From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755294AbbK3XDG (ORCPT ); Mon, 30 Nov 2015 18:03:06 -0500 Received: from a.ns.miles-group.at ([95.130.255.143]:11949 "EHLO radon.swed.at" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755218AbbK3XDD (ORCPT ); Mon, 30 Nov 2015 18:03:03 -0500 Subject: Re: user controllable usermodehelper in br_stp_if.c To: Kees Cook , "Eric W. Biederman" References: <565B7F7D.80208@nod.at> Cc: "netdev@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "kernel-hardening@lists.openwall.com" , bridge@lists.linux-foundation.org, Stephen Hemminger , shayan@liveve.org From: Richard Weinberger Message-ID: <565CD5A4.4010106@nod.at> Date: Tue, 1 Dec 2015 00:03:00 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.4.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Am 30.11.2015 um 21:14 schrieb Kees Cook: > On Sun, Nov 29, 2015 at 2:43 PM, Richard Weinberger wrote: >> Hi! >> >> By spawning new network and user namesapces an unprivileged user >> is able to execute /sbin/bridge-stp within the initial mount namespace >> with global root rights. >> While this cannot directly be used to break out of a container or gain >> global root rights it could be used by exploit writers as valuable building block. >> >> e.g. >> $ unshare -U -r -n /bin/sh >> $ brctl addbr br0 >> $ brctl stp br0 on # this will execute /sbin/bridge-stp >> >> As this mechanism clearly cannot work with containers and seems to be legacy code >> I suggest not calling call_usermodehelper() at all if we're not in the initial user namespace. >> What do you think? > > I'm not familiar with how bridge-stp is expected to operate with a > network namespace, but if it's meaningless, then yeah, that seems like > a reasonable change. Can you send a patch? (Also, if it's legacy code, > maybe it could be turned off entirely, not just for containers?) Eric was faster than me. :-) BTW: kernel.core_pattern is also worth a look. If the pipe mode is used, "|/bin/core_tool", it will be executed in the initial namespace and any user/container can trigger it. Shayan reported that some weeks ago: https://lkml.org/lkml/2015/10/24/134 Thanks, //richard