cgroup: fix use-after-free when umounting cgroupfs
Try:
# mount -t cgroup xxx /cgroup
# mkdir /cgroup/sub && rmdir /cgroup/sub && umount /cgroup
And you might see this:
ida_remove called for id=1 which is not allocated.
It's because cgroup_kill_sb() is called to destroy root->cgroup_ida
and free cgrp->root before ida_simple_removed() is called. What's
worse is we're accessing cgrp->root while it has been freed.
Signed-off-by: Li Zefan <lizefan@huawei.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 192d762..bd4de46 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -848,9 +848,12 @@
*/
dput(cgrp->parent->dentry);
+ ida_simple_remove(&cgrp->root->cgroup_ida, cgrp->id);
+
/*
* Drop the active superblock reference that we took when we
- * created the cgroup
+ * created the cgroup. This will free cgrp->root, if we are
+ * holding the last reference to @sb.
*/
deactivate_super(cgrp->root->sb);
@@ -862,7 +865,6 @@
simple_xattrs_free(&cgrp->xattrs);
- ida_simple_remove(&cgrp->root->cgroup_ida, cgrp->id);
kfree(rcu_dereference_raw(cgrp->name));
kfree(cgrp);
}