net/tcp: Sign SYN-ACK segments with TCP-AO

Similarly to RST segments, wire SYN-ACKs to TCP-AO.
tcp_rsk_used_ao() is handy here to check if the request socket used AO
and needs a signature on the outgoing segments.

Co-developed-by: Francesco Ruggeri <fruggeri@arista.com>
Signed-off-by: Francesco Ruggeri <fruggeri@arista.com>
Co-developed-by: Salam Noureddine <noureddine@arista.com>
Signed-off-by: Salam Noureddine <noureddine@arista.com>
Signed-off-by: Dmitry Safonov <dima@arista.com>
Acked-by: David Ahern <dsahern@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/tcp.h

@@ -2221,6 +2221,9 @@ struct tcp_request_sock_ops {
 					struct request_sock *req,
 					int sndid, int rcvid);
 	int (*ao_calc_key)(struct tcp_ao_key *mkt, u8 *key, struct request_sock *sk);
+	int (*ao_synack_hash)(char *ao_hash, struct tcp_ao_key *mkt,
+			      struct request_sock *req, const struct sk_buff *skb,
+			      int hash_offset, u32 sne);
 #endif
 #ifdef CONFIG_SYN_COOKIES
 	__u32 (*cookie_init_seq)(const struct sk_buff *skb,

include/net/tcp_ao.h

@@ -147,6 +147,9 @@ int tcp_ao_prepare_reset(const struct sock *sk, struct sk_buff *skb,
 int tcp_v4_parse_ao(struct sock *sk, int cmd, sockptr_t optval, int optlen);
 struct tcp_ao_key *tcp_v4_ao_lookup(const struct sock *sk, struct sock *addr_sk,
 				    int sndid, int rcvid);
+int tcp_v4_ao_synack_hash(char *ao_hash, struct tcp_ao_key *mkt,
+			  struct request_sock *req, const struct sk_buff *skb,
+			  int hash_offset, u32 sne);
 int tcp_v4_ao_calc_key_sk(struct tcp_ao_key *mkt, u8 *key,
 			  const struct sock *sk,
 			  __be32 sisn, __be32 disn, bool send);
@@ -181,6 +184,9 @@ int tcp_v6_ao_hash_skb(char *ao_hash, struct tcp_ao_key *key,
 		       const struct sock *sk, const struct sk_buff *skb,
 		       const u8 *tkey, int hash_offset, u32 sne);
 int tcp_v6_parse_ao(struct sock *sk, int cmd, sockptr_t optval, int optlen);
+int tcp_v6_ao_synack_hash(char *ao_hash, struct tcp_ao_key *ao_key,
+			  struct request_sock *req, const struct sk_buff *skb,
+			  int hash_offset, u32 sne);
 void tcp_ao_established(struct sock *sk);
 void tcp_ao_finish_connect(struct sock *sk, struct sk_buff *skb);
 void tcp_ao_connect_init(struct sock *sk);

net/ipv4/tcp_ao.c

@@ -568,6 +568,28 @@ int tcp_v4_ao_hash_skb(char *ao_hash, struct tcp_ao_key *key,
 			       tkey, hash_offset, sne);
 }
 
+int tcp_v4_ao_synack_hash(char *ao_hash, struct tcp_ao_key *ao_key,
+			  struct request_sock *req, const struct sk_buff *skb,
+			  int hash_offset, u32 sne)
+{
+	void *hash_buf = NULL;
+	int err;
+
+	hash_buf = kmalloc(tcp_ao_digest_size(ao_key), GFP_ATOMIC);
+	if (!hash_buf)
+		return -ENOMEM;
+
+	err = tcp_v4_ao_calc_key_rsk(ao_key, hash_buf, req);
+	if (err)
+		goto out;
+
+	err = tcp_ao_hash_skb(AF_INET, ao_hash, ao_key, req_to_sk(req), skb,
+			      hash_buf, hash_offset, sne);
+out:
+	kfree(hash_buf);
+	return err;
+}
+
 struct tcp_ao_key *tcp_v4_ao_lookup_rsk(const struct sock *sk,
 					struct request_sock *req,
 					int sndid, int rcvid)

