Re: veritysetup forward error correction failure

On 18/07/2019 13:41, Tom Eccles wrote:
> On 17/07/2019 8:49 pm, Milan Broz wrote:
>> If you can still reproduce it, please send version of the utility and
>> kernel (and --debug output as suggested in another mail) and if you have some
>> data/hash/fec images that can be used to reproduce it, let me know where I can find it.
> 
> Attached is a bash script gen_image.sh which should reproduce the issue.
> find_and_corrupt.c should be in the working directory when gen_image.sh is
> run. find_and_corrupt.c corrupts the disk image by simply searching for a
> known string and introducing an error (see the diff outputted by gen_image.sh).
> 
> See in particular the error and dmesg sample when reading the corrupted file
> (gen_image.sh:77) and the success when running veritysetup verify
> (gen_image.sh:86).
> 
> I have created an issue at https://gitlab.com/cryptsetup/cryptsetup/issues/462

Thanks.

I think I see the problem, and it is actually not FEC related.

Could you please try to manually allocate loop devices in RW mode (not read-only
as we have during automatic loop allocation if mapping image is in file)
over the provided images, and then use these loop device as arguments for
the veritysetup?

Like
 # losetup /dev/loop0 data8M.img.corrupt 
 # losetup /dev/loop1 hash-img 
 # losetup /dev/loop2 fec-img 

and

 # veritysetup open --fec-roots 24 --fec-device /dev/loop2 /dev/loop0 test /dev/loop1 15546e6799bb13608c77fa9cb840682a2dec3cfdb948d942ff3487f537966c01 --debug

Does it correct the data now? For me it prints

  kernel: device-mapper: verity: sha256 using implementation "sha256-generic"
  kernel: fec_decode_bufs: 13 callbacks suppressed
  kernel: device-mapper: verity-fec: 7:0: FEC 0: corrected 153 errors

Milan
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