On Sun, Nov 29, 2015 at 2:43 PM, Richard Weinberger <richard@xxxxxx> 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
