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dm-verity: disable recursive forward error correction

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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>
This commit is contained in:
Mikulas Patocka 2025-11-14 16:54:01 +01:00
parent 7fa3e7d114
commit d9f3e47d3f
3 changed files with 2 additions and 7 deletions
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4
drivers/md/dm-verity-fec.c
View File

@ -418,10 +418,8 @@ int verity_fec_decode(struct dm_verity *v, struct dm_verity_io *io,
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++;

3
drivers/md/dm-verity-fec.h
View File

@ -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"

2
drivers/md/dm-verity-target.c
View File

@ -1789,7 +1789,7 @@ static struct target_type verity_target = {
.name = "verity",
/* Note: the LSMs depend on the singleton and immutable features */
.features = DM_TARGET_SINGLETON | DM_TARGET_IMMUTABLE,
.version = {1, 12, 0},
.version = {1, 13, 0},
.module = THIS_MODULE,
.ctr = verity_ctr,
.dtr = verity_dtr,