Commit 961ccddd authored by Rusty Russell's avatar Rusty Russell Committed by Ingo Molnar
Browse files

sched: add new API sched_setscheduler_nocheck: add a flag to control access checks 



Hidehiro Kawai noticed that sched_setscheduler() can fail in
stop_machine: it calls sched_setscheduler() from insmod, which can
have CAP_SYS_MODULE without CAP_SYS_NICE.

Two cases could have failed, so are changed to sched_setscheduler_nocheck:
  kernel/softirq.c:cpu_callback()
	- CPU hotplug callback
  kernel/stop_machine.c:__stop_machine_run()
	- Called from various places, including modprobe()

Signed-off-by: default avatarRusty Russell <rusty@rustcorp.com.au>
Cc: Jeremy Fitzhardinge <jeremy@goop.org>
Cc: Hidehiro Kawai <hidehiro.kawai.ez@hitachi.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: linux-mm@kvack.org
Cc: sugita <yumiko.sugita.yf@hitachi.com>
Cc: Satoshi OSHIMA <satoshi.oshima.fk@hitachi.com>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent 481c5346

include/linux/sched.h

+2 −0
Original line number Diff line number Diff line
@@ -1655,6 +1655,8 @@ extern int can_nice(const struct task_struct *p, const int nice); 
extern int task_curr(const struct task_struct *p);

extern int idle_cpu(int cpu);

extern int sched_setscheduler(struct task_struct *, int, struct sched_param *);

extern int sched_setscheduler_nocheck(struct task_struct *, int,

				      struct sched_param *);

extern struct task_struct *idle_task(int cpu);

extern struct task_struct *curr_task(int cpu);

extern void set_curr_task(int cpu, struct task_struct *p);

kernel/sched.c

+36 −12
Original line number Diff line number Diff line
@@ -4746,16 +4746,8 @@ __setscheduler(struct rq *rq, struct task_struct *p, int policy, int prio) 
	set_load_weight(p);

}



/**

 * sched_setscheduler - change the scheduling policy and/or RT priority of a thread.

 * @p: the task in question.

 * @policy: new policy.

 * @param: structure containing the new RT priority.

 *

 * NOTE that the task may be already dead.

 */

int sched_setscheduler(struct task_struct *p, int policy,

		       struct sched_param *param)

static int __sched_setscheduler(struct task_struct *p, int policy,

				struct sched_param *param, bool user)

{

	int retval, oldprio, oldpolicy = -1, on_rq, running;

	unsigned long flags;
@@ -4787,7 +4779,7 @@ recheck: 
	/*

	 * Allow unprivileged RT tasks to decrease priority:

	 */

	if (!capable(CAP_SYS_NICE)) {

	if (user && !capable(CAP_SYS_NICE)) {

		if (rt_policy(policy)) {

			unsigned long rlim_rtprio;
@@ -4823,7 +4815,8 @@ recheck: 
	 * Do not allow realtime tasks into groups that have no runtime

	 * assigned.

	 */

	if (rt_policy(policy) && task_group(p)->rt_bandwidth.rt_runtime == 0)

	if (user

	    && rt_policy(policy) && task_group(p)->rt_bandwidth.rt_runtime == 0)

		return -EPERM;

#endif
@@ -4872,8 +4865,39 @@ recheck: 


	return 0;

}



/**

 * sched_setscheduler - change the scheduling policy and/or RT priority of a thread.

 * @p: the task in question.

 * @policy: new policy.

 * @param: structure containing the new RT priority.

 *

 * NOTE that the task may be already dead.

 */

int sched_setscheduler(struct task_struct *p, int policy,

		       struct sched_param *param)

{

	return __sched_setscheduler(p, policy, param, true);

}

EXPORT_SYMBOL_GPL(sched_setscheduler);



/**

 * sched_setscheduler_nocheck - change the scheduling policy and/or RT priority of a thread from kernelspace.

 * @p: the task in question.

 * @policy: new policy.

 * @param: structure containing the new RT priority.

 *

 * Just like sched_setscheduler, only don't bother checking if the

 * current context has permission.  For example, this is needed in

 * stop_machine(): we create temporary high priority worker threads,

 * but our caller might not have that capability.

 */

int sched_setscheduler_nocheck(struct task_struct *p, int policy,

			       struct sched_param *param)

{

	return __sched_setscheduler(p, policy, param, false);

}



static int

do_sched_setscheduler(pid_t pid, int policy, struct sched_param __user *param)

{

kernel/softirq.c

+1 −1
Original line number Diff line number Diff line
@@ -645,7 +645,7 @@ static int __cpuinit cpu_callback(struct notifier_block *nfb, 


		p = per_cpu(ksoftirqd, hotcpu);

		per_cpu(ksoftirqd, hotcpu) = NULL;

		sched_setscheduler(p, SCHED_FIFO, &param);

		sched_setscheduler_nocheck(p, SCHED_FIFO, &param);

		kthread_stop(p);

		takeover_tasklets(hotcpu);

		break;

kernel/stop_machine.c

+1 −1
Original line number Diff line number Diff line
@@ -187,7 +187,7 @@ struct task_struct *__stop_machine_run(int (*fn)(void *), void *data, 
		struct sched_param param = { .sched_priority = MAX_RT_PRIO-1 };



		/* One high-prio thread per cpu.  We'll do this one. */

		sched_setscheduler(p, SCHED_FIFO, &param);

		sched_setscheduler_nocheck(p, SCHED_FIFO, &param);

		kthread_bind(p, cpu);

		wake_up_process(p);

		wait_for_completion(&smdata.done);

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