[PATCH 3.16 117/254] posix-timer: Properly check sigevent->sigev_notify

Ben Hutchings
2018-02-28T16:30:27Z

From: Thomas Gleixner <tglx@linutronix.de>

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.

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>
[bwh: Backported to 3.16:
- Add sig_none variable in common_timer_get(), added earlier upstream
- Adjust filename, context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
kernel/posix-timers.c | 29 +++++++++++++++++------------
1 file changed, 17 insertions(+), 12 deletions(-)

--- a/kernel/posix-timers.c
+++ b/kernel/posix-timers.c
@@ -498,17 +498,22 @@ 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);
+ }
}

void posix_timers_register_clock(const clockid_t clock_id,
@@ -728,16 +733,17 @@ common_timer_get(struct k_itimer *timr,
{
ktime_t now, remaining, iv;
struct hrtimer *timer = &timr->it.real.timer;
+ bool sig_none;

memset(cur_setting, 0, sizeof(struct itimerspec));

+ sig_none = timr->it_sigev_notify == SIGEV_NONE;
iv = timr->it.real.interval;

/* 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) && !sig_none)
return;

now = timer->base->get_time();
@@ -747,8 +753,7 @@ common_timer_get(struct k_itimer *timr,
* timer move the expiry time forward by intervals, so
* expiry is > now.
*/
- if (iv.tv64 && (timr->it_requeue_pending & REQUEUE_PENDING ||
- (timr->it_sigev_notify & ~SIGEV_THREAD_ID) == SIGEV_NONE))
+ if (iv.tv64 && (timr->it_requeue_pending & REQUEUE_PENDING || sig_none))
timr->it_overrun += (unsigned int) hrtimer_forward(timer, now, iv);

remaining = ktime_sub(hrtimer_get_expires(timer), now);
@@ -758,7 +763,7 @@ common_timer_get(struct k_itimer *timr,
* A single shot SIGEV_NONE timer must return 0, when
* it is expired !
*/
- if ((timr->it_sigev_notify & ~SIGEV_THREAD_ID) != SIGEV_NONE)
+ if (!sig_none)
cur_setting->it_value.tv_nsec = 1;
} else
cur_setting->it_value = ktime_to_timespec(remaining);
@@ -856,7 +861,7 @@ common_timer_set(struct k_itimer *timr,
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());