linux-kernel - Re: [PATCH] vfs: move_mount: reject moving kernel internal mounts

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Message-ID: <20190701154317.GB790@sol.localdomain>
Date:   Mon, 1 Jul 2019 08:43:17 -0700
From:   Eric Biggers <ebiggers@...nel.org>
To:     Al Viro <viro@...iv.linux.org.uk>
Cc:     linux-fsdevel@...r.kernel.org, David Howells <dhowells@...hat.com>,
        linux-kernel@...r.kernel.org, syzkaller-bugs@...glegroups.com
Subject: Re: [PATCH] vfs: move_mount: reject moving kernel internal mounts

On Mon, Jul 01, 2019 at 02:08:48AM +0100, Al Viro wrote:
> 
> Let's reorder that a bit:
>         /* The mountpoint must be in our namespace. */
>         if (!check_mnt(p))
>                 goto out;
> 
> 	/* The thing moved must be mounted... */
> 	if (!is_mounted(old_path->mnt))
> 		goto out;
> 
>         /* ... and either ours or the root of anon namespace */
> 	if (!(attached ? check_mnt(old) : is_anon_ns(ns)))
> 		goto out;
> 
> IMO that looks saner and all it costs us is a redundant check
> in attached case.  Objections?

Looks good to me.

- Eric