In the Linux kernel, the following vulnerability has been resolved: userns and mnt_idmap leak in open_tree_attr(2) Once want_mount_setattr() has returned a positive, it does require finish_mount_kattr() to release ->mnt_userns. Failing do_mount_setattr() does not change that. As the result, we can end up leaking userns and possibly mnt_idmap as well.
https://git.kernel.org/stable/c/142db4e76110dd80239f4e79810f85ea1735ad60
https://git.kernel.org/stable/c/0748e553df0225754c316a92af3a77fdc057b358