[dm-devel] [PATCH] dm-verity: Fix biovecs hash calculation regression

[Milan Broz]

The commit
  003b5c5719f159f4f4bf97511c4702a0638313dd
  block: Convert drivers to immutable biovecs

incorrectly converted biovec iteration in dm-verity to always
calculate hash from full biovec, while the function need
to calculate hash only from part of it (up to "todo"
calculated value).

This patch fixes the issue by limiting hash input to only
really requested data size.

The problem is easily reproducible using cryptsetup
regression test for veritysetup (verity-compat-test).

(Patch should be applied also to 3.14 stable.)

Signed-off-by: Milan Broz <gmazyland at gmail.com>
---
 drivers/md/dm-verity.c | 15 +++++++++------
 1 file changed, 9 insertions(+), 6 deletions(-)

diff --git a/drivers/md/dm-verity.c b/drivers/md/dm-verity.c
index 796007a..7a7bab8 100644
--- a/drivers/md/dm-verity.c
+++ b/drivers/md/dm-verity.c
@@ -330,15 +330,17 @@ test_block_hash:
 				return r;
 			}
 		}
-
 		todo = 1 << v->data_dev_block_bits;
-		while (io->iter.bi_size) {
+		do {
 			u8 *page;
+			unsigned len;
 			struct bio_vec bv = bio_iter_iovec(bio, io->iter);
 
 			page = kmap_atomic(bv.bv_page);
-			r = crypto_shash_update(desc, page + bv.bv_offset,
-						bv.bv_len);
+			len = bv.bv_len;
+			if (likely(len >= todo))
+				len = todo;
+			r = crypto_shash_update(desc, page + bv.bv_offset, len);
 			kunmap_atomic(page);
 
 			if (r < 0) {
@@ -346,8 +348,9 @@ test_block_hash:
 				return r;
 			}
 
-			bio_advance_iter(bio, &io->iter, bv.bv_len);
-		}
+			bio_advance_iter(bio, &io->iter, len);
+			todo -= len;
+		} while (todo);
 
 		if (!v->version) {
 			r = crypto_shash_update(desc, v->salt, v->salt_size);
-- 
1.9.2