linux-kernel - [PATCH 3.16 029/125] sched: Fix sched

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Date:	Wed,  3 Sep 2014 15:06:26 -0700
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	stable@...r.kernel.org,
	Daniel Bristot de Oliveira <bristot@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...nel.org>
Subject: [PATCH 3.16 029/125] sched: Fix sched_setparam() policy == -1 logic

3.16-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Daniel Bristot de Oliveira <bristot@...hat.com>

commit d8d28c8f00e84a72e8bee39a85835635417bee49 upstream.

The scheduler uses policy == -1 to preserve the current policy state to
implement sched_setparam(). But, as (int) -1 is equals to 0xffffffff,
it's matching the if (policy & SCHED_RESET_ON_FORK) on
_sched_setscheduler(). This match changes the policy value to an
invalid value, breaking the sched_setparam() syscall.

This patch checks policy == -1 before check the SCHED_RESET_ON_FORK flag.

The following program shows the bug:

int main(void)
{
	struct sched_param param = {
		.sched_priority = 5,
	};

	sched_setscheduler(0, SCHED_FIFO, &param);
	param.sched_priority = 1;
	sched_setparam(0, &param);
	param.sched_priority = 0;
	sched_getparam(0, &param);
	if (param.sched_priority != 1)
		printf("failed priority setting (found %d instead of 1)\n",
			param.sched_priority);
	else
		printf("priority setting fine\n");
}

Signed-off-by: Daniel Bristot de Oliveira <bristot@...hat.com>
Signed-off-by: Peter Zijlstra <peterz@...radead.org>
Reviewed-by: Steven Rostedt <rostedt@...dmis.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: linux-kernel@...r.kernel.org
Fixes: 7479f3c9cf67 "sched: Move SCHED_RESET_ON_FORK into attr::sched_flags"
Link: http://lkml.kernel.org/r/9ebe0566a08dbbb3999759d3f20d6004bb2dbcfa.1406079891.git.bristot@redhat.com
Signed-off-by: Ingo Molnar <mingo@...nel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 kernel/sched/core.c |    5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -3558,9 +3558,10 @@ static int _sched_setscheduler(struct ta
 	};
 
 	/*
-	 * Fixup the legacy SCHED_RESET_ON_FORK hack
+	 * Fixup the legacy SCHED_RESET_ON_FORK hack, except if
+	 * the policy=-1 was passed by sched_setparam().
 	 */
-	if (policy & SCHED_RESET_ON_FORK) {
+	if ((policy != -1) && (policy & SCHED_RESET_ON_FORK)) {
 		attr.sched_flags |= SCHED_FLAG_RESET_ON_FORK;
 		policy &= ~SCHED_RESET_ON_FORK;
 		attr.sched_policy = policy;


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