Re: [6.8-rc1 Regression] Unable to exec apparmor_parser from virt-aa-helper

Kees Cook
2024-01-24T16:35:30Z

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