cgroupns: Close race between cgroup_post_fork and copy_cgroup_ns (eedd0f4c) · Commits · 戴 / test

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: ("cgroup: introduce cgroup namespaces") Signed-off-by:

"Eric W. Biederman" <ebiederm@xmission.com> Signed-off-by:

Tejun Heo <tj@kernel.org>

kernel/cgroup.c

+5 −0

Original line number	Diff line number	Diff line
		@@ -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;
		}

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