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

From: Andy Lutomirski
Date: Fri Sep 04 2015 - 17:48:28 EST

On Fri, Sep 4, 2015 at 1:45 PM, Tycho Andersen
<tycho.andersen@xxxxxxxxxxxxx> 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@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.

I disagree a bit. I think we want the actual hierarchy to be a
well-defined thing, because I have plans to make the hierarchy
actually do something. That means that we'll need to have a more
exact way to dump the hierarchy than "these two filters are identical"
or "these two filters are not identical".

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