Messages in this thread Patch in this message | | | Date | Thu, 24 Jan 2013 14:43:28 +0800 | From | Li Zefan <> | Subject | [PATCH 1/2] cgroup: fix exit() vsrmdir() race |
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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: Li Zefan <lizefan@huawei.com> --- kernel/cgroup.c | 8 ++++++++ 1 file changed, 8 insertions(+)
diff --git a/kernel/cgroup.c b/kernel/cgroup.c index 368cff1..09c5869 100644 --- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -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); } -- 1.8.0.2
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