bug#71226: ‘guix shell -C’ doesn’t work on Ubuntu 24.04

[Ricardo Wurmus]

On Ubuntu 24.04 I created /etc/apparmor.d/guix-shell-container with the
following contents:

--8<---------------cut here---------------start------------->8---
abi <abi/3.0>,

include <tunables/global>

/gnu/store/*-guix-*/bin/guix flags=(attach_disconnected) {
  include <abstractions/base>
  include <abstractions/consoles>
  include <abstractions/nameservice>

  capability net_admin, # for "guix shell -CN"
  capability sys_admin, # for clone
  capability sys_ptrace, # for user namespaces

  # Allow preparing file systems inside the container root
  mount fstype=(devpts) none -> /tmp/guix-directory.*/dev/pts/,
  mount fstype=(mqueue) options=(nodev, noexec, nosuid, rw) mqueue -> 
/tmp/guix-directory.*/dev/mqueue/,
  mount fstype=(proc) options=(nodev, noexec, nosuid, rw) none -> 
/tmp/guix-directory.*/proc/,
  mount fstype=(sysfs) options=(nodev, noexec, nosuid, ro) none -> 
/tmp/guix-directory.*/sys/,
  mount fstype=(tmpfs) none -> /tmp/guix-directory.*/**,
  mount fstype=(tmpfs) none -> /tmp/guix-directory.*/,
  mount fstype=(tmpfs) options=(nodev, noexec, nosuid, rw) tmpfs -> 
/tmp/guix-directory.*/dev/shm/,
  mount fstype=(tmpfs) options=(noexec, rw, strictatime) none -> 
/tmp/guix-directory.*/dev/,
  mount options=(bind, rw) /** -> /tmp/guix-directory.*/**,
  mount options=(rbind, relatime, remount, ro) -> /tmp/guix-directory.*/**/,
  mount options=(rbind, relatime, remount, ro) -> /tmp/guix-directory.*/**,
  mount options=(rbind, rw) /** -> /tmp/guix-directory.*/**,
  umount /real-root/,

  pivot_root,

  /etc/nsswitch.conf r,
  /etc/passwd r,
  /gnu/store/** r,
  /gnu/store/**/** r,
  /gnu/store/*-guix-*/etc/ld.so.cache r,
  /gnu/store/*-guix-*/libexec/guix/guile ix,
  /gnu/store/*/bin/* mrix,
  /gnu/store/*/lib/**.so** mr,
  /gnu/store/*/lib/lib*.so* mr,
  /gnu/store/*/libexec/** ix,
  /gnu/store/*/sbin/* mrix,
  /tmp/ rw,
  /tmp/guix-directory** rw,
  /var/guix/** r,
  /var/guix/daemon-socket/socket rw,
  @{PROC}/*/ns/net rw,
  @{PROC}/*/ns/user rw,
  @{PROC}/@{pid}/** rw,
  @{PROC}/self/ rw,
  @{PROC}/self/** rw,
  @{PROC}/sys/kernel/unprivileged_userns_clone rw,

  # These are permissions inside the container after pivot root
  owner / w,
  owner /bin/ w,
  owner /bin/sh w,
  owner /etc/ w,
  owner /etc/group w,
  owner /etc/group.* r,
  owner /etc/group.* w,
  owner /etc/hosts w,
  owner /etc/passwd rw,
  owner /etc/passwd.* r,
  owner /etc/passwd.* w,
  
  owner /home/*/* ra,
  owner /home/*/.cache/guix/profiles/ r,
  owner /home/*/.cache/guix/profiles/* w,
  owner /home/*/.cache/guix/profiles/last-expiry-cleanup r,
  owner /real-root/ w,

  allow userns,

}
--8<---------------cut here---------------end--------------->8---

I then loaded the profile with "sudo apparmor_parser -qr
/etc/apparmor.d/guix-shell-container".  "guix shell -C hello" and "guix
shell -CN hello" worked fine.

To refine this policy I used the following process:

1. run "sudo aa-genprof guix" in one terminal
2. run "guix shell -CN hello" in another
3. update /etc/apparmor.d/guix-shell-container as needed (often
replacing temporary directory names with glob patterns)
4. repeat

We may want to create a template file in which we replace all instances
of /gnu/store and /var/guix with their respective configured values and
install the file in the same manner as we do etc/guix-daemon.cil.

I wonder if we need to provide something similar for SELinux where we
only have the guix-daemon policy.

-- 
Ricardo