[PATCH] ptrace: use safer wake up on ptrace_detach()

[Tejun Heo]

The wake_up_process() call in ptrace_detach() is spurious and not
interlocked with the tracee state.  IOW, the tracee could be running
or sleeping in any place in the kernel by the time wake_up_process()
is called.  This can lead to the tracee waking up unexpectedly which
can be dangerous.

The wake_up is spurious and should be removed but for now reduce its
toxicity by only waking up if the tracee is in TRACED or STOPPED
state.

Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
Cc: Roland McGrath <roland@xxxxxxxxxx>
Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
Cc: stable@xxxxxxxxxx
---
So, something like this.  Roland, Oleg, can you guys please ack this?
Also, should these ptrace patches be routed?  Shall I set up a git
tree?

Thank you.

 kernel/ptrace.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Index: work/kernel/ptrace.c
===================================================================
--- work.orig/kernel/ptrace.c
+++ work/kernel/ptrace.c
@@ -313,7 +313,7 @@ int ptrace_detach(struct task_struct *ch
 		child->exit_code = data;
 		dead = __ptrace_detach(current, child);
 		if (!child->exit_state)
-			wake_up_process(child);
+			wake_up_state(child, TASK_TRACED | TASK_STOPPED);
 	}
 	write_unlock_irq(&tasklist_lock);
 
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