Re: [ 020/184] ptrace: ensure arch_ptrace/ptrace_request can never

[Willy Tarreau]

Hi Oleg,

On Wed, Jun 05, 2013 at 05:49:51PM +0200, Oleg Nesterov wrote:
> On 06/05, Oleg Nesterov wrote:
> >
> > Note: I can make a _much_ simpler patch for 2.6.32, please let me know
> > if you need it.
> >
> > We can rely on sys_ptrace()->lock_kernel() and simply do lock/unlock
> > if fatal_signal_pending() in ptrace_stop/do_signal_stop. This is not
> > the same, this doesn't prevent wakeup(), but this should be enough.
> 
> Something like below. Untested/uncompiled. I think it should close the
> security problems.
> 
> Oleg.
> 
> 
> --- x/kernel/signal.c
> +++ x/kernel/signal.c
> @@ -1545,6 +1545,14 @@ static int sigkill_pending(struct task_s
>  		sigismember(&tsk->signal->shared_pending.signal, SIGKILL);
>  }
>  
> +static void ptrace_sync(void)
> +{
> +	if (fatal_signal_pending(current)) {
> +		lock_kernel();
> +		unlock_kernel();
> +	}
> +}
> +
>  /*
>   * This must be called with current->sighand->siglock held.
>   *
> @@ -1603,6 +1611,7 @@ static void ptrace_stop(int exit_code, i
>  		read_unlock(&tasklist_lock);
>  		preempt_enable_no_resched();
>  		schedule();
> +		ptrace_sync();
>  	} else {
>  		/*
>  		 * By the time we got the lock, our tracer went away.
> @@ -1722,6 +1731,9 @@ static int do_signal_stop(int signr)
>  		schedule();
>  	} while (try_to_freeze());
>  
> +	if (current->ptrace)
> +		ptrace_sync();
> +
>  	tracehook_finish_jctl();
>  	current->exit_code = 0;
>  

While I'm unable to tell whether the patch fixes the issue, I totally
trust you on this. So if you have the time to propose a tested patch
(or suggest me how to reliably test it), I'd gladly apply it instead.

Thanks!
Willy

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