[PATCH] cgroups: fix possible use after free

[Li Zefan]

In cgroup_kill_sb(), root is freed before sb is detached from the list,
so another sget() may find this sb and call cgroup_test_super(),
which will access the root that has been freed.

Reported-by: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Li Zefan <lizf@xxxxxxxxxxxxxx>
---
 kernel/cgroup.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 5a54ff4..42fd3f2 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -1122,8 +1122,8 @@ static void cgroup_kill_sb(struct super_block *sb) {
 
 	mutex_unlock(&cgroup_mutex);
 
-	kfree(root);
 	kill_litter_super(sb);
+	kfree(root);
 }
 
 static struct file_system_type cgroup_fs_type = {
-- 
1.5.4.rc3
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