dm integrity: change memcmp to strncmp in dm_integrity_ctr

If the string opt_string is small, the function memcmp can access bytes
that are beyond the terminating nul character. In theory, it could cause
segfault, if opt_string were located just below some unmapped memory.

Change from memcmp to strncmp so that we don't read bytes beyond the end
of the string.

Cc: stable@vger.kernel.org # v4.12+
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

1 files changed, 4 insertions, 4 deletions

diff --git a/drivers/md/dm-integrity.c b/drivers/md/dm-integrity.c
index d57d997a52c8..33fac437569f 100644
--- a/drivers/md/dm-integrity.c
+++ b/drivers/md/dm-integrity.c
@@ -3185,7 +3185,7 @@ static int dm_integrity_ctr(struct dm_target *ti, unsigned argc, char **argv)
                         journal_watermark = val;
                 else if (sscanf(opt_string, "commit_time:%u%c", &val, &dummy) == 1)
                         sync_msec = val;
-                else if (!memcmp(opt_string, "meta_device:", strlen("meta_device:"))) {
+                else if (!strncmp(opt_string, "meta_device:", strlen("meta_device:"))) {
                         if (ic->meta_dev) {
                                 dm_put_device(ti, ic->meta_dev);
                                 ic->meta_dev = NULL;
@@ -3204,17 +3204,17 @@ static int dm_integrity_ctr(struct dm_target *ti, unsigned argc, char **argv)
                                 goto bad;
                         }
                         ic->sectors_per_block = val >> SECTOR_SHIFT;
-                } else if (!memcmp(opt_string, "internal_hash:", strlen("internal_hash:"))) {
+                } else if (!strncmp(opt_string, "internal_hash:", strlen("internal_hash:"))) {
                         r = get_alg_and_key(opt_string, &ic->internal_hash_alg, &ti->error,
                                             "Invalid internal_hash argument");
                         if (r)
                                 goto bad;
-                } else if (!memcmp(opt_string, "journal_crypt:", strlen("journal_crypt:"))) {
+                } else if (!strncmp(opt_string, "journal_crypt:", strlen("journal_crypt:"))) {
                         r = get_alg_and_key(opt_string, &ic->journal_crypt_alg, &ti->error,
                                             "Invalid journal_crypt argument");
                         if (r)
                                 goto bad;
-                } else if (!memcmp(opt_string, "journal_mac:", strlen("journal_mac:"))) {
+                } else if (!strncmp(opt_string, "journal_mac:", strlen("journal_mac:"))) {
                         r = get_alg_and_key(opt_string, &ic->journal_mac_alg,  &ti->error,
                                             "Invalid journal_mac argument");
                         if (r)