Comment 4 for bug 2031398

Thank,
Calvin and I looked at it and you are right.

This is in cloud-init since [1] and used -sf as in [2] to avoid any side effects by the content of that file.
=> "... If unspecified, the default /sbin/dhclient-script is used. ..."

I think it should be safe to allow execution of that as a common pattern to avoid falling back to the default.

For the severity we need to find out, if
a) call dhclient with -sf /bin/true to do nothing
isn't just the same as
b) call dhclient with -sf /bin/true, get denied, but do everything else the same

If they are the same then this would only cause the annoying log message.
If they actually behave different

We can recreate this in a VM:

ubuntu@l:~$ sudo dhclient -v -1 -sf /bin/true
Internet Systems Consortium DHCP Client 4.4.3-P1
Copyright 2004-2022 Internet Systems Consortium.
All rights reserved.
For info, please visit https://www.isc.org/software/dhcp/

execve (/bin/true, ...): Permission denied
Listening on LPF/enp1s0/52:54:00:be:7a:d2
Sending on LPF/enp1s0/52:54:00:be:7a:d2
Sending on Socket/fallback
xid: warning: no netdev with useable HWADDR found for seed's uniqueness enforcement
xid: rand init seed (0x649ac969) built using gethostid
DHCPREQUEST for 192.168.122.239 on enp1s0 to 255.255.255.255 port 67 (xid=0x7ee9d4f5)
DHCPACK of 192.168.122.239 from 192.168.122.1 (xid=0xf5d4e97e)
execve (/bin/true, ...): Permission denied
bound to 192.168.122.239 -- renewal in 1781 seconds.
ubuntu@l:~$ echo $?
0

We see it is denied, but otherwise happy.

So my point is.
We try to use -sf /bin/true so it does not execute anything with a side-effect
Being denied by apparmor means no side-effect happens.
So - as assumed - the only "impact" is the annoying log message.

[1]: https://git.launchpad.net/cloud-init/commit/?id=d5f855dd96ccbea77f61b0515b574ad2c43d116d
[2]: https://manpages.ubuntu.com/manpages/jammy/man8/dhclient.8.html