[Bug 1886115] Re: libseccomp 2.4.3-1ubuntu3.18.04.2 causes systemd to segfault on boot

[Alex Murray]

If this is indeed related to the Gentoo bug, I cannot see anywhere in
libseccomp where the environment is being modified. As such I suspect
this is likely actually a bug in systemd where it is modifying the
environment across the exec() and the libseccomp update has just caused
it to actually manifest (due to changed memory layouts as a result of
this new library version / size etc). So assigning this to systemd as
well for now.

** Also affects: systemd (Ubuntu)
   Importance: Undecided
       Status: New

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Title:
  libseccomp 2.4.3-1ubuntu3.18.04.2 causes systemd to segfault on boot

Status in libseccomp package in Ubuntu:
  New
Status in systemd package in Ubuntu:
  New

Bug description:
    After applying updates to Ubuntu 18.04 my desktop (apple mini with
  i5-2415M CPU) failed to complete the boot process.  A few seconds into
  the boot, the last message displayed is "/var mounted".  The system
  then appears to hang indefinitely.

    Luckily, the 'rescue' boot image allows the boot process to proceed sufficiently far to allow a root shell to be spawned.  Unfortunately no log files were written during the unsuccessful attempts to boot.  Spawning a 2nd root shell (# nohup getty tty5) on a 2nd virtual terminal (tty5) I was able to observe the message 'systemd freezing execution' after I closed the first root shell and resumed the boot process.  Further a core file was created (belonging to /sbin/init) in the root fs
  --8<--
  (gdb) bt
  #0  0x00007f16807ba187 in kill () at ../sysdeps/unix/syscall-template.S:78
  #1  0x0000563b957223b7 in ?? ()
  #2  <signal handler called>
  #3  __GI___libc_free (mem=0x4a60d140dfd9a5) at malloc.c:3103
  #4  0x0000563b9577c22e in ?? ()
  #5  0x0000563b957672d6 in ?? ()
  #6  0x0000563b9576ba22 in ?? ()
  #7  0x0000563b9574f51a in ?? ()
  #8  0x00007f16803a509a in ?? () from /lib/systemd/libsystemd-shared-237.so
  #9  0x00007f16803a53ea in sd_event_dispatch () from /lib/systemd/libsystemd-shared-237.so
  #10 0x00007f16803a5579 in sd_event_run () from /lib/systemd/libsystemd-shared-237.so
  #11 0x0000563b9572a49d in ?? ()
  #12 0x0000563b9571560c in ?? ()
  #13 0x00007f168079cb97 in __libc_start_main (main=0x563b957139c0, argc=3, argv=0x7ffe78153758, 
      init=<optimized out>, fini=<optimized out>, rtld_fini=<optimized out>, 
      stack_end=0x7ffe78153748) at ../csu/libc-start.c:310
  #14 0x0000563b957164fa in ?? ()
  (gdb) 
  -->8--
   and the kernel message buffer lists 
  --8<--
  traps: systemd[1] general protection fault ip:7f17ebf6e98d sp:7ffd774d6020 error:0 in libc-2.27.so[7f17ebed7000+1e7000]
  -->8--
  . 

    To me that looked a bit like Bug 669702 of Gentoo
  (https://bugs.gentoo.org/669702) and indeed one of the (few) updates
  applied just prior the reboot was the update of libseccomp.

    I was able to circumvent the problem by disabling (commenting out)
  the syscall filtering requested by systemd (on my system, only
  /etc/systemd/system/dbus-org.freedesktop.resolve1.service needed to be
  modified).

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