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Commit cef31d9a authored by Thomas Gleixner's avatar Thomas Gleixner
Browse files

posix-timer: Properly check sigevent->sigev_notify 



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.

Reported-by: default avatarEric Biggers <ebiggers3@gmail.com>
Reported-by: default avatarDmitry Vyukov <dvyukov@google.com>
Reported-by: default avatarAlexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Cc: John Stultz <john.stultz@linaro.org>
Cc: stable@vger.kernel.org
parent 50c4c4e2

kernel/time/posix-timers.c

+17 −12
Original line number Diff line number Diff line
@@ -434,17 +434,22 @@ static struct pid *good_sigevent(sigevent_t * event) 
{

	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;



	if (((event->sigev_notify & ~SIGEV_THREAD_ID) != SIGEV_NONE) &&

	    ((event->sigev_signo <= 0) || (event->sigev_signo > SIGRTMAX)))

		/* 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;

	}

}



static struct k_itimer * alloc_posix_timer(void)
@@ -669,7 +674,7 @@ void common_timer_get(struct k_itimer *timr, struct itimerspec64 *cur_setting) 
	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 *timr, int flags, 


	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;