userns: Teach trace to use from_kuid

- When tracing capture the kuid.
- When displaying the data to user space convert the kuid into the
  user namespace of the process that opened the report file.

Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@redhat.com>
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 5c38c81..c9ace83 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -2060,7 +2060,8 @@
 	seq_puts(m, "#    -----------------\n");
 	seq_printf(m, "#    | task: %.16s-%d "
 		   "(uid:%d nice:%ld policy:%ld rt_prio:%ld)\n",
-		   data->comm, data->pid, data->uid, data->nice,
+		   data->comm, data->pid,
+		   from_kuid_munged(seq_user_ns(m), data->uid), data->nice,
 		   data->policy, data->rt_priority);
 	seq_puts(m, "#    -----------------\n");