HMRC Basic PAYE Tools P60 generation error on Linux

Posted: 2024-04-12 09:52:59 by Alasdair Keyes

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TL;DR if you are just looking for the fix scroll down to see the The Fix section.

As I run a UK company, I have to supply various bits of information to HMRC (the UK tax office) for payroll.

HMRC offer a free tool called Basic PAYE Tools for small businesses to make this possible (https://www.gov.uk/basic-paye-tools). It's a great tool, without it small companies would have to shell out money for proprietary solutions just to fulfil basic payroll/tax obligations. The tool is available for Windows, Mac and Linux. This is specifically for the Linux version, but a similar bug/fix may work for Mac.

The tool is a binary rti.linux that starts a web-server which listens on a http://127.0.0.1:46729/. A browser is then opened to automatically connect to that URL to provide the user with a GUI. The server stores data in a local sqlite database. When any actions are performed that require HMRC to be notified (such as paying employees), these transactions are stored locally and then sent via a batch process to HMRC.

As we have just passed into the 24-25 tax year, I have to 'close' the old year so that I can start the new one. Part of this process is to generate a P60 form for all employees. However, when doing this, the page just appeared to refresh and no form was displayed. This action is not one that requires any transfer of information to HMRC as the P60 is just a summary of an employees payments and tax contributions for that tax year.

A Google didn't show any similar issues and there was no easy 'File bug report' option. The only reporting is to call up HMRC on the phone. I didn't really want to try explaining the issue over the phone so I thought I'd investigate myself.

I could find no information about log files for the tool so I found the process of the rti.linux and looks in /proc/ for any possible logs.

$ ls -al /proc/24876/fd/
total 0
dr-x------ 2 user user  0 Apr 12 09:56 . 
dr-xr-xr-x 9 user user  0 Apr 12 09:52 ..
lr-x------ 1 user user 64 Apr 12 09:56 0 -> /dev/null
l-wx------ 1 user user 64 Apr 12 09:56 1 -> /home/user/.xsession-errors
lrwx------ 1 user user 64 Apr 12 09:56 10 -> 'socket:[147745]'
lrwx------ 1 user user 64 Apr 12 09:56 11 -> 'socket:[148555]'
lrwx------ 1 user user 64 Apr 12 09:56 12 -> 'anon_inode:[eventfd]'
lrwx------ 1 user user 64 Apr 12 09:56 13 -> 'socket:[148556]'
lrwx------ 1 user user 64 Apr 12 09:56 14 -> 'socket:[147746]'
lrwx------ 1 user user 64 Apr 12 09:56 15 -> 'socket:[147747]'
lrwx------ 1 user user 64 Apr 12 09:56 18 -> 'socket:[147819]'
l-wx------ 1 user user 64 Apr 12 09:56 2 -> /home/user/.xsession-errors
lrwx------ 1 user user 64 Apr 12 09:56 21 -> 'anon_inode:[eventfd]'
lr-x------ 1 user user 64 Apr 12 09:56 3 -> /dev/urandom
l-wx------ 1 user user 64 Apr 12 09:56 4 -> /tmp/rti.log
lrwx------ 1 user user 64 Apr 12 09:56 5 -> 'anon_inode:[eventfd]'
lr-x------ 1 user user 64 Apr 12 09:56 6 -> 'pipe:[144859]'
l-wx------ 1 user user 64 Apr 12 09:56 7 -> 'pipe:[144859]'
lrwx------ 1 user user 64 Apr 12 09:56 8 -> 'socket:[144860]'
lrwx------ 1 user user 64 Apr 12 09:56 9 -> 'socket:[144024]'

The /tmp/rti.log shows one entry.

24876 Server has asked us to open_file

And /home/user/.xsession-errors shows something a little more helpful.

evince: error while loading shared libraries: libjpeg.so.62: failed to map segment from shared object

So it looks like an error in libjpeg.so.62, but nothing specific.

