On Fri, May 09, 2014 at 10:23:22AM +0200, Michael Kerrisk (man-pages) wrote:
> Hi Peter,
>
> I'm working on this text. I see the following in kernel/sched/core.c:
>
> [[
> static int __sched_setscheduler(struct task_struct *p,
> const struct sched_attr *attr,
> bool user)
> {
> ...
>
> int policy = attr->sched_policy;
> ...
> if (policy < 0) {
> reset_on_fork = p->sched_reset_on_fork;
> policy = oldpolicy = p->policy;
> ]]
>
> What's a negative policy about? Is this something that should
> be documented?That's for sched_setparam(), which internally passes policy = -1, it wasn't meant to be user visible, lemme double check that. sys_sched_setscheduler() -- explicit check for policy < 0 sys_sched_setparam() -- explicitly passes policy=-1, not user visible sys_sched_setattr() -- hmm, it looks like fail --- Subject: sched: Disallow sched_attr::sched_policy < 0 From: Peter Zijlstra <[email protected]> Date: Fri May 9 10:49:03 CEST 2014 The scheduler uses policy=-1 to preserve the current policy state to implement sys_sched_setparam(), this got exposed to userspace by accident through sys_sched_setattr(), cure this. Reported-by: Michael Kerrisk <[email protected]> Signed-off-by: Peter Zijlstra <[email protected]> Link: http://lkml.kernel.org/n/[email protected] --- kernel/sched/core.c | 3 +++ 1 file changed, 3 insertions(+) --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -3711,6 +3711,9 @@ SYSCALL_DEFINE3(sched_setattr, pid_t, pi if (sched_copy_attr(uattr, &attr)) return -EFAULT; + if (attr.sched_policy < 0) + return -EINVAL; + rcu_read_lock(); retval = -ESRCH; p = find_process_by_pid(pid);
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