** Changed in: apparmor (Ubuntu Jammy)
Assignee: Michał Małoszewski (michal-maloszewski99) => Andreas Hasenack
(ahasenack)
** Changed in: apparmor (Ubuntu)
Assignee: Michał Małoszewski (michal-maloszewski99) => Andreas Hasenack
(ahasenack)
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https://bugs.launchpad.net/bugs/1979879
Title:
Apparmor profile in 22.04 jammy - fails to start when printing enabled
Status in apparmor package in Ubuntu:
Invalid
Status in samba package in Ubuntu:
Fix Released
Status in apparmor source package in Jammy:
In Progress
Bug description:
[Impact]
Users who have:
a) opted in to confining samba with apparmor (by installing
apparmor-profiles); and
b) changed the usr.sbin.smbd and samba-bgqd apparmor profiles to enforce mode;
will experience an error in starting the smbd service in jammy:
[2022/08/25 16:04:05.848067, 0]
../../lib/util/become_daemon.c:119(exit_daemon)
exit_daemon: daemon failed to start: Samba failed to init printing
subsystem, error code 13
This "printing subsystem" is actually a new daemon called samba-bgqd.
This errors prevents "smbd" from starting.
The reason it failed to start is that this binary is installed on a
different path than what is allowed in the samba apparmor profiles,
and as a result its execution is denied.
The chosen fix for this is to change the path of samba-bgqd in the
samba apparmor profiles to match where it is actually being installed
in the jammy packaging. Changing the actual path in the samba
packaging would be a more invasive fix.
In kinetic and later, the installation path of samba-bgqd was changed
instead, and requires no changes to the apparmor profiles.
However, once the path in the apparmor profiles was fixed for jammy,
another error comes up which also requires an apparmor change. samba-
bgqd is using locking when opening the *.tdb files in /run/samba, and
that requires an extra "k" flag to apparmor rules that cover that
directory and its tdb files.
This bug doesn't affect jammy samba users by default, as they have to
complete steps (a) and (b) from above to be impacted. Therefore, on
its own, this bug does not warrant an SRU, and we are using the block-
proposed-jammy tag to prevent its release until such time when another
more SRU-worthy apparmor bug is fixed for Jammy.
[Test Plan]
Make a container for testing:
$ lxc launch ubuntu-daily:jammy jammy-test
$ lxc shell jammy-test
Install the needed packages:
# apt update && apt install apparmor-profiles apparmor-utils samba
Confirm that you have smbd and samba-bgqd processes confined and in complain
mode (check first column):
# ps faxZ | grep -E "(smbd|bgqd)" | grep -v grep
smbd (complain) 2432 ? Ss 0:00 /usr/sbin/smbd
--foreground --no-process-group
smbd (complain) 2434 ? S 0:00 \_
/usr/sbin/smbd --foreground --no-process-group
smbd (complain) 2435 ? S 0:00 \_
/usr/sbin/smbd --foreground --no-process-group
smbd//null-/usr/lib/x86_64-linux-gnu/samba/samba-bgqd (complain) 2436 ? S
0:00 \_ /usr/lib/x86_64-linux-gnu/samba/samba-bgqd
Change the samba profiles to enforce mode:
# aa-enforce /etc/apparmor.d/usr.sbin.smbd /etc/apparmor.d/samba-bgqd
Setting /etc/apparmor.d/usr.sbin.smbd to enforce mode.
Setting /etc/apparmor.d/samba-bgqd to enforce mode.
Restart smbd:
# systemctl restart smbd
systemctl won't complain, but smbd failed to start:
root@jammy-test:~# ps faxZ | grep smbd | grep -v smbd
root@jammy-test:~#
# tail -2 /var/log/samba/log.smbd
[2022/09/09 18:20:35.200901, 0]
../../lib/util/become_daemon.c:119(exit_daemon)
exit_daemon: daemon failed to start: Samba failed to init printing
subsystem, error code 13
And dmesg on the *host* (not the container) will log a few DENIED messages
like this:
[sex set 9 15:20:30 2022] audit: type=1400 audit(1662747635.194:10356):
apparmor="DENIED" operation="exec"
namespace="root//lxd-jammy-test_<var-snap-lxd-common-lxd>" profile="smbd"
name="/usr/lib/x86_64-linux-gnu/samba/samba-bgqd" pid=994396 comm="smbd"
requested_mask="x" denied_mask="x" fsuid=1000000 ouid=1000000
After installing the fixed package (and accepting the dpkg conf prompt
changes), the new profile will be loaded in complain mode again. So
let's put it in enforce mode one more time:
# aa-enforce /etc/apparmor.d/usr.sbin.smbd /etc/apparmor.d/samba-bgqd
Setting /etc/apparmor.d/usr.sbin.smbd to enforce mode.
Setting /etc/apparmor.d/samba-bgqd to enforce mode.
Restart:
# systemctl restart smbd
And confirm that smbd and samba-bgqd are running this time, and in
enforce mode:
TBD
[Where problems could occur]
An apparmor update will impact all ubuntu users, regardless if they are using
samba or not. One has to weigh this carefully with the importance of the bug
that is being fixed.
This update will restart apparmor on the target system. All sorts of things
can happen due to that:
- all apparmor profiles will be reloaded and reapplied
- if users have modified default profiles in /etc/apparmor.d/* (not inside
local/*), they will get a dpkg conf prompt during this update
- in particular, users who have changed the samba profiles to be in enforce
mode (via aa-enforce) will definitely get a dpkg conf prompt, because the samba
profiles coming in via the apparmor-profiles package are in complain mode. This
is good, actually, as it will raise awareness about the change the update is
bringing
- if apparmor profile files have syntax mistakes, these will show up at this
time, and might end up leaving a service that was confined before, unconfined
after the update
- the "k" change is being done in abstractions/samba, instead of samba-bgqd
specifically, because it already had a rule to allow "rw" access to *.tdb files
in there. That abstraction is only included by other samba profiles at the
moment, so the change seems contained, but one might argue that it would be
best to add the explicit "k" rule to the samba-bgqd profile instead.
[Other information]
This fix alone does not warrant an apparmor SRU, therefore we are
using the block-proposed-jammy tag so that the fix can be bundled with
another future apparmor SRU.
Apparmor in Kinetic does not need the samba-bgqd path fix, but it
might need the "k" locking one. We are waiting for an apparmor version
update that will still happen in Kinetic to evaluate if some change
will be needed there.
-------------------original report-------------------
See bug here:
https://bugzilla.opensuse.org/show_bug.cgi?id=1191532
Fix was backported, but the path to samba-bgqd is wrong on 22.04.
Currently apparmor profile has it like this:
/usr/lib*/samba/samba-bgqd
When in fact 22.04 has it on /usr/lib/x86_64-linux-gnu/samba/samba-
bgqd
Moreover, the dmesg output failed and it has showed that the 'k' flag
is required for the *.tdb files within
/etc/apparmor.d/abstractions/samba.
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