tcp: ipv4: Add AO signing for skb-less replies

The code in tcp_v4_send_ack and tcp_v4_send_reset does not allocate a
full skb so special handling is required for tcp-authopt handling.

Signed-off-by: Leonard Crestez <cdleonard@gmail.com>

net/ipv4/tcp_ipv4.c

@@ -646,6 +646,46 @@ void tcp_v4_send_check(struct sock *sk, struct sk_buff *skb)
 }
 EXPORT_SYMBOL(tcp_v4_send_check);
 
+#ifdef CONFIG_TCP_AUTHOPT
+/** tcp_v4_authopt_handle_reply - Insert TCPOPT_AUTHOPT if required
+ *
+ * returns number of bytes (always aligned to 4) or zero
+ */
+static int tcp_v4_authopt_handle_reply(const struct sock *sk,
+				       struct sk_buff *skb,
+				       __be32 *optptr,
+				       struct tcphdr *th)
+{
+	struct tcp_authopt_info *info;
+	struct tcp_authopt_key_info *key_info;
+	u8 rnextkeyid;
+
+	if (sk->sk_state == TCP_TIME_WAIT)
+		info = tcp_twsk(sk)->tw_authopt_info;
+	else
+		info = tcp_sk(sk)->authopt_info;
+	if (!info)
+		return 0;
+	key_info = __tcp_authopt_select_key(sk, info, sk, &rnextkeyid);
+	if (!key_info)
+		return 0;
+	*optptr = htonl((TCPOPT_AUTHOPT << 24) |
+			(TCPOLEN_AUTHOPT_OUTPUT << 16) |
+			(key_info->send_id << 8) |
+			(rnextkeyid));
+	/* must update doff before signature computation */
+	th->doff += TCPOLEN_AUTHOPT_OUTPUT / 4;
+	tcp_v4_authopt_hash_reply((char *)(optptr + 1),
+				  info,
+				  key_info,
+				  ip_hdr(skb)->daddr,
+				  ip_hdr(skb)->saddr,
+				  th);
+
+	return TCPOLEN_AUTHOPT_OUTPUT;
+}
+#endif
+
 /*
  *	This routine will send an RST to the other tcp.
  *
@@ -661,6 +701,8 @@ EXPORT_SYMBOL(tcp_v4_send_check);
 
 #ifdef CONFIG_TCP_MD5SIG
 #define OPTION_BYTES TCPOLEN_MD5SIG_ALIGNED
+#elif defined(OPTION_BYTES_TCP_AUTHOPT)
+#define OPTION_BYTES TCPOLEN_AUTHOPT_OUTPUT
 #else
 #define OPTION_BYTES sizeof(__be32)
 #endif
@@ -714,8 +756,25 @@ static void tcp_v4_send_reset(const struct sock *sk, struct sk_buff *skb)
 	arg.iov[0].iov_len  = sizeof(rep.th);
 
 	net = sk ? sock_net(sk) : dev_net(skb_dst(skb)->dev);
-#ifdef CONFIG_TCP_MD5SIG
+#if defined(CONFIG_TCP_MD5SIG) || defined(CONFIG_TCP_AUTHOPT)
 	rcu_read_lock();
+#endif
+#ifdef CONFIG_TCP_AUTHOPT
+	/* Unlike TCP-MD5 the signatures for TCP-AO depend on initial sequence
+	 * numbers so we can only handle established and time-wait sockets.
+	 */
+	if (tcp_authopt_needed && sk &&
+	    sk->sk_state != TCP_NEW_SYN_RECV &&
+	    sk->sk_state != TCP_LISTEN) {
+		int tcp_authopt_ret = tcp_v4_authopt_handle_reply(sk, skb, rep.opt, &rep.th);
+
+		if (tcp_authopt_ret) {
+			arg.iov[0].iov_len += tcp_authopt_ret;
+			goto skip_md5sig;
+		}
+	}
+#endif
+#ifdef CONFIG_TCP_MD5SIG
 	hash_location = tcp_parse_md5sig_option(th);
 	if (sk && sk_fullsock(sk)) {
 		const union tcp_md5_addr *addr;
@@ -757,7 +816,6 @@ static void tcp_v4_send_reset(const struct sock *sk, struct sk_buff *skb)
 		if (!key)
 			goto out;
 
-
 		genhash = tcp_v4_md5_hash_skb(newhash, key, NULL, skb);
 		if (genhash || memcmp(hash_location, newhash, 16) != 0)
 			goto out;
@@ -777,6 +835,9 @@ static void tcp_v4_send_reset(const struct sock *sk, struct sk_buff *skb)
 				     key, ip_hdr(skb)->saddr,
 				     ip_hdr(skb)->daddr, &rep.th);
 	}
+#endif
+#ifdef CONFIG_TCP_AUTHOPT
+skip_md5sig:
 #endif
 	/* Can't co-exist with TCPMD5, hence check rep.opt[0] */
 	if (rep.opt[0] == 0) {
@@ -830,8 +891,10 @@ static void tcp_v4_send_reset(const struct sock *sk, struct sk_buff *skb)
 	__TCP_INC_STATS(net, TCP_MIB_OUTRSTS);
 	local_bh_enable();
 
-#ifdef CONFIG_TCP_MD5SIG
+#if defined(CONFIG_TCP_MD5SIG)
 out:
+#endif
+#if defined(CONFIG_TCP_MD5SIG) || defined(CONFIG_TCP_AUTHOPT)
 	rcu_read_unlock();
 #endif
 }
@@ -852,6 +915,8 @@ static void tcp_v4_send_ack(const struct sock *sk,
 		__be32 opt[(TCPOLEN_TSTAMP_ALIGNED >> 2)
 #ifdef CONFIG_TCP_MD5SIG
 			   + (TCPOLEN_MD5SIG_ALIGNED >> 2)
+#elif defined(CONFIG_TCP_AUTHOPT)
+			   + (TCPOLEN_AUTHOPT_OUTPUT >> 2)
 #endif
 			];
 	} rep;
@@ -883,6 +948,17 @@ static void tcp_v4_send_ack(const struct sock *sk,
 	rep.th.ack     = 1;
 	rep.th.window  = htons(win);
 
+#ifdef CONFIG_TCP_AUTHOPT
+	if (tcp_authopt_needed) {
+		int aoret, offset = (tsecr) ? 3 : 0;
+
+		aoret = tcp_v4_authopt_handle_reply(sk, skb, &rep.opt[offset], &rep.th);
+		if (aoret) {
+			arg.iov[0].iov_len += aoret;
+			key = NULL;
+		}
+	}
+#endif
 #ifdef CONFIG_TCP_MD5SIG
 	if (key) {
 		int offset = (tsecr) ? 3 : 0;