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

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Date:	Thu, 19 Mar 2015 17:33:41 +0300
From:	Vladimir Davydov <vdavydov@...allels.com>
To:	Oleg Nesterov <oleg@...hat.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 Thu, Mar 19, 2015 at 02:00:46PM +0100, Oleg Nesterov wrote:
> 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?

We can, I suppose. Personally, I do not have any strong preference. The
patch removing the warning is attached.
---
From: Vladimir Davydov <vdavydov@...allels.com>
Subject: [PATCH] signal: remove warning about using SI_TKILL in
 rt_[tg]sigqueueinfo

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.

It does not look like we need this warning at all, because the behaviour
changed quite a long time ago (2.6.39), and if an application relies on
the old API, it gets EPERM anyway and can issue a warning by itself.

So let us zap the warning in kernel.

Signed-off-by: Vladimir Davydov <vdavydov@...allels.com>

diff --git a/kernel/signal.c b/kernel/signal.c
index a390499943e4..d51c5ddd855c 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -2992,11 +2992,9 @@ static int do_rt_sigqueueinfo(pid_t pid, int sig, siginfo_t *info)
 	 * Nor can they impersonate a kill()/tgkill(), which adds source 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);
+	    (task_pid_vnr(current) != pid))
 		return -EPERM;
-	}
+
 	info->si_signo = sig;
 
 	/* POSIX.1b doesn't mention process groups.  */
@@ -3041,12 +3039,10 @@ 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)) &&
-	    (task_pid_vnr(current) != pid)) {
-		/* We used to allow any < 0 si_code */
-		WARN_ON_ONCE(info->si_code < 0);
+	if ((info->si_code >= 0 || info->si_code == SI_TKILL) &&
+	    (task_pid_vnr(current) != pid))
 		return -EPERM;
-	}
+
 	info->si_signo = sig;
 
 	return do_send_specific(tgid, pid, sig, info);
--
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