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    SubjectRe: [PATCH][RFC] v2 exec: move core_pattern pipe helper into the crashing namespace
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    On Mon, Sep 20, 2010 at 2:12 PM, Andi Kleen <andi@firstfloor.org> wrote:
    >> The pipe process needs to run in the namespaces of the process who set
    >> the core pattern, not in the namespaces of the dumping process.
    >> Otherwise it is possible to trigger a privileged process to run in a
    >> context where it's reality that it expected, causing it to misuse
    >> it's privileges.  Even if we don't have a privilege problem I think
    >> we will have a case of mismatched functionality where the core pattern
    >> will not work as expected.
    >
    > For me it seems rather the other way around: running the helper in some
    > highly priviledged namespace is more dangerous. If it runs in the
    > same context as the crasher it can do the least amount of damage
    > relative to the crash process.
    >
    > And as Will pointed out it's the only sane way to deal with net namespaces.


    I think you're both right. How it is implemented right now is an
    escape from the linux container. If you allow the root user in a
    container to mount proc and update core_pattern, they can escape.
    (core_pattern = |/well/known/binary_or_scripting_lang) I'm sure there
    are other escapes too (and any umh call is likely an escape like this
    one -- e.g., modprobe_path). That said, using my patch above might
    let you traverse a path otherwise blocked by an LSM enforcement (E.g.,
    root user runs a process which sets up a vfs namespace with an
    encrypted mount and the lsm blocks access to the /proc/[pid]/root -
    but core_pattern still runs and with access).

    That said, using the setters namespace makes sense to me as a consumer
    of core_pattern too. You can set the core_pattern outside of a
    chroot/container and collect core dumps there _or_ you can let a
    "root" user in a container have their own core collector without
    providing a simple escape. Making format_corename use the correct pid
    namespace for translation would make these cases even more seamless.

    Unfortunately, I haven't yet looked at doing it that way yet. The
    namespace-transition patch posted is what occurred to me initially.
    Perhaps it won't be so hard. I'll take a look at what it'd take to do
    move core_pattern since it'd resolve both the escape/lsm-bypass
    scenarios and the mismatch between the arbitrary namespace and the
    core_pattern values.

    Thanks!
    will
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