Add newer apparmor profile for bubblewrap (#337)

Fix several issues with Flatpak application (like GNOME Builder or Nextcloud)

Author: tintou

apparmor/bwrap-userns-restrict

@@ -0,0 +1,85 @@
+# This profile allows almost everything and only exists to allow bwrap
+# to work on a system with user namespace restrictions being enforced.
+# bwrap is allowed access to user namespaces and capabilities within
+# the user namespace, but its children do not have capabilities,
+# blocking bwrap from being able to be used to arbitrarily by-pass the
+# user namespace restrictions.
+
+# Note: the bwrap child is stacked against the bwrap profile due to
+# bwraps use of no-new-privs.
+
+abi <abi/4.0>,
+
+include <tunables/global>
+
+profile bwrap /usr/bin/bwrap flags=(attach_disconnected,mediate_deleted) {
+  allow capability,
+  # not allow all, to allow for pix stack on systems that don't support
+  # rule priority.
+  #
+  # sadly we have to allow 'm' every where to allow children to work under
+  # profile stacking atm.
+  allow file rwlkm /{**,},
+  allow network,
+  allow unix,
+  allow ptrace,
+  allow signal,
+  allow mqueue,
+  allow io_uring,
+  allow userns,
+  allow mount,
+  allow umount,
+  allow pivot_root,
+  allow dbus,
+
+  # stacked like this due to no-new-privs restriction
+  # this will stack a target profile against bwrap and unpriv_bwrap
+  # Ideally
+  # - there would be a transition at userns creation first. This would allow
+  #   for the bwrap profile to be tighter, and looser within the user
+  #   ns. bwrap will still have to fairly loose until a transition at
+  #   namespacing in general (not just user ns) is available.
+  # - there would be an independent second target as fallback
+  #   This would allow for select target profiles to be used, and not
+  #   necessarily stack the unpriv_bwrap in cases where this is desired
+  #
+  # the ix works here because stack will apply to ix fallback
+  # Ideally we would sanitize the environment across a privilege boundry
+  # (leaving bwarp into application) but flatpak etc use environment glibc
+  # sanitized environment variables as part of the sandbox setup.
+  allow pix /** -> &bwrap//&unpriv_bwrap,
+
+  # the local include should not be used without understanding the userns
+  # restriction.
+  # Site-specific additions and overrides. See local/README for details.
+  include if exists <local/bwrap-userns-restrict>
+}
+
+# The unpriv_bwrap profile is used to strip capabilities within the userns
+profile unpriv_bwrap flags=(attach_disconnected,mediate_deleted) {
+  # not allow all, to allow for pix stack
+  allow file rwlkm /{**,},
+  allow network,
+  allow unix,
+  allow ptrace,
+  allow signal,
+  allow mqueue,
+  allow io_uring,
+  allow userns,
+  allow mount,
+  allow umount,
+  allow pivot_root,
+  allow dbus,
+
+  # bwrap profile does stacking against itself this will keep the target
+  # profile from having elevated privileges in the container.
+  # If done recursively the stack will remove any duplicate
+  allow pix /** -> &unpriv_bwrap,
+
+  audit deny capability,
+
+  # the local include should not be used without understanding the userns
+  # restriction.
+  # Site-specific additions and overrides. See local/README for details.
+  include if exists <local/unpriv_bwrap>
+}

meson.build

@@ -38,6 +38,13 @@ install_data(
     install_dir: datadir / 'xdg-desktop-portal'
 )
 
+# AppArmor Flatpak profile
+install_data(
+    'apparmor/bwrap-userns-restrict',
+    install_dir: datadir / 'apparmor' / 'extra-profiles',
+    rename: 'bwrap-userns-restrict-patched',
+)
+
 # Default gsettings overrides
 subdir('overrides')