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

[Andrew Morton]

On Tue, 1 Feb 2011 11:26:18 +0100
Tejun Heo <tj@xxxxxxxxxx> wrote:

> 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

Am unable to work out why you tagged it for backporting.  It fixes some
observed bug?  Perhaps a regression?

> 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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