[Bug 1820888] Re: unattended-upgrades may hold back upgrades due to comparing package versions by their string representation

[Balint Reczey]

** Description changed:

- This is part of the reason why the autopkgtes installing all security updates is failing for cosmic with 1.10ubuntu1:
+ [Impact]
+ 
+  * Without the fix u-u could not upgrade particular packages from -security. It could be observed in Cosmic with systemd security updates failing to install partly due to 239-7ubuntu10.10 being smaller than 239-7ubuntu10.8 when comparing them as strings:
  https://objectstorage.prodstack4-5.canonical.com/v1/AUTH_77e2ada1e7a84929a74ba3b87153c0ac/autopkgtest-disco/disco/amd64/u/unattended-upgrades/20190318_182031_fe4fe@/log.gz
+ 
+ [Test Case]
+ 
+  * The fix includes the extension of the build-time test cases to cover
+ package sets with which u-u fails with without the fallback:
+ 
  ...
- Checking: libnss-systemd ([<Origin component:'main' archive:'cosmic-updates' origin:'Ubuntu' label:'Ubuntu' site:'archive.ubuntu.com' isTrusted:True>])
- pkg libsystemd0 not in allowed origin
- sanity check failed
+ Running ./test_rewind.py with python3
+ DEBUG:root:APT::VersionedKernelPackages is not set
+ DEBUG:root:adjusting candidate version: test-package=2.0
  ...
+ 
+ With the unfixed version the test case fails here because u-u tries to
+ upgrade test-package to version 12.0 because it does not find version
+ 2.0 smaller.
+ 
+ [Regression Potential]
+ 
+ * The change is very small and isolated, but fixing it revealed the
+ issue fixed in LP: #1821101. Since the found issue's fix introduces
+ fallbacks when apt's resolver can't find a the solution it is unlikely
+ that other failures are triggered by the fix.

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https://bugs.launchpad.net/bugs/1820888

Title:
  unattended-upgrades may hold back upgrades due to comparing package
  versions by their string representation

Status in unattended-upgrades package in Ubuntu:
  Fix Released

Bug description:
  [Impact]

   * Without the fix u-u could not upgrade particular packages from -security. It could be observed in Cosmic with systemd security updates failing to install partly due to 239-7ubuntu10.10 being smaller than 239-7ubuntu10.8 when comparing them as strings:
  https://objectstorage.prodstack4-5.canonical.com/v1/AUTH_77e2ada1e7a84929a74ba3b87153c0ac/autopkgtest-disco/disco/amd64/u/unattended-upgrades/20190318_182031_fe4fe@/log.gz

  [Test Case]

   * The fix includes the extension of the build-time test cases to
  cover package sets with which u-u fails with without the fallback:

  ...
  Running ./test_rewind.py with python3
  DEBUG:root:APT::VersionedKernelPackages is not set
  DEBUG:root:adjusting candidate version: test-package=2.0
  ...

  With the unfixed version the test case fails here because u-u tries to
  upgrade test-package to version 12.0 because it does not find version
  2.0 smaller.

  [Regression Potential]

  * The change is very small and isolated, but fixing it revealed the
  issue fixed in LP: #1821101. Since the found issue's fix introduces
  fallbacks when apt's resolver can't find a the solution it is unlikely
  that other failures are triggered by the fix.

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