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Date: Tue, 16 Jul 2019 12:34:52 +0100
From: Lorenz Bauer <lmb@...udflare.com>
To: Petar Penkov <ppenkov.kernel@...il.com>
Cc: Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
davem@...emloft.net, Alexei Starovoitov <ast@...nel.org>,
Daniel Borkmann <daniel@...earbox.net>,
Eric Dumazet <edumazet@...gle.com>, sdf@...gle.com,
Petar Penkov <ppenkov@...gle.com>
Subject: Re: [bpf-next RFC 2/6] tcp: add skb-less helpers to retrieve SYN cookie
On Tue, 16 Jul 2019 at 01:27, Petar Penkov <ppenkov.kernel@...il.com> wrote:
>
> From: Petar Penkov <ppenkov@...gle.com>
>
> This patch allows generation of a SYN cookie before an SKB has been
> allocated, as is the case at XDP.
>
> Signed-off-by: Petar Penkov <ppenkov@...gle.com>
> ---
> include/net/tcp.h | 11 ++++++
> net/ipv4/tcp_input.c | 79 ++++++++++++++++++++++++++++++++++++++++++++
> net/ipv4/tcp_ipv4.c | 8 +++++
> net/ipv6/tcp_ipv6.c | 8 +++++
> 4 files changed, 106 insertions(+)
>
> diff --git a/include/net/tcp.h b/include/net/tcp.h
> index cca3c59b98bf..a128e22c0d5d 100644
> --- a/include/net/tcp.h
> +++ b/include/net/tcp.h
> @@ -414,6 +414,17 @@ void tcp_parse_options(const struct net *net, const struct sk_buff *skb,
> int estab, struct tcp_fastopen_cookie *foc);
> const u8 *tcp_parse_md5sig_option(const struct tcphdr *th);
>
> +/*
> + * BPF SKB-less helpers
> + */
> +u16 tcp_v4_get_syncookie(struct sock *sk, struct iphdr *iph,
> + struct tcphdr *tch, u32 *cookie);
> +u16 tcp_v6_get_syncookie(struct sock *sk, struct ipv6hdr *iph,
> + struct tcphdr *tch, u32 *cookie);
> +u16 tcp_get_syncookie(struct request_sock_ops *rsk_ops,
> + const struct tcp_request_sock_ops *af_ops,
> + struct sock *sk, void *iph, struct tcphdr *tch,
> + u32 *cookie);
> /*
> * TCP v4 functions exported for the inet6 API
> */
> diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
> index 8892df6de1d4..1406d7e0953c 100644
> --- a/net/ipv4/tcp_input.c
> +++ b/net/ipv4/tcp_input.c
> @@ -3782,6 +3782,52 @@ static void smc_parse_options(const struct tcphdr *th,
> #endif
> }
>
> +/* Try to parse the MSS option from the TCP header. Return 0 on failure, clamped
> + * value on success.
> + *
> + * Invoked for BPF SYN cookie generation, so th should be a SYN.
> + */
> +static u16 tcp_parse_mss_option(const struct net *net, const struct tcphdr *th,
> + u16 user_mss)
net seems unused?
> +{
> + const unsigned char *ptr = (const unsigned char *)(th + 1);
> + int length = (th->doff * 4) - sizeof(struct tcphdr);
> + u16 mss = 0;
> +
> + while (length > 0) {
> + int opcode = *ptr++;
> + int opsize;
> +
> + switch (opcode) {
> + case TCPOPT_EOL:
> + return mss;
> + case TCPOPT_NOP: /* Ref: RFC 793 section 3.1 */
> + length--;
> + continue;
> + default:
> + if (length < 2)
> + return mss;
> + opsize = *ptr++;
> + if (opsize < 2) /* "silly options" */
> + return mss;
> + if (opsize > length)
> + return mss; /* fail on partial options */
> + if (opcode == TCPOPT_MSS && opsize == TCPOLEN_MSS) {
> + u16 in_mss = get_unaligned_be16(ptr);
> +
> + if (in_mss) {
> + if (user_mss && user_mss < in_mss)
> + in_mss = user_mss;
> + mss = in_mss;
> + }
> + }
> + ptr += opsize - 2;
> + length -= opsize;
> + }
> + }
> + return mss;
> +}
> +
> /* Look for tcp options. Normally only called on SYN and SYNACK packets.