net/ipv4/tcp_ipv4.c

@@ -1681,6 +1681,7 @@ const struct tcp_request_sock_ops tcp_request_sock_ipv4_ops = {
 #ifdef CONFIG_TCP_AO
 	.ao_lookup	=	tcp_v4_ao_lookup_rsk,
 	.ao_calc_key	=	tcp_v4_ao_calc_key_rsk,
+	.ao_synack_hash	=	tcp_v4_ao_synack_hash,
 #endif
 #ifdef CONFIG_SYN_COOKIES
 	.cookie_init_seq =	cookie_v4_init_sequence,

net/ipv4/tcp_output.c

@@ -886,7 +886,7 @@ static unsigned int tcp_synack_options(const struct sock *sk,
 				       struct request_sock *req,
 				       unsigned int mss, struct sk_buff *skb,
 				       struct tcp_out_options *opts,
-				       const struct tcp_md5sig_key *md5,
+				       const struct tcp_key *key,
 				       struct tcp_fastopen_cookie *foc,
 				       enum tcp_synack_type synack_type,
 				       struct sk_buff *syn_skb)
@@ -894,8 +894,7 @@ static unsigned int tcp_synack_options(const struct sock *sk,
 	struct inet_request_sock *ireq = inet_rsk(req);
 	unsigned int remaining = MAX_TCP_OPTION_SPACE;
 
-#ifdef CONFIG_TCP_MD5SIG
+	if (tcp_key_is_md5(key)) {
-	if (md5) {
 		opts->options |= OPTION_MD5;
 		remaining -= TCPOLEN_MD5SIG_ALIGNED;
 
@@ -906,8 +905,11 @@ static unsigned int tcp_synack_options(const struct sock *sk,
 		 */
 		if (synack_type != TCP_SYNACK_COOKIE)
 			ireq->tstamp_ok &= !ireq->sack_ok;
+	} else if (tcp_key_is_ao(key)) {
+		opts->options |= OPTION_AO;
+		remaining -= tcp_ao_len(key->ao_key);
+		ireq->tstamp_ok &= !ireq->sack_ok;
 	}
-#endif
 
 	/* We always send an MSS option. */
 	opts->mss = mss;
@@ -3653,7 +3655,6 @@ struct sk_buff *tcp_make_synack(const struct sock *sk, struct dst_entry *dst,
 {
 	struct inet_request_sock *ireq = inet_rsk(req);
 	const struct tcp_sock *tp = tcp_sk(sk);
-	struct tcp_md5sig_key *md5 = NULL;
 	struct tcp_out_options opts;
 	struct tcp_key key = {};
 	struct sk_buff *skb;
@@ -3707,18 +3708,48 @@ struct sk_buff *tcp_make_synack(const struct sock *sk, struct dst_entry *dst,
 			tcp_rsk(req)->snt_synack = tcp_skb_timestamp_us(skb);
 	}
 
-#ifdef CONFIG_TCP_MD5SIG
+#if defined(CONFIG_TCP_MD5SIG) || defined(CONFIG_TCP_AO)
 	rcu_read_lock();
-	md5 = tcp_rsk(req)->af_specific->req_md5_lookup(sk, req_to_sk(req));
-	if (md5)
-		key.type = TCP_KEY_MD5;
 #endif
+	if (tcp_rsk_used_ao(req)) {
+#ifdef CONFIG_TCP_AO
+		struct tcp_ao_key *ao_key = NULL;
+		u8 maclen = tcp_rsk(req)->maclen;
+		u8 keyid = tcp_rsk(req)->ao_keyid;
+
+		ao_key = tcp_sk(sk)->af_specific->ao_lookup(sk, req_to_sk(req),
+							    keyid, -1);
+		/* If there is no matching key - avoid sending anything,
+		 * especially usigned segments. It could try harder and lookup
+		 * for another peer-matching key, but the peer has requested
+		 * ao_keyid (RFC5925 RNextKeyID), so let's keep it simple here.
+		 */
+		if (unlikely(!ao_key || tcp_ao_maclen(ao_key) != maclen)) {
+			u8 key_maclen = ao_key ? tcp_ao_maclen(ao_key) : 0;
+
+			rcu_read_unlock();
+			kfree_skb(skb);
+			net_warn_ratelimited("TCP-AO: the keyid %u with maclen %u|%u from SYN packet is not present - not sending SYNACK\n",
+					     keyid, maclen, key_maclen);
+			return NULL;
+		}
+		key.ao_key = ao_key;
+		key.type = TCP_KEY_AO;
+#endif
+	} else {
+#ifdef CONFIG_TCP_MD5SIG
+		key.md5_key = tcp_rsk(req)->af_specific->req_md5_lookup(sk,
+					req_to_sk(req));
+		if (key.md5_key)
+			key.type = TCP_KEY_MD5;
+#endif
+	}
 	skb_set_hash(skb, READ_ONCE(tcp_rsk(req)->txhash), PKT_HASH_TYPE_L4);
 	/* bpf program will be interested in the tcp_flags */
 	TCP_SKB_CB(skb)->tcp_flags = TCPHDR_SYN | TCPHDR_ACK;
-	tcp_header_size = tcp_synack_options(sk, req, mss, skb, &opts, md5,
+	tcp_header_size = tcp_synack_options(sk, req, mss, skb, &opts,
-					     foc, synack_type,
+					     &key, foc, synack_type, syn_skb)
-					     syn_skb) + sizeof(*th);
+					+ sizeof(*th);
 
