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Date:   Sat, 29 Jun 2019 21:39:16 +0100
From:   Al Viro <viro@zeniv.linux.org.uk>
To:     Eric Biggers <ebiggers@kernel.org>
Cc:     linux-fsdevel@vger.kernel.org, David Howells <dhowells@redhat.com>,
        linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com
Subject: Re: [PATCH] vfs: move_mount: reject moving kernel internal mounts
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 <20190629202744.12396-1-ebiggers@kernel.org>
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On Sat, Jun 29, 2019 at 01:27:44PM -0700, Eric Biggers wrote:

> @@ -2600,7 +2600,7 @@ static int do_move_mount(struct path *old_path, struct path *new_path)
>  	if (attached && !check_mnt(old))
>  		goto out;
>  
> -	if (!attached && !(ns && is_anon_ns(ns)))
> +	if (!attached && !(ns && ns != MNT_NS_INTERNAL && is_anon_ns(ns)))
>  		goto out;
>  
>  	if (old->mnt.mnt_flags & MNT_LOCKED)

*UGH*

Applied, but that code is getting really ugly ;-/