linux-kernel - Re: [PATCH v3 0/7] User namespace mount updates

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Message-ID: <20151117170556.GV22011@ZenIV.linux.org.uk>
Date:	Tue, 17 Nov 2015 17:05:56 +0000
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Seth Forshee <seth.forshee@...onical.com>
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	linux-bcache@...r.kernel.org, dm-devel@...hat.com,
	linux-raid@...r.kernel.org, linux-mtd@...ts.infradead.org,
	linux-fsdevel@...r.kernel.org,
	linux-security-module@...r.kernel.org, selinux@...ho.nsa.gov,
	Serge Hallyn <serge.hallyn@...onical.com>,
	Andy Lutomirski <luto@...capital.net>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 0/7] User namespace mount updates

On Tue, Nov 17, 2015 at 10:39:03AM -0600, Seth Forshee wrote:
> Hi Eric,
> 
> Here's another update to my patches for user namespace mounts, based on
> your for-testing branch. These patches add safeguards necessary to allow
> unprivileged mounts and update SELinux and Smack to safely handle
> device-backed mounts from unprivileged users.
> 
> The v2 posting received very little in the way of feedback, so changes
> are minimal. I've made a trivial style change to the Smack changes at
> Casey's request, and I've added Stephen's ack for the SELinux changes.

Would you mind explaining which filesystem types do you plan to allow?
SELinux and the rest of Linux S&M bunch do fuck-all for attacks via
handcrafted fs image fed to the code in fs driver that does not expect
a given kind of inconsistencies.

As it is, validation of on-disk metadata is not particularly strong;
what's more, protection against concurrent malicious *changes* of
fs image (via direct writes by root) is simply inexistent.

So what is that about?
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