[PATCH 6.12 275/460] dm-verity: disable recursive forward error correction

Greg Kroah-Hartman
2026-03-23T14:42:58Z

6.12-stable review patch. If anyone has any objections, please let me know.

------------------

From: Mikulas Patocka <mpatocka@redhat.com>

[ Upstream commit d9f3e47d3fae0c101d9094bc956ed24e7a0ee801 ]

There are two problems with the recursive correction:

1. It may cause denial-of-service. In fec_read_bufs, there is a loop that
has 253 iterations. For each iteration, we may call verity_hash_for_block
recursively. There is a limit of 4 nested recursions - that means that
there may be at most 253^4 (4 billion) iterations. Red Hat QE team
actually created an image that pushes dm-verity to this limit - and this
image just makes the udev-worker process get stuck in the 'D' state.

2. It doesn't work. In fec_read_bufs we store data into the variable
"fio->bufs", but fio bufs is shared between recursive invocations, if
"verity_hash_for_block" invoked correction recursively, it would
overwrite partially filled fio->bufs.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Reported-by: Guangwu Zhang <guazhang@redhat.com>
Reviewed-by: Sami Tolvanen <samitolvanen@google.com>
Reviewed-by: Eric Biggers <ebiggers@kernel.org>
[ The context change is due to the commit bdf253d580d7
("dm-verity: remove support for asynchronous hashes")
in v6.18 which is irrelevant to the logic of this patch. ]
Signed-off-by: Rahul Sharma <black.hawk@163.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/md/dm-verity-fec.c | 4 +---
drivers/md/dm-verity-fec.h | 3 ---
2 files changed, 1 insertion(+), 6 deletions(-)

--- a/drivers/md/dm-verity-fec.c
+++ b/drivers/md/dm-verity-fec.c
@@ -424,10 +424,8 @@ int verity_fec_decode(struct dm_verity *
if (!verity_fec_is_enabled(v))
return -EOPNOTSUPP;

- if (fio->level >= DM_VERITY_FEC_MAX_RECURSION) {
- DMWARN_LIMIT("%s: FEC: recursion too deep", v->data_dev->name);
+ if (fio->level)
return -EIO;
- }

fio->level++;

--- a/drivers/md/dm-verity-fec.h
+++ b/drivers/md/dm-verity-fec.h
@@ -23,9 +23,6 @@
#define DM_VERITY_FEC_BUF_MAX \
(1 << (PAGE_SHIFT - DM_VERITY_FEC_BUF_RS_BITS))

-/* maximum recursion level for verity_fec_decode */
-#define DM_VERITY_FEC_MAX_RECURSION 4
-
#define DM_VERITY_OPT_FEC_DEV "use_fec_from_device"
#define DM_VERITY_OPT_FEC_BLOCKS "fec_blocks"
#define DM_VERITY_OPT_FEC_START "fec_start"