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

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Message-ID: <20190701111950.GY17978@ZenIV.linux.org.uk>
Date:   Mon, 1 Jul 2019 12:19:51 +0100
From:   Al Viro <viro@...iv.linux.org.uk>
To:     David Howells <dhowells@...hat.com>
Cc:     Eric Biggers <ebiggers@...nel.org>, linux-fsdevel@...r.kernel.org,
        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 08:38:10AM +0100, David Howells wrote:
> Al Viro <viro@...iv.linux.org.uk> wrote:
> 
> > 	/* The thing moved must be mounted... */
> > 	if (!is_mounted(old_path->mnt))
> > 		goto out;
> 
> Um...  Doesn't that stuff up fsmount()?

Nope - check is_mounted() definition.  Stuff in anon namespace
*is* mounted there, so that's not a problem.

FWIW, is_mounted() would've been better off spelled as
ns != NULL && ns != MNT_NS_INTERNAL; the use of IS_ERR_OR_NULL
in there works, but is unidiomatic and I don't think it yields
better code...