dm integrity: fix memory corruption when tag_size is less than digest size

It is possible to set up dm-integrity in such a way that the
"tag_size" parameter is less than the actual digest size. In this
situation, a part of the digest beyond tag_size is ignored.

In this case, dm-integrity would write beyond the end of the
ic->recalc_tags array and corrupt memory. The corruption happened in
integrity_recalc->integrity_sector_checksum->crypto_shash_final.

Fix this corruption by increasing the tags array so that it has enough
padding at the end to accomodate the loop in integrity_recalc() being
able to write a full digest size for the last member of the tags
array.

Cc: stable@vger.kernel.org # v4.19+
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@kernel.org>

Author: Mikulas Patocka

drivers/md/dm-integrity.c

@@ -4399,6 +4399,7 @@ static int dm_integrity_ctr(struct dm_target *ti, unsigned argc, char **argv)
 	}
 
 	if (ic->internal_hash) {
+		size_t recalc_tags_size;
 		ic->recalc_wq = alloc_workqueue("dm-integrity-recalc", WQ_MEM_RECLAIM, 1);
 		if (!ic->recalc_wq ) {
 			ti->error = "Cannot allocate workqueue";
@@ -4412,8 +4413,10 @@ static int dm_integrity_ctr(struct dm_target *ti, unsigned argc, char **argv)
 			r = -ENOMEM;
 			goto bad;
 		}
-		ic->recalc_tags = kvmalloc_array(RECALC_SECTORS >> ic->sb->log2_sectors_per_block,
-						 ic->tag_size, GFP_KERNEL);
+		recalc_tags_size = (RECALC_SECTORS >> ic->sb->log2_sectors_per_block) * ic->tag_size;
+		if (crypto_shash_digestsize(ic->internal_hash) > ic->tag_size)
+			recalc_tags_size += crypto_shash_digestsize(ic->internal_hash) - ic->tag_size;
+		ic->recalc_tags = kvmalloc(recalc_tags_size, GFP_KERNEL);
 		if (!ic->recalc_tags) {
 			ti->error = "Cannot allocate tags for recalculating";
 			r = -ENOMEM;