Re: [PATCH bpf-next v1 00/10] bpfilter

[Dmitrii Banshchikov <me@ubique.spb.ru>]

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.


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

-- 

Dmitrii Banshchikov