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
