[PATCH] sched/uclamp: Avoid setting cpu.uclamp.min bigger than cpu.uclamp.max

[Xuewen Yan]

From: Xuewen Yan <xuewen.yan@xxxxxxxxxx>

When setting cpu.uclamp.min/max in cgroup, there is no validating
like uclamp_validate() in __sched_setscheduler(). It may cause the
cpu.uclamp.min is bigger than cpu.uclamp.max.

Although there is protection in cpu_util_update_eff():
“eff[UCLAMP_MIN] = min(eff[UCLAMP_MIN], eff[UCLAMP_MAX])”, it's better
not to let it happen.

Judging the uclamp value before setting uclamp_min/max, avoid
the cpu.uclamp.min is bigger than cpu.uclamp.max.

Signed-off-by: Xuewen Yan <xuewen.yan@xxxxxxxxxx>
---
 kernel/sched/core.c | 26 +++++++++++++++++++++++++-
 1 file changed, 25 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 5226cc26a095..520a2da40dc9 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -8867,6 +8867,30 @@ static ssize_t cpu_uclamp_write(struct kernfs_open_file *of, char *buf,
 	rcu_read_lock();
 
 	tg = css_tg(of_css(of));
+
+	switch (clamp_id) {
+	case UCLAMP_MIN: {
+		unsigned int uc_req_max = tg->uclamp_req[UCLAMP_MAX].value;
+
+		if (req.util > uc_req_max) {
+			nbytes = -EINVAL;
+			goto unlock;
+		}
+		break;
+	}
+	case UCLAMP_MAX: {
+		unsigned int uc_req_min = tg->uclamp_req[UCLAMP_MIN].value;
+
+		if (req.util < uc_req_min) {
+			nbytes = -EINVAL;
+			goto unlock;
+		}
+		break;
+	}
+	default:
+		nbytes = -EINVAL;
+		goto unlock;
+	}
 	if (tg->uclamp_req[clamp_id].value != req.util)
 		uclamp_se_set(&tg->uclamp_req[clamp_id], req.util, false);
 
@@ -8878,7 +8902,7 @@ static ssize_t cpu_uclamp_write(struct kernfs_open_file *of, char *buf,
 
 	/* Update effective clamps to track the most restrictive value */
 	cpu_util_update_eff(of_css(of));
-
+unlock:
 	rcu_read_unlock();
 	mutex_unlock(&uclamp_mutex);
 
-- 
2.25.1