linux-kernel - Re: overlayfs access checks on underlying layers

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Message-ID: <CAJfpegtFVvq286HAorGLg6ywMsfs51KqaQwFkcuV7Dtu8TLaLg@mail.gmail.com>
Date:   Tue, 4 Dec 2018 16:31:09 +0100
From:   Miklos Szeredi <miklos@...redi.hu>
To:     Vivek Goyal <vgoyal@...hat.com>
Cc:     Stephen Smalley <sds@...ho.nsa.gov>,
        Ondrej Mosnacek <omosnace@...hat.com>,
        "J. Bruce Fields" <bfields@...ldses.org>,
        Mark Salyzyn <salyzyn@...roid.com>,
        Paul Moore <paul@...l-moore.com>, linux-kernel@...r.kernel.org,
        overlayfs <linux-unionfs@...r.kernel.org>,
        linux-fsdevel@...r.kernel.org, selinux@...r.kernel.org,
        Daniel J Walsh <dwalsh@...hat.com>
Subject: Re: overlayfs access checks on underlying layers

On Tue, Dec 4, 2018 at 4:22 PM Vivek Goyal <vgoyal@...hat.com> wrote:

> Having said that, this still create little anomaly when mknod to client
> is not allowed on context label. So a device file, which is on lower
> and client can not open it for read/write on host, it can now be opened
> for read/write because mounter will allow access. So why it is different
> that regular copy up. Well, in regular copy up, we created a copy of
> the original object and allowed writing to that object (cp --preserve=all)
> model. But in case of device file, writes will go to same original
> object. (And not a separate copy).

That's true.

In that sense copy up of special file should result in upper having
the same label as of lower, right?

Thanks,
Miklos