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cgroups: relax ns_can_attach checks to allow attaching to grandchild cgroups

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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: Grzegorz Nosek <root@localdomain.pl>
Acked-by: Serge Hallyn <serue@us.ibm.com>
Reviewed-by: Li Zefan <lizf@cn.fujitsu.com>
Cc: Paul Menage <menage@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Grzegorz Nosek 2009-04-02 16:57:23 -07:00 committed by Linus Torvalds
parent d20a390a0e
commit 313e924c08
3 changed files with 12 additions and 17 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

4
include/linux/cgroup.h
View file

@ -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 */

11
kernel/cgroup.c
View file

@ -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);

14
kernel/ns_cgroup.c
View file

@ -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);