[Bug 1840995] Re: check_stamp() function of apt.systemd.daily should not assume interval is a number

[Steve Langasek]

** Changed in: apt (Ubuntu Disco)
       Status: Fix Committed => Won't Fix

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https://bugs.launchpad.net/bugs/1840995

Title:
  check_stamp() function of apt.systemd.daily should not assume interval
  is a number

Status in apt package in Ubuntu:
  Fix Released
Status in apt source package in Disco:
  Won't Fix

Bug description:
  [Impact]
  Warning messages when using suffixes in intervals such as d for day

  /usr/lib/apt/apt.systemd.daily: 87: [: Illegal number: 20h

  [Test case]
  Create 99local in apt.conf.d with
  APT::Periodic::Update-Package-Lists "1d";
  and run /usr/lib/apt/apt.systemd.daily - make sure no warning appears.

  [Regression potential]
  The fix replaces -eq 0 checks with = 0 checks which might have different behavior in case -eq also accepts some values as equal to 0 that are not literally 0 and that now no longer match. But then you'd have to do stuff like set the interval to "+0", and it seems unrealistic people do that.

  [Original bug report]
  In the second half of the function there is

      # Calculate the interval in seconds depending on the unit specified
      if [ "${interval%s}" != "$interval" ] ; then
          interval="${interval%s}"
      elif [ "${interval%m}" != "$interval" ] ; then
          interval="${interval%m}"
          interval=$((interval*60))
      elif [ "${interval%h}" != "$interval" ] ; then
          interval="${interval%h}"
          interval=$((interval*60*60))
      else
          interval="${interval%d}"
          interval=$((interval*60*60*24))
      fi

  so, a variable might hold something like "1d", "100m", etc.

  Yet in the first there is a condition

      if [ "$interval" -eq 0 ]; then
          debug_echo "check_stamp: interval=0"
          # treat as no time has passed
          return 1
      fi

  which treats the value as a number and leads to

  /usr/lib/apt/apt.systemd.daily: 87: [: Illegal number: 20h

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