netdev - Re: [PATCH] net: filter: fix upper BPF instruction limit

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Date:	Fri, 20 Jun 2014 09:48:59 -0700
From:	Kees Cook <keescook@...omium.org>
To:	Daniel Borkmann <dborkman@...hat.com>
Cc:	Alexei Starovoitov <ast@...mgrid.com>,
	LKML <linux-kernel@...r.kernel.org>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Chema Gonzalez <chema@...gle.com>,
	Network Development <netdev@...r.kernel.org>
Subject: Re: [PATCH] net: filter: fix upper BPF instruction limit

On Fri, Jun 20, 2014 at 3:13 AM, Daniel Borkmann <dborkman@...hat.com> wrote:
> Hi Kees,
>
>
> On 06/19/2014 01:28 AM, Kees Cook wrote:
>>
>> On Wed, Jun 18, 2014 at 4:19 PM, Alexei Starovoitov <ast@...mgrid.com>
>> wrote:
>>>
>>> On Wed, Jun 18, 2014 at 3:55 PM, Kees Cook <keescook@...omium.org> wrote:
>>>>
>>>> On Wed, Jun 18, 2014 at 3:48 PM, Alexei Starovoitov <ast@...mgrid.com>
>>>> wrote:
>>>>>
>>>>> On Wed, Jun 18, 2014 at 3:34 PM, Kees Cook <keescook@...omium.org>
>>>>> wrote:
>
> ...
>
>>>>> I wonder how did you catch this? :)
>>>>> Just code inspection or seccomp actually generating such programs?
>>>>
>>>>
>>>> In the process of merging my seccomp thread-sync series back with
>>>> mainline, I got uncomfortable that I was moving filter size validation
>>>> around without actually testing it. When I added it, I was happy that
>>>> my series was correctly checking size limits, but then discovered my
>>>> newly added check actually failed on an earlier kernel (3.2). Tracking
>>>> it down found the corner case under 3.15.
>>>>
>>>> Here's the test I added to the seccomp regression tests, if you're
>>>> interested:
>>>>
>>>> https://github.com/kees/seccomp/commit/794d54a340cde70a3bdf7fe0ade1f95d160b2883
>>>
>>>
>>> Nice. I'm assuming https://github.com/redpig/seccomp is still the main
>>> tree
>>> for seccomp testsuite…
>>
>>
>> Yes. Will hasn't pulled this most recent set of changes.
>
>
> We were actually thinking about extending lib/test_bpf module with seccomp
> tests, which is possible to a limited extend, but seccomp is also a bit
> more than just running a BPF program and making sure results fit.
>
> Are there any plans to put and extend test cases from [1] via user space
> side into the kernel self-test directory, i.e. into something like
> tools/testing/selftests/seccomp/ so that in future new tests can be added
> or run from there? Might be worth to consider.

Yeah, I have this on my TODO list, but we need to juggle relicensing
the test suite (it is currently BSD, not GPLv2). I'll keep chasing
this.

-Kees

>
> Thanks,
>
> Daniel
>
>  [1] https://github.com/redpig/seccomp



-- 
Kees Cook
Chrome OS Security
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