> * But, this can also be called on packets in the established flow when
> * the fast version below fails.
> @@ -6464,6 +6510,39 @@ static void tcp_reqsk_record_syn(const struct sock *sk,
> }
> }
>
> +u16 tcp_get_syncookie(struct request_sock_ops *rsk_ops,
> + const struct tcp_request_sock_ops *af_ops,
> + struct sock *sk, void *iph, struct tcphdr *th,
> + u32 *cookie)
> +{
> + u16 mss = 0;
> +#ifdef CONFIG_SYN_COOKIES
> + bool is_v4 = rsk_ops->family == AF_INET;
> + struct tcp_sock *tp = tcp_sk(sk);
> +
> + if (sock_net(sk)->ipv4.sysctl_tcp_syncookies != 2 &&
> + !inet_csk_reqsk_queue_is_full(sk))
> + return 0;
> +
> + if (!tcp_syn_flood_action(sk, rsk_ops->slab_name))
> + return 0;
> +
> + if (sk_acceptq_is_full(sk)) {
> + NET_INC_STATS(sock_net(sk), LINUX_MIB_LISTENOVERFLOWS);
> + return 0;
> + }
> +
> + mss = tcp_parse_mss_option(sock_net(sk), th, tp->rx_opt.user_mss);
> + if (!mss)
> + mss = af_ops->mss_clamp;
> +
> + tcp_synq_overflow(sk);
> + *cookie = is_v4 ? __cookie_v4_init_sequence(iph, th, &mss)
> + : __cookie_v6_init_sequence(iph, th, &mss);
> +#endif
> + return mss;
> +}
> +
> int tcp_conn_request(struct request_sock_ops *rsk_ops,
> const struct tcp_request_sock_ops *af_ops,
> struct sock *sk, struct sk_buff *skb)
> diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
> index d57641cb3477..0e06e59784bd 100644
> --- a/net/ipv4/tcp_ipv4.c
> +++ b/net/ipv4/tcp_ipv4.c
> @@ -1515,6 +1515,14 @@ static struct sock *tcp_v4_cookie_check(struct sock *sk, struct sk_buff *skb)
> return sk;
> }
>
> +u16 tcp_v4_get_syncookie(struct sock *sk, struct iphdr *iph,
> + struct tcphdr *tch, u32 *cookie)
> +{
> + return tcp_get_syncookie(&tcp_request_sock_ops,
> + &tcp_request_sock_ipv4_ops, sk, iph, tch,
> + cookie);
> +}
> +
> /* The socket must have it's spinlock held when we get
> * here, unless it is a TCP_LISTEN socket.
> *
> diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
> index d56a9019a0fe..ce46cdba54bc 100644
> --- a/net/ipv6/tcp_ipv6.c
> +++ b/net/ipv6/tcp_ipv6.c
> @@ -1058,6 +1058,14 @@ static struct sock *tcp_v6_cookie_check(struct sock *sk, struct sk_buff *skb)
> return sk;
> }
>
> +u16 tcp_v6_get_syncookie(struct sock *sk, struct ipv6hdr *iph,
> + struct tcphdr *tch, u32 *cookie)
> +{
> + return tcp_get_syncookie(&tcp6_request_sock_ops,
> + &tcp_request_sock_ipv6_ops, sk, iph, tch,
> + cookie);
> +}
> +
> static int tcp_v6_conn_request(struct sock *sk, struct sk_buff *skb)
> {
> if (skb->protocol == htons(ETH_P_IP))
> --
> 2.22.0.510.g264f2c817a-goog
>
--
Lorenz Bauer | Systems Engineer
6th Floor, County Hall/The Riverside Building, SE1 7PB, UK
www.cloudflare.com
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