mptcp: add allow_join_id0 in mptcp_out_options

This patch defined a new flag MPTCP_CAP_DENY_JOIN_ID0 for the third bit,
labeled "C" of the MP_CAPABLE option.

Add a new flag allow_join_id0 in struct mptcp_out_options. If this flag is
set, send out the MP_CAPABLE option with the flag MPTCP_CAP_DENY_JOIN_ID0.
Acked-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Geliang Tang <geliangtang@gmail.com>
Signed-off-by: Mat Martineau <mathew.j.martineau@linux.intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/mptcp.h

@@ -67,7 +67,8 @@ struct mptcp_out_options {
 	u8 backup;
 	u8 reset_reason:4,
 	   reset_transient:1,
-	   csum_reqd:1;
+	   csum_reqd:1,
+	   allow_join_id0:1;
 	u32 nonce;
 	u64 thmac;
 	u32 token;

net/mptcp/options.c

@@ -402,6 +402,7 @@ bool mptcp_syn_options(struct sock *sk, const struct sk_buff *skb,
 	if (subflow->request_mptcp) {
 		opts->suboptions = OPTION_MPTCP_MPC_SYN;
 		opts->csum_reqd = mptcp_is_checksum_enabled(sock_net(sk));
+		opts->allow_join_id0 = mptcp_allow_join_id0(sock_net(sk));
 		*size = TCPOLEN_MPTCP_MPC_SYN;
 		return true;
 	} else if (subflow->request_join) {
@@ -490,6 +491,7 @@ static bool mptcp_established_options_mp(struct sock *sk, struct sk_buff *skb,
 		opts->sndr_key = subflow->local_key;
 		opts->rcvr_key = subflow->remote_key;
 		opts->csum_reqd = READ_ONCE(msk->csum_enabled);
+		opts->allow_join_id0 = mptcp_allow_join_id0(sock_net(sk));
 
 		/* Section 3.1.
 		 * The MP_CAPABLE option is carried on the SYN, SYN/ACK, and ACK
@@ -827,6 +829,7 @@ bool mptcp_synack_options(const struct request_sock *req, unsigned int *size,
 		opts->suboptions = OPTION_MPTCP_MPC_SYNACK;
 		opts->sndr_key = subflow_req->local_key;
 		opts->csum_reqd = subflow_req->csum_reqd;
+		opts->allow_join_id0 = subflow_req->allow_join_id0;
 		*size = TCPOLEN_MPTCP_MPC_SYNACK;
 		pr_debug("subflow_req=%p, local_key=%llu",
 			 subflow_req, subflow_req->local_key);
@@ -1201,6 +1204,9 @@ void mptcp_write_options(__be32 *ptr, const struct tcp_sock *tp,
 		if (opts->csum_reqd)
 			flag |= MPTCP_CAP_CHECKSUM_REQD;
 
+		if (!opts->allow_join_id0)
+			flag |= MPTCP_CAP_DENY_JOIN_ID0;
+
 		*ptr++ = mptcp_option(MPTCPOPT_MP_CAPABLE, len,
 				      MPTCP_SUPPORTED_VERSION,
 				      flag);

net/mptcp/protocol.h

@@ -79,8 +79,9 @@
 #define MPTCP_VERSION_MASK	(0x0F)
 #define MPTCP_CAP_CHECKSUM_REQD	BIT(7)
 #define MPTCP_CAP_EXTENSIBILITY	BIT(6)
+#define MPTCP_CAP_DENY_JOIN_ID0	BIT(5)
 #define MPTCP_CAP_HMAC_SHA256	BIT(0)
-#define MPTCP_CAP_FLAG_MASK	(0x3F)
+#define MPTCP_CAP_FLAG_MASK	(0x1F)
 
 /* MPTCP DSS flags */
 #define MPTCP_DSS_DATA_FIN	BIT(4)
@@ -350,7 +351,8 @@ struct mptcp_subflow_request_sock {
 	u16	mp_capable : 1,
 		mp_join : 1,
 		backup : 1,
-		csum_reqd : 1;
+		csum_reqd : 1,
+		allow_join_id0 : 1;
 	u8	local_id;
 	u8	remote_id;
 	u64	local_key;

net/mptcp/subflow.c

@@ -109,6 +109,7 @@ static void subflow_init_req(struct request_sock *req, const struct sock *sk_lis
 	subflow_req->mp_capable = 0;
 	subflow_req->mp_join = 0;
 	subflow_req->csum_reqd = mptcp_is_checksum_enabled(sock_net(sk_listener));
+	subflow_req->allow_join_id0 = mptcp_allow_join_id0(sock_net(sk_listener));
 	subflow_req->msk = NULL;
 	mptcp_token_init_request(req);
 }