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Date:   Sat, 27 Jun 2020 09:44:55 -0700
From:   Eric Dumazet <edumazet@...gle.com>
To:     Martin KaFai Lau <kafai@...com>
Cc:     bpf <bpf@...r.kernel.org>, Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        kernel-team <kernel-team@...com>,
        Lawrence Brakmo <brakmo@...com>,
        Neal Cardwell <ncardwell@...gle.com>,
        netdev <netdev@...r.kernel.org>,
        Yuchung Cheng <ycheng@...gle.com>
Subject: Re: [PATCH bpf-next 02/10] tcp: bpf: Parse BPF experimental header option

On Fri, Jun 26, 2020 at 10:55 AM Martin KaFai Lau <kafai@...com> wrote:
>
> This patch adds logic to parse experimental kind 254 with 16 bit magic
> 0xeB9F.  The latter patch will allow bpf prog to write and parse data
> under this experimental kind and magic.
>
> A one byte bpf_hdr_opt_off is added to tcp_skb_cb by using an existing
> 4 byte hole.  It is only used in rx.  It stores the offset to the
> bpf experimental option and will be made available to BPF prog
> in a latter patch.  This offset is also stored in the saved_syn.
>
> Signed-off-by: Martin KaFai Lau <kafai@...com>
> ---
>  include/net/request_sock.h | 1 +
>  include/net/tcp.h          | 3 +++
>  net/ipv4/tcp_input.c       | 6 ++++++
>  net/ipv4/tcp_ipv4.c        | 1 +
>  net/ipv6/tcp_ipv6.c        | 1 +
>  5 files changed, 12 insertions(+)
>
> diff --git a/include/net/request_sock.h b/include/net/request_sock.h
> index d77237ec9fb4..55297286c066 100644
> --- a/include/net/request_sock.h
> +++ b/include/net/request_sock.h
> @@ -43,6 +43,7 @@ int inet_rtx_syn_ack(const struct sock *parent, struct request_sock *req);
>
>  struct saved_syn {
>         u32 network_hdrlen;
> +       u32 bpf_hdr_opt_off;
>         u8 data[];
>  };
>
> diff --git a/include/net/tcp.h b/include/net/tcp.h
> index eab1c7d0facb..07a9dfe35242 100644
> --- a/include/net/tcp.h
> +++ b/include/net/tcp.h
> @@ -191,6 +191,7 @@ void tcp_time_wait(struct sock *sk, int state, int timeo);
>   */
>  #define TCPOPT_FASTOPEN_MAGIC  0xF989
>  #define TCPOPT_SMC_MAGIC       0xE2D4C3D9
> +#define TCPOPT_BPF_MAGIC       0xEB9F
>
>  /*
>   *     TCP option lengths
> @@ -204,6 +205,7 @@ void tcp_time_wait(struct sock *sk, int state, int timeo);
>  #define TCPOLEN_FASTOPEN_BASE  2
>  #define TCPOLEN_EXP_FASTOPEN_BASE  4
>  #define TCPOLEN_EXP_SMC_BASE   6
> +#define TCPOLEN_EXP_BPF_BASE   4
>
>  /* But this is what stacks really send out. */
>  #define TCPOLEN_TSTAMP_ALIGNED         12
> @@ -857,6 +859,7 @@ struct tcp_skb_cb {
>                         has_rxtstamp:1, /* SKB has a RX timestamp       */
>                         unused:5;
>         __u32           ack_seq;        /* Sequence number ACK'd        */
> +       __u8            bpf_hdr_opt_off;/* offset to bpf hdr option. rx only. */
>         union {
>                 struct {
>                         /* There is space for up to 24 bytes */
> diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
> index eb0e32b2def9..640408a80b3d 100644
> --- a/net/ipv4/tcp_input.c
> +++ b/net/ipv4/tcp_input.c
> @@ -3924,6 +3924,10 @@ void tcp_parse_options(const struct net *net,
>                                         tcp_parse_fastopen_option(opsize -
>                                                 TCPOLEN_EXP_FASTOPEN_BASE,
>                                                 ptr + 2, th->syn, foc, true);
> +                               else if (opsize >= TCPOLEN_EXP_BPF_BASE &&
> +                                        get_unaligned_be16(ptr) ==
> +                                        TCPOPT_BPF_MAGIC)
> +                                       TCP_SKB_CB(skb)->bpf_hdr_opt_off = (ptr - 2) - (unsigned char *)th;
>                                 else
>                                         smc_parse_options(th, opt_rx, ptr,
>                                                           opsize);
> @@ -6562,6 +6566,8 @@ static void tcp_reqsk_record_syn(const struct sock *sk,
>                 saved_syn = kmalloc(len + sizeof(*saved_syn), GFP_ATOMIC);
>                 if (saved_syn) {
>                         saved_syn->network_hdrlen = skb_network_header_len(skb);
> +                       saved_syn->bpf_hdr_opt_off =
> +                               TCP_SKB_CB(skb)->bpf_hdr_opt_off;
>                         memcpy(saved_syn->data, skb_network_header(skb), len);
>                         req->saved_syn = saved_syn;
>                 }
> diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
> index ea0df9fd7618..a3535b7fe002 100644
> --- a/net/ipv4/tcp_ipv4.c
> +++ b/net/ipv4/tcp_ipv4.c
> @@ -1864,6 +1864,7 @@ static void tcp_v4_fill_cb(struct sk_buff *skb, const struct iphdr *iph,
>         TCP_SKB_CB(skb)->sacked  = 0;
>         TCP_SKB_CB(skb)->has_rxtstamp =
>                         skb->tstamp || skb_hwtstamps(skb)->hwtstamp;
> +       TCP_SKB_CB(skb)->bpf_hdr_opt_off = 0;
>  }
>
>  /*
> diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
> index f67d45ff00b4..8356d0562279 100644
> --- a/net/ipv6/tcp_ipv6.c
> +++ b/net/ipv6/tcp_ipv6.c
> @@ -1545,6 +1545,7 @@ static void tcp_v6_fill_cb(struct sk_buff *skb, const struct ipv6hdr *hdr,
>         TCP_SKB_CB(skb)->sacked = 0;
>         TCP_SKB_CB(skb)->has_rxtstamp =
>                         skb->tstamp || skb_hwtstamps(skb)->hwtstamp;
> +       TCP_SKB_CB(skb)->bpf_hdr_opt_off = 0;
>  }
>
>  INDIRECT_CALLABLE_SCOPE int tcp_v6_rcv(struct sk_buff *skb)
> --
> 2.24.1
>

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