Date:   Thu, 10 Jun 2021 07:56:47 -0700
From:   Yonghong Song <yhs@...com>
To:     Dmitrii Banshchikov <me@...que.spb.ru>
CC:     <bpf@...r.kernel.org>, <ast@...nel.org>, <davem@...emloft.net>,
        <daniel@...earbox.net>, <andrii@...nel.org>, <kafai@...com>,
        <songliubraving@...com>, <john.fastabend@...il.com>,
        <kpsingh@...nel.org>, <netdev@...r.kernel.org>, <rdna@...com>
Subject: Re: [PATCH bpf-next v1 00/10] bpfilter



On 6/10/21 6:36 AM, Dmitrii Banshchikov wrote:
> On Wed, Jun 09, 2021 at 05:50:13PM -0700, Yonghong Song wrote:
>>
>>
>> On 6/3/21 3:14 AM, Dmitrii Banshchikov wrote:
>>> The patchset is based on the patches from David S. Miller [1] and
>>> Daniel Borkmann [2].
>>>
>>> The main goal of the patchset is to prepare bpfilter for
>>> iptables' configuration blob parsing and code generation.
>>>
>>> The patchset introduces data structures and code for matches,
>>> targets, rules and tables.
>>>
>>> The current version misses handling of counters. Postpone its
>>> implementation until the code generation phase as it's not clear
>>> yet how to better handle them.
>>>
>>> Beside that there is no support of net namespaces at all.
>>>
>>> In the next iteration basic code generation shall be introduced.
>>>
>>> The rough plan for the code generation.
>>>
>>> It seems reasonable to assume that the first rules should cover
>>> most of the packet flow.  This is why they are critical from the
>>> performance point of view.  At the same time number of user
>>> defined rules might be pretty large. Also there is a limit on
>>> size and complexity of a BPF program introduced by the verifier.
>>>
>>> There are two approaches how to handle iptables' rules in
>>> generated BPF programs.
>>>
>>> The first approach is to generate a BPF program that is an
>>> equivalent to a set of rules on a rule by rule basis. This
>>> approach should give the best performance. The drawback is the
>>> limitation from the verifier on size and complexity of BPF
>>> program.
>>>
>>> The second approach is to use an internal representation of rules
>>> stored in a BPF map and use bpf_for_each_map_elem() helper to
>>> iterate over them. In this case the helper's callback is a BPF
>>> function that is able to process any valid rule.
>>>
>>> Combination of the two approaches should give most of the
>>> benefits - a heuristic should help to select a small subset of
>>> the rules for code generation on a rule by rule basis. All other
>>> rules are cold and it should be possible to store them in an
>>> internal form in a BPF map. The rules will be handled by
>>> bpf_for_each_map_elem().  This should remove the limit on the
>>> number of supported rules.
>>
>> Agree. A bpf program inlines some hot rule handling and put
>> the rest in for_each_map_elem() sounds reasonable to me.
>>
>>>
>>> During development it was useful to use statically linked
>>> sanitizers in bpfilter usermode helper. Also it is possible to
>>> use fuzzers but it's not clear if it is worth adding them to the
>>> test infrastructure - because there are no other fuzzers under
>>> tools/testing/selftests currently.
>>>
>>> Patch 1 adds definitions of the used types.
>>> Patch 2 adds logging to bpfilter.
>>> Patch 3 adds bpfilter header to tools
>>> Patch 4 adds an associative map.
>>> Patches 5/6/7/8 add code for matches, targets, rules and table.
>>> Patch 9 handles hooked setsockopt(2) calls.
>>> Patch 10 uses prepared code in main().
>>>
>>> Here is an example:
>>> % dmesg  | tail -n 2
>>> [   23.636102] bpfilter: Loaded bpfilter_umh pid 181
>>> [   23.658529] bpfilter: started
>>> % /usr/sbin/iptables-legacy -L -n
>>
>> So this /usr/sbin/iptables-legacy is your iptables variant to
>> translate iptable command lines to BPFILTER_IPT_SO_*,
>> right? It could be good to provide a pointer to the source
>> or binary so people can give a try.
>>
>> I am not an expert in iptables. Reading codes, I kind of
>> can grasp the high-level ideas of the patch, but probably
>> Alexei or Daniel can review some details whether the
>> design is sufficient to be an iptable replacement.
>>
> 
> The goal of a complete iptables replacement is too ambigious for
> the moment - because existings hooks and helpers don't cover all
> required functionality.
> 
> A more achievable goal is to have something simple that could
> replace a significant part of use cases for filter table.
> 
> Having something simple that would work as a stateless firewall
> and provide some performance benefits is a good start. For more
> complex scenarios there is a safe fallback to the existing
> implementation.

Thanks for explanation. It would be good to put the above
into cover letter so reviewers/users can get a realistic
expectation.

> 
> 
>>
>>> Chain INPUT (policy ACCEPT)
>>> target     prot opt source               destination
>>>
>>> Chain FORWARD (policy ACCEPT)
>>> target     prot opt source               destination
>>>
>> [...]
> 

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