dm-verity: disable recursive forward error correction

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>

diff --git a/drivers/md/dm-verity-fec.c b/drivers/md/dm-verity-fec.c
index d792eaed079265d44d0abd66abf725383ce2432a..9dbb68c9afe4d2bc9c1063751eb12fa28c7643e5 100644 (file)
--- a/drivers/md/dm-verity-fec.c
+++ b/drivers/md/dm-verity-fec.c
@@ -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++;
 

diff --git a/drivers/md/dm-verity-fec.h b/drivers/md/dm-verity-fec.h
index dd55037377b6d7a2e4d8fd8c0b8113eae2d9238d..f0e991a613f02f8f4fedcfc4651b4fea62ccb98b 100644 (file)
--- 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"

diff --git a/drivers/md/dm-verity-target.c b/drivers/md/dm-verity-target.c
index 52a0e052a5e8526cf45e4f6b1b56783cb13dddff..5c17472d7896666fa8ee5cec12574b93aba24061 100644 (file)
--- a/drivers/md/dm-verity-target.c
+++ b/drivers/md/dm-verity-target.c
@@ -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,