profiles: dhclient: allow setting task comm name

dhclient wants to set its thread names to functional names for
introspection purposes. Eg.

$ pstree -at 3395
dhclient ens3
  ├─{isc-socket}
  ├─{isc-timer}
  └─{isc-worker0000}

When denied this can result in dhclient breaking and failing to obtain
IPv4 addresses.

Fixes: https://bugs.launchpad.net/ubuntu/+source/isc-dhcp/+bug/1918410
Signed-off-by: John Johansen <john.johansen@canonical.com>
Acked-by: Christian Boltz <apparmor@cboltz.de>
(cherry picked from commit c734839551)
Signed-off-by: John Johansen <john.johansen@canonical.com>

profiles/apparmor/profiles/extras/sbin.dhclient

@@ -43,6 +43,11 @@ profile dhclient /{usr/,}sbin/dhclient {
   @{PROC}/interrupts          r,
   @{PROC}/@{pid}/net/dev      r,
   @{PROC}/rtc                 r,
+
+  # dhcliet wants to update its threads with functional names
+  # see lp1918410
+  owner @{PROC}/@{pid}/task/[0-9]*/comm rw,
+
   # following rule shouldn't work, self is a symlink
   @{PROC}/self/status         r,
   /{usr/,}sbin/arp            mrix,