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>

Author: nvmmax

include/net/tcp.h

@@ -432,6 +432,7 @@ u16 tcp_v4_get_syncookie(struct sock *sk, struct iphdr *iph,
  struct tcphdr *th, u32 *cookie);
 u16 tcp_v6_get_syncookie(struct sock *sk, struct ipv6hdr *iph,
  struct tcphdr *th, u32 *cookie);
+u16 tcp_parse_mss_option(const struct tcphdr *th, u16 user_mss);
 u16 tcp_get_syncookie_mss(struct request_sock_ops *rsk_ops,
  const struct tcp_request_sock_ops *af_ops,
  struct sock *sk, struct tcphdr *th);

include/uapi/linux/bpf.h

@@ -5145,6 +5145,80 @@ union bpf_attr {
  *	The **hash_algo** is returned on success,
  *	**-EOPNOTSUP** if the hash calculation failed or **-EINVAL** if
  *	invalid arguments are passed.
+ *
+ * s64 bpf_tcp_raw_gen_syncookie_ipv4(struct iphdr *iph, struct tcphdr *th, u32 th_len)
+ *	Description
+ *	Try to issue a SYN cookie for the packet with corresponding
+ *	IPv4/TCP headers, *iph* and *th*, without depending on a
+ *	listening socket.
+ *
+ *	*iph* points to the IPv4 header.
+ *
+ *	*th* points to the start of the TCP header, while *th_len*
+ *	contains the length of the TCP header (at least
+ *	**sizeof**\ (**struct tcphdr**)).
+ *	Return
+ *	On success, lower 32 bits hold the generated SYN cookie in
+ *	followed by 16 bits which hold the MSS value for that cookie,
+ *	and the top 16 bits are unused.
+ *
+ *	On failure, the returned value is one of the following:
+ *
+ *	**-EINVAL** if *th_len* is invalid.
+ *
+ * s64 bpf_tcp_raw_gen_syncookie_ipv6(struct ipv6hdr *iph, struct tcphdr *th, u32 th_len)
+ *	Description
+ *	Try to issue a SYN cookie for the packet with corresponding
+ *	IPv6/TCP headers, *iph* and *th*, without depending on a
+ *	listening socket.
+ *
+ *	*iph* points to the IPv6 header.
+ *
+ *	*th* points to the start of the TCP header, while *th_len*
+ *	contains the length of the TCP header (at least
+ *	**sizeof**\ (**struct tcphdr**)).
+ *	Return
+ *	On success, lower 32 bits hold the generated SYN cookie in
+ *	followed by 16 bits which hold the MSS value for that cookie,
+ *	and the top 16 bits are unused.
+ *
+ *	On failure, the returned value is one of the following:
+ *
+ *	**-EINVAL** if *th_len* is invalid.
+ *
+ *	**-EPROTONOSUPPORT** if CONFIG_IPV6 is not builtin.
+ *
+ * int bpf_tcp_raw_check_syncookie_ipv4(struct iphdr *iph, struct tcphdr *th)
+ *	Description
+ *	Check whether *iph* and *th* contain a valid SYN cookie ACK
+ *	without depending on a listening socket.
+ *
+ *	*iph* points to the IPv4 header.
+ *
+ *	*th* points to the TCP header.
+ *	Return
+ *	0 if *iph* and *th* are a valid SYN cookie ACK.
+ *
+ *	On failure, the returned value is one of the following:
+ *
+ *	**-EACCES** if the SYN cookie is not valid.
+ *
+ * int bpf_tcp_raw_check_syncookie_ipv6(struct ipv6hdr *iph, struct tcphdr *th)
+ *	Description
+ *	Check whether *iph* and *th* contain a valid SYN cookie ACK
+ *	without depending on a listening socket.
+ *
+ *	*iph* points to the IPv6 header.
+ *
+ *	*th* points to the TCP header.
+ *	Return
+ *	0 if *iph* and *th* are a valid SYN cookie ACK.
+ *
+ *	On failure, the returned value is one of the following:
+ *
+ *	**-EACCES** if the SYN cookie is not valid.
+ *
+ *	**-EPROTONOSUPPORT** if CONFIG_IPV6 is not builtin.
  */
 #define __BPF_FUNC_MAPPER(FN)	\
 FN(unspec),	\
@@ -5341,6 +5415,10 @@ union bpf_attr {
 FN(copy_from_user_task),	\
 FN(skb_set_tstamp),	\
 FN(ima_file_hash),	\
+FN(tcp_raw_gen_syncookie_ipv4),	\
+FN(tcp_raw_gen_syncookie_ipv6),	\
+FN(tcp_raw_check_syncookie_ipv4),	\
+FN(tcp_raw_check_syncookie_ipv6),	\
 /* */
 
