Commit d505b8af authored by Huaixin Chang's avatar Huaixin Chang Committed by Peter Zijlstra
Browse files

sched: Defend cfs and rt bandwidth quota against overflow 



When users write some huge number into cpu.cfs_quota_us or
cpu.rt_runtime_us, overflow might happen during to_ratio() shifts of
schedulable checks.

to_ratio() could be altered to avoid unnecessary internal overflow, but
min_cfs_quota_period is less than 1 << BW_SHIFT, so a cutoff would still
be needed. Set a cap MAX_BW for cfs_quota_us and rt_runtime_us to
prevent overflow.

Signed-off-by: default avatarHuaixin Chang <changhuaixin@linux.alibaba.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: default avatarBen Segall <bsegall@google.com>
Link: https://lkml.kernel.org/r/20200425105248.60093-1-changhuaixin@linux.alibaba.com
parent dbe93371

kernel/sched/core.c

+8 −0
Original line number Diff line number Diff line
@@ -7379,6 +7379,8 @@ static DEFINE_MUTEX(cfs_constraints_mutex); 


const u64 max_cfs_quota_period = 1 * NSEC_PER_SEC; /* 1s */

static const u64 min_cfs_quota_period = 1 * NSEC_PER_MSEC; /* 1ms */

/* More than 203 days if BW_SHIFT equals 20. */

static const u64 max_cfs_runtime = MAX_BW * NSEC_PER_USEC;



static int __cfs_schedulable(struct task_group *tg, u64 period, u64 runtime);
@@ -7406,6 +7408,12 @@ static int tg_set_cfs_bandwidth(struct task_group *tg, u64 period, u64 quota) 
	if (period > max_cfs_quota_period)

		return -EINVAL;



	/*

	 * Bound quota to defend quota against overflow during bandwidth shift.

	 */

	if (quota != RUNTIME_INF && quota > max_cfs_runtime)

		return -EINVAL;



	/*

	 * Prevent race between setting of cfs_rq->runtime_enabled and

	 * unthrottle_offline_cfs_rqs().

kernel/sched/rt.c

+11 −1
Original line number Diff line number Diff line
@@ -9,6 +9,8 @@ 


int sched_rr_timeslice = RR_TIMESLICE;

int sysctl_sched_rr_timeslice = (MSEC_PER_SEC / HZ) * RR_TIMESLICE;

/* More than 4 hours if BW_SHIFT equals 20. */

static const u64 max_rt_runtime = MAX_BW;



static int do_sched_rt_period_timer(struct rt_bandwidth *rt_b, int overrun);
@@ -2585,6 +2587,12 @@ static int tg_set_rt_bandwidth(struct task_group *tg, 
	if (rt_period == 0)

		return -EINVAL;



	/*

	 * Bound quota to defend quota against overflow during bandwidth shift.

	 */

	if (rt_runtime != RUNTIME_INF && rt_runtime > max_rt_runtime)

		return -EINVAL;



	mutex_lock(&rt_constraints_mutex);

	err = __rt_schedulable(tg, rt_period, rt_runtime);

	if (err)
@@ -2702,7 +2710,9 @@ static int sched_rt_global_validate(void) 
		return -EINVAL;



	if ((sysctl_sched_rt_runtime != RUNTIME_INF) &&

		(sysctl_sched_rt_runtime > sysctl_sched_rt_period))

		((sysctl_sched_rt_runtime > sysctl_sched_rt_period) ||

		 ((u64)sysctl_sched_rt_runtime *

			NSEC_PER_USEC > max_rt_runtime)))

		return -EINVAL;



	return 0;

kernel/sched/sched.h

+2 −0
Original line number Diff line number Diff line
@@ -1915,6 +1915,8 @@ extern void init_dl_inactive_task_timer(struct sched_dl_entity *dl_se); 
#define BW_SHIFT		20

#define BW_UNIT			(1 << BW_SHIFT)

#define RATIO_SHIFT		8

#define MAX_BW_BITS		(64 - BW_SHIFT)

#define MAX_BW			((1ULL << MAX_BW_BITS) - 1)

unsigned long to_ratio(u64 period, u64 runtime);



extern void init_entity_runnable_average(struct sched_entity *se);

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