[PATCH AUTOSEL 5.4 132/175] sched: Defend cfs and rt bandwidth quota against overflow

Sasha Levin
2020-06-09T00:04:24Z

From: Huaixin Chang <changhuaixin@linux.alibaba.com>

[ Upstream commit d505b8af58912ae1e1a211fabc9995b19bd40828 ]

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: Huaixin Chang <changhuaixin@linux.alibaba.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Ben Segall <bsegall@google.com>
Link: https://lkml.kernel.org/r/20200425105248.60093-1-changhuaixin@linux.alibaba.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
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 4874e1468279..361cbc2dc966 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -7374,6 +7374,8 @@ 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);

@@ -7401,6 +7403,12 @@ 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 7bf917e4d63a..5b04bba4500d 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);

@@ -2513,6 +2515,12 @@ 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);
read_lock(&tasklist_lock);
err = __rt_schedulable(tg, rt_period, rt_runtime);
@@ -2634,7 +2642,9 @@ 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 c7e7481968bf..570659f1c6e2 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1889,6 +1889,8 @@ extern void init_dl_rq_bw_ratio(struct dl_rq *dl_rq);
#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);
--
2.25.1