cgroup: fix use-after-free when umounting cgroupfs (cc20e01c) · Commits · 戴 / test

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>

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);
		}

Admin message