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Date: Tue, 17 Oct 2023 18:08:34 -0700
From: Martin KaFai Lau <martin.lau@...ux.dev>
To: Kuniyuki Iwashima <kuniyu@...zon.com>
Cc: Kuniyuki Iwashima <kuni1840@...il.com>, bpf@...r.kernel.org,
netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>,
Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>,
Paolo Abeni <pabeni@...hat.com>, David Ahern <dsahern@...nel.org>,
Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>,
Andrii Nakryiko <andrii@...nel.org>, Song Liu <song@...nel.org>,
Yonghong Song <yonghong.song@...ux.dev>,
John Fastabend <john.fastabend@...il.com>, KP Singh <kpsingh@...nel.org>,
Stanislav Fomichev <sdf@...gle.com>, Hao Luo <haoluo@...gle.com>,
Jiri Olsa <jolsa@...nel.org>, Mykola Lysenko <mykolal@...com>
Subject: Re: [PATCH v1 bpf-next 10/11] bpf: tcp: Make WS, SACK, ECN
configurable from BPF SYN Cookie.
On 10/13/23 3:04 PM, Kuniyuki Iwashima wrote:
> This patch allows BPF_SOCK_OPS_CHECK_SYNCOOKIE_CB hook to enable WScale,
> SACK, and ECN by passing corresponding flags to bpf_sock_ops.replylong[1].
>
> The same flags are passed to BPF_SOCK_OPS_GEN_SYNCOOKIE_CB hook as
> bpf_sock_ops.args[1] so that the BPF prog need not parse the TCP header to
> check if WScale, SACK, ECN, and TS are available in SYN.
>
> Signed-off-by: Kuniyuki Iwashima <kuniyu@...zon.com>
> ---
> include/uapi/linux/bpf.h | 18 ++++++++++++++++++
> net/ipv4/syncookies.c | 20 ++++++++++++++++++++
> net/ipv4/tcp_input.c | 11 +++++++++++
> tools/include/uapi/linux/bpf.h | 18 ++++++++++++++++++
> 4 files changed, 67 insertions(+)
>
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index 24f673d88c0d..cdae4dd5d797 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -6869,6 +6869,7 @@ enum {
> * option.
> *
> * args[0]: MSS
> + * args[1]: BPF_SYNCOOKIE_XXX
> *
> * replylong[0]: ISN
> * replylong[1]: TS
> @@ -6883,6 +6884,7 @@ enum {
> * args[1]: TS
> *
> * replylong[0]: MSS
> + * replylong[1]: BPF_SYNCOOKIE_XXX
> */
> };
>
> @@ -6970,6 +6972,22 @@ enum {
> */
> };
>
> +/* arg[1] value for BPF_SOCK_OPS_GEN_SYNCOOKIE_CB and
> + * replylong[1] for BPF_SOCK_OPS_CHECK_SYNCOOKIE_CB.
> + *
> + * MSB LSB
> + * | 31 ... | 6 | 5 | 4 | 3 2 1 0 |
> + * | ... | TS | ECN | SACK | WScale |
> + */
> +enum {
> + /* 0xf is invalid thus means that SYN did not have WScale. */
> + BPF_SYNCOOKIE_WSCALE_MASK = (1 << 4) - 1,
> + BPF_SYNCOOKIE_SACK = (1 << 4),
> + BPF_SYNCOOKIE_ECN = (1 << 5),
> + /* Only available for BPF_SOCK_OPS_GEN_SYNCOOKIE_CB to check if SYN has TS */
> + BPF_SYNCOOKIE_TS = (1 << 6),
> +};
This details should not be exposed to uapi (more below).
