linux-kernel - [PATCH] sched/uclamp: reject negative values in cpu_uclamp

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Date:   Sun, 12 Jan 2020 23:52:17 +0000
From:   Qais Yousef <qais.yousef@....com>
To:     Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>
Cc:     Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Patrick Bellasi <patrick.bellasi@...bug.net>,
        linux-kernel@...r.kernel.org, Qais Yousef <qais.yousef@....com>
Subject: [PATCH] sched/uclamp: reject negative values in cpu_uclamp_write

The check to ensure that the new written value into cpu.uclamp.{min,max}
is within range, [0:100], wasn't working because of the signed
comparison

7301                 if (req.percent > UCLAMP_PERCENT_SCALE) {
7302                         req.ret = -ERANGE;
7303                         return req;
7304                 }

Cast req.percent into u64 to force the comparison to be unsigned and
work as intended in capacity_from_percent().

Fixes: 2480c093130f ("sched/uclamp: Extend CPU's cgroup controller")
Signed-off-by: Qais Yousef <qais.yousef@....com>
---
 kernel/sched/core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 90e4b00ace89..e66b131e3aeb 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -7254,7 +7254,7 @@ capacity_from_percent(char *buf)
 					     &req.percent);
 		if (req.ret)
 			return req;
-		if (req.percent > UCLAMP_PERCENT_SCALE) {
+		if ((u64)req.percent > UCLAMP_PERCENT_SCALE) {
 			req.ret = -ERANGE;
 			return req;
 		}
-- 
2.17.1