On Mon, 17 Nov 2025, Sami Tolvanen wrote:
> Hi Mikulas, > > On Fri, Nov 14, 2025 at 7:54 AM Mikulas Patocka <[email protected]> wrote: > > > > Hi > > > > What do you think about this patch? > > > > 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 that pushes dm-verity to this limit - and > > this image just makes the udev-worker process get stuck in the 'D' state. > > > > 2. It probably 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. > > > > So, I'm suggesting to remove recursive correction at all. This patch > > passed the cryptsetup testsuite. Does it pass your tests too? > > > > Signed-off-by: Mikulas Patocka <[email protected]> > > Reported-by: Guangwu Zhang <[email protected]> > > This looks reasonable to me. I only remember seeing recursive error > correction trigger in a real system when someone attempts to use the > wrong root hash, which is obviously not recoverable. > > Reviewed-by: Sami Tolvanen <[email protected]> > > Sami Thanks, OK. I staged the patch for 6.19. Mikulas
