Comment 0 for bug 1912214

Hi,
to be clear I consider it quite likely that the error is on my side, but I'd appreciate guidance how to continue resolve. I have rubber ducked my setup with a coworker and talked to jjohansen if the profile would contain an obvious fault (it did not).

So hereby I'm filing a bug hoping to get some help on this case.

## 1. What happened

I was trying to add a feature to libvirt to support chained qcow files.
That means instead of adding just one path libvirt has to process the chain of backing files and add all of those. That works already on guest start, but not on hot-add of devices.

But while I see my code appending the rules I'd expect and issuing the apparmor_parser calls I'd expect it still fails.

I'd love to get the profile at runtime to ensure things really are loaded as expected.
But as discussed on IRC that won't work. So I tested and simplified and wonder for the test below why things fail.

## 2. how to reproduce

I was taking my new code out of the equation - and to do so I was adding the path that is needed to the local overrides. But it still is blocked. So - right now - I'm assuming that my code worked in adding the lines, but the access is still blocked. Therefore let us try to fix this one first and only then I can debug into what might be failing on the new code.

# Allow the access that libvirt does not yet allow
$ echo '"/var/lib/libvirt/images/testdisk-snap-snapshot.qcow2" rwk,' > /etc/apparmor.d/local/abstractions/libvirt-qemu

# prep the disk chain to be hot-added
qemu-img create -f qcow2 /var/lib/libvirt/images/testdisk-snap-base.qcow2 100M
qemu-img create -f qcow2 -b /var/lib/libvirt/images/testdisk-snap-base.qcow2 /var/lib/libvirt/images/testdisk-snap-snapshot.qcow2
cat > hot-add-test.xml << EOF
<disk type='file' device='disk'>
      <driver name='qemu' type='qcow2'/>
      <source file='/var/lib/libvirt/images/testdisk-snap-base.qcow2' index='1'/>
      <backingStore type='file' index='2'>
        <format type='qcow2'/>
        <source file='/var/lib/libvirt/images/testdisk-snap-snapshot.qcow2'/>
        <backingStore/>
      </backingStore>
      <target dev='vdc' bus='virtio'/>
</disk>
EOF

# prep a guest to attach to
uvt-simplestreams-libvirt --verbose sync --source http://cloud-images.ubuntu.com/daily arch=amd64 label=daily release=focal
uvt-kvm create --host-passthrough --password=ubuntu f-test2 release=focal arch=amd64 label=daily

We have checked the "effective" profile that is loaded. JJohanssen didn't see an obvious flaw in it. But for reference here:
root@h-libvirt-orig:~# apparmor_parser -p /etc/apparmor.d/libvirt/libvirt-e033b910-be06-4975-826f-b6fba368d928 | pastebinit
https://paste.ubuntu.com/p/yxdmMT6638/

# attach the disk
virsh attach-device f-test2 hot-add-test.xm

Libvirt/Qemu works as usual - except (known and expected) does not add a rule for "/var/lib/libvirt/images/testdisk-snap-snapshot.qcow2". But for that we have added out local override.
Yet it is denied access.

apparmor="DENIED" operation="open" namespace="root//lxd-h-libvirt-new_<var-snap-lxd-common-lxd>" profile="libvirt-a2caaf89-0682-464d-92ba-5295cb5f5128" name="/var/lib/libvirt/images/testdisk-snap-snapshot.qcow2" pid=2889044 comm="qemu-system-x86" requested_mask="r" denied_mask="r" fsuid=64055 ouid=64055

## 3. The rule is generally working

To be clear, on the same system if I just open up a new profile and allow this path to be accessed it works fine. See the working example below.
It must be somewhat that is tied to the way KVM guests get their profile updates/assigned.

root@h-libvirt-orig:~# cat /etc/apparmor.d/test
#include <tunables/global>

profile test flags=(attach_disconnected) {
    #include <abstractions/base>

    "/var/lib/libvirt/images/testdisk-snap-snapshot.qcow2" rwk,
    "/usr/bin/md5sum" rmix,
}
root@h-libvirt-orig:~# apparmor_parser -r /etc/apparmor.d/test; aa-exec -v -p test -- md5sum /var/lib/libvirt/images/testdisk-snap-snapshot.qcow2
[6939] aa_change_onexec("test")
[6939] exec md5sum /var/lib/libvirt/images/testdisk-snap-snapshot.qcow2
0f7fc62d270b69ee1b51453fa614d3e4 /var/lib/libvirt/images/testdisk-snap-snapshot.qcow2
root@h-libvirt-orig:~# apparmor_parser -r /etc/apparmor.d/test; aa-exec -v -p test -- md5sum /var/lib/libvirt/images/testdisk-snap-base.qcow2
[6944] aa_change_onexec("test")
[6944] exec md5sum /var/lib/libvirt/images/testdisk-snap-base.qcow2
md5sum: /var/lib/libvirt/images/testdisk-snap-base.qcow2: Permission denied

## 4. tracking apparmor_parser

I was using (for debug) a wrapper for apparmro_parser but all really looks as expected

$ cat /usr/sbin/apparmor_parser.wrap
#!/bin/bash
echo "ARGS $@" | /usr/bin/systemd-cat
echo "Content of ${2}:" | /usr/bin/systemd-cat
/usr/bin/ls -laF "${2}" | /usr/bin/systemd-cat
/usr/bin/cat "${2}" | /usr/bin/systemd-cat
echo "Content of ${2}.files:" | /usr/bin/systemd-cat
/usr/bin/ls -laF "${2}.files" | /usr/bin/systemd-cat
/usr/bin/cat "${2}.files" | /usr/bin/systemd-cat
/usr/sbin/apparmor_parser.orig "$@" | /usr/bin/systemd-cat

It is called with "-r filepath" and the content of that filepath contain the aforementioned rules. So what else might be wrong - why else could the access be denied despite the rule that should allow it.