In the Linux kernel, the following vulnerability has been resolved: dm-verity: disable recursive forward error correction There are two pr

In the Linux kernel, the following vulnerability has been resolved:

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.