 /* integer value in 'imm' field of BPF_CALL instruction selects which helper

net/core/filter.c

@@ -7434,6 +7434,114 @@ 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_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_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_MEM,
+.arg1_size= sizeof(struct iphdr),
+.arg2_type= ARG_PTR_TO_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_MEM,
+.arg1_size= sizeof(struct ipv6hdr),
+.arg2_type= ARG_PTR_TO_MEM,
+.arg2_size= sizeof(struct tcphdr),
+};
+#endif /* CONFIG_SYN_COOKIES */
+
 #endif /* CONFIG_INET */
 
 bool bpf_helper_changes_pkt_data(void *func)
@@ -7846,6 +7954,16 @@ 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);

net/ipv4/tcp_input.c

@@ -3963,7 +3963,7 @@ 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);
@@ -4002,6 +4002,7 @@ 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

scripts/bpf_doc.py

@@ -633,6 +633,8 @@ def __init__(self, parser):
  'struct socket',
  'struct file',
  'struct bpf_timer',
+ 'struct iphdr',
+ 'struct ipv6hdr',
  ]
  known_types = {
  '...',
@@ -682,6 +684,8 @@ def __init__(self, parser):
  'struct socket',
  'struct file',
  'struct bpf_timer',
+ 'struct iphdr',
+ 'struct ipv6hdr',
  }
  mapped_types = {
  'u8': '__u8',

tools/include/uapi/linux/bpf.h

@@ -5145,6 +5145,80 @@ union bpf_attr {
  *	The **hash_algo** is returned on success,
  *	**-EOPNOTSUP** if the hash calculation failed or **-EINVAL** if
  *	invalid arguments are passed.
+ *
+ * s64 bpf_tcp_raw_gen_syncookie_ipv4(struct iphdr *iph, struct tcphdr *th, u32 th_len)
+ *	Description
+ *	Try to issue a SYN cookie for the packet with corresponding
+ *	IPv4/TCP headers, *iph* and *th*, without depending on a
+ *	listening socket.
+ *
+ *	*iph* points to the IPv4 header.
+ *
+ *	*th* points to the start of the TCP header, while *th_len*
+ *	contains the length of the TCP header (at least
+ *	**sizeof**\ (**struct tcphdr**)).
+ *	Return
+ *	On success, lower 32 bits hold the generated SYN cookie in
+ *	followed by 16 bits which hold the MSS value for that cookie,
+ *	and the top 16 bits are unused.
+ *
+ *	On failure, the returned value is one of the following:
+ *
+ *	**-EINVAL** if *th_len* is invalid.
+ *
+ * s64 bpf_tcp_raw_gen_syncookie_ipv6(struct ipv6hdr *iph, struct tcphdr *th, u32 th_len)
+ *	Description
+ *	Try to issue a SYN cookie for the packet with corresponding
+ *	IPv6/TCP headers, *iph* and *th*, without depending on a
+ *	listening socket.
+ *
+ *	*iph* points to the IPv6 header.
+ *
+ *	*th* points to the start of the TCP header, while *th_len*
+ *	contains the length of the TCP header (at least
+ *	**sizeof**\ (**struct tcphdr**)).
+ *	Return
+ *	On success, lower 32 bits hold the generated SYN cookie in
+ *	followed by 16 bits which hold the MSS value for that cookie,
+ *	and the top 16 bits are unused.
+ *
+ *	On failure, the returned value is one of the following:
+ *
+ *	**-EINVAL** if *th_len* is invalid.
+ *
+ *	**-EPROTONOSUPPORT** if CONFIG_IPV6 is not builtin.
+ *
+ * int bpf_tcp_raw_check_syncookie_ipv4(struct iphdr *iph, struct tcphdr *th)
+ *	Description
+ *	Check whether *iph* and *th* contain a valid SYN cookie ACK
+ *	without depending on a listening socket.
+ *
+ *	*iph* points to the IPv4 header.
+ *
+ *	*th* points to the TCP header.
+ *	Return
+ *	0 if *iph* and *th* are a valid SYN cookie ACK.
+ *
+ *	On failure, the returned value is one of the following:
+ *
+ *	**-EACCES** if the SYN cookie is not valid.
+ *
+ * int bpf_tcp_raw_check_syncookie_ipv6(struct ipv6hdr *iph, struct tcphdr *th)
+ *	Description
+ *	Check whether *iph* and *th* contain a valid SYN cookie ACK
+ *	without depending on a listening socket.
+ *
+ *	*iph* points to the IPv6 header.
+ *
+ *	*th* points to the TCP header.
+ *	Return
+ *	0 if *iph* and *th* are a valid SYN cookie ACK.
+ *
+ *	On failure, the returned value is one of the following:
+ *
+ *	**-EACCES** if the SYN cookie is not valid.
+ *
+ *	**-EPROTONOSUPPORT** if CONFIG_IPV6 is not builtin.
  */
 #define __BPF_FUNC_MAPPER(FN)	\
 FN(unspec),	\
@@ -5341,6 +5415,10 @@ union bpf_attr {
 FN(copy_from_user_task),	\
 FN(skb_set_tstamp),	\
 FN(ima_file_hash),	\
+FN(tcp_raw_gen_syncookie_ipv4),	\
+FN(tcp_raw_gen_syncookie_ipv6),	\
+FN(tcp_raw_check_syncookie_ipv4),	\
+FN(tcp_raw_check_syncookie_ipv6),	\
 /* */
 
 /* integer value in 'imm' field of BPF_CALL instruction selects which helper