netdev - Re: [PATCH bpf-next 07/11] bpf: Add helper to retrieve socket in BPF

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Date:   Thu, 13 Sep 2018 12:06:04 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Joe Stringer <joe@...d.net.nz>
Cc:     Daniel Borkmann <daniel@...earbox.net>,
        Network Development <netdev@...r.kernel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        John Fastabend <john.fastabend@...il.com>,
        Thomas Graf <tgraf@...g.ch>, Martin KaFai Lau <kafai@...com>,
        Nitin Hande <nitin.hande@...il.com>,
        Mauricio Vasquez <mauricio.vasquez@...ito.it>
Subject: Re: [PATCH bpf-next 07/11] bpf: Add helper to retrieve socket in BPF

On Wed, Sep 12, 2018 at 5:06 PM, Alexei Starovoitov
<alexei.starovoitov@...il.com> wrote:
> On Tue, Sep 11, 2018 at 05:36:36PM -0700, Joe Stringer wrote:
>> This patch adds new BPF helper functions, bpf_sk_lookup_tcp() and
>> bpf_sk_lookup_udp() which allows BPF programs to find out if there is a
>> socket listening on this host, and returns a socket pointer which the
>> BPF program can then access to determine, for instance, whether to
>> forward or drop traffic. bpf_sk_lookup_xxx() may take a reference on the
>> socket, so when a BPF program makes use of this function, it must
>> subsequently pass the returned pointer into the newly added sk_release()
>> to return the reference.
>>
>> By way of example, the following pseudocode would filter inbound
>> connections at XDP if there is no corresponding service listening for
>> the traffic:
>>
>>   struct bpf_sock_tuple tuple;
>>   struct bpf_sock_ops *sk;
>>
>>   populate_tuple(ctx, &tuple); // Extract the 5tuple from the packet
>>   sk = bpf_sk_lookup_tcp(ctx, &tuple, sizeof tuple, netns, 0);
> ...
>> +struct bpf_sock_tuple {
>> +     union {
>> +             __be32 ipv6[4];
>> +             __be32 ipv4;
>> +     } saddr;
>> +     union {
>> +             __be32 ipv6[4];
>> +             __be32 ipv4;
>> +     } daddr;
>> +     __be16 sport;
>> +     __be16 dport;
>> +     __u8 family;
>> +};
>
> since we can pass ptr_to_packet into map lookup and other helpers now,
> can you move 'family' out of bpf_sock_tuple and combine with netns_id arg?
> then progs wouldn't need to copy bytes from the packet into tuple
> to do a lookup.

have been thinking more about it.
since only ipv4 and ipv6 supported may be use size of bpf_sock_tuple
to infer family inside the helper, so it doesn't need to be passed explicitly?