Date: Tue, 1 Dec 2015 00:03:00 +0100 From: Richard Weinberger <richard@....at> To: Kees Cook <keescook@...omium.org>, "Eric W. Biederman" <ebiederm@...ssion.com> Cc: "netdev@...r.kernel.org" <netdev@...r.kernel.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>, bridge@...ts.linux-foundation.org, Stephen Hemminger <stephen@...workplumber.org>, shayan@...eve.org Subject: Re: user controllable usermodehelper in br_stp_if.c Am 30.11.2015 um 21:14 schrieb Kees Cook: > On Sun, Nov 29, 2015 at 2:43 PM, Richard Weinberger <richard@....at> 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
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