To get more information, I ran strace to find more about what was being called. (The read() call data is truncated to save space).

$ strace -Ff -v -s 1000 -p 24876
[pid 25497] openat(AT_FDCWD, "/home/user/HMRC/payetools-rti/libjpeg.so.62", O_RDONLY|O_CLOEXEC) = 3
[pid 25497] read(3, "\177ELF\2\1\----TRUNCATED----\0)\0\0\0", 832) = 832
[pid 25497] newfstatat(3, "", {st_dev=makedev(0xfd, 0x1), st_ino=23609456, st_mode=S_IFREG|0644, st_nlink=1, st_uid=1000, st_gid=1000, st_blksize=4096, st_blocks=848, st_size=432128, st_atime=1712911963 /* 2024-04-12T09:52:43.275396143+0100 */, st_atime_nsec=275396143, st_mtime=1602102343 /* 2020-10-07T21:25:43+0100 */, st_mtime_nsec=0, st_ctime=1712611938 /* 2024-04-08T22:32:18.204486045+0100 */, st_ctime_nsec=204486045}, AT_EMPTY_PATH) = 0
[pid 25497] mmap(NULL, 434200, PROT_READ, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7f318954d000
[pid 25497] mprotect(0x7f3189551000, 413696, PROT_NONE) = 0
[pid 25497] mmap(0x7f3189551000, 241664, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x4000) = -1 EACCES (Permission denied)
[pid 25497] close(3)                    = 0
[pid 25497] writev(2, [{iov_base="evince", iov_len=6}, {iov_base=": ", iov_len=2}, {iov_base="error while loading shared libraries", iov_len=36}, {iov_base=": ", iov_len=2}, {iov_base="libjpeg.so.62", iov_len=13}, {iov_base=": ", iov_len=2}, {iov_base="failed to map segment from shared object", iov_len=40}, {iov_base="", iov_len=0}, {iov_base="", iov_len=0}, {iov_base="\n", iov_len=1}], 10) = 102
[pid 25497] exit_group(127)             = ?
[pid 25497] +++ exited with 127 +++

Here we see /home/user/HMRC/payetools-rti/libjpeg.so.62 is opened for reading, the data is read and then mmap() and mprotect() are run, the file is closed and then we see the log error above is written to file handle #2 (/home/user/.xsession-errors) before the process exits with a non-zero code.

This indeed looks to be the issue, I don't know enough about the codebase to determine if it is corrupt or perhaps it wasn't updated when the rest of the code? It's very likely a FOSS library. So I checked if Debian supplied a version.

$ apt-file search libjpeg.so.62
libjpeg62-turbo: /usr/lib/x86_64-linux-gnu/libjpeg.so.62
libjpeg62-turbo: /usr/lib/x86_64-linux-gnu/libjpeg.so.62.3.0

Great, maybe I can use that?

The Fix

1. Make sure paye-tools is closed.

2. Install the libjpeg62-turbo package

It turns out I already had the libjpeg62-turbo package installed, but if you don't you can use.

apt install libjpeg62-turbo

I checked if the files were the same.... it turns out they're different versions.

$ sha256sum /home/user/HMRC/payetools-rti/libjpeg.so.62.paye-tools-version /usr/lib/x86_64-linux-gnu/libjpeg.so.62
4f3446bc4c2a2d3c75b7c62062305ff8c5fcdaa447d5a2461d5995d40f728d00  /home/user/HMRC/payetools-rti/libjpeg.so.62
dad87949ccad2be7e40a02986306087fdcfb35ccaadd59aea923a3f96d290eec  /usr/lib/x86_64-linux-gnu/libjpeg.so.62

3. Back-up and link to the system version

$ cd /home/user/HMRC/payetools-rti
$ mv libjpeg.so.62 libjpeg.so.62.orig
$ ln -s /usr/lib/x86_64-linux-gnu/libjpeg.so.62 libjpeg.so.62

I started the tool back up and I was able to get the P60.

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