From: Thomas Gleixner tglx@linutronix.de

commit cef31d9af908243421258f1df35a4a644604efbe upstream. Please apply to 4.9-stable, 4.4-stable, and 3.18-stable.

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: Eric Biggers ebiggers3@gmail.com Reported-by: Dmitry Vyukov dvyukov@google.com Reported-by: Alexey Dobriyan adobriyan@gmail.com Signed-off-by: Thomas Gleixner tglx@linutronix.de Cc: John Stultz john.stultz@linaro.org Signed-off-by: Eric Biggers ebiggers@google.com --- kernel/time/posix-timers.c | 34 +++++++++++++++++++--------------- 1 file changed, 19 insertions(+), 15 deletions(-)

diff --git a/kernel/time/posix-timers.c b/kernel/time/posix-timers.c index f2826c35e918..fc7c37ad90a0 100644 --- a/kernel/time/posix-timers.c +++ b/kernel/time/posix-timers.c @@ -507,17 +507,22 @@ 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; + /* 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); + } }

void posix_timers_register_clock(const clockid_t clock_id, @@ -745,8 +750,7 @@ common_timer_get(struct k_itimer *timr, struct itimerspec *cur_setting) /* interval timer ? */ if (iv.tv64) cur_setting->it_interval = ktime_to_timespec(iv); - else if (!hrtimer_active(timer) && - (timr->it_sigev_notify & ~SIGEV_THREAD_ID) != SIGEV_NONE) + else if (!hrtimer_active(timer) && timr->it_sigev_notify != SIGEV_NONE) return;

now = timer->base->get_time(); @@ -757,7 +761,7 @@ common_timer_get(struct k_itimer *timr, struct itimerspec *cur_setting) * expiry is > now. */ if (iv.tv64 && (timr->it_requeue_pending & REQUEUE_PENDING || - (timr->it_sigev_notify & ~SIGEV_THREAD_ID) == SIGEV_NONE)) + timr->it_sigev_notify == SIGEV_NONE)) timr->it_overrun += (unsigned int) hrtimer_forward(timer, now, iv);

remaining = __hrtimer_expires_remaining_adjusted(timer, now); @@ -767,7 +771,7 @@ common_timer_get(struct k_itimer *timr, struct itimerspec *cur_setting) * A single shot SIGEV_NONE timer must return 0, when * it is expired ! */ - if ((timr->it_sigev_notify & ~SIGEV_THREAD_ID) != SIGEV_NONE) + if (timr->it_sigev_notify != SIGEV_NONE) cur_setting->it_value.tv_nsec = 1; } else cur_setting->it_value = ktime_to_timespec(remaining); @@ -865,7 +869,7 @@ common_timer_set(struct k_itimer *timr, int flags, timr->it.real.interval = timespec_to_ktime(new_setting->it_interval);

/* SIGEV_NONE timers are not queued ! See common_timer_get */ - if (((timr->it_sigev_notify & ~SIGEV_THREAD_ID) == SIGEV_NONE)) { + if (timr->it_sigev_notify == SIGEV_NONE) { /* Setup correct expiry time for relative timers */ if (mode == HRTIMER_MODE_REL) { hrtimer_add_expires(timer, timer->base->get_time());