From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754337AbaGWC3a (ORCPT ); Tue, 22 Jul 2014 22:29:30 -0400 Received: from mx1.redhat.com ([209.132.183.28]:18997 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751875AbaGWC33 (ORCPT ); Tue, 22 Jul 2014 22:29:29 -0400 From: Daniel Bristot de Oliveira To: linux-kernel@vger.kernel.org Cc: peterz@infradead.org, mingo@kernel.org, tglx@linutronix.de, stable@vger.kernel.org, rostedt@goodmis.org Subject: [PATCH] sched: fix sched_setparam() policy=-1 logic Date: Tue, 22 Jul 2014 23:27:41 -0300 Message-Id: <9ebe0566a08dbbb3999759d3f20d6004bb2dbcfa.1406079891.git.bristot@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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, ¶m); param.sched_priority = 1; sched_setparam(0, ¶m); param.sched_priority = 0; sched_getparam(0, ¶m); if (param.sched_priority != 1) printf("failed priority setting (found %d instead of 1)\n", param.sched_priority); else printf("priority setting fine\n"); } Cc: Peter Zijlstra Cc: Ingo Molnar Cc: Thomas Gleixner Cc: stable@vger.kernel.org # 3.14+ Fixes: 7479f3c9cf67 "sched: Move SCHED_RESET_ON_FORK into attr::sched_flags" Reviewed-by: Steven Rostedt Signed-off-by: Daniel Bristot de Oliveira --- kernel/sched/core.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index bc1638b..0acf96b 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -3558,9 +3558,10 @@ static int _sched_setscheduler(struct task_struct *p, int policy, }; /* - * 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; -- 1.9.3