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Commit cc20e01c authored by Li Zefan's avatar Li Zefan Committed by Tejun Heo
Browse files

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: default avatarLi Zefan <lizefan@huawei.com>
Signed-off-by: default avatarTejun Heo <tj@kernel.org>
parent 712317ad

kernel/cgroup.c

+4 −2
Original line number Diff line number Diff line
@@ -848,9 +848,12 @@ static void cgroup_free_fn(struct work_struct *work) 
	 */

	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 @@ static void cgroup_free_fn(struct work_struct *work) 


	simple_xattrs_free(&cgrp->xattrs);



	ida_simple_remove(&cgrp->root->cgroup_ida, cgrp->id);

	kfree(rcu_dereference_raw(cgrp->name));

	kfree(cgrp);

}