereference
a misaligned 'struct dm_target_spec *'.

Signed-off-by: Demi Marie Obenour <demi@invisiblethingslab.com>
Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au> # use %zu
Reviewed-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@kernel.org>

diff --git a/drivers/md/dm-ioctl.c b/drivers/md/dm-ioctl.c
index 8ba4cbb92351f5140b30e5117d846e9e31264ad3..3a6989b7817d6904ef5b527ad489efe3b7d4164e 100644 (file)
--- a/drivers/md/dm-ioctl.c
+++ b/drivers/md/dm-ioctl.c
@@ -1394,6 +1394,15 @@ static inline blk_mode_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 must not require more than 8-byte alignment");
+
+       if (next % __alignof__(struct dm_target_spec)) {
+               DMERR("Next dm_target_spec (offset %u) is not %zu-byte aligned",
+                     next, __alignof__(struct dm_target_spec));
+               return -EINVAL;
+       }
+
        *spec = (struct dm_target_spec *) ((unsigned char *) last + next);
        *target_params = (char *) (*spec + 1);