[Bug 2012943] Re: systemd-resolved crashes due to use-after-free bug

[Nick Rosbrook]

** Description changed:

  [ Impact ]
  
  The continuous systemd-resolved crashes delay/hang the device startup.
  And this leads to unresponsive devices in the system. Specifically, the crash looks like:
  
  Dec 16 12:51:21 TREND-24-AF-7A systemd[1]: Started Time & Date Service.
  Dec 16 12:51:24 TREND-24-AF-7A systemd[1]: systemd-resolved.service: Main process exited, code=killed, status=11/SEGV
  [...]
  Dec 16 12:53:47 TREND-24-AF-7A systemd-resolved[2591]: Assertion 'DNS_TRANSACTION_IS_LIVE(q->state)' failed at src/resolve/resolved-dns-query.c:520, function dns_query_complete(). Aborting.
  Dec 16 12:53:47 TREND-24-AF-7A systemd[1]: systemd-resolved.service: Main process exited, code=killed, status=6/ABRT
  
  [ Test Plan ]
  
  The exact steps to reproduce this issue are still not known.
  But we see this crash only in Static IP Addressing mode enabled, where systemd-resolved is enabled for LLMNR service.
  But we were not able to see this crash in DHCP mode.
  
  Steps to reproduce:
  1) Powercycle the device.
  2) Soft-reboot.
  
+ It was also pointed out by Brian Murray that this error in the Ubuntu
+ error tracker is likely the same bug:
+ https://errors.ubuntu.com/problem/3cb08ae5efaa4d8c6ce992f7cebd2751ae3f168f.
+ Therefore, we would expect to stop seeing this error in the tracker as a
+ result of this patch.
+ 
  [ Where problems could occur ]
  
  The patch[1] simply disables the timer event source for a DNS query when
  the struct representing that query is free'd. I cannot see any realistic
  regression potential, because if the timer event fired on the DNS query
  after it has been free'd, then that would be this bug. I.e. no working
  code should be relying on the timer event source still being around
  after the query is free'd.
  
  [1]
  https://github.com/systemd/systemd/commit/73bfd7be042cc63e7649242b377ad494bf74ea4b

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https://bugs.launchpad.net/bugs/2012943

Title:
  systemd-resolved crashes due to use-after-free bug

Status in systemd package in Ubuntu:
  Fix Released
Status in systemd source package in Focal:
  Fix Committed

Bug description:
  [ Impact ]

  The continuous systemd-resolved crashes delay/hang the device startup.
  And this leads to unresponsive devices in the system. Specifically, the crash looks like:

  Dec 16 12:51:21 TREND-24-AF-7A systemd[1]: Started Time & Date Service.
  Dec 16 12:51:24 TREND-24-AF-7A systemd[1]: systemd-resolved.service: Main process exited, code=killed, status=11/SEGV
  [...]
  Dec 16 12:53:47 TREND-24-AF-7A systemd-resolved[2591]: Assertion 'DNS_TRANSACTION_IS_LIVE(q->state)' failed at src/resolve/resolved-dns-query.c:520, function dns_query_complete(). Aborting.
  Dec 16 12:53:47 TREND-24-AF-7A systemd[1]: systemd-resolved.service: Main process exited, code=killed, status=6/ABRT

  [ Test Plan ]

  The exact steps to reproduce this issue are still not known.
  But we see this crash only in Static IP Addressing mode enabled, where systemd-resolved is enabled for LLMNR service.
  But we were not able to see this crash in DHCP mode.

  Steps to reproduce:
  1) Powercycle the device.
  2) Soft-reboot.

  It was also pointed out by Brian Murray that this error in the Ubuntu
  error tracker is likely the same bug:
  https://errors.ubuntu.com/problem/3cb08ae5efaa4d8c6ce992f7cebd2751ae3f168f.
  Therefore, we would expect to stop seeing this error in the tracker as
  a result of this patch.

  [ Where problems could occur ]

  The patch[1] simply disables the timer event source for a DNS query
  when the struct representing that query is free'd. I cannot see any
  realistic regression potential, because if the timer event fired on
  the DNS query after it has been free'd, then that would be this bug.
  I.e. no working code should be relying on the timer event source still
  being around after the query is free'd.

  [1]
  https://github.com/systemd/systemd/commit/73bfd7be042cc63e7649242b377ad494bf74ea4b

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