itimer: Schedule silent NULL pointer fixup in setitimer() for removal

setitimer() should return -EFAULT if called with an invalid pointer
for value. The current code excludes a NULL pointer from this rule and
silently uses it to stop the timer. This violates the spec.

Warn about user space apps which rely on that feature and schedule it
for removal.

[ tglx: Massaged changelog, warn message and Doc entry ]

Signed-off-by: Sasikantha babu <sasikanth.v19@gmail.com>
Link: http://lkml.kernel.org/r/1332340854-26053-1-git-send-email-sasikanth.v19@gmail.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

Documentation/feature-removal-schedule.txt

@@ -529,3 +529,11 @@ When:	3.5
 Why:	The old kmap_atomic() with two arguments is deprecated, we only
 	keep it for backward compatibility for few cycles and then drop it.
 Who:	Cong Wang <amwang@redhat.com>
+
+----------------------------
+
+What:	setitimer accepts user NULL pointer (value)
+When:	3.6
+Why:	setitimer is not returning -EFAULT if user pointer is NULL. This
+	violates the spec.
+Who:	Sasikantha Babu <sasikanth.v19@gmail.com>

kernel/itimer.c

@@ -284,8 +284,11 @@ SYSCALL_DEFINE3(setitimer, int, which, struct itimerval __user *, value,
 	if (value) {
 		if(copy_from_user(&set_buffer, value, sizeof(set_buffer)))
 			return -EFAULT;
-	} else
+	} else {
 		memset((char *) &set_buffer, 0, sizeof(set_buffer));
+		WARN_ONCE(1, "setitimer: new_value pointer is NULL."
+			  " Misfeature support will be removed\n");
+	}
 
 	error = do_setitimer(which, &set_buffer, ovalue ? &get_buffer : NULL);
 	if (error || !ovalue)