[dm-devel] [PATCH] dm-integrity: fix memory corruption when tag_size is less than the actual digest size

[Mikulas Patocka]

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.

This patch fixes the corruption.

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

---
 drivers/md/dm-integrity.c |    7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

Index: linux-2.6/drivers/md/dm-integrity.c
===================================================================
--- linux-2.6.orig/drivers/md/dm-integrity.c	2022-04-02 14:17:13.000000000 +0200
+++ linux-2.6/drivers/md/dm-integrity.c	2022-04-02 14:43:06.000000000 +0200
@@ -4399,6 +4399,7 @@ try_smaller_buffer:
 	}
 
 	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 @@ try_smaller_buffer:
 			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;