 	skb_push(skb, tcp_header_size);
 	skb_reset_transport_header(skb);
@@ -3738,15 +3769,24 @@ struct sk_buff *tcp_make_synack(const struct sock *sk, struct dst_entry *dst,
 
 	/* RFC1323: The window in SYN & SYN/ACK segments is never scaled. */
 	th->window = htons(min(req->rsk_rcv_wnd, 65535U));
-	tcp_options_write(th, NULL, NULL, &opts, &key);
+	tcp_options_write(th, NULL, tcp_rsk(req), &opts, &key);
 	th->doff = (tcp_header_size >> 2);
 	TCP_INC_STATS(sock_net(sk), TCP_MIB_OUTSEGS);
 
-#ifdef CONFIG_TCP_MD5SIG
 	/* Okay, we have all we need - do the md5 hash if needed */
-	if (md5)
+	if (tcp_key_is_md5(&key)) {
+#ifdef CONFIG_TCP_MD5SIG
 		tcp_rsk(req)->af_specific->calc_md5_hash(opts.hash_location,
-					       md5, req_to_sk(req), skb);
+					key.md5_key, req_to_sk(req), skb);
+#endif
+	} else if (tcp_key_is_ao(&key)) {
+#ifdef CONFIG_TCP_AO
+		tcp_rsk(req)->af_specific->ao_synack_hash(opts.hash_location,
+					key.ao_key, req, skb,
+					opts.hash_location - (u8 *)th, 0);
+#endif
+	}
+#if defined(CONFIG_TCP_MD5SIG) || defined(CONFIG_TCP_AO)
 	rcu_read_unlock();
 #endif
 

net/ipv6/tcp_ao.c

@@ -144,3 +144,25 @@ int tcp_v6_parse_ao(struct sock *sk, int cmd,
 {
 	return tcp_parse_ao(sk, cmd, AF_INET6, optval, optlen);
 }
+
+int tcp_v6_ao_synack_hash(char *ao_hash, struct tcp_ao_key *ao_key,
+			  struct request_sock *req, const struct sk_buff *skb,
+			  int hash_offset, u32 sne)
+{
+	void *hash_buf = NULL;
+	int err;
+
+	hash_buf = kmalloc(tcp_ao_digest_size(ao_key), GFP_ATOMIC);
+	if (!hash_buf)
+		return -ENOMEM;
+
+	err = tcp_v6_ao_calc_key_rsk(ao_key, hash_buf, req);
+	if (err)
+		goto out;
+
+	err = tcp_ao_hash_skb(AF_INET6, ao_hash, ao_key, req_to_sk(req), skb,
+			      hash_buf, hash_offset, sne);
+out:
+	kfree(hash_buf);
+	return err;
+}

net/ipv6/tcp_ipv6.c

@@ -839,6 +839,7 @@ const struct tcp_request_sock_ops tcp_request_sock_ipv6_ops = {
 #ifdef CONFIG_TCP_AO
 	.ao_lookup	=	tcp_v6_ao_lookup_rsk,
 	.ao_calc_key	=	tcp_v6_ao_calc_key_rsk,
+	.ao_synack_hash =	tcp_v6_ao_synack_hash,
 #endif
 #ifdef CONFIG_SYN_COOKIES
 	.cookie_init_seq =	cookie_v6_init_sequence,