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

Kees Cook
2015-09-04T20:50:58Z

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