net/tcp: Add option for TCP-AO to (not) hash header

Provide setsockopt() key flag that makes TCP-AO exclude hashing TCP
header for peers that match the key. This is needed for interraction
with middleboxes that may change TCP options, see RFC5925 (9.2).
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/uapi/linux/tcp.h

@@ -367,6 +367,11 @@ struct tcp_diag_md5sig {
 #define TCP_AO_MAXKEYLEN	80
 
 #define TCP_AO_KEYF_IFINDEX	(1 << 0)	/* L3 ifindex for VRF */
+#define TCP_AO_KEYF_EXCLUDE_OPT	(1 << 1)	/* "Indicates whether TCP
+						 *  options other than TCP-AO
+						 *  are included in the MAC
+						 *  calculation"
+						 */
 
 struct tcp_ao_add { /* setsockopt(TCP_AO_ADD_KEY) */
 	struct __kernel_sockaddr_storage addr;	/* peer's address for the key */

net/ipv4/tcp_ao.c

@@ -562,7 +562,8 @@ int tcp_ao_hash_hdr(unsigned short int family, char *ao_hash,
 		WARN_ON_ONCE(1);
 		goto clear_hash;
 	}
-	if (tcp_ao_hash_header(&hp, th, false,
+	if (tcp_ao_hash_header(&hp, th,
+			       !!(key->keyflags & TCP_AO_KEYF_EXCLUDE_OPT),
 			       ao_hash, hash_offset, tcp_ao_maclen(key)))
 		goto clear_hash;
 	ahash_request_set_crypt(hp.req, NULL, hash_buf, 0);
@@ -610,7 +611,8 @@ int tcp_ao_hash_skb(unsigned short int family,
 		goto clear_hash;
 	if (tcp_ao_hash_pseudoheader(family, sk, skb, &hp, skb->len))
 		goto clear_hash;
-	if (tcp_ao_hash_header(&hp, th, false,
+	if (tcp_ao_hash_header(&hp, th,
+			       !!(key->keyflags & TCP_AO_KEYF_EXCLUDE_OPT),
 			       ao_hash, hash_offset, tcp_ao_maclen(key)))
 		goto clear_hash;
 	if (tcp_sigpool_hash_skb_data(&hp, skb, th->doff << 2))
@@ -1454,7 +1456,7 @@ static struct tcp_ao_info *setsockopt_ao_info(struct sock *sk)
 	return ERR_PTR(-ESOCKTNOSUPPORT);
 }
 
-#define TCP_AO_KEYF_ALL		(0)
+#define TCP_AO_KEYF_ALL		(TCP_AO_KEYF_EXCLUDE_OPT)
 
 static struct tcp_ao_key *tcp_ao_key_alloc(struct sock *sk,
 					   struct tcp_ao_add *cmd)