linux-kernel - [PATCH v2] sched/uclamp: reject negative values in cpu_uclamp

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Message-Id: <20200114210947.14083-1-qais.yousef@arm.com>
Date:   Tue, 14 Jan 2020 21:09:47 +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, ouwen210@...mail.com,
        Qais Yousef <qais.yousef@....com>
Subject: [PATCH v2] 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                 }

	# echo -1 > cpu.uclamp.min
	# cat cpu.uclamp.min
	42949671.96

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

	# echo -1 > cpu.uclamp.min
	sh: write error: Numerical result out of range

Fixes: 2480c093130f ("sched/uclamp: Extend CPU's cgroup controller")
Signed-off-by: Qais Yousef <qais.yousef@....com>
---

Changes in v2:
	- Improve the commit message as suggested by T. Zhou

 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