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    SubjectRe: user controllable usermodehelper in br_stp_if.c
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    Am 30.11.2015 um 21:14 schrieb Kees Cook:
    > 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?)

    Eric was faster than me. :-)

    BTW: kernel.core_pattern is also worth a look.
    If the pipe mode is used, "|/bin/core_tool", it will be executed in the
    initial namespace and any user/container can trigger it.
    Shayan reported that some weeks ago: https://lkml.org/lkml/2015/10/24/134

    Thanks,
    //richard


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