dm-verity: disable recursive forward error correction

[ 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>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/drivers/md/dm-verity-fec.c b/drivers/md/dm-verity-fec.c
index 72047b47a7a0a3cbdb5c0f5a4fcfa38b7bc05ec3..e41bde1d3b15b89590d913992b9528302f524266 100644 (file)
--- a/drivers/md/dm-verity-fec.c
+++ b/drivers/md/dm-verity-fec.c
@@ -413,10 +413,8 @@ 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 09123a612953871f17e71ff37204478b388c25dc..ec37e607cb3f09f950884ef77ead652c28895ac4 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 66a00a8ccb398b6bcd9cfe09ab9bbf7f94f29b1c..c8695c079cfe08280899a60333f7ff68e10d95b6 100644 (file)
--- a/drivers/md/dm-verity-target.c
+++ b/drivers/md/dm-verity-target.c
@@ -1690,7 +1690,7 @@ 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,