[tip: sched/core] sched/uclamp: Reject negative values in cpu_uclamp_write()

[tip-bot2 for Qais Yousef]

The following commit has been merged into the sched/core branch of tip:

Commit-ID:     b562d140649966d4daedd0483a8fe59ad3bb465a
Gitweb:        https://git.kernel.org/tip/b562d140649966d4daedd0483a8fe59ad3bb465a
Author:        Qais Yousef <qais.yousef@xxxxxxx>
AuthorDate:    Tue, 14 Jan 2020 21:09:47 
Committer:     Ingo Molnar <mingo@xxxxxxxxxx>
CommitterDate: Tue, 28 Jan 2020 21:36:56 +01:00

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@xxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Link: https://lkml.kernel.org/r/20200114210947.14083-1-qais.yousef@xxxxxxx
---
 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 4ff03c2..55b9a9c 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -7264,7 +7264,7 @@ 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;
 		}