[PATCH] signal: improve warning about using SI_TKILL in rt_[tg]sigqueueinfo

[PATCH] signal: improve warning about using SI_TKILL in rt_[tg]sigqueueinfo

[Vladimir Davydov]

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.

Signed-off-by: Vladimir Davydov <vdavydov@parallels.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

Re: [PATCH] signal: improve warning about using SI_TKILL in rt_[tg]sigqueueinfo

[Oleg Nesterov]

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@parallels.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
> 

Re: [PATCH] signal: improve warning about using SI_TKILL in rt_[tg]sigqueueinfo

[Vladimir Davydov]

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@parallels.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@parallels.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);

Re: [PATCH] signal: improve warning about using SI_TKILL in rt_[tg]sigqueueinfo

[Oleg Nesterov]

On 03/19, Vladimir Davydov wrote:
>
> On Thu, Mar 19, 2015 at 02:00:46PM +0100, Oleg Nesterov wrote:
> >
> > Agreed.
> >
> > but perhaps we can simply remove this warning at all?
>
> We can, I suppose. Personally, I do not have any strong preference.

Me too, but personally I like this version more ;)

> From: Vladimir Davydov <vdavydov@parallels.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@parallels.com>

Acked-by: Oleg Nesterov <oleg@redhat.com>