[PATCH bpf-next 09/10] bpf: Add a helper to issue timestamp cookies in XDP

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The new helper bpf_tcp_raw_gen_tscookie allows an XDP program to
generate timestamp cookies (to be used together with SYN cookies) which
encode different options set by the client in the SYN packet: SACK
support, ECN support, window scale. These options are encoded in lower
bits of the timestamp, which will be returned by the client in a
subsequent ACK packet. The format is the same used by synproxy.

Signed-off-by: Maxim Mikityanskiy <maximmi@xxxxxxxxxx>
Reviewed-by: Tariq Toukan <tariqt@xxxxxxxxxx>
---
 include/net/tcp.h              |  1 +
 include/uapi/linux/bpf.h       | 27 +++++++++++++++
 net/core/filter.c              | 38 +++++++++++++++++++++
 net/ipv4/syncookies.c          | 60 ++++++++++++++++++++++++++++++++++
 tools/include/uapi/linux/bpf.h | 27 +++++++++++++++
 5 files changed, 153 insertions(+)

diff --git a/include/net/tcp.h b/include/net/tcp.h
index 1cc96a225848..651820bef6a2 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -564,6 +564,7 @@ u32 __cookie_v4_init_sequence(const struct iphdr *iph, const struct tcphdr *th,
 			      u16 *mssp);
 __u32 cookie_v4_init_sequence(const struct sk_buff *skb, __u16 *mss);
 u64 cookie_init_timestamp(struct request_sock *req, u64 now);
+bool cookie_init_timestamp_raw(struct tcphdr *th, __be32 *tsval, __be32 *tsecr);
 bool cookie_timestamp_decode(const struct net *net,
 			     struct tcp_options_received *opt);
 bool cookie_ecn_ok(const struct tcp_options_received *opt,
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index e32f72077250..791790b41874 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -5053,6 +5053,32 @@ union bpf_attr {
  *
  *		**-EPROTONOSUPPORT** if the IP version is not 4 or 6 (or 6, but
  *		CONFIG_IPV6 is disabled).
+ *
+ * int bpf_tcp_raw_gen_tscookie(struct tcphdr *th, u32 th_len, __be32 *tsopt, u32 tsopt_len)
+ *	Description
+ *		Try to generate a timestamp cookie which encodes some of the
+ *		flags sent by the client in the SYN packet: SACK support, ECN
+ *		support, window scale. To be used with SYN cookies.
+ *
+ *		*th* points to the start of the TCP header of the client's SYN
+ *		packet, while *th_len* contains the length of the TCP header (at
+ *		least **sizeof**\ (**struct tcphdr**)).
+ *
+ *		*tsopt* points to the output location where to put the resulting
+ *		timestamp values: tsval and tsecr, in the format of the TCP
+ *		timestamp option.
+ *
+ *	Return
+ *		On success, 0.
+ *
+ *		On failure, the returned value is one of the following:
+ *
+ *		**-EINVAL** if the input arguments are invalid.
+ *
+ *		**-ENOENT** if the TCP header doesn't have the timestamp option.
+ *
+ *		**-EOPNOTSUPP** if the kernel configuration does not enable SYN
+ *		cookies (CONFIG_SYN_COOKIES is off).
  */
 #define __BPF_FUNC_MAPPER(FN)		\
 	FN(unspec),			\
@@ -5238,6 +5264,7 @@ union bpf_attr {
 	FN(ct_release),			\
 	FN(tcp_raw_gen_syncookie),	\
 	FN(tcp_raw_check_syncookie),	\
+	FN(tcp_raw_gen_tscookie),	\
 	/* */
 
 /* integer value in 'imm' field of BPF_CALL instruction selects which helper
diff --git a/net/core/filter.c b/net/core/filter.c
index 5f03d4a282a0..73fe20ef7442 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -7403,6 +7403,42 @@ static const struct bpf_func_proto bpf_tcp_raw_check_syncookie_proto = {
 	.arg4_type	= ARG_CONST_SIZE,
 };
 
+BPF_CALL_4(bpf_tcp_raw_gen_tscookie, struct tcphdr *, th, u32, th_len,
+	   __be32 *, tsopt, u32, tsopt_len)
+{
+	int err;
+
+#ifdef CONFIG_SYN_COOKIES
+	if (tsopt_len != sizeof(u64)) {
+		err = -EINVAL;
+		goto err_out;
+	}
+
+	if (!cookie_init_timestamp_raw(th, &tsopt[0], &tsopt[1])) {
+		err = -ENOENT;
+		goto err_out;
+	}
+
+	return 0;
+err_out:
+#else
+	err = -EOPNOTSUPP;
+#endif
+	memset(tsopt, 0, tsopt_len);
+	return err;
+}
+
+static const struct bpf_func_proto bpf_tcp_raw_gen_tscookie_proto = {
+	.func		= bpf_tcp_raw_gen_tscookie,
+	.gpl_only	= false,
+	.pkt_access	= true,
+	.ret_type	= RET_INTEGER,
+	.arg1_type	= ARG_PTR_TO_MEM,
+	.arg2_type	= ARG_CONST_SIZE,
+	.arg3_type	= ARG_PTR_TO_UNINIT_MEM,
+	.arg4_type	= ARG_CONST_SIZE,
+};
+
 #endif /* CONFIG_INET */
 
