linux-kernel - Re: [PATCH] [226/275] Prevent rt_sigqueueinfo and rt_tgsigqueueinfo from spoofing the signal code

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Date:	Wed, 30 Mar 2011 23:33:38 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	jln@...gle.com, torvalds@...ux-foundation.org, gregkh@...e.de,
	ak@...ux.intel.com, linux-kernel@...r.kernel.org,
	stable@...nel.org, tim.bird@...sony.com,
	Roland Dreier <roland@...estorage.com>
Subject: Re: [PATCH] [226/275] Prevent rt_sigqueueinfo and
	rt_tgsigqueueinfo from spoofing the signal code

On 03/30, Andi Kleen wrote:
>
> --- linux-2.6.35.y.orig/kernel/signal.c	2011-03-29 22:50:25.616602954 -0700
> +++ linux-2.6.35.y/kernel/signal.c	2011-03-29 23:03:02.941224912 -0700
> @@ -2410,9 +2410,13 @@
>  		return -EFAULT;
>
>  	/* Not even root can pretend to send signals from the kernel.
> -	   Nor can they impersonate a kill(), which adds source info.  */
> -	if (info.si_code >= 0)
> +	 * Nor can they impersonate a kill()/tgkill(), which adds source info.
> +	 */
> +	if (info.si_code != SI_QUEUE) {
> +		/* We used to allow any < 0 si_code */
> +		WARN_ON_ONCE(info.si_code < 0);
>  		return -EPERM;

Oh, please don't.

Quoting Roland:

	Commit da48524eb206 ("Prevent rt_sigqueueinfo and rt_tgsigqueueinfo
	from spoofing the signal code") made the check on si_code too strict:
	glibc's aio implementation wants to queue signals with SI_ASYNCIO, and
	indeed glibc's tst-aio4 fails with the patched kernel.

If stable needs this change, then it probably needs

	Relax si_code check in rt_sigqueueinfo and rt_tgsigqueueinfo
	commit 243b422af9ea9af4ead07a8ad54c90d4f9b6081a

as well.

Oleg.

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