Date: Mon, 30 Nov 2015 12:14:41 -0800 From: Kees Cook <keescook@...omium.org> To: Richard Weinberger <richard@....at>, "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> Subject: Re: user controllable usermodehelper in br_stp_if.c 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?) -Kees -- Kees Cook Chrome OS & Brillo Security
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