binder: Configurable global PID lookups

This reshakes commit d2587ce3968c6fdde3cf09d785bb957c4b75572f
and implements a kernel parameter to explicitly allow disabling
the behavior change to look up caller PIDs in the global namespace.

Author: fredldotme

drivers/android/binder.c

@@ -148,6 +148,9 @@ static int binder_set_stop_on_user_error(const char *val,
 module_param_call(stop_on_user_error, binder_set_stop_on_user_error,
 	param_get_int, &binder_stop_on_user_error, 0644);
 
+static bool binder_global_pid_lookups = true;
+module_param_named(global_pid_lookups, binder_global_pid_lookups, bool, S_IRUGO);
+
 #define binder_debug(mask, x...) \
 	do { \
 		if (binder_debug_mask & mask) \
@@ -4450,6 +4453,8 @@ static int binder_thread_read(struct binder_proc *proc,
 			trd->sender_pid =
 				task_tgid_nr_ns(sender,
 						task_active_pid_ns(current));
+			if (binder_global_pid_lookups && trd->sender_pid == 0)
+				trd->sender_pid = task_tgid_nr(sender);
 		} else {
 			trd->sender_pid = 0;
 		}