[Bug 2087535] [NEW] Apport GUI triggering is very fragile

[Simon Chopin]

Public bug reported:

The mechanism used by apport/update-notifier to prompt the user when a
crash occurs is both buggy and fragile.

It's buggy because it suffers from a pretty big TOCTOU race, with a
sizeable gap between the "check if seen" and "mark as seen" steps where
apport collects some data about the crash.

It's fragile because it relies on specific values for the mtime and
atime filesystem attributes, and the latter is not that reliable: it
depends on the FS atime granularity as well as mount options (noatime
remaining a fairly popular one, and the default being relatime).

Furthermore, anytime there is FS activity in the crash directory the
script will check *all* crashes rather than whichever files triggered
the systemd unit in the first place, exacerbating the issues. Sadly, I
don't think that one is solvable.

I believe this might be the actual culprit for bug 2066995 which we
actually saw live at Ubuntu Summit on a demo Framework laptop :)

** Affects: apport (Ubuntu)
     Importance: Undecided
         Status: New

** Affects: update-notifier (Ubuntu)
     Importance: Undecided
         Status: New

** Also affects: update-notifier (Ubuntu)
   Importance: Undecided
       Status: New

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https://bugs.launchpad.net/bugs/2087535

Title:
  Apport GUI triggering is very fragile

Status in apport package in Ubuntu:
  New
Status in update-notifier package in Ubuntu:
  New

Bug description:
  The mechanism used by apport/update-notifier to prompt the user when a
  crash occurs is both buggy and fragile.

  It's buggy because it suffers from a pretty big TOCTOU race, with a
  sizeable gap between the "check if seen" and "mark as seen" steps
  where apport collects some data about the crash.

  It's fragile because it relies on specific values for the mtime and
  atime filesystem attributes, and the latter is not that reliable: it
  depends on the FS atime granularity as well as mount options (noatime
  remaining a fairly popular one, and the default being relatime).

  Furthermore, anytime there is FS activity in the crash directory the
  script will check *all* crashes rather than whichever files triggered
  the systemd unit in the first place, exacerbating the issues. Sadly, I
  don't think that one is solvable.

  I believe this might be the actual culprit for bug 2066995 which we
  actually saw live at Ubuntu Summit on a demo Framework laptop :)

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