[Bug 1953610] Update Released

[Łukasz Zemczak]

The verification of the Stable Release Update for command-not-found has
completed successfully and the package is now being released to
-updates.  Subsequently, the Ubuntu Stable Release Updates Team is being
unsubscribed and will not receive messages about this bug report.  In
the event that you encounter a regression using the package from
-updates please report a new bug using ubuntu-bug and tag the bug report
regression-update so we can easily find any regressions.

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https://bugs.launchpad.net/bugs/1953610

Title:
  cnf-update-db creates unreadable database if wrong umask

Status in command-not-found package in Ubuntu:
  Fix Released
Status in command-not-found source package in Bionic:
  Fix Committed
Status in command-not-found source package in Focal:
  Fix Released
Status in command-not-found source package in Impish:
  Fix Committed
Status in command-not-found source package in Jammy:
  Fix Released

Bug description:
  [Impact]
  If a non-default umask is set for the root user, then the database created by cnf-update-db is not readable by users. This causes exceptions when cnf is invoked.

  This fix ensures databases are created with the correct permissions,
  but it does not automatically reset permissions for broken databases.

  [Test Plan]
  To reproduce the issue, use the annotated steps below. Confirmed working as a reproducer for Bionic, Focal and Impish. Bionic appears to use a -data package instead of building the db on "apt update", however, adding a non-default repo with CNF metadata will also reproduce the issue. Bionic was tested by adding focal-updates to the APT configuration.

  Notes:
  1) The "ubuntu" user below is unprivileged, the result of the "adduser ubuntu" command being run and accepting defaults.
  2) The "lck" and "ack" commands were randomly selected as commands that were unavailable on the default Ubuntu images used by LXD.
  3) Bionic requires the addition of a non-default repo with CNF metadata. The focal-updates repo was used in my testing, any repo meeting the conditions should do.

  ### Reproduction
  # Add repo with CNF metadata if testing Bionic
  # Confirm UMASK
  grep "^UMASK" /etc/login.defs
  # Set /etc/login.defs to umask 027
  sed -i -e 's/^UMASK\t\t022/UMASK\t\t027/' /etc/login.defs
  # Confirm
  grep "^UMASK" /etc/login.defs
  # Log out and back in
  exit

  # Log back in
  # Force rebuild of DB
  rm -rf /var/lib/command-not-found/*
  apt update
  ls -lah /var/lib/command-not-found/
  # Verify failure
  su - ubuntu
  lck
  ack
  exit
  ## END Reproduction

  ### Verification
  # Install updated command-not-found from -proposed
  # https://wiki.ubuntu.com/Testing/EnableProposed
  # Update command-not-found.
  apt upgrade command-not-found
  # Verify version
  dpkg -l | grep command-not-found
  # Force rebuild of DB
  rm -rf /var/lib/command-not-found/*
  apt update
  ls -lah /var/lib/command-not-found/
  # Verify success
  su - ubuntu
  lck
  ack
  exit
  ## END Verification

  The failures expected to be seen when running the "lck" and "ack" commands are similar to:
  ubuntu at lp1953610-focal:~$ ack
  Sorry, command-not-found has crashed! Please file a bug report at:
  https://bugs.launchpad.net/command-not-found/+filebug
  Please include the following information with the report:

  command-not-found version: 0.3
  Python version: 3.8.10 final 0
  Distributor ID: Ubuntu
  Description: Ubuntu 20.04.3 LTS
  Release: 20.04
  Codename: focal
  Exception information:

  unable to open database file
  Traceback (most recent call last):
    File "/usr/lib/python3/dist-packages/CommandNotFound/util.py", line 23, in crash_guard
      callback()
    File "/usr/lib/command-not-found", line 90, in main
      cnf = CommandNotFound.CommandNotFound(options.data_dir)
    File "/usr/lib/python3/dist-packages/CommandNotFound/CommandNotFound.py", line 79, in __init__
      self.db = SqliteDatabase(dbpath)
    File "/usr/lib/python3/dist-packages/CommandNotFound/db/db.py", line 12, in __init__
      self.con = sqlite3.connect(filename)
  sqlite3.OperationalError: unable to open database file

  A successful run should look like:
  ubuntu at lp1953610-focal:~$ lck

  Command 'lck' not found, did you mean:

    command 'ack' from deb ack (3.3.1-1)
    command 'ick' from deb intercal (30:0.30-3)
    command 'lcp' from deb lsh-client (2.1-12build3)
    command 'lc' from deb mono-devel (6.8.0.105+dfsg-2)
    command 'lcf' from deb ucf (3.0038+nmu1)
    command 'ck' from deb python3-ck (1.9.4-1.1)

  Try: apt install <deb name>

  The umask changes have little regression potential, are tested in a
  smoke test, and there is a larger test suite that ensures it does not
  regress other bits (which again, it really shouldn't)

  [Where problems could occur]
  In general, regressions due to this bug would continue showing up as file access errors, either in automated tooling that currently works around the faulty database permissions, or in other packages relying on CNF. 

  Admins could be relying on the incorrect behavior for some reason
  (e.g. security), and some users could have existing automation in
  place to correct the issue manually. We'd expect the fix to have
  little impact on such scenarios, and the patches have been tested for
  these cases.

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