auto-import from udev does not work on jammy

[Valentin David]

`66-snapd-autoimport.rules` in udev rules calls `/usr/bin/unshare -m /usr/bin/snap auto-import --mount=/dev/%k`.

This should try to mount `/dev/%k` to read file `auto-import.assert`.

However according to udev(7) for `RUN`:

> Note that running programs that access the network or mount/unmount filesystems is not allowed inside of udev rules, due to the default sandbox that is enforced on systemd-udevd.service.

Here is the error logs from UC22 when running `systemd-udevd` with `SYSTEMD_LOG_LEVEL=debug`
```
Mar 10 22:18:57 ubuntu systemd-udevd[2078]: dm-2: '/usr/bin/unshare -m /usr/bin/snap auto-import --mount=/dev/dm-2'(err) 'unshare: '
Mar 10 22:18:57 ubuntu systemd-udevd[2078]: dm-2: '/usr/bin/unshare -m /usr/bin/snap auto-import --mount=/dev/dm-2'(err) 'cannot change root filesystem propagation'
Mar 10 22:18:57 ubuntu systemd-udevd[2078]: dm-2: '/usr/bin/unshare -m /usr/bin/snap auto-import --mount=/dev/dm-2'(err) ': Operation not permitted'
```

Note that `unshare -m` will try re-mount / as recursive private in the namespace. This is likely where it fails. But even if we remove `unshare`, I suspect

Instead of using udev, we should listen to udisks through dbus to find added filesystems which are marked as automatic.

[Maciej Borzecki (maciek-borzecki)]

My bet is on SystemCallFilter which is set to `@system-service @module @raw-io bpf` which IIRC would deny mount among other things.

[Maciej Borzecki (maciek-borzecki)]

Possibly related to https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1971955 which AFAIU the root cause was identified as the SystemCallFilter blocking unshare() syscall.

[Maciej Borzecki (maciek-borzecki)]

Sorry this bug: https://bugs.launchpad.net/ubuntu/+source/systemd/+bug/1966203

[Alberto Mardegan (mardy)]

This bug has already been fixed by Valentin in Ubuntu Core with https://github.com/snapcore/core-base/pull/35

For the issue on desktop systems, we'll continue working on bug 1966203 (and the solution there will be just to remove the udev script).