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cgroupns: Close race between cgroup_post_fork and copy_cgroup_ns

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In most code paths involving cgroup migration cgroup_threadgroup_rwsem
is taken.  There are two exceptions:

- remove_tasks_in_empty_cpuset calls cgroup_transfer_tasks
- vhost_attach_cgroups_work calls cgroup_attach_task_all

With cgroup_threadgroup_rwsem held it is guaranteed that cgroup_post_fork
and copy_cgroup_ns will reference the same css_set from the process calling
fork.

Without such an interlock there process after fork could reference one
css_set from it's new cgroup namespace and another css_set from
task->cgroups, which semantically is nonsensical.

Cc: stable@vger.kernel.org
Fixes: a79a908fd2 ("cgroup: introduce cgroup namespaces")
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
This commit is contained in:
Eric W. Biederman 2016-07-15 06:35:51 -05:00 committed by Tejun Heo
parent 7bd8830875
commit eedd0f4cbf
1 changed files with 5 additions and 0 deletions
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5
kernel/cgroup.c
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@ -2962,6 +2962,7 @@ int cgroup_attach_task_all(struct task_struct *from, struct task_struct *tsk)
int retval = 0;
mutex_lock(&cgroup_mutex);
percpu_down_write(&cgroup_threadgroup_rwsem);
for_each_root(root) {
struct cgroup *from_cgrp;
@ -2976,6 +2977,7 @@ int cgroup_attach_task_all(struct task_struct *from, struct task_struct *tsk)
if (retval)
break;
}
percpu_up_write(&cgroup_threadgroup_rwsem);
mutex_unlock(&cgroup_mutex);
return retval;
@ -4343,6 +4345,8 @@ int cgroup_transfer_tasks(struct cgroup *to, struct cgroup *from)
mutex_lock(&cgroup_mutex);
percpu_down_write(&cgroup_threadgroup_rwsem);
/* all tasks in @from are being moved, all csets are source */
spin_lock_irq(&css_set_lock);
list_for_each_entry(link, &from->cset_links, cset_link)
@ -4371,6 +4375,7 @@ int cgroup_transfer_tasks(struct cgroup *to, struct cgroup *from)
} while (task && !ret);
out_err:
cgroup_migrate_finish(&preloaded_csets);
percpu_up_write(&cgroup_threadgroup_rwsem);
mutex_unlock(&cgroup_mutex);
return ret;
}