net/tcp: Add tcp_parse_auth_options()

Introduce a helper that:
(1) shares the common code with TCP-MD5 header options parsing
(2) looks for hash signature only once for both TCP-MD5 and TCP-AO
(3) fails with -EEXIST if any TCP sign option is present twice, see
    RFC5925 (2.2):
    ">> A single TCP segment MUST NOT have more than one TCP-AO in its
    options sequence. When multiple TCP-AOs appear, TCP MUST discard
    the segment."

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>

3 files changed, 41 insertions, 16 deletions

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index b6faee8a1e67..369e2a41bc1b 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -4398,7 +4398,8 @@ tcp_inbound_md5_hash(const struct sock *sk, const struct sk_buff *skb,
 	l3index = sdif ? dif : 0;
 
 	hash_expected = tcp_md5_do_lookup(sk, l3index, saddr, family);
-	hash_location = tcp_parse_md5sig_option(th);
+	if (tcp_parse_auth_options(th, &hash_location, NULL))
+		return SKB_DROP_REASON_TCP_AUTH_HDR;
 
 	/* We've parsed the options - do we have a hash? */
 	if (!hash_expected && !hash_location)
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 6ee0342b5338..fc42b172abf6 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -4255,39 +4255,58 @@ static bool tcp_fast_parse_options(const struct net *net,
 	return true;
 }
 
-#ifdef CONFIG_TCP_MD5SIG
+#if defined(CONFIG_TCP_MD5SIG) || defined(CONFIG_TCP_AO)
 /*
- * Parse MD5 Signature option
+ * Parse Signature options
  */
-const u8 *tcp_parse_md5sig_option(const struct tcphdr *th)
+int tcp_do_parse_auth_options(const struct tcphdr *th,
+			      const u8 **md5_hash, const u8 **ao_hash)
 {
 	int length = (th->doff << 2) - sizeof(*th);
 	const u8 *ptr = (const u8 *)(th + 1);
+	unsigned int minlen = TCPOLEN_MD5SIG;
+
+	if (IS_ENABLED(CONFIG_TCP_AO))
+		minlen = sizeof(struct tcp_ao_hdr) + 1;
+
+	*md5_hash = NULL;
+	*ao_hash = NULL;
 
 	/* If not enough data remaining, we can short cut */
-	while (length >= TCPOLEN_MD5SIG) {
+	while (length >= minlen) {
 		int opcode = *ptr++;
 		int opsize;
 
 		switch (opcode) {
 		case TCPOPT_EOL:
-			return NULL;
+			return 0;
 		case TCPOPT_NOP:
 			length--;
 			continue;
 		default:
 			opsize = *ptr++;
 			if (opsize < 2 || opsize > length)
-				return NULL;
-			if (opcode == TCPOPT_MD5SIG)
-				return opsize == TCPOLEN_MD5SIG ? ptr : NULL;
+				return -EINVAL;
+			if (opcode == TCPOPT_MD5SIG) {
+				if (opsize != TCPOLEN_MD5SIG)
+					return -EINVAL;
+				if (unlikely(*md5_hash || *ao_hash))
+					return -EEXIST;
+				*md5_hash = ptr;
+			} else if (opcode == TCPOPT_AO) {
+				if (opsize <= sizeof(struct tcp_ao_hdr))
+					return -EINVAL;
+				if (unlikely(*md5_hash || *ao_hash))
+					return -EEXIST;
+				*ao_hash = ptr;
+			}
 		}
 		ptr += opsize - 2;
 		length -= opsize;
 	}
-	return NULL;
+	return 0;
 }
-EXPORT_SYMBOL(tcp_parse_md5sig_option);
+EXPORT_SYMBOL(tcp_do_parse_auth_options);
 #endif
 
 /* Sorry, PAWS as specified is broken wrt. pure-ACKs -DaveM
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index b002f6497d19..83e069d0f778 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -670,7 +670,9 @@ EXPORT_SYMBOL(tcp_v4_send_check);
  *	Exception: precedence violation. We do not implement it in any case.
  */
 
-#ifdef CONFIG_TCP_MD5SIG
+#ifdef CONFIG_TCP_AO
+#define OPTION_BYTES MAX_TCP_OPTION_SPACE
+#elif defined(CONFIG_TCP_MD5SIG)
 #define OPTION_BYTES TCPOLEN_MD5SIG_ALIGNED
 #else
 #define OPTION_BYTES sizeof(__be32)
@@ -685,8 +687,8 @@ static void tcp_v4_send_reset(const struct sock *sk, struct sk_buff *skb)
 	} rep;
 	struct ip_reply_arg arg;
 #ifdef CONFIG_TCP_MD5SIG
+	const __u8 *md5_hash_location = NULL;
 	struct tcp_md5sig_key *key = NULL;
-	const __u8 *hash_location = NULL;
 	unsigned char newhash[16];
 	int genhash;
 	struct sock *sk1 = NULL;
@@ -727,8 +729,11 @@ static void tcp_v4_send_reset(const struct sock *sk, struct sk_buff *skb)
 
 	net = sk ? sock_net(sk) : dev_net(skb_dst(skb)->dev);
 #ifdef CONFIG_TCP_MD5SIG
+	/* Invalid TCP option size or twice included auth */
+	if (tcp_parse_auth_options(tcp_hdr(skb), &md5_hash_location, NULL))
+		return;
+
 	rcu_read_lock();
-	hash_location = tcp_parse_md5sig_option(th);
 	if (sk && sk_fullsock(sk)) {
 		const union tcp_md5_addr *addr;
 		int l3index;
@@ -739,7 +744,7 @@ static void tcp_v4_send_reset(const struct sock *sk, struct sk_buff *skb)
 		l3index = tcp_v4_sdif(skb) ? inet_iif(skb) : 0;
 		addr = (union tcp_md5_addr *)&ip_hdr(skb)->saddr;
 		key = tcp_md5_do_lookup(sk, l3index, addr, AF_INET);
-	} else if (hash_location) {
+	} else if (md5_hash_location) {
 		const union tcp_md5_addr *addr;
 		int sdif = tcp_v4_sdif(skb);
 		int dif = inet_iif(skb);
@@ -771,7 +776,7 @@ static void tcp_v4_send_reset(const struct sock *sk, struct sk_buff *skb)
 
 
 		genhash = tcp_v4_md5_hash_skb(newhash, key, NULL, skb);
-		if (genhash || memcmp(hash_location, newhash, 16) != 0)
+		if (genhash || memcmp(md5_hash_location, newhash, 16) != 0)
 			goto out;
 
 	}