> +
> struct bpf_perf_event_value {
> __u64 counter;
> __u64 enabled;
> diff --git a/net/ipv4/syncookies.c b/net/ipv4/syncookies.c
> index ff979cc314da..22353a9af52d 100644
> --- a/net/ipv4/syncookies.c
> +++ b/net/ipv4/syncookies.c
> @@ -286,6 +286,7 @@ int bpf_skops_cookie_check(struct sock *sk, struct request_sock *req, struct sk_
> {
> struct bpf_sock_ops_kern sock_ops;
> struct net *net = sock_net(sk);
> + u32 options;
>
> if (tcp_opt->saw_tstamp) {
> if (!READ_ONCE(net->ipv4.sysctl_tcp_timestamps))
> @@ -309,6 +310,25 @@ int bpf_skops_cookie_check(struct sock *sk, struct request_sock *req, struct sk_
> if (!sock_ops.replylong[0])
> goto err;
>
> + options = sock_ops.replylong[1];
> +
> + if ((options & BPF_SYNCOOKIE_WSCALE_MASK) != BPF_SYNCOOKIE_WSCALE_MASK) {
> + if (!READ_ONCE(net->ipv4.sysctl_tcp_window_scaling))
> + goto err;
> +
> + tcp_opt->wscale_ok = 1;
> + tcp_opt->snd_wscale = options & BPF_SYNCOOKIE_WSCALE_MASK;
> + }
> +
> + if (options & BPF_SYNCOOKIE_SACK) {
> + if (!READ_ONCE(net->ipv4.sysctl_tcp_sack))
> + goto err;
> +
> + tcp_opt->sack_ok = 1;
> + }
> +
> + inet_rsk(req)->ecn_ok = options & BPF_SYNCOOKIE_ECN;
> +
> __NET_INC_STATS(sock_net(sk), LINUX_MIB_SYNCOOKIESRECV);
>
> return sock_ops.replylong[0];
> diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
> index feb44bff29ef..483e2f36afe5 100644
> --- a/net/ipv4/tcp_input.c
> +++ b/net/ipv4/tcp_input.c
> @@ -6970,14 +6970,25 @@ EXPORT_SYMBOL_GPL(tcp_get_syncookie_mss);
> static int bpf_skops_cookie_init_sequence(struct sock *sk, struct request_sock *req,
> struct sk_buff *skb, __u32 *isn)
> {
> + struct inet_request_sock *ireq = inet_rsk(req);
> struct bpf_sock_ops_kern sock_ops;
> + u32 options;
> int ret;
>
> + options = ireq->wscale_ok ? ireq->snd_wscale : BPF_SYNCOOKIE_WSCALE_MASK;
> + if (ireq->sack_ok)
> + options |= BPF_SYNCOOKIE_SACK;
> + if (ireq->ecn_ok)
> + options |= BPF_SYNCOOKIE_ECN;
> + if (ireq->tstamp_ok)
> + options |= BPF_SYNCOOKIE_TS;
No need to set "options" (which becomes args[1]). sock_ops.sk is available to
the bpf prog. The bpf prog can directly read it. The recent AF_UNIX bpf support
could be a reference on how the bpf_cast_to_kern_ctx() and bpf_rdonly_cast() are
used.
https://lore.kernel.org/bpf/20231011185113.140426-10-daan.j.demeyer@gmail.com/
> +
> memset(&sock_ops, 0, offsetof(struct bpf_sock_ops_kern, temp));
>
> sock_ops.op = BPF_SOCK_OPS_GEN_SYNCOOKIE_CB;
> sock_ops.sk = req_to_sk(req);
> sock_ops.args[0] = req->mss;
> + sock_ops.args[1] = options;
>
> bpf_skops_init_skb(&sock_ops, skb, tcp_hdrlen(skb));
>
> diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
> index 24f673d88c0d..cdae4dd5d797 100644
> --- a/tools/include/uapi/linux/bpf.h
> +++ b/tools/include/uapi/linux/bpf.h
> @@ -6869,6 +6869,7 @@ enum {
> * option.
> *
> * args[0]: MSS
> + * args[1]: BPF_SYNCOOKIE_XXX
> *
> * replylong[0]: ISN
> * replylong[1]: TS
> @@ -6883,6 +6884,7 @@ enum {
> * args[1]: TS
> *
> * replylong[0]: MSS
> + * replylong[1]: BPF_SYNCOOKIE_XXX
> */
> };
>
> @@ -6970,6 +6972,22 @@ enum {
> */
> };
>
> +/* arg[1] value for BPF_SOCK_OPS_GEN_SYNCOOKIE_CB and
> + * replylong[1] for BPF_SOCK_OPS_CHECK_SYNCOOKIE_CB.
> + *
> + * MSB LSB
> + * | 31 ... | 6 | 5 | 4 | 3 2 1 0 |
> + * | ... | TS | ECN | SACK | WScale |
> + */
> +enum {
> + /* 0xf is invalid thus means that SYN did not have WScale. */
> + BPF_SYNCOOKIE_WSCALE_MASK = (1 << 4) - 1,
> + BPF_SYNCOOKIE_SACK = (1 << 4),
> + BPF_SYNCOOKIE_ECN = (1 << 5),
> + /* Only available for BPF_SOCK_OPS_GEN_SYNCOOKIE_CB to check if SYN has TS */
> + BPF_SYNCOOKIE_TS = (1 << 6),
> +};
> +
> struct bpf_perf_event_value {
> __u64 counter;
> __u64 enabled;
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