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

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Date:	Fri, 4 Sep 2015 13:50:55 -0700
From:	Kees Cook <keescook@...omium.org>
To:	Tycho Andersen <tycho.andersen@...onical.com>
Cc:	Alexei Starovoitov <ast@...nel.org>,
	Will Drewry <wad@...omium.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Andy Lutomirski <luto@...capital.net>,
	Pavel Emelyanov <xemul@...allels.com>,
	"Serge E. Hallyn" <serge.hallyn@...ntu.com>,
	Daniel Borkmann <daniel@...earbox.net>,
	LKML <linux-kernel@...r.kernel.org>,
	Network Development <netdev@...r.kernel.org>
Subject: Re: [PATCH 3/6] ebpf: add a way to dump an eBPF program

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