Re: [PATCH 3/6] ebpf: add a way to dump an eBPF program

From: Tycho Andersen
Date: Fri Sep 04 2015 - 16:46:00 EST

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@xxxxxxxxxxxxx> 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.

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