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    SubjectRe: user controllable usermodehelper in br_stp_if.c
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    On Sun, Nov 29, 2015 at 2:43 PM, Richard Weinberger <richard@nod.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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