Patch "posix-timer: Properly check sigevent->sigev_notify" has been added to the 4.14-stable tree

This is a note to let you know that I've just added the patch titled

    posix-timer: Properly check sigevent->sigev_notify

to the 4.14-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
posix-timer-properly-check-sigevent-sigev_notify.patch
and it can be found in the queue-4.14 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Thomas Gleixner <[email protected]>
Date: Fri, 15 Dec 2017 10:32:03 +0100
Subject: posix-timer: Properly check sigevent->sigev_notify

From: Thomas Gleixner <[email protected]>

commit cef31d9af908243421258f1df35a4a644604efbe upstream.

timer_create() specifies via sigevent->sigev_notify the signal delivery for the new timer. The valid modes are SIGEV_NONE, SIGEV_SIGNAL, SIGEV_THREAD and (SIGEV_SIGNAL | SIGEV_THREAD_ID).

The sanity check in good_sigevent() is only checking the valid combination for the SIGEV_THREAD_ID bit, i.e. SIGEV_SIGNAL, but if SIGEV_THREAD_ID is not set it accepts any random value.

This has no real effects on the posix timer and signal delivery code, but it affects show_timer() which handles the output of /proc/$PID/timers. That function uses a string array to pretty print sigev_notify. The access to that array has no bound checks, so random sigev_notify cause access beyond the array bounds.

Add proper checks for the valid notify modes and remove the SIGEV_THREAD_ID masking from various code pathes as SIGEV_NONE can never be set in combination with SIGEV_THREAD_ID.

---
 kernel/time/posix-timers.c |   29 +++++++++++++++++------------
 1 file changed, 17 insertions(+), 12 deletions(-)

@@ -434,17 +434,22 @@ static struct pid *good_sigevent(sigeven
 {
 	struct task_struct *rtn = current->group_leader;
 
-	if ((event->sigev_notify & SIGEV_THREAD_ID ) &&
-		(!(rtn = find_task_by_vpid(event->sigev_notify_thread_id)) ||
-		 !same_thread_group(rtn, current) ||
-		 (event->sigev_notify & ~SIGEV_THREAD_ID) != SIGEV_SIGNAL))
+	switch (event->sigev_notify) {
+	case SIGEV_SIGNAL | SIGEV_THREAD_ID:
+		rtn = find_task_by_vpid(event->sigev_notify_thread_id);
+		if (!rtn || !same_thread_group(rtn, current))
+			return NULL;
+		/* FALLTHRU */
+	case SIGEV_SIGNAL:
+	case SIGEV_THREAD:
+		if (event->sigev_signo <= 0 || event->sigev_signo > SIGRTMAX)
+			return NULL;
+		/* FALLTHRU */
+	case SIGEV_NONE:
+		return task_pid(rtn);
+	default:
 		return NULL;
-
-	if (((event->sigev_notify & ~SIGEV_THREAD_ID) != SIGEV_NONE) &&
-	    ((event->sigev_signo <= 0) || (event->sigev_signo > SIGRTMAX)))
-		return NULL;
-
-	return task_pid(rtn);
+	}
 }
 
 static struct k_itimer * alloc_posix_timer(void)

@@ -669,7 +674,7 @@ void common_timer_get(struct k_itimer *t
 	struct timespec64 ts64;
 	bool sig_none;
 
-	sig_none = (timr->it_sigev_notify & ~SIGEV_THREAD_ID) == SIGEV_NONE;
+	sig_none = timr->it_sigev_notify == SIGEV_NONE;
 	iv = timr->it_interval;
 
 	/* interval timer ? */

@@ -856,7 +861,7 @@ int common_timer_set(struct k_itimer *ti
 
 	timr->it_interval = timespec64_to_ktime(new_setting->it_interval);
 	expires = timespec64_to_ktime(new_setting->it_value);
-	sigev_none = (timr->it_sigev_notify & ~SIGEV_THREAD_ID) == SIGEV_NONE;
+	sigev_none = timr->it_sigev_notify == SIGEV_NONE;
 
 	kc->timer_arm(timr, expires, flags & TIMER_ABSTIME, sigev_none);
 	timr->it_active = !sigev_none;

Patches currently in stable-queue which might be from [email protected] are

queue-4.14/sched-rt-do-not-pull-from-current-cpu-if-only-one-cpu-to-pull.patch queue-4.14/x86-boot-compressed-64-print-error-if-5-level-paging-is-not-supported.patch queue-4.14/posix-timer-properly-check-sigevent-sigev_notify.patch queue-4.14/x86-boot-compressed-64-detect-and-handle-5-level-paging-at-boot-time.patch