linux-kernel - Re: [PATCH 5/5] ptrace: implement PTRACE

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Date:	Fri, 23 Sep 2011 12:17:30 +0100
From:	Matt Fleming <matt@...sole-pimps.org>
To:	Tejun Heo <tj@...nel.org>
Cc:	oleg@...hat.com, vda.linux@...glemail.com,
	jan.kratochvil@...hat.com, linux-kernel@...r.kernel.org,
	torvalds@...ux-foundation.org, akpm@...ux-foundation.org,
	indan@....nu, bdonlan@...il.com, pedro@...esourcery.com
Subject: Re: [PATCH 5/5] ptrace: implement PTRACE_LISTEN

On Tue, 2011-06-14 at 11:20 +0200, Tejun Heo wrote:

[...]

> +	case PTRACE_LISTEN:
> +		/*
> +		 * Listen for events.  Tracee must be in STOP.  It's not
> +		 * resumed per-se but is not considered to be in TRACED by
> +		 * wait(2) or ptrace(2).  If an async event (e.g. group
> +		 * stop state change) happens, tracee will enter STOP trap
> +		 * again.  Alternatively, ptracer can issue INTERRUPT to
> +		 * finish listening and re-trap tracee into STOP.
> +		 */
> +		if (unlikely(!seized || !lock_task_sighand(child, &flags)))
> +			break;
> +
> +		si = child->last_siginfo;
> +		if (unlikely(!si || si->si_code >> 8 != PTRACE_EVENT_STOP))
> +			break;

I've only just noticed this. You really don't want to break out of the
switch while holding sighand->siglock. This should read,

		if (unlikely(!si || si->si_code >> 8 != PTRACE_EVENT_STOP)) {
			unlock_task_sighand(child, &flags);
			break;
		}

-- 
Matt Fleming, Intel Open Source Technology Center

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