[Bug 1929370] Re: Backport support for the -lln command-line option to unsquashfs for 18.04

[Alex Murray]

** Changed in: squashfs-tools (Ubuntu Bionic)
       Status: New => In Progress

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Title:
  Backport support for the -lln command-line option to unsquashfs for
  18.04

Status in squashfs-tools package in Ubuntu:
  Fix Released
Status in squashfs-tools source package in Bionic:
  In Progress

Bug description:
  [Impact]
  unsquashfs gains a new flag to list numeric uid/gid in the contents of squashfs files. This can be used by the snap store dashboard and review-tools to accurately assess the owner of files within a snap etc.

  [Test Case]
  snap download core 
  unsquashfs -lln core_*.snap

  The above should succeed and output numeric uid/gid information, e.g.:

  ...
  drwxrwsr-x 0/50                      3 2016-04-13 05:44 squashfs-root/var/local
  drwxrwxr-x 0/114                    94 2021-04-28 17:53 squashfs-root/var/log
  -rw------- 0/43                      0 2021-04-28 17:49 squashfs-root/var/log/btmp
  -rw-r----- 0/4                      31 2021-04-28 17:49 squashfs-root/var/log/dmesg
  -rw-r----- 0/4                      31 2021-04-28 17:49 squashfs-root/var/log/fsck/checkfs
  -rw-r----- 0/4                      31 2021-04-28 17:49 squashfs-root/var/log/fsck/checkroot
  -rw-rw-r-- 0/43                  30660 2021-04-28 17:49 squashfs-root/var/log/lastlog
  -rw-rw-r-- 0/43                      0 2021-04-28 17:49 squashfs-root/var/log/wtmp
  drwxrwsr-x 0/8                       3 2021-04-28 17:49 squashfs-root/var/mail
  drwx-wx--T 0/102                     3 2016-04-06 07:29 squashfs-root/var/spool/cron/crontabs
  drwx------ 108/4                     3 2019-03-25 23:44 squashfs-root/var/spool/rsyslog
  ...

  As a more detailed test, the test-squashfs-tools.py script from qa-
  regression-testing can be used to exercise both this -lln output
  option as well as the existing -lls output option since
  https://git.launchpad.net/qa-regression-
  testing/commit/?id=2bc14c225b91b7283e57e2d63a88c164be43df5a to ensure
  both function as expected.

  
  [Where problems could occur]
  unsquashfs could fail to properly run and so the snap store review-tools could fail as a result. The review-tools and the store are coded to fail-closed such that any resulting problems with unsquashfs should not allow snaps that would otherwise be flagged by the review-tools to pass automated review. 

  ------- original description follows --------

  
  The snap store review-tools is changing to compare snaps based on their numeric uid/gids rather than user/group names (see https://code.launchpad.net/~alexmurray/review-tools/+git/review-tools/+merge/403103 for more details).

  Currently the snap store dashboard, where the review-tools are run, is
  running Ubuntu 18.04 - which is based on squashfs-tools 4.3 - however
  support for the -lln command-line option was only added in the 4.4
  release. This change https://github.com/plougher/squashfs-
  tools/commit/a78a589a55a8524ef31ba06ea7c752b8aa8b3604 is relatively
  simple and can be backported to squashfs-tools in 18.04 with minimal
  effort.

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