sched: Fix __sched_setscheduler() nice test

Peter Zijlstra · Ingo Molnar · commit eaad45132c56 · 2014-01-16T18:07:08.000+01:00
With the introduction of sched_attr::sched_nice we need to check if we've got permission to actually change the nice value. Daniel found that can_nice() would always fail; and upon inspection it turns out that can_nice() only tests to see if we can lower the nice value, but it doesn't validate if we're lowering or not. Therefore amend the test to only call can_nice() when we lower the nice value. Reported-and-Tested-by: Daniel Lezcano <daniel.lezcano@linaro.org> Signed-off-by: Peter Zijlstra <peterz@infradead.org> Cc: raistlin@linux.it Cc: juri.lelli@gmail.com Cc: Daniel Lezcano <daniel.lezcano@linaro.org> Fixes: d50dde5 ("sched: Add new scheduler syscalls to support an extended scheduling parameters ABI") Link: http://lkml.kernel.org/r/20140116165425.GA9481@laptop.programming.kicks-ass.net Signed-off-by: Ingo Molnar <mingo@kernel.org>
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
@@ -3296,7 +3296,8 @@ static int __sched_setscheduler(struct task_struct *p,
 	 */
 	if (user && !capable(CAP_SYS_NICE)) {
 		if (fair_policy(policy)) {
-			if (!can_nice(p, attr->sched_nice))
+			if (attr->sched_nice < TASK_NICE(p) &&
+			    !can_nice(p, attr->sched_nice))
 				return -EPERM;
 		}
 

Original file line number	Diff line number	Diff line change
`@@ -3296,7 +3296,8 @@ static int __sched_setscheduler(struct task_struct *p,`
`3296`	`3296`	`*/`
`3297`	`3297`	`if (user && !capable(CAP_SYS_NICE)) {`
`3298`	`3298`	`if (fair_policy(policy)) {`
`3299`		`- if (!can_nice(p, attr->sched_nice))`
	`3299`	`+ if (attr->sched_nice < TASK_NICE(p) &&`
	`3300`	`+ !can_nice(p, attr->sched_nice))`
`3300`	`3301`	`return -EPERM;`
`3301`	`3302`	`}`
`3302`	`3303`