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

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Date: Wed, 24 Jan 2024 08:35:29 -0800
From: Kees Cook <keescook@...omium.org>
To: Kevin Locke <kevin@...inlocke.name>,
	John Johansen <john.johansen@...onical.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>,
	Josh Triplett <josh@...htriplett.org>,
	Mateusz Guzik <mjguzik@...il.com>,
	Al Viro <viro@...iv.linux.org.uk>, linux-mm@...ck.org,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-security-module@...r.kernel.org
Subject: Re: [6.8-rc1 Regression] Unable to exec apparmor_parser from
 virt-aa-helper

On Wed, Jan 24, 2024 at 09:19:54AM -0700, Kevin Locke wrote:
> 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

Oh, yikes. This means the LSM lost the knowledge that this open is an
_exec_, not a _read_.

I will starting looking at this. John might be able to point me in the
right direction more quickly, though.

Thanks for the report!

-Kees

> 
> 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

-- 
Kees Cook