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

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Message-ID: <20181204154243.GA16818@redhat.com>
Date:   Tue, 4 Dec 2018 10:42:43 -0500
From:   Vivek Goyal <vgoyal@...hat.com>
To:     Miklos Szeredi <miklos@...redi.hu>
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 04, 2018 at 04:31:09PM +0100, Miklos Szeredi wrote:
> 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?

I guess that might be reasonable (if this behavior is a concern). So even
after copy up, client will not be able to read/write a device if it was
not allowed on lower. 

Stephen, what do you think about retaining label of lower for device
files during copy up. What about socket/fifo.

Thanks
Vivek