[Bug 1815129] Re: apt segfaults when generating cache file

[Heitor R. Alves de Siqueira]

There are two armhf autopkgtest regressions for apt-1.0.1ubuntu2.20, in
tests for apt [0] and autopkgtest [1]. From the autopkgtest pages we can
see that these regressions were introduced long before this SRU, so it
seems like a long standing issue unrelated to this patch.

[0] http://autopkgtest.ubuntu.com/packages/a/apt/trusty/armhf
[1] http://autopkgtest.ubuntu.com/packages/a/autopkgtest/trusty/armhf

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Title:
  apt segfaults when generating cache file

Status in apt package in Ubuntu:
  Fix Released
Status in apt source package in Trusty:
  Fix Committed
Status in apt package in Debian:
  Fix Released

Bug description:
  [Impact]
  apt crashes (core dump) during cache creation

  [Description]
  When executing apt-cache several times on a memory constrained system, apt-cache can sometimes crash with a core dump file. This is related to mmap() failing allocations during cache generation, according to an upstream bug report (803417).
  There is an upstream patch for this bug (6789e01e do not segfault in cache generation on mmap failure) and it's included in the apt package for other series (see below), so we only need to backport it to Trusty.

  Upstream commit: https://salsa.debian.org/apt-
  team/apt/commit/6789e01e9370b3b7f65d52138c5657eaa712b4d1

  $ git describe --contains 6789e01e9370
  1.1_exp16~5

  $ rmadison apt
   apt | 1.0.1ubuntu2            | trusty           | source, ...
   apt | 1.0.1ubuntu2.19         | trusty-security  | source, ...
   apt | 1.0.1ubuntu2.19         | trusty-updates   | source, ...
   apt | 1.2.10ubuntu1           | xenial           | source, ...
   apt | 1.6.1                   | bionic           | source, ...
   apt | 1.7.0                   | cosmic           | source, ...
   apt | 1.8.0~rc2               | disco            | source, ...

  [Test Case]
  1) Deploy a Trusty (14.04 LTS) vm w/ 128M
  2) Fetch latest stress-ng src code
   2.1) git clone git://kernel.ubuntu.com/cking/stress-ng
   2.2) cd stress-ng
   2.3) make clean
   2.4) make
  3) Stress the mmap() with stress-ng
   3.1) ./stress-ng --brk 2 --mmap 5 --vm 1 --mmap-bytes 90%
  4) Disable swap (if any)
   4.1) swapoff -a
  5) for i in `seq 1 10000`;do apt-cache policy vsftpd;done
  ...
  vsftpd:
    Installed: (none)
    Candidate: 3.0.2-1ubuntu2.14.04.1
    Version table:
       3.0.2-1ubuntu2.14.04.1 0
          500 http://us.archive.ubuntu.com/ubuntu/ trusty-updates/main amd64 Packages
       3.0.2-1ubuntu2 0
          500 http://us.archive.ubuntu.com/ubuntu/ trusty/main amd64 Packages
  Segmentation fault (core dumped)
  Segmentation fault (core dumped)
  Segmentation fault (core dumped)
  Segmentation fault (core dumped)
  Segmentation fault (core dumped)
  Segmentation fault (core dumped)
  ...

  [Regression Potential]
  The regression potential for this should be low, as it's a change in the failure path for memory allocations. This shouldn't be triggered during normal usage, and we'll thoroughly test the patched package with autopkgtests and perform scripted runs in memory-constrained systems with stress-ng.
  We also have a confirmation from an impacted user that the upstream patch fixes their issue without further problems.

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