Commit 313e924c authored by Grzegorz Nosek's avatar Grzegorz Nosek Committed by Linus Torvalds
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cgroups: relax ns_can_attach checks to allow attaching to grandchild cgroups 



The ns_proxy cgroup allows moving processes to child cgroups only one
level deep at a time.  This commit relaxes this restriction and makes it
possible to attach tasks directly to grandchild cgroups, e.g.:

($pid is in the root cgroup)
echo $pid > /cgroup/CG1/CG2/tasks

Previously this operation would fail with -EPERM and would have to be
performed as two steps:
echo $pid > /cgroup/CG1/tasks
echo $pid > /cgroup/CG1/CG2/tasks

Also, the target cgroup no longer needs to be empty to move a task there.

Signed-off-by: default avatarGrzegorz Nosek <root@localdomain.pl>
Acked-by: default avatarSerge Hallyn <serue@us.ibm.com>
Reviewed-by: default avatarLi Zefan <lizf@cn.fujitsu.com>
Cc: Paul Menage <menage@google.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent d20a390a

include/linux/cgroup.h

+2 −2
Original line number Diff line number Diff line
@@ -348,8 +348,8 @@ int cgroup_path(const struct cgroup *cgrp, char *buf, int buflen); 


int cgroup_task_count(const struct cgroup *cgrp);



/* Return true if the cgroup is a descendant of the current cgroup */

int cgroup_is_descendant(const struct cgroup *cgrp);

/* Return true if cgrp is a descendant of the task's cgroup */

int cgroup_is_descendant(const struct cgroup *cgrp, struct task_struct *task);



/* Control Group subsystem type. See Documentation/cgroups.txt for details */

kernel/cgroup.c

+6 −5
Original line number Diff line number Diff line
@@ -3084,18 +3084,19 @@ int cgroup_clone(struct task_struct *tsk, struct cgroup_subsys *subsys, 
}



/**

 * cgroup_is_descendant - see if @cgrp is a descendant of current task's cgrp

 * cgroup_is_descendant - see if @cgrp is a descendant of @task's cgrp

 * @cgrp: the cgroup in question

 * @task: the task in question

 *

 * See if @cgrp is a descendant of the current task's cgroup in

 * the appropriate hierarchy.

 * See if @cgrp is a descendant of @task's cgroup in the appropriate

 * hierarchy.

 *

 * If we are sending in dummytop, then presumably we are creating

 * the top cgroup in the subsystem.

 *

 * Called only by the ns (nsproxy) cgroup.

 */

int cgroup_is_descendant(const struct cgroup *cgrp)

int cgroup_is_descendant(const struct cgroup *cgrp, struct task_struct *task)

{

	int ret;

	struct cgroup *target;
@@ -3105,7 +3106,7 @@ int cgroup_is_descendant(const struct cgroup *cgrp) 
		return 1;



	get_first_subsys(cgrp, NULL, &subsys_id);

	target = task_cgroup(current, subsys_id);

	target = task_cgroup(task, subsys_id);

	while (cgrp != target && cgrp!= cgrp->top_cgroup)

		cgrp = cgrp->parent;

	ret = (cgrp == target);

kernel/ns_cgroup.c

+4 −10
Original line number Diff line number Diff line
@@ -34,7 +34,7 @@ int ns_cgroup_clone(struct task_struct *task, struct pid *pid) 


/*

 * Rules:

 *   1. you can only enter a cgroup which is a child of your current

 *   1. you can only enter a cgroup which is a descendant of your current

 *     cgroup

 *   2. you can only place another process into a cgroup if

 *     a. you have CAP_SYS_ADMIN
@@ -45,21 +45,15 @@ int ns_cgroup_clone(struct task_struct *task, struct pid *pid) 
static int ns_can_attach(struct cgroup_subsys *ss,

		struct cgroup *new_cgroup, struct task_struct *task)

{

	struct cgroup *orig;



	if (current != task) {

		if (!capable(CAP_SYS_ADMIN))

			return -EPERM;



		if (!cgroup_is_descendant(new_cgroup))

		if (!cgroup_is_descendant(new_cgroup, current))

			return -EPERM;

	}



	if (atomic_read(&new_cgroup->count) != 0)

		return -EPERM;



	orig = task_cgroup(task, ns_subsys_id);

	if (orig && orig != new_cgroup->parent)

	if (!cgroup_is_descendant(new_cgroup, task))

		return -EPERM;



	return 0;
@@ -77,7 +71,7 @@ static struct cgroup_subsys_state *ns_create(struct cgroup_subsys *ss, 


	if (!capable(CAP_SYS_ADMIN))

		return ERR_PTR(-EPERM);

	if (!cgroup_is_descendant(cgroup))

	if (!cgroup_is_descendant(cgroup, current))

		return ERR_PTR(-EPERM);



	ns_cgroup = kzalloc(sizeof(*ns_cgroup), GFP_KERNEL);

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