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>

init/Kconfig

@@ -927,7 +927,6 @@ config UIDGID_CONVERTED
 	# Features
 	depends on IMA = n
 	depends on EVM = n
-	depends on TRACING = n
 	depends on FS_POSIX_ACL = n
 	depends on QUOTA = n
 	depends on QUOTACTL = n

kernel/trace/trace.c

@@ -2060,7 +2060,8 @@ print_trace_header(struct seq_file *m, struct trace_iterator *iter)
 	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");
 

kernel/trace/trace.h

@@ -147,7 +147,7 @@ struct trace_array_cpu {
 	unsigned long		skipped_entries;
 	cycle_t			preempt_timestamp;
 	pid_t			pid;
-	uid_t			uid;
+	kuid_t			uid;
 	char			comm[TASK_COMM_LEN];
 };