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    SubjectRe: [PATCH 3/6] ebpf: add a way to dump an eBPF program
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    On Fri, Sep 4, 2015 at 1:45 PM, Tycho Andersen
    <tycho.andersen@canonical.com> wrote:
    > On Fri, Sep 04, 2015 at 01:17:30PM -0700, Kees Cook wrote:
    >> On Fri, Sep 4, 2015 at 9:04 AM, Tycho Andersen
    >> <tycho.andersen@canonical.com> wrote:
    >> > This commit adds a way to dump eBPF programs. The initial implementation
    >> > doesn't support maps, and therefore only allows dumping seccomp ebpf
    >> > programs which themselves don't currently support maps.
    >> >
    >> > We export the GPL bit as well as a unique ID for the program so that
    >>
    >> This unique ID appears to be the heap address for the prog. That's a
    >> huge leak, and should not be done. We don't want to introduce new
    >> kernel address leaks while we're trying to fix the remaining ones.
    >> Shouldn't the "unique ID" be the fd itself? I imagine KCMP_FILE
    >> could be used, for example.
    >
    > No; we acquire the fd per process, so if a task installs a filter and
    > then forks N times, we'll grab N (+1) copies of the filter from N (+1)
    > different file descriptors. Ideally, we'd have some way to figure out
    > that these were all the same. Some sort of prog_id is one way,
    > although there may be others.

    If KCMP_FILE or a new KCMP_BPF isn't possible, then we'll probably
    have to add a unique id (counter) to all bpf programs as they're
    created.

    -Kees

    --
    Kees Cook
    Chrome OS Security


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