linux-kernel - user ns: arbitrary module loading

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Message-ID: <CAGXu5jK7x+gFKgCN5=ZF+kSc4xSNbGtSERHCoOnCEgiJ1_wNGg@mail.gmail.com>
Date:	Fri, 1 Mar 2013 17:22:44 -0800
From:	Kees Cook <keescook@...gle.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Serge Hallyn <serge.hallyn@...onical.com>,
	Brad Spengler <spender@...ecurity.net>,
	Al Viro <viro@...iv.linux.org.uk>
Subject: user ns: arbitrary module loading

The rearranging done for user ns has resulted in allowing arbitrary
kernel module loading[1] (i.e. re-introducing a form of CVE-2011-1019)
by what is assumed to be an unprivileged process.

At present, it does look to require at least CAP_SETUID along the way
to set up the uidmap (but things like the setuid helper newuidmap
might soon start providing such a thing by default).

It might be worth examining GRKERNSEC_MODHARDEN in grsecurity, which
examines module symbols to verify that request_module() for a
filesystem only loads a module that defines "register_filesystem"
(among other things).

-Kees

[1] https://twitter.com/grsecurity/status/307473816672665600

--
Kees Cook
Chrome OS Security
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