linux-kernel - [6.8-rc1 Regression] Unable to exec apparmor

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Date: Wed, 24 Jan 2024 09:19:54 -0700
From: Kevin Locke <kevin@...inlocke.name>
To: Linus Torvalds <torvalds@...ux-foundation.org>,
	Josh Triplett <josh@...htriplett.org>,
	Kees Cook <keescook@...omium.org>,
	Mateusz Guzik <mjguzik@...il.com>,
	Al Viro <viro@...iv.linux.org.uk>
Cc: linux-mm@...ck.org, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [6.8-rc1 Regression] Unable to exec apparmor_parser from
 virt-aa-helper

Hello Linux developers,

Using AppArmor 3.0.12 and libvirt 10.0.0 (from Debian packages) with
Linux 6.8-rc1 (unpatched), I'm unable to start KVM domains due to
AppArmor errors. Everything works fine on Linux 6.7.  After attempting
to start a domain, syslog contains:

libvirtd[38705]: internal error: Child process (LIBVIRT_LOG_OUTPUTS=3:stderr /usr/lib/libvirt/virt-aa-helper -c -u libvirt-4fad83ef-4285-4cf5-953c-5c13d943c1fb) unexpected exit status 1: virt-aa-helper: error: apparmor_parser exited with error
libvirtd[38705]: internal error: cannot load AppArmor profile 'libvirt-4fad83ef-4285-4cf5-953c-5c13d943c1fb'

dmesg contains the additional message:

audit: type=1400 audit(1706112657.438:74): apparmor="DENIED" operation="open" class="file" profile="virt-aa-helper" name="/usr/sbin/apparmor_parser" pid=6333 comm="virt-aa-helper" requested_mask="r" denied_mask="r" fsuid=0 ouid=0

The libvirt-$GUID file is not created in /etc/apparmor.d/libvirt and
apparmor_parser is not executed as far as I can tell.

I've bisected the regression to 978ffcbf00d82b03b79e64b5c8249589b50e7463.
Perhaps the change in this commit causes AppArmor to deny opening
/usr/sbin/apparmor_parser in preparation for exec?  For reference, 
/etc/apparmor.d/usr.lib.libvirt.virt-aa-helper contains:

  /{usr/,}sbin/apparmor_parser Ux,

I'd appreciate any help debugging the issue further.  Let me know if I
should take it up with the AppArmor or libvirt developers to better
understand the issue.

Thanks,
Kevin