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Commit 54e99124 authored by Dhaval Giani's avatar Dhaval Giani Committed by Ingo Molnar
Browse files

sched: don't allow setuid to succeed if the user does not have rt bandwidth 



Impact: fix hung task with certain (non-default) rt-limit settings

Corey Hickey reported that on using setuid to change the uid of a
rt process, the process would be unkillable and not be running.
This is because there was no rt runtime for that user group. Add
in a check to see if a user can attach an rt task to its task group.
On failure, return EINVAL, which is also returned in
CONFIG_CGROUP_SCHED.

Reported-by: default avatarCorey Hickey <bugfood-ml@fatooh.org>
Signed-off-by: default avatarDhaval Giani <dhaval@linux.vnet.ibm.com>
Acked-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent cac64d00

include/linux/sched.h

+4 −0
Original line number Diff line number Diff line
@@ -2291,9 +2291,13 @@ extern long sched_group_rt_runtime(struct task_group *tg); 
extern int sched_group_set_rt_period(struct task_group *tg,

				      long rt_period_us);

extern long sched_group_rt_period(struct task_group *tg);

extern int sched_rt_can_attach(struct task_group *tg, struct task_struct *tsk);

#endif

#endif



extern int task_can_switch_user(struct user_struct *up,

					struct task_struct *tsk);



#ifdef CONFIG_TASK_XACCT

static inline void add_rchar(struct task_struct *tsk, ssize_t amt)

{

kernel/sched.c

+11 −2
Original line number Diff line number Diff line
@@ -9224,6 +9224,16 @@ static int sched_rt_global_constraints(void) 


	return ret;

}



int sched_rt_can_attach(struct task_group *tg, struct task_struct *tsk)

{

	/* Don't accept realtime tasks when there is no way for them to run */

	if (rt_task(tsk) && tg->rt_bandwidth.rt_runtime == 0)

		return 0;



	return 1;

}



#else /* !CONFIG_RT_GROUP_SCHED */

static int sched_rt_global_constraints(void)

{
@@ -9317,8 +9327,7 @@ cpu_cgroup_can_attach(struct cgroup_subsys *ss, struct cgroup *cgrp, 
		      struct task_struct *tsk)

{

#ifdef CONFIG_RT_GROUP_SCHED

	/* Don't accept realtime tasks when there is no way for them to run */

	if (rt_task(tsk) && cgroup_tg(cgrp)->rt_bandwidth.rt_runtime == 0)

	if (!sched_rt_can_attach(cgroup_tg(cgrp), tsk))

		return -EINVAL;

#else

	/* We don't support RT-tasks being in separate groups */

kernel/sys.c

+20 −11
Original line number Diff line number Diff line
@@ -571,6 +571,11 @@ static int set_user(struct cred *new) 
	if (!new_user)

		return -EAGAIN;



	if (!task_can_switch_user(new_user, current)) {

		free_uid(new_user);

		return -EINVAL;

	}



	if (atomic_read(&new_user->processes) >=

				current->signal->rlim[RLIMIT_NPROC].rlim_cur &&

			new_user != INIT_USER) {
@@ -631,10 +636,11 @@ SYSCALL_DEFINE2(setreuid, uid_t, ruid, uid_t, euid) 
			goto error;

	}



	retval = -EAGAIN;

	if (new->uid != old->uid && set_user(new) < 0)

	if (new->uid != old->uid) {

		retval = set_user(new);

		if (retval < 0)

			goto error;



	}

	if (ruid != (uid_t) -1 ||

	    (euid != (uid_t) -1 && euid != old->uid))

		new->suid = new->euid;
@@ -680,8 +686,9 @@ SYSCALL_DEFINE1(setuid, uid_t, uid) 
	retval = -EPERM;

	if (capable(CAP_SETUID)) {

		new->suid = new->uid = uid;

		if (uid != old->uid && set_user(new) < 0) {

			retval = -EAGAIN;

		if (uid != old->uid) {

			retval = set_user(new);

			if (retval < 0)

				goto error;

		}

	} else if (uid != old->uid && uid != new->suid) {
@@ -734,12 +741,14 @@ SYSCALL_DEFINE3(setresuid, uid_t, ruid, uid_t, euid, uid_t, suid) 
			goto error;

	}



	retval = -EAGAIN;

	if (ruid != (uid_t) -1) {

		new->uid = ruid;

		if (ruid != old->uid && set_user(new) < 0)

		if (ruid != old->uid) {

			retval = set_user(new);

			if (retval < 0)

				goto error;

		}

	}

	if (euid != (uid_t) -1)

		new->euid = euid;

	if (suid != (uid_t) -1)

kernel/user.c

+18 −0
Original line number Diff line number Diff line
@@ -362,6 +362,24 @@ static void free_user(struct user_struct *up, unsigned long flags) 


#endif



#if defined(CONFIG_RT_GROUP_SCHED) && defined(CONFIG_USER_SCHED)

/*

 * We need to check if a setuid can take place. This function should be called

 * before successfully completing the setuid.

 */

int task_can_switch_user(struct user_struct *up, struct task_struct *tsk)

{



	return sched_rt_can_attach(up->tg, tsk);



}

#else

int task_can_switch_user(struct user_struct *up, struct task_struct *tsk)

{

	return 1;

}

#endif



/*

 * Locate the user_struct for the passed UID.  If found, take a ref on it.  The

 * caller must undo that ref with free_uid().