From 8185982aa13b9000ac7c42f936c23cbbb882a31e Mon Sep 17 00:00:00 2001 From: Daniel Bristot de Oliveira Date: Tue, 22 Jul 2014 23:27:41 -0300 Subject: [PATCH] sched: Fix sched_setparam() policy == -1 logic 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, ¶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"); } Signed-off-by: Daniel Bristot de Oliveira Signed-off-by: Peter Zijlstra Reviewed-by: Steven Rostedt Cc: Linus Torvalds Cc: linux-kernel@vger.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 Signed-off-by: Greg Kroah-Hartman --- 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 515e212..677ebad 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -3511,9 +3511,10 @@ 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; -- 2.7.4