From 8dc3e9099e01dfdd53f27f329c268eced03dfef6 Mon Sep 17 00:00:00 2001 From: Oleg Nesterov Date: Fri, 29 Sep 2006 02:00:50 -0700 Subject: [PATCH] [PATCH] sched_setscheduler: fix? policy checks I am not sure this patch is correct: I can't understand what the current code does, and I don't know what it was supposed to do. The comment says: * can't change policy, except between SCHED_NORMAL * and SCHED_BATCH: The code: if (((policy != SCHED_NORMAL && p->policy != SCHED_BATCH) && (policy != SCHED_BATCH && p->policy != SCHED_NORMAL)) && But this is equivalent to: if ( (is_rt_policy(policy) && has_rt_policy(p)) && which means something different. We can't _decrease_ the current ->rt_priority with such a check (if rlim[RLIMIT_RTPRIO] == 0). Probably, it was supposed to be: if ( !(policy == SCHED_NORMAL && p->policy == SCHED_BATCH) && !(policy == SCHED_BATCH && p->policy == SCHED_NORMAL) this matches the comment, but strange: it doesn't allow to _drop_ the realtime priority when rlim[RLIMIT_RTPRIO] == 0. I think the right check would be: /* can't set/change rt policy */ if (is_rt_policy(policy) && policy != p->policy && !rlim_rtprio) return -EPERM; Signed-off-by: Oleg Nesterov Cc: Thomas Gleixner Cc: Ingo Molnar Cc: Steven Rostedt Cc: Nick Piggin Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- kernel/sched.c | 36 +++++++++++++++++------------------- 1 file changed, 17 insertions(+), 19 deletions(-) diff --git a/kernel/sched.c b/kernel/sched.c index c3c718aea618..155a33da7aa7 100644 --- a/kernel/sched.c +++ b/kernel/sched.c @@ -4116,27 +4116,25 @@ int sched_setscheduler(struct task_struct *p, int policy, * Allow unprivileged RT tasks to decrease priority: */ if (!capable(CAP_SYS_NICE)) { - unsigned long rlim_rtprio; - unsigned long flags; + if (is_rt_policy(policy)) { + unsigned long rlim_rtprio; + unsigned long flags; - if (!lock_task_sighand(p, &flags)) - return -ESRCH; - rlim_rtprio = p->signal->rlim[RLIMIT_RTPRIO].rlim_cur; - unlock_task_sighand(p, &flags); + if (!lock_task_sighand(p, &flags)) + return -ESRCH; + rlim_rtprio = p->signal->rlim[RLIMIT_RTPRIO].rlim_cur; + unlock_task_sighand(p, &flags); + + /* can't set/change the rt policy */ + if (policy != p->policy && !rlim_rtprio) + return -EPERM; + + /* can't increase priority */ + if (param->sched_priority > p->rt_priority && + param->sched_priority > rlim_rtprio) + return -EPERM; + } - /* - * can't change policy, except between SCHED_NORMAL - * and SCHED_BATCH: - */ - if (((policy != SCHED_NORMAL && p->policy != SCHED_BATCH) && - (policy != SCHED_BATCH && p->policy != SCHED_NORMAL)) && - !rlim_rtprio) - return -EPERM; - /* can't increase priority */ - if (is_rt_policy(policy) && - param->sched_priority > p->rt_priority && - param->sched_priority > rlim_rtprio) - return -EPERM; /* can't change other user's priorities */ if ((current->euid != p->euid) && (current->euid != p->uid))