提交 71b5707e 编写于 作者: L Li Zefan 提交者: Tejun Heo

cgroup: fix exit() vs rmdir() race

In cgroup_exit() put_css_set_taskexit() is called without any lock,
which might lead to accessing a freed cgroup:

thread1                           thread2
---------------------------------------------
exit()
  cgroup_exit()
    put_css_set_taskexit()
      atomic_dec(cgrp->count);
                                   rmdir();
      /* not safe !! */
      check_for_release(cgrp);

rcu_read_lock() can be used to make sure the cgroup is alive.
Signed-off-by: NLi Zefan <lizefan@huawei.com>
Signed-off-by: NTejun Heo <tj@kernel.org>
Cc: stable@vger.kernel.org
上级 9ed8a659
......@@ -422,12 +422,20 @@ static void __put_css_set(struct css_set *cg, int taskexit)
struct cgroup *cgrp = link->cgrp;
list_del(&link->cg_link_list);
list_del(&link->cgrp_link_list);
/*
* We may not be holding cgroup_mutex, and if cgrp->count is
* dropped to 0 the cgroup can be destroyed at any time, hence
* rcu_read_lock is used to keep it alive.
*/
rcu_read_lock();
if (atomic_dec_and_test(&cgrp->count) &&
notify_on_release(cgrp)) {
if (taskexit)
set_bit(CGRP_RELEASABLE, &cgrp->flags);
check_for_release(cgrp);
}
rcu_read_unlock();
kfree(link);
}
......
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