APPLIED/cmnt: [SRU][Xenial][PATCH v2 1/1] posix-timers: Sanitize overrun handling

[Kleber Souza]

On 12/3/18 8:49 AM, Khaled Elmously wrote:
> Applied, with the indentation fix that Kleber pointed out.
>
>
> On 2018-11-29 01:42:41 , Khalid Elmously wrote:
>> From: Thomas Gleixner <tglx at linutronix.de>
>>
>> The posix timer overrun handling is broken because the forwarding functions
>> can return a huge number of overruns which does not fit in an int. As a
>> consequence timer_getoverrun(2) and siginfo::si_overrun can turn into
>> random number generators.
>>
>> The k_clock::timer_forward() callbacks return a 64 bit value now. Make
>> k_itimer::ti_overrun[_last] 64bit as well, so the kernel internal
>> accounting is correct. 3Remove the temporary (int) casts.
>>
>> Add a helper function which clamps the overrun value returned to user space
>> via timer_getoverrun(2) or siginfo::si_overrun limited to a positive value
>> between 0 and INT_MAX. INT_MAX is an indicator for user space that the
>> overrun value has been clamped.
>>
>> Reported-by: Team OWL337 <icytxw at gmail.com>
>> Signed-off-by: Thomas Gleixner <tglx at linutronix.de>
>> Acked-by: John Stultz <john.stultz at linaro.org>
>> Cc: Peter Zijlstra <peterz at infradead.org>
>> Cc: Michael Kerrisk <mtk.manpages at gmail.com>
>> Link: https://lkml.kernel.org/r/20180626132705.018623573@linutronix.de
>> (backported from commit 78c9c4dfbf8c04883941445a195276bb4bb92c76)
>> [kmously: Mostly context adjustments or adjusting for slightly refactored
>> code. A cosmetic change from the original (changing '-1' to
>> '-1LL') was dropped because it's not applicable ]
>> Signed-off-by: Khalid Elmously <khalid.elmously at canonical.com>
>> ---

The fix for Xenial was also missing the CVE reference, amended the
commit to fix it.


