parser: Check for kernel support prior to processing dbus entries

When a parser that is aware of dbus rules is running under a kernel
that is unaware of dbus rules, the parser should ignore the dbus rules
instead of attempting to load them into the kernel. Otherwise, the
kernel will reject the entire profile, leaving the application
unconfined.

Similar to what is done for mount rules, the features listed in
apparmorfs should be checked to see if dbus is supported under the
current kernel.

Signed-off-by: Tyler Hicks <tyhicks@canonical.com>
Acked-by: John Johansen <john.johansen@canonical.com>

parser/parser_main.c

@@ -757,6 +757,8 @@ static void get_match_string(void) {
 			kernel_supports_network = 0;
 		if (strstr(flags_string, "mount"))
 			kernel_supports_mount = 1;
+		if (strstr(flags_string, "dbus"))
+			kernel_supports_dbus = 1;
 		return;
 	}