 bool bpf_helper_changes_pkt_data(void *func)
@@ -7825,6 +7861,8 @@ xdp_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
 		return &bpf_tcp_raw_gen_syncookie_proto;
 	case BPF_FUNC_tcp_raw_check_syncookie:
 		return &bpf_tcp_raw_check_syncookie_proto;
+	case BPF_FUNC_tcp_raw_gen_tscookie:
+		return &bpf_tcp_raw_gen_tscookie_proto;
 #endif
 	default:
 		return bpf_sk_base_func_proto(func_id);
diff --git a/net/ipv4/syncookies.c b/net/ipv4/syncookies.c
index 8696dc343ad2..4dd2c7a096eb 100644
--- a/net/ipv4/syncookies.c
+++ b/net/ipv4/syncookies.c
@@ -85,6 +85,66 @@ u64 cookie_init_timestamp(struct request_sock *req, u64 now)
 	return (u64)ts * (NSEC_PER_SEC / TCP_TS_HZ);
 }
 
+bool cookie_init_timestamp_raw(struct tcphdr *th, __be32 *tsval, __be32 *tsecr)
+{
+	int length = (th->doff * 4) - sizeof(*th);
+	u8 wscale = TS_OPT_WSCALE_MASK;
+	bool option_timestamp = false;
+	bool option_sack = false;
+	u32 cookie;
+	u8 *ptr;
+
+	ptr = (u8 *)(th + 1);
+
+	while (length > 0) {
+		u8 opcode = *ptr++;
+		u8 opsize;
+
+		if (opcode == TCPOPT_EOL)
+			break;
+		if (opcode == TCPOPT_NOP) {
+			length--;
+			continue;
+		}
+
+		if (length < 2)
+			break;
+		opsize = *ptr++;
+		if (opsize < 2)
+			break;
+		if (opsize > length)
+			break;
+
+		switch (opcode) {
+		case TCPOPT_WINDOW:
+			wscale = min_t(u8, *ptr, TCP_MAX_WSCALE);
+			break;
+		case TCPOPT_TIMESTAMP:
+			option_timestamp = true;
+			/* Client's tsval becomes our tsecr. */
+			*tsecr = cpu_to_be32(get_unaligned_be32(ptr));
+			break;
+		case TCPOPT_SACK_PERM:
+			option_sack = true;
+			break;
+		}
+
+		ptr += opsize - 2;
+		length -= opsize;
+	}
+
+	if (!option_timestamp)
+		return false;
+
+	cookie = tcp_time_stamp_raw() & ~TSMASK;
+	cookie |= wscale & TS_OPT_WSCALE_MASK;
+	if (option_sack)
+		cookie |= TS_OPT_SACK;
+	if (th->ece && th->cwr)
+		cookie |= TS_OPT_ECN;
+	*tsval = cpu_to_be32(cookie);
+	return true;
+}
 
 static __u32 secure_tcp_syn_cookie(__be32 saddr, __be32 daddr, __be16 sport,
 				   __be16 dport, __u32 sseq, __u32 data)
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index e32f72077250..791790b41874 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -5053,6 +5053,32 @@ union bpf_attr {
  *
  *		**-EPROTONOSUPPORT** if the IP version is not 4 or 6 (or 6, but
  *		CONFIG_IPV6 is disabled).
+ *
+ * int bpf_tcp_raw_gen_tscookie(struct tcphdr *th, u32 th_len, __be32 *tsopt, u32 tsopt_len)
+ *	Description
+ *		Try to generate a timestamp cookie which encodes some of the
+ *		flags sent by the client in the SYN packet: SACK support, ECN
+ *		support, window scale. To be used with SYN cookies.
+ *
+ *		*th* points to the start of the TCP header of the client's SYN
+ *		packet, while *th_len* contains the length of the TCP header (at
+ *		least **sizeof**\ (**struct tcphdr**)).
+ *
+ *		*tsopt* points to the output location where to put the resulting
+ *		timestamp values: tsval and tsecr, in the format of the TCP
+ *		timestamp option.
+ *
+ *	Return
+ *		On success, 0.
+ *
+ *		On failure, the returned value is one of the following:
+ *
+ *		**-EINVAL** if the input arguments are invalid.
+ *
+ *		**-ENOENT** if the TCP header doesn't have the timestamp option.
+ *
+ *		**-EOPNOTSUPP** if the kernel configuration does not enable SYN
+ *		cookies (CONFIG_SYN_COOKIES is off).
  */
 #define __BPF_FUNC_MAPPER(FN)		\
 	FN(unspec),			\
@@ -5238,6 +5264,7 @@ union bpf_attr {
 	FN(ct_release),			\
 	FN(tcp_raw_gen_syncookie),	\
 	FN(tcp_raw_check_syncookie),	\
+	FN(tcp_raw_gen_tscookie),	\
 	/* */
 
 /* integer value in 'imm' field of BPF_CALL instruction selects which helper
-- 
2.30.2




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