linux-kernel - Re: [PATCH 0/2] userns: automount cleanups

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Date:   Wed, 29 Nov 2017 23:21:24 -0600
From:   ebiederm@...ssion.com (Eric W. Biederman)
To:     Ian Kent <raven@...maw.net>
Cc:     Linux Containers <containers@...ts.linux-foundation.org>,
        linux-kernel@...r.kernel.org, Miklos Szeredi <mszeredi@...hat.com>,
        linux-fsdevel@...r.kernel.org,
        Seth Forshee <seth.forshee@...onical.com>
Subject: Re: [PATCH 0/2] userns: automount cleanups

Ian Kent <raven@...maw.net> writes:

> On 30/11/17 08:01, Eric W. Biederman wrote:
>> 
>> While reviewing some code I realized that in getting d_automount working
>> with s_user_ns I had left behind some unnecessary relics of the blind
>> path I started down.  Here are two patches that remove those relics.
>> 
>> Unless someone has another preference I will drop them in my userns tree
>> and merge them that way.
>
> I saw the "<etc>->s_user_ns != &init_user_ns" and wondered if that would
> trigger for automount(8) run entirely with a container (eg. docker)?

autofs still needs FS_USERNS_MOUNT before you can reach that point.  But
docker does have a mode ?--userns-remap? where it sets up the containers
mounts that way.

I think in principle that should work and be safe.  I don't know how
robust autofs is against malicious users.  Which is the question to ask
before actually adding FS_USERNS_MOUNT in struct file_system_type.

> Anyway, it's gone now, so ACK to these two, thanks Eric.

Eric