Date: Sun, 29 Nov 2015 23:43:09 +0100 From: Richard Weinberger <richard@....at> To: "netdev@...r.kernel.org" <netdev@...r.kernel.org> Cc: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>, "keescook@...omium.org" <keescook@...omium.org>, bridge@...ts.linux-foundation.org, Stephen Hemminger <stephen@...workplumber.org> Subject: user controllable usermodehelper in br_stp_if.c 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? Thanks, //richard
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