dropbear-initramfs init-bottom script uses wrong ps options, can't kill descendants

[Kevin McCormick]

/usr/share/initramfs-tools/scripts/init-bottom/dropbear uses 'ps -o' to find dropbear descendants to kill, but the busybox ps inside initramfs doesn't support -o so nothing is killed other than the main dropbear.

My session drops briefly when init-bottom/dropbear brings down the network interfaces then comes back when the same IP is assigned. At that point I'm left in a busybox shell with access to nothing. For some reason I can run find and ls but not other busybox built-in commands like ps, sleep, etc. `pwd` puts me at /root-yMx7eP, and `find /` returns only "/" and "/root". Exiting from this shell prints "Aiee, segfault! You should probably report this as a bug to the developer" on the main console.

Of note is that /bin/busybox (shipped with busybox-static) supports 'ps -o' but /usr/lib/initramfs-tools/bin/busybox is used in initramfs and does not:
===========================================
$ /bin/busybox ps --help
BusyBox v1.27.2 (Ubuntu 1:1.27.2-2ubuntu3) multi-call binary.

Usage: ps [-o COL1,COL2=HEADER] [-T]

Show list of processes

     -o COL1,COL2=HEADER Select columns for display
 -T Show threads
$ /usr/lib/initramfs-tools/bin/busybox ps --help
BusyBox v1.27.2 (Ubuntu 1:1.27.2-2ubuntu3) multi-call binary.

Usage: ps

Show list of processes

 w Wide output
 l Long output
===========================================

My system is amd64 18.04.1.
busybox-initramfs 1:1.27.2-2ubuntu3
busybox-static 1:1.27.2-2ubuntu3
dropbear-bin 2017.75-3build1
dropbear-initramfs 2017.75-3build1
initramfs-tools 0.130ubuntu3.5

Here's relevant console output during boot:
===========================================
Begin: Running /scripts/init-bottom ... Begin: Stopping dropbear ... ps: invalid option -- 'o'
BusyBox v1.27.2 (Ubuntu 1:1.27.2-2ubuntu3) multi-call binary.

Usage: ps

Show list of processes

        w Wide output
        l Long output
ps: invalid option -- 'o'
BusyBox v1.27.2 (Ubuntu 1:1.27.2-2ubuntu3) multi-call binary.

Usage: ps

Show list of processes

        w Wide output
        l Long output
done.
Begin: Bringing down ens3 ... done.
Begin: Bringing down lo ... done.
done.
===========================================

[Kevin McCormick (kmccormick)]

I'm using the attached patch on my system without issue, but it only kills direct children instead of everything in the process group. (busybox's kill doesn't support PGID at all from what I can see)

It might be possible to solve this with a change to busybox-initramfs for additional ps options, or include /bin/busybox instead of /usr/lib/initramfs-tools/bin/busybox.

[Ubuntu Foundations Team Bug Bot (crichton)]

The attachment "dropbear.patch" seems to be a patch. If it isn't, please remove the "patch" flag from the attachment, remove the "patch" tag, and if you are a member of the ~ubuntu-reviewers, unsubscribe the team.

[This is an automated message performed by a Launchpad user owned by ~brian-murray, for any issues please contact him.]

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[klemens_u (klemens)]

Same problem for me, the provided path eliminates the problem.
Please accept the patch and release soon.

[klemens_u (klemens)]

Sorry "path" should read "patch"

[Rafael (rvallel)]

I patched this issue with the following fragment

if PID="$(cat /run/dropbear.pid)" 2>/dev/null &&
        [ "$(readlink -f "/proc/$PID/exe")" = /sbin/dropbear ]; then
    log_begin_msg "Stopping dropbear"

    # Patch issue #1804508
    # Kill all children and the parent dropbear
    kill -TERM $(ps l | awk '$4~/^'$PID'$/ {print $3}') $PID

    log_end_msg
fi

[asdasda (kinnaman)]

This seems to be fixed since at least focal.

dropbear (2018.76-3) unstable; urgency=medium
  * debian/initramfs/bottom-dropbear:
    + Read and parse /proc/*/stat instead of ps(1)'s output, as ps(1) options
      differ between Debian and Ubunt's busybox. Thanks to 'eviljoel' for the
      patch. (LP: #1652091.)