From e472f88891abbc535a5e16a68a104073985f6061 Mon Sep 17 00:00:00 2001 From: Kuniyuki Iwashima Date: Mon, 15 Jan 2024 12:55:13 -0800 Subject: [PATCH] bpf: tcp: Support arbitrary SYN Cookie. This patch adds a new kfunc available at TC hook to support arbitrary SYN Cookie. The basic usage is as follows: struct bpf_tcp_req_attrs attrs = { .mss = mss, .wscale_ok = wscale_ok, .rcv_wscale = rcv_wscale, /* Server's WScale < 15 */ .snd_wscale = snd_wscale, /* Client's WScale < 15 */ .tstamp_ok = tstamp_ok, .rcv_tsval = tsval, .rcv_tsecr = tsecr, /* Server's Initial TSval */ .usec_ts_ok = usec_ts_ok, .sack_ok = sack_ok, .ecn_ok = ecn_ok, } skc = bpf_skc_lookup_tcp(...); sk = (struct sock *)bpf_skc_to_tcp_sock(skc); bpf_sk_assign_tcp_reqsk(skb, sk, attrs, sizeof(attrs)); bpf_sk_release(skc); bpf_sk_assign_tcp_reqsk() takes skb, a listener sk, and struct bpf_tcp_req_attrs and allocates reqsk and configures it. Then, bpf_sk_assign_tcp_reqsk() links reqsk with skb and the listener. The notable thing here is that we do not hold refcnt for both reqsk and listener. To differentiate that, we mark reqsk->syncookie, which is only used in TX for now. So, if reqsk->syncookie is 1 in RX, it means that the reqsk is allocated by kfunc. When skb is freed, sock_pfree() checks if reqsk->syncookie is 1, and in that case, we set NULL to reqsk->rsk_listener before calling reqsk_free() as reqsk does not hold a refcnt of the listener. When the TCP stack looks up a socket from the skb, we steal the listener from the reqsk in skb_steal_sock() and create a full sk in cookie_v[46]_check(). The refcnt of reqsk will finally be set to 1 in tcp_get_cookie_sock() after creating a full sk. Note that we can extend struct bpf_tcp_req_attrs in the future when we add a new attribute that is determined in 3WHS. Signed-off-by: Kuniyuki Iwashima Link: https://lore.kernel.org/r/20240115205514.68364-6-kuniyu@amazon.com Signed-off-by: Martin KaFai Lau Signed-off-by: Alexei Starovoitov --- include/net/tcp.h | 14 ++++++ net/core/filter.c | 111 +++++++++++++++++++++++++++++++++++++++++++++- net/core/sock.c | 14 +++++- 3 files changed, 135 insertions(+), 4 deletions(-) diff --git a/include/net/tcp.h b/include/net/tcp.h index dfe99a084a71..451dc1373970 100644 --- a/include/net/tcp.h +++ b/include/net/tcp.h @@ -600,6 +600,20 @@ static inline bool cookie_ecn_ok(const struct net *net, const struct dst_entry * } #if IS_ENABLED(CONFIG_BPF) +struct bpf_tcp_req_attrs { + u32 rcv_tsval; + u32 rcv_tsecr; + u16 mss; + u8 rcv_wscale; + u8 snd_wscale; + u8 ecn_ok; + u8 wscale_ok; + u8 sack_ok; + u8 tstamp_ok; + u8 usec_ts_ok; + u8 reserved[3]; +}; + static inline bool cookie_bpf_ok(struct sk_buff *skb) { return skb->sk; diff --git a/net/core/filter.c b/net/core/filter.c index 8c9f67c81e22..6a7abbaa50b8 100644 --- a/net/core/filter.c +++ b/net/core/filter.c @@ -11837,6 +11837,103 @@ __bpf_kfunc int bpf_sock_addr_set_sun_path(struct bpf_sock_addr_kern *sa_kern, return 0; } + +__bpf_kfunc int bpf_sk_assign_tcp_reqsk(struct sk_buff *skb, struct sock *sk, + struct bpf_tcp_req_attrs *attrs, int attrs__sz) +{ +#if IS_ENABLED(CONFIG_SYN_COOKIES) + const struct request_sock_ops *ops; + struct inet_request_sock *ireq; + struct tcp_request_sock *treq; + struct request_sock *req; + struct net *net; + __u16 min_mss; + u32 tsoff = 0; + + if (attrs__sz != sizeof(*attrs) || + attrs->reserved[0] || attrs->reserved[1] || attrs->reserved[2]) + return -EINVAL; + + if (!skb_at_tc_ingress(skb)) + return -EINVAL; + + net = dev_net(skb->dev); + if (net != sock_net(sk)) + return -ENETUNREACH; + + switch (skb->protocol) { + case htons(ETH_P_IP): + ops = &tcp_request_sock_ops; + min_mss = 536; + break; +#if IS_BUILTIN(CONFIG_IPV6) + case htons(ETH_P_IPV6): + ops = &tcp6_request_sock_ops; + min_mss = IPV6_MIN_MTU - 60; + break; +#endif + default: + return -EINVAL; + } + + if (sk->sk_type != SOCK_STREAM || sk->sk_state != TCP_LISTEN || + sk_is_mptcp(sk)) + return -EINVAL; + + if (attrs->mss < min_mss) + return -EINVAL; + + if (attrs->wscale_ok) { + if (!READ_ONCE(net->ipv4.sysctl_tcp_window_scaling)) + return -EINVAL; + + if (attrs->snd_wscale > TCP_MAX_WSCALE || + attrs->rcv_wscale > TCP_MAX_WSCALE) + return -EINVAL; + } + + if (attrs->sack_ok && !READ_ONCE(net->ipv4.sysctl_tcp_sack)) + return -EINVAL; + + if (attrs->tstamp_ok) { + if (!READ_ONCE(net->ipv4.sysctl_tcp_timestamps)) + return -EINVAL; + + tsoff = attrs->rcv_tsecr - tcp_ns_to_ts(attrs->usec_ts_ok, tcp_clock_ns()); + } + + req = inet_reqsk_alloc(ops, sk, false); + if (!req) + return -ENOMEM; + + ireq = inet_rsk(req); + treq = tcp_rsk(req); + + req->rsk_listener = sk; + req->syncookie = 1; + req->mss = attrs->mss; + req->ts_recent = attrs->rcv_tsval; + + ireq->snd_wscale = attrs->snd_wscale; + ireq->rcv_wscale = attrs->rcv_wscale; + ireq->tstamp_ok = !!attrs->tstamp_ok; + ireq->sack_ok = !!attrs->sack_ok; + ireq->wscale_ok = !!attrs->wscale_ok; + ireq->ecn_ok = !!attrs->ecn_ok; + + treq->req_usec_ts = !!attrs->usec_ts_ok; + treq->ts_off = tsoff; + + skb_orphan(skb); + skb->sk = req_to_sk(req); + skb->destructor = sock_pfree; + + return 0; +#else + return -EOPNOTSUPP; +#endif +} + __bpf_kfunc_end_defs(); int bpf_dynptr_from_skb_rdonly(struct sk_buff *skb, u64 flags, @@ -11865,6 +11962,10 @@ BTF_SET8_START(bpf_kfunc_check_set_sock_addr) BTF_ID_FLAGS(func, bpf_sock_addr_set_sun_path) BTF_SET8_END(bpf_kfunc_check_set_sock_addr) +BTF_SET8_START(bpf_kfunc_check_set_tcp_reqsk) +BTF_ID_FLAGS(func, bpf_sk_assign_tcp_reqsk, KF_TRUSTED_ARGS) +BTF_SET8_END(bpf_kfunc_check_set_tcp_reqsk) + static const struct btf_kfunc_id_set bpf_kfunc_set_skb = { .owner = THIS_MODULE, .set = &bpf_kfunc_check_set_skb, @@ -11880,6 +11981,11 @@ static const struct btf_kfunc_id_set bpf_kfunc_set_sock_addr = { .set = &bpf_kfunc_check_set_sock_addr, }; +static const struct btf_kfunc_id_set bpf_kfunc_set_tcp_reqsk = { + .owner = THIS_MODULE, + .set = &bpf_kfunc_check_set_tcp_reqsk, +}; + static int __init bpf_kfunc_init(void) { int ret; @@ -11895,8 +12001,9 @@ static int __init bpf_kfunc_init(void) ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_LWT_SEG6LOCAL, &bpf_kfunc_set_skb); ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_NETFILTER, &bpf_kfunc_set_skb); ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_XDP, &bpf_kfunc_set_xdp); - return ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_CGROUP_SOCK_ADDR, - &bpf_kfunc_set_sock_addr); + ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_CGROUP_SOCK_ADDR, + &bpf_kfunc_set_sock_addr); + return ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_SCHED_CLS, &bpf_kfunc_set_tcp_reqsk); } late_initcall(bpf_kfunc_init); diff --git a/net/core/sock.c b/net/core/sock.c index 158dbdebce6a..147fb2656e6b 100644 --- a/net/core/sock.c +++ b/net/core/sock.c @@ -2582,8 +2582,18 @@ EXPORT_SYMBOL(sock_efree); #ifdef CONFIG_INET void sock_pfree(struct sk_buff *skb) { - if (sk_is_refcounted(skb->sk)) - sock_gen_put(skb->sk); + struct sock *sk = skb->sk; + + if (!sk_is_refcounted(sk)) + return; + + if (sk->sk_state == TCP_NEW_SYN_RECV && inet_reqsk(sk)->syncookie) { + inet_reqsk(sk)->rsk_listener = NULL; + reqsk_free(inet_reqsk(sk)); + return; + } + + sock_gen_put(sk); } EXPORT_SYMBOL(sock_pfree); #endif /* CONFIG_INET */