/usr/sbin/runc is confined with "runc" profile[1] introduced in AppArmor
v4.0.0. This change breaks stopping of containers, because the profile
assigned to containers doesn't accept signals from the "runc" peer.
AppArmor >= v4.0.0 is currently part of Ubuntu Mantic (23.10) and later.

In the case of Docker, this regression is hidden by the fact that
dockerd itself sends SIGKILL to the running container after runc fails
to stop it. It is still a regression, because graceful shutdowns of
containers via "docker stop" are no longer possible, as SIGTERM from
runc is not delivered to them. This can be seen in logs from dockerd
when run with debug logging enabled and also from tracing signals with
killsnoop utility from bcc[2] (in bpfcc-tools package in Debian/Ubuntu):

  Test commands:

    root@cloudimg:~# docker run -d --name test redis
    ba04c137827df8468358c274bc719bf7fc291b1ed9acf4aaa128ccc52816fe46
    root@cloudimg:~# docker stop test

  Relevant syslog messages (with wrapped long lines):

    Apr 23 20:45:26 cloudimg kernel: audit:
      type=1400 audit(1713905126.444:253): apparmor="DENIED"
      operation="signal" class="signal" profile="docker-default" pid=9289
      comm="runc" requested_mask="receive" denied_mask="receive"
      signal=kill peer="runc"
    Apr 23 20:45:36 cloudimg dockerd[9030]:
      time="2024-04-23T20:45:36.447016467Z"
      level=warning msg="Container failed to exit within 10s of kill - trying direct SIGKILL"
      container=ba04c137827df8468358c274bc719bf7fc291b1ed9acf4aaa128ccc52816fe46
      error="context deadline exceeded"

  Killsnoop output after "docker stop ...":

    root@cloudimg:~# killsnoop-bpfcc
    TIME      PID      COMM             SIG  TPID     RESULT
    20:51:00  9631     runc             3    9581     -13
    20:51:02  9637     runc             9    9581     -13
    20:51:12  9030     dockerd          9    9581     0

This change extends the docker-default profile with rules that allow
receiving signals from processes that run confined with either runc or
crun profile (crun[4] is an alternative OCI runtime that's also confined
in AppArmor >= v4.0.0, see [1]). It is backward compatible because the
peer value is a regular expression (AARE) so the referenced profile
doesn't have to exist for this profile to successfully compile and load.

Note that the runc profile has an attachment to /usr/sbin/runc. This is
the path where the runc package in Debian/Ubuntu puts the binary. When
the docker-ce package is installed from the upstream repository[3], runc
is installed as part of the containerd.io package at /usr/bin/runc.
Therefore it's still running unconfined and has no issues sending
signals to containers.

[1] https://gitlab.com/apparmor/apparmor/-/commit/2594d936
[2] https://github.com/iovisor/bcc/blob/master/tools/killsnoop.py
[3] https://download.docker.com/linux/ubuntu
[4] https://github.com/containers/crun

Signed-off-by: Tomáš Virtus <nechtom@gmail.com>
(cherry picked from commit 5ebe2c0)
Signed-off-by: Paweł Gronowski <pawel.gronowski@docker.com>

If a container is configured with the internal DNS resolver's own
address as an external server, try the next ext server rather than
recursing (return SERVFAIL if there are no other servers).

Signed-off-by: Rob Murray <rob.murray@docker.com>
(cherry picked from commit 8750614)
Signed-off-by: Paweł Gronowski <pawel.gronowski@docker.com>

[26.1 backport] apparmor: Allow confined runc to kill containers

[26.1 backport] Do not forward DNS requests to self.

A recent change to prevent containers only connected to --internal
networks from communicating with external DNS servers inadvertently
prevented the daemon's internal DNS server from forwarding requests
within an internal network to a containerised DNS server.

Relax the check, so that only requests that need to be forwarded
from the host's network namespace are dropped.

External DNS servers remain unreachable from the internal network.

Signed-off-by: Rob Murray <rob.murray@docker.com>
(cherry picked from commit 77a47db)
Signed-off-by: Paweł Gronowski <pawel.gronowski@docker.com>

[26.1 backport] Forward DNS requests into --internal networks