bpf: Add helpers to issue and check SYN cookies in XDP

The new helpers bpf_tcp_raw_{gen,check}_syncookie_ipv{4,6} allow an XDP
program to generate SYN cookies in response to TCP SYN packets and to
check those cookies upon receiving the first ACK packet (the final
packet of the TCP handshake).

Unlike bpf_tcp_{gen,check}_syncookie these new helpers don't need a
listening socket on the local machine, which allows to use them together
with synproxy to accelerate SYN cookie generation.

Signed-off-by: Maxim Mikityanskiy <maximmi@nvidia.com>
Reviewed-by: Tariq Toukan <tariqt@nvidia.com>
Link: https://lore.kernel.org/r/20220615134847.3753567-4-maximmi@nvidia.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

2 files changed, 120 insertions, 1 deletions

diff --git a/net/core/filter.c b/net/core/filter.c
index 5af58eb48587..b62d4126a561 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -7444,6 +7444,114 @@ static const struct bpf_func_proto bpf_skb_set_tstamp_proto = {
 	.arg3_type      = ARG_ANYTHING,
 };
 
+#ifdef CONFIG_SYN_COOKIES
+BPF_CALL_3(bpf_tcp_raw_gen_syncookie_ipv4, struct iphdr *, iph,
+	   struct tcphdr *, th, u32, th_len)
+{
+	u32 cookie;
+	u16 mss;
+
+	if (unlikely(th_len < sizeof(*th) || th_len != th->doff * 4))
+		return -EINVAL;
+
+	mss = tcp_parse_mss_option(th, 0) ?: TCP_MSS_DEFAULT;
+	cookie = __cookie_v4_init_sequence(iph, th, &mss);
+
+	return cookie | ((u64)mss << 32);
+}
+
+static const struct bpf_func_proto bpf_tcp_raw_gen_syncookie_ipv4_proto = {
+	.func		= bpf_tcp_raw_gen_syncookie_ipv4,
+	.gpl_only	= true, /* __cookie_v4_init_sequence() is GPL */
+	.pkt_access	= true,
+	.ret_type	= RET_INTEGER,
+	.arg1_type	= ARG_PTR_TO_FIXED_SIZE_MEM,
+	.arg1_size	= sizeof(struct iphdr),
+	.arg2_type	= ARG_PTR_TO_MEM,
+	.arg3_type	= ARG_CONST_SIZE,
+};
+
+BPF_CALL_3(bpf_tcp_raw_gen_syncookie_ipv6, struct ipv6hdr *, iph,
+	   struct tcphdr *, th, u32, th_len)
+{
+#if IS_BUILTIN(CONFIG_IPV6)
+	const u16 mss_clamp = IPV6_MIN_MTU - sizeof(struct tcphdr) -
+		sizeof(struct ipv6hdr);
+	u32 cookie;
+	u16 mss;
+
+	if (unlikely(th_len < sizeof(*th) || th_len != th->doff * 4))
+		return -EINVAL;
+
+	mss = tcp_parse_mss_option(th, 0) ?: mss_clamp;
+	cookie = __cookie_v6_init_sequence(iph, th, &mss);
+
+	return cookie | ((u64)mss << 32);
+#else
+	return -EPROTONOSUPPORT;
+#endif
+}
+
+static const struct bpf_func_proto bpf_tcp_raw_gen_syncookie_ipv6_proto = {
+	.func		= bpf_tcp_raw_gen_syncookie_ipv6,
+	.gpl_only	= true, /* __cookie_v6_init_sequence() is GPL */
+	.pkt_access	= true,
+	.ret_type	= RET_INTEGER,
+	.arg1_type	= ARG_PTR_TO_FIXED_SIZE_MEM,
+	.arg1_size	= sizeof(struct ipv6hdr),
+	.arg2_type	= ARG_PTR_TO_MEM,
+	.arg3_type	= ARG_CONST_SIZE,
+};
+
+BPF_CALL_2(bpf_tcp_raw_check_syncookie_ipv4, struct iphdr *, iph,
+	   struct tcphdr *, th)
+{
+	u32 cookie = ntohl(th->ack_seq) - 1;
+
+	if (__cookie_v4_check(iph, th, cookie) > 0)
+		return 0;
+
+	return -EACCES;
+}
+
+static const struct bpf_func_proto bpf_tcp_raw_check_syncookie_ipv4_proto = {
+	.func		= bpf_tcp_raw_check_syncookie_ipv4,
+	.gpl_only	= true, /* __cookie_v4_check is GPL */
+	.pkt_access	= true,
+	.ret_type	= RET_INTEGER,
+	.arg1_type	= ARG_PTR_TO_FIXED_SIZE_MEM,
+	.arg1_size	= sizeof(struct iphdr),
+	.arg2_type	= ARG_PTR_TO_FIXED_SIZE_MEM,
+	.arg2_size	= sizeof(struct tcphdr),
+};
+
+BPF_CALL_2(bpf_tcp_raw_check_syncookie_ipv6, struct ipv6hdr *, iph,
+	   struct tcphdr *, th)
+{
+#if IS_BUILTIN(CONFIG_IPV6)
+	u32 cookie = ntohl(th->ack_seq) - 1;
+
+	if (__cookie_v6_check(iph, th, cookie) > 0)
+		return 0;
+
+	return -EACCES;
+#else
+	return -EPROTONOSUPPORT;
+#endif
+}
+
+static const struct bpf_func_proto bpf_tcp_raw_check_syncookie_ipv6_proto = {
+	.func		= bpf_tcp_raw_check_syncookie_ipv6,
+	.gpl_only	= true, /* __cookie_v6_check is GPL */
+	.pkt_access	= true,
+	.ret_type	= RET_INTEGER,
+	.arg1_type	= ARG_PTR_TO_FIXED_SIZE_MEM,
+	.arg1_size	= sizeof(struct ipv6hdr),
+	.arg2_type	= ARG_PTR_TO_FIXED_SIZE_MEM,
+	.arg2_size	= sizeof(struct tcphdr),
+};
+#endif /* CONFIG_SYN_COOKIES */
+
 #endif /* CONFIG_INET */
 
