netdev - Re: [PATCH bpf-next] bpf/verifier: enable ctx + const + 0.

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Message-ID: <CALDO+Sbx_fkW19N5F=vHfZCawoYCvoyS7jp_sTMp3Bz0FPQ8aw@mail.gmail.com>
Date:   Wed, 2 May 2018 10:54:56 -0700
From:   William Tu <u9012063@...il.com>
To:     Daniel Borkmann <daniel@...earbox.net>
Cc:     Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        Yonghong Song <yhs@...com>, Yifeng Sun <pkusunyifeng@...il.com>
Subject: Re: [PATCH bpf-next] bpf/verifier: enable ctx + const + 0.

On Wed, May 2, 2018 at 1:29 AM, Daniel Borkmann <daniel@...earbox.net> wrote:
> On 05/02/2018 06:52 AM, Alexei Starovoitov wrote:
>> On Tue, May 01, 2018 at 09:35:29PM -0700, William Tu wrote:
>>>
>>>> How did you test this patch?
>>>>
>>> Without the patch, the test case will fail.
>>> With the patch, the test case passes.
>>
>> Please test it with real program and you'll see crashes and garbage returned.
>
> +1, *convert_ctx_access() use bpf_insn's off to determine what to rewrite,
> so this is definitely buggy, and wasn't properly tested as it should have
> been. The test case is also way too simple, just the LDX and then doing a
> return 0 will get you past verifier, but won't give you anything in terms
> of runtime testing that test_verifier is doing. A single test case for a
> non trivial verifier change like this is also _completely insufficient_,
> this really needs to test all sort of weird corner cases (involving out of
> bounds accesses, overflows, etc).

Thanks, now I understand.
It's much more complicated than I thought.

William