Thanks,

Kleber


>>  include/linux/posix-timers.h   |  4 ++--
>>  kernel/time/posix-cpu-timers.c |  2 +-
>>  kernel/time/posix-timers.c     | 23 ++++++++++++++++-------
>>  3 files changed, 19 insertions(+), 10 deletions(-)
>>
>> diff --git a/include/linux/posix-timers.h b/include/linux/posix-timers.h
>> index 907f3fd191ac..3e28a1a8d823 100644
>> --- a/include/linux/posix-timers.h
>> +++ b/include/linux/posix-timers.h
>> @@ -65,8 +65,8 @@ struct k_itimer {
>>  	spinlock_t it_lock;
>>  	clockid_t it_clock;		/* which timer type */
>>  	timer_t it_id;			/* timer id */
>> -	int it_overrun;			/* overrun on pending signal  */
>> -	int it_overrun_last;		/* overrun on last delivered signal */
>> +	s64 it_overrun;			/* overrun on pending signal  */
>> +	s64 it_overrun_last;		/* overrun on last delivered signal */
>>  	int it_requeue_pending;		/* waiting to requeue this timer */
>>  #define REQUEUE_PENDING 1
>>  	int it_sigev_notify;		/* notify word of sigevent struct */
>> diff --git a/kernel/time/posix-cpu-timers.c b/kernel/time/posix-cpu-timers.c
>> index 80016b329d94..8fc68e60c795 100644
>> --- a/kernel/time/posix-cpu-timers.c
>> +++ b/kernel/time/posix-cpu-timers.c
>> @@ -103,7 +103,7 @@ static void bump_cpu_timer(struct k_itimer *timer,
>>  			continue;
>>  
>>  		timer->it.cpu.expires += incr;
>> -		timer->it_overrun += 1 << i;
>> +		timer->it_overrun += 1LL << i;
>>  		delta -= incr;
>>  	}
>>  }
>> diff --git a/kernel/time/posix-timers.c b/kernel/time/posix-timers.c
>> index fc7c37ad90a0..cb77eeab669f 100644
>> --- a/kernel/time/posix-timers.c
>> +++ b/kernel/time/posix-timers.c
>> @@ -354,6 +354,16 @@ static __init int init_posix_timers(void)
>>  }
>>  
>>  __initcall(init_posix_timers);
>> +/*
>> + * The siginfo si_overrun field and the return value of timer_getoverrun(2)
>> + * are of type int. Clamp the overrun value to INT_MAX
>> + */
>> +static inline int timer_overrun_to_int(struct k_itimer *timr, int baseval)
>> +{
>> +	s64 sum = timr->it_overrun_last + (s64)baseval;
>> +
>> +	return sum > (s64)INT_MAX ? INT_MAX : (int)sum;
>> +}
>>  
>>  static void schedule_next_timer(struct k_itimer *timr)
>>  {
>> @@ -362,7 +372,7 @@ static void schedule_next_timer(struct k_itimer *timr)
>>  	if (timr->it.real.interval.tv64 == 0)
>>  		return;
>>  
>> -	timr->it_overrun += (unsigned int) hrtimer_forward(timer,
>> +	timr->it_overrun += hrtimer_forward(timer,
>>  						timer->base->get_time(),
>>  						timr->it.real.interval);
>>  
>> @@ -396,7 +406,7 @@ void do_schedule_next_timer(struct siginfo *info)
>>  		else
>>  			schedule_next_timer(timr);
>>  
>> -		info->si_overrun += timr->it_overrun_last;
>> +		info->si_overrun = timer_overrun_to_int(timr, info->si_overrun);
>>  	}
>>  
>>  	if (timr)
>> @@ -491,8 +501,7 @@ static enum hrtimer_restart posix_timer_fn(struct hrtimer *timer)
>>  					now = ktime_add(now, kj);
>>  			}
>>  #endif
>> -			timr->it_overrun += (unsigned int)
>> -				hrtimer_forward(timer, now,
>> +			timr->it_overrun += hrtimer_forward(timer, now,
>>  						timr->it.real.interval);
>>  			ret = HRTIMER_RESTART;
>>  			++timr->it_requeue_pending;
>> @@ -633,7 +642,7 @@ SYSCALL_DEFINE3(timer_create, const clockid_t, which_clock,
>>  	it_id_set = IT_ID_SET;
>>  	new_timer->it_id = (timer_t) new_timer_id;
>>  	new_timer->it_clock = which_clock;
>> -	new_timer->it_overrun = -1;
>> +	new_timer->it_overrun = -1LL;
>>  
>>  	if (timer_event_spec) {
>>  		if (copy_from_user(&event, timer_event_spec, sizeof (event))) {
>> @@ -762,7 +771,7 @@ common_timer_get(struct k_itimer *timr, struct itimerspec *cur_setting)
>>  	 */
>>  	if (iv.tv64 && (timr->it_requeue_pending & REQUEUE_PENDING ||
>>  			timr->it_sigev_notify == SIGEV_NONE))
>> -		timr->it_overrun += (unsigned int) hrtimer_forward(timer, now, iv);
>> +		timr->it_overrun += hrtimer_forward(timer, now, iv);
>>  
>>  	remaining = __hrtimer_expires_remaining_adjusted(timer, now);
>>  	/* Return 0 only, when the timer is expired and not pending */
>> @@ -824,7 +833,7 @@ SYSCALL_DEFINE1(timer_getoverrun, timer_t, timer_id)
>>  	if (!timr)
>>  		return -EINVAL;
>>  
>> -	overrun = timr->it_overrun_last;
>> +	overrun = timer_overrun_to_int(timr, 0);
>>  	unlock_timer(timr, flags);
>>  
>>  	return overrun;
>> -- 
>> 2.17.1
>>