### Issue description I'm not sure if this is within the expected usage scenarios at all or if I am doing something incorrectly but I am trying to append both hash and fec blocks to a data file, so they all reside in one file – with appropriate offsets. The ultimate goal might or might not be burning a disc from that file then, so I am mainly interested in forward error correction here. Formatting in a single file works fine and verification succeeds as long as there is no corruption in the data. But as soon as I introduce some wrong data `verify` says the errors cannot be rapaired. When I then split the file into its parts and verify with hash and fec in separate files, the *errors are successfully repaired*. ### Steps for reproducing the issue I'm using a ca. 100 MB mksquashfs archive as `data`. I can reproduce it with 64 MiB of zeroes, however: `truncate -s 64M data`. ```bash #!/usr/bin/env bash say() { printf '\033[1m> %s\033[0m\n' "$*"; } # data file required [[ ! -r data ]] && { echo "data file required" >/dev/stderr exit 1 } # when DEBUG=yes add --debug to veritysetup debug() { [[ $DEBUG == "yes" ]] && echo "--debug"; } # check that data size is 4k aligned stat -c%s data |\ awk '{ if ($1 % 4096 != 0) { print "not 4k aligned"; exit 1; }}' || exit 1 # format hash and fec into seperate files say "veritysetup format .." veritysetup $(debug) format --fec-device=fec data hash |\ awk '/^Root hash/{ print $3 }' > roothash # get parts sizes say "get sizes for offsets" ls -l data hash fec datasize=$(stat -c%s data) hashsize=$(stat -c%s hash) fecsize=$(stat -c%s fec) # concatenate into one file say "concatenate into a single file" cat hash fec >> data # dummy verify, shouldn't fail say "test verification" veritysetup $(debug) verify \ --data-blocks=$(( $datasize / 4096 )) \ --hash-offset=$datasize \ --fec-device=data --fec-offset=$(( $datasize + $hashsize )) \ data data $(<roothash) -v # introduce some corruption in the file say "introduce corruption" dd if=/dev/urandom of=data bs=20 count=1 conv=notrunc # verify again, should repair errors say "attempt to verify again" veritysetup $(debug) verify \ --data-blocks=$(( $datasize / 4096 )) \ --hash-offset=$datasize \ --fec-device=data --fec-offset=$(( $datasize + $hashsize )) \ data data $(<roothash) -v # truncate data file to original size say "truncate data file" truncate -s $datasize data # verify again, should be repaired this time say "verify again from separate files" veritysetup $(debug) verify --fec-device=fec data hash $(<roothash) ``` The script assumes that a file `data` exists, it requires no arguments. Passing `DEBUG=yes` as an environment variable enables debug output in all veritysetup commands. ### Additional info ``` $ uname -srvm Linux 5.6.6-arch1-1 #1 SMP PREEMPT Tue, 21 Apr 2020 10:35:16 +0000 x86_64 $ veritysetup --version veritysetup 2.3.1 ``` ### Debug log Verification from a single file: ``` # cryptsetup 2.3.1 processing "veritysetup --debug verify --data-blocks=16384 --hash-offset=67108864 --fec-device=data --fec-offset=67641344 data data 193c6e984093ef39160b0965151b4b85142600947bb38940790a96facbacbe68 -v" # Running command verify. # Allocating context for crypt device data. # Trying to open and read device data with direct-io. # Trying to open device data without direct-io. # Initialising device-mapper backend library. # Trying to load VERITY crypt type from device data. # Crypto backend (OpenSSL 1.1.1g 21 Apr 2020) initialized in cryptsetup library version 2.3.1. # Detected kernel Linux 5.6.6-arch1-1 x86_64. # Reading VERITY header of size 512 on device data, offset 67108864. # Trying to open and read device data with direct-io. # Trying to open device data without direct-io. # Checking volume by signed key. # Trying to activate VERITY device [none] using hash sha256. # Verification of data in userspace required. # Hash verification sha256, data device data, data blocks 16384, hash_device data, offset 16385. # Using 2 hash levels. # Data device size required: 67108864 bytes. # Hash device size required: 67641344 bytes. Verification failed at position 0. Verification of data area failed. # Verification failed, trying to repair with FEC device. Failed to repair parity for block 0. Errors cannot be repaired with FEC device. # Releasing crypt device data context. # Releasing device-mapper backend. # Closing read only fd for data. Command failed with code -2 (no permission or bad passphrase). ``` Truncated data to original size and verify from separate files *with the exact same hash and fec blocks*: ``` # cryptsetup 2.3.1 processing "veritysetup --debug verify --fec-device=fec data hash 193c6e984093ef39160b0965151b4b85142600947bb38940790a96facbacbe68" # Running command verify. # Allocating context for crypt device hash. # Trying to open and read device hash with direct-io. # Trying to open device hash without direct-io. # Initialising device-mapper backend library. # Setting ciphertext data device to data. # Trying to open and read device data with direct-io. # Trying to open device data without direct-io. # Trying to load VERITY crypt type from device hash. # Crypto backend (OpenSSL 1.1.1g 21 Apr 2020) initialized in cryptsetup library version 2.3.1. # Detected kernel Linux 5.6.6-arch1-1 x86_64. # Reading VERITY header of size 512 on device hash, offset 0. # Trying to open and read device fec with direct-io. # Trying to open device fec without direct-io. # Checking volume by signed key. # Trying to activate VERITY device [none] using hash sha256. # Verification of data in userspace required. # Hash verification sha256, data device data, data blocks 16384, hash_device hash, offset 1. # Using 2 hash levels. # Data device size required: 67108864 bytes. # Hash device size required: 532480 bytes. Verification failed at position 0. Verification of data area failed. # Verification failed, trying to repair with FEC device. Found 20 repairable errors with FEC device. # Releasing crypt device hash context. # Releasing device-mapper backend. # Closing read only fd for hash. Command successful. ```