linux-kernel - Re: [PATCH] signal: improve warning about using SI_TKILL in rt

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Message-ID: <20150319130045.GA7201@redhat.com>
Date:	Thu, 19 Mar 2015 14:00:46 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Vladimir Davydov <vdavydov@...allels.com>
Cc:	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Richard Weinberger <richard@....at>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: Re: [PATCH] signal: improve warning about using SI_TKILL in
	rt_[tg]sigqueueinfo

On 03/19, Vladimir Davydov wrote:
>
> Sending SI_TKILL from rt_[tg]sigqueueinfo was deprecated, so now we
> issue a warning on the first attempt of doing it. We use WARN_ON_ONCE,
> which is not informative and, what is worse, taints the kernel, making
> the trinity syscall fuzzer complain false-positively from time to time.
>
> This patch therefore substitutes the WARN_ON_ONCE with a pr_warn_once.

Agreed.

but perhaps we can simply remove this warning at all?

> Signed-off-by: Vladimir Davydov <vdavydov@...allels.com>
> ---
>  kernel/signal.c |   16 +++++++++++-----
>  1 file changed, 11 insertions(+), 5 deletions(-)
> 
> diff --git a/kernel/signal.c b/kernel/signal.c
> index a390499943e4..3cbcd94457af 100644
> --- a/kernel/signal.c
> +++ b/kernel/signal.c
> @@ -2993,8 +2993,11 @@ static int do_rt_sigqueueinfo(pid_t pid, int sig, siginfo_t *info)
>  	 */
>  	if ((info->si_code >= 0 || info->si_code == SI_TKILL) &&
>  	    (task_pid_vnr(current) != pid)) {
> -		/* We used to allow any < 0 si_code */
> -		WARN_ON_ONCE(info->si_code < 0);
> +		/* We used to allow SI_TKILL */
> +		if (info->si_code == SI_TKILL)
> +			pr_warn_once("%s (%d): Sending SI_TKILL from "
> +				     "rt_sigqueueinfo is deprecated\n",
> +				     current->comm, current->pid);
>  		return -EPERM;
>  	}
>  	info->si_signo = sig;
> @@ -3041,10 +3044,13 @@ static int do_rt_tgsigqueueinfo(pid_t tgid, pid_t pid, int sig, siginfo_t *info)
>  	/* Not even root can pretend to send signals from the kernel.
>  	 * Nor can they impersonate a kill()/tgkill(), which adds source info.
>  	 */
> -	if (((info->si_code >= 0 || info->si_code == SI_TKILL)) &&
> +	if ((info->si_code >= 0 || info->si_code == SI_TKILL) &&
>  	    (task_pid_vnr(current) != pid)) {
> -		/* We used to allow any < 0 si_code */
> -		WARN_ON_ONCE(info->si_code < 0);
> +		/* We used to allow SI_TKILL */
> +		if (info->si_code == SI_TKILL)
> +			pr_warn_once("%s (%d): Sending SI_TKILL from "
> +				     "rt_tgsigqueueinfo is deprecated\n",
> +				     current->comm, current->pid);
>  		return -EPERM;
>  	}
>  	info->si_signo = sig;
> -- 
> 1.7.10.4
> 

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