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authorOlivier Croquette <ocroquette@free.fr>2005-06-25 14:57:32 -0700
committerLinus Torvalds <torvalds@ppc970.osdl.org>2005-06-25 16:24:44 -0700
commit37e4ab3f0cba13adf3535d373fd98e5ee47b5410 (patch)
tree8891a73f2a6d4257835064ab45d167154abad71f /kernel
parenta3464a102a69a4e00efb0a763e274ce290995b4b (diff)
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[PATCH] Changing RT priority without CAP_SYS_NICE
Presently, a process without the capability CAP_SYS_NICE can not change its own policy, which is OK. But it can also not decrease its RT priority (if scheduled with policy SCHED_RR or SCHED_FIFO), which is what this patch changes. The rationale is the same as for the nice value: a process should be able to require less priority for itself. Increasing the priority is still not allowed. This is for example useful if you give a multithreaded user process a RT priority, and the process would like to organize its internal threads using priorities also. Then you can give the process the highest priority needed N, and the process starts its threads with lower priorities: N-1, N-2... The POSIX norm says that the permissions are implementation specific, so I think we can do that. In a sense, it makes the permissions consistent whatever the policy is: with this patch, process scheduled by SCHED_FIFO, SCHED_RR and SCHED_OTHER can all decrease their priority. From: Ingo Molnar <mingo@elte.hu> cleaned up and merged to -mm. Signed-off-by: Ingo Molnar <mingo@elte.hu> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/sched.c25
1 files changed, 18 insertions, 7 deletions
diff --git a/kernel/sched.c b/kernel/sched.c
index a3d1c8e43d3..d3d81b82e37 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -3531,13 +3531,24 @@ recheck:
if ((policy == SCHED_NORMAL) != (param->sched_priority == 0))
return -EINVAL;
- if ((policy == SCHED_FIFO || policy == SCHED_RR) &&
- param->sched_priority > p->signal->rlim[RLIMIT_RTPRIO].rlim_cur &&
- !capable(CAP_SYS_NICE))
- return -EPERM;
- if ((current->euid != p->euid) && (current->euid != p->uid) &&
- !capable(CAP_SYS_NICE))
- return -EPERM;
+ /*
+ * Allow unprivileged RT tasks to decrease priority:
+ */
+ if (!capable(CAP_SYS_NICE)) {
+ /* can't change policy */
+ if (policy != p->policy)
+ return -EPERM;
+ /* can't increase priority */
+ if (policy != SCHED_NORMAL &&
+ param->sched_priority > p->rt_priority &&
+ param->sched_priority >
+ p->signal->rlim[RLIMIT_RTPRIO].rlim_cur)
+ return -EPERM;
+ /* can't change other user's priorities */
+ if ((current->euid != p->euid) &&
+ (current->euid != p->uid))
+ return -EPERM;
+ }
retval = security_task_setscheduler(p, policy, param);
if (retval)