 bool bpf_helper_changes_pkt_data(void *func)
@@ -7856,6 +7964,16 @@ xdp_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
 		return &bpf_tcp_check_syncookie_proto;
 	case BPF_FUNC_tcp_gen_syncookie:
 		return &bpf_tcp_gen_syncookie_proto;
+#ifdef CONFIG_SYN_COOKIES
+	case BPF_FUNC_tcp_raw_gen_syncookie_ipv4:
+		return &bpf_tcp_raw_gen_syncookie_ipv4_proto;
+	case BPF_FUNC_tcp_raw_gen_syncookie_ipv6:
+		return &bpf_tcp_raw_gen_syncookie_ipv6_proto;
+	case BPF_FUNC_tcp_raw_check_syncookie_ipv4:
+		return &bpf_tcp_raw_check_syncookie_ipv4_proto;
+	case BPF_FUNC_tcp_raw_check_syncookie_ipv6:
+		return &bpf_tcp_raw_check_syncookie_ipv6_proto;
+#endif
 #endif
 	default:
 		return bpf_sk_base_func_proto(func_id);
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 2e2a9ece9af2..6426f6a2e744 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -3967,7 +3967,7 @@ static bool smc_parse_options(const struct tcphdr *th,
 /* Try to parse the MSS option from the TCP header. Return 0 on failure, clamped
  * value on success.
  */
-static u16 tcp_parse_mss_option(const struct tcphdr *th, u16 user_mss)
+u16 tcp_parse_mss_option(const struct tcphdr *th, u16 user_mss)
 {
 	const unsigned char *ptr = (const unsigned char *)(th + 1);
 	int length = (th->doff * 4) - sizeof(struct tcphdr);
@@ -4006,6 +4006,7 @@ static u16 tcp_parse_mss_option(const struct tcphdr *th, u16 user_mss)
 	}
 	return mss;
 }
+EXPORT_SYMBOL_GPL(tcp_parse_mss_option);
 
 /* 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