apparmor: Allow version-specific bits in profiles

Perform an additional preprocessing step before the existing
variable substitution. This is the same approach that we already
use to customize systemd unit files based on whether the service
supports TCP connections.

Signed-off-by: Andrea Bolognani <abologna@redhat.com>
Reviewed-by: Jim Fehlig <jfehlig@suse.com>

src/security/apparmor/meson.build

@@ -14,9 +14,41 @@ apparmor_gen_profiles_conf = configuration_data({
 
 apparmor_dir = sysconfdir / 'apparmor.d'
 
+# Our profiles use some features that only work well on AppArmor 3.x,
+# specifically the 'include if exists' directive. In order to keep
+# supporting AppArmor 2.x, the bits that are version-specific are
+# enclosed in special markers and we decide which ones to include
+# based on the AppArmor version detected on the host.
+#
+# TODO: drop the additional complexity once we no longer target
+#       distros that ship AppArmor 2.x (Debian 11, Ubuntu 20.04)
+if conf.has('WITH_APPARMOR_3')
+  apparmor_gen_cmd = [
+    'sed',
+    '-e', '/[@]BEGIN_APPARMOR_3[@]/d',
+    '-e', '/[@]END_APPARMOR_3[@]/d',
+    '-e', '/[@]BEGIN_APPARMOR_2[@]/,/[@]END_APPARMOR_2[@]/d',
+    '@INPUT@'
+  ]
+else
+  apparmor_gen_cmd = [
+    'sed',
+    '-e', '/[@]BEGIN_APPARMOR_3[@]/,/[@]END_APPARMOR_3[@]/d',
+    '-e', '/[@]BEGIN_APPARMOR_2[@]/d',
+    '-e', '/[@]END_APPARMOR_2[@]/d',
+    '@INPUT@'
+  ]
+endif
+
 foreach name : apparmor_gen_profiles
-  configure_file(
+  tmp = configure_file(
     input: '@0@.in'.format(name),
+    output: '@0@.tmp'.format(name),
+    command: apparmor_gen_cmd,
+    capture: true,
+  )
+  configure_file(
+    input: tmp,
     output: name,
     configuration: apparmor_gen_profiles_conf,
     install: true,