linux-kernel - Re: [PATCH 02/11] mtd: Check permissions towards mtd block device inode when mounting

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Date:   Sat, 23 Dec 2017 13:56:51 +0100
From:   Richard Weinberger <richard@....at>
To:     Dongsu Park <dongsu@...volk.io>
Cc:     Richard Weinberger <richard.weinberger@...il.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Miklos Szeredi <mszeredi@...hat.com>,
        Linux Containers <containers@...ts.linux-foundation.org>,
        Seth Forshee <seth.forshee@...onical.com>,
        Alban Crequy <alban@...volk.io>,
        "Eric W . Biederman" <ebiederm@...ssion.com>,
        Sargun Dhillon <sargun@...gun.me>,
        "linux-mtd@...ts.infradead.org" <linux-mtd@...ts.infradead.org>
Subject: Re: [PATCH 02/11] mtd: Check permissions towards mtd block device inode when mounting

Dongsu,

Am Samstag, 23. Dezember 2017, 13:18:30 CET schrieb Dongsu Park:
> Hi,
> 
> On Fri, Dec 22, 2017 at 10:06 PM, Richard Weinberger
> 
> <richard.weinberger@...il.com> wrote:
> > Dongsu,
> > 
> > On Fri, Dec 22, 2017 at 3:32 PM, Dongsu Park <dongsu@...volk.io> wrote:
> >> From: Seth Forshee <seth.forshee@...onical.com>
> >> 
> >> Unprivileged users should not be able to mount mtd block devices
> >> when they lack sufficient privileges towards the block device
> >> inode.  Update mount_mtd() to validate that the user has the
> >> required access to the inode at the specified path. The check
> >> will be skipped for CAP_SYS_ADMIN, so privileged mounts will
> >> continue working as before.
> > 
> > What is the big picture of this?
> > Can in future an unprivileged user just mount UBIFS?
> 
> I'm not sure I'm aware of all use cases w.r.t mtd & ubifs.
> To my understanding, in these days many container runtimes allow
> unprivileged users to run containers. (docker, lxc, runc, bubblewrap, etc)
> That's why the kernel should deal with additional permission checks
> that might have not been necessary in the past.
> This MTD patch is one of those special cases.

My fear is that a corner case is forgotten and all of a sudden someone can do 
funky things with MTD in a container...

Thanks,
//richard