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@arm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lkml.kernel.org/r/20200114210947.14083-1-qais.yousef@arm.com

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 4ff03c27779ea8f4e27a4cd6c85e7cc5465e91e4..55b9a9c53b915356d919de1503bd6aaeaaee6dd0 100644 (file)
--- 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;
                }