Bugzilla: 1117942 Upstream-status: Sent for 3.16 and seen by peterz 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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/