[Bug 1205407] Re: su: kill child process group on signal, not just immediate child

[Adam Conrad]

Hello Colin, or anyone else affected,

Accepted shadow into raring-proposed. The package will build now and be
available at
http://launchpad.net/ubuntu/+source/shadow/1:4.1.5.1-1ubuntu4.1 in a few
hours, and then in the -proposed repository.

Please help us by testing this new package.  See
https://wiki.ubuntu.com/Testing/EnableProposed for documentation how to
enable and use -proposed.  Your feedback will aid us getting this update
out to other Ubuntu users.

If this package fixes the bug for you, please add a comment to this bug,
mentioning the version of the package you tested, and change the tag
from verification-needed to verification-done. If it does not fix the
bug for you, please add a comment stating that, and change the tag to
verification-failed.  In either case, details of your testing will help
us make a better decision.

Further information regarding the verification process can be found at
https://wiki.ubuntu.com/QATeam/PerformingSRUVerification .  Thank you in
advance!

** Changed in: shadow (Ubuntu Raring)
       Status: New => Fix Committed

** Tags added: verification-needed

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https://bugs.launchpad.net/bugs/1205407

Title:
  su: kill child process group on signal, not just immediate child

Status in “shadow” package in Ubuntu:
  In Progress
Status in “shadow” source package in Raring:
  Fix Committed
Status in “shadow” package in Debian:
  New

Bug description:
  [Impact] Operational pain on Ubuntu builders every time a build hangs.
  [Test Case] See below, starting with 'pgrep sleep'.
  [Regression Potential] It's su; we should be pretty careful.  Running saucy builds with this for a while will help, and seeing whether anyone objects to the broader process-killing.

  Original report follows:

  Imported from Debian bug http://bugs.debian.org/713979:

  Package: shadow
  Version: 1:4.1.5.1-1
  Severity: normal
  User: ubuntu-devel at lists.ubuntu.com
  Usertags: origin-ubuntu saucy

  For some time I've noticed that, when an Ubuntu build times out (150
  minutes with no output), sbuild tries to terminate it, and I see a
  "Session terminated, terminating shell... ...terminated." message in the
  log (which is from su), but the build does not actually terminate
  properly.  Now, in both Debian and Ubuntu, sbuild invokes builds using
  something like this simplified command:

    sudo chroot $chroot su $username -s sh -c "cd $dir && exec dpkg-
  buildpackage"

  When su receives a signal, it passes it on to its child process (it has
  to go to unusual lengths here because it starts new sessions).  However,
  it only kills its immediate child, not the associated process group.
  This means that you can do something like this:

    $ pgrep sleep
    $ su cjwatson -c 'sh -c "sleep 1h"'
    Password:
    [wait a few seconds]
    ^C
    Session terminated, terminating shell...Sessions still open, not unmounting
     ...killed.
    $ pgrep sleep
    32421

  This is inconvenient; in this case it means we often have to ask
  sysadmins to manually kill processes for us.  I don't have much
  visibility into Debian buildds but I suspect there are similar problems
  there from time to time.

  Could su please kill the process group associated with its immediate
  child process instead?  This should just be a matter of negating the pid
  passed to kill.  If it did that, then I think it would do a much better
  job of cleaning up after itself.

  Thanks,

  --
  Colin Watson                                       [cjwatson at ubuntu.com]

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