[tip:sched/core] sched: Fix __sched_setscheduler() nice test

[tip-bot for Peter Zijlstra <tipbot@zytor.com>]

Commit-ID:  eaad45132c564ce377e6dce05e78e08e456d5315
Gitweb:     http://git.kernel.org/tip/eaad45132c564ce377e6dce05e78e08e456d5315
Author:     Peter Zijlstra <peterz@infradead.org>
AuthorDate: Thu, 16 Jan 2014 17:54:25 +0100
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Thu, 16 Jan 2014 18:07:08 +0100

sched: Fix __sched_setscheduler() nice test

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: d50dde5a10f3 ("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>
---
 kernel/sched/core.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 93a2836..36c951b 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -3296,7 +3296,8 @@ recheck:
 	 */
 	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;
 		}