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SubjectRe: [PATCH v2] sched: Defend cfs and rt bandwidth quota against overflow
Date
Huaixin Chang <changhuaixin@linux.alibaba.com> writes:

> 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.

Reviewed-by: Ben Segall <bsegall@google.com>

>
> Signed-off-by: Huaixin Chang <changhuaixin@linux.alibaba.com>
> ---
> kernel/sched/core.c | 8 ++++++++
> kernel/sched/rt.c | 12 +++++++++++-
> kernel/sched/sched.h | 2 ++
> 3 files changed, 21 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 3a61a3b8eaa9..0be1782e15c9 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -7390,6 +7390,8 @@ 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);
>
> @@ -7417,6 +7419,12 @@ 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().
> diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
> index df11d88c9895..6d60ba21ed29 100644
> --- a/kernel/sched/rt.c
> +++ b/kernel/sched/rt.c
> @@ -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;
> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
> index db3a57675ccf..1f58677a8f23 100644
> --- a/kernel/sched/sched.h
> +++ b/kernel/sched/sched.h
> @@ -1918,6 +1918,8 @@ 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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