Re: [PATCH 104/173] Prevent rt_sigqueueinfo and rt_tgsigqueueinfofrom spoofing the signal code

[Oleg Nesterov]

On 04/25, Willy Tarreau wrote:
>
> 2.6.27.59-stable review patch.  If anyone has any objections, please let us know.
>
> ------------------
>
> From: Julien Tinnes <jln@xxxxxxxxxx>
>
> commit da48524eb20662618854bb3df2db01fc65f3070c upstream.

This also needs 243b422af9ea9af4ead07a8ad54c90d4f9b6081a

> Userland should be able to trust the pid and uid of the sender of a
> signal if the si_code is SI_TKILL.
>
> Unfortunately, the kernel has historically allowed sigqueueinfo() to
> send any si_code at all (as long as it was negative - to distinguish it
> from kernel-generated signals like SIGILL etc), so it could spoof a
> SI_TKILL with incorrect siginfo values.
>
> Happily, it looks like glibc has always set si_code to the appropriate
> SI_QUEUE, so there are probably no actual user code that ever uses
> anything but the appropriate SI_QUEUE flag.
>
> So just tighten the check for si_code (we used to allow any negative
> value), and add a (one-time) warning in case there are binaries out
> there that might depend on using other si_code values.
>
> Signed-off-by: Julien Tinnes <jln@xxxxxxxxxx>
> Acked-by: Oleg Nesterov <oleg@xxxxxxxxxx>
> Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxx>
> [wt: 2.6.27 does not have do_rt_tgsigqueueinfo()]
>
> ---
>  kernel/signal.c |   16 ++++++++++++----
>  1 file changed, 12 insertions(+), 4 deletions(-)
>
> Index: longterm-2.6.27/kernel/signal.c
> ===================================================================
> --- longterm-2.6.27.orig/kernel/signal.c	2011-01-23 10:52:37.000000000 +0100
> +++ longterm-2.6.27/kernel/signal.c	2011-04-25 16:06:27.491278774 +0200
> @@ -2294,9 +2294,13 @@
>  		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;
> +	}
>  	info.si_signo = sig;
>
>  	/* POSIX.1b doesn't mention process groups.  */
>
>

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