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 <peterz@xxxxxxxxxxxxx>
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 <mtk.manpages@xxxxxxxxx>
Signed-off-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Link: http://lkml.kernel.org/n/tip-b4kbwz2qh21xlngdzje00t55@xxxxxxxxxxxxxx
---
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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