mptcp: add csum_reqd in mptcp_out_options

This patch added a new member csum_reqd in struct mptcp_out_options and
struct mptcp_subflow_request_sock. Initialized it with the helper
function mptcp_is_checksum_enabled().

In mptcp_write_options, if this field is enabled, send out the MP_CAPABLE
suboption with the MPTCP_CAP_CHECKSUM_REQD flag.
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

@@ -64,8 +64,9 @@ struct mptcp_out_options {
 	struct mptcp_rm_list rm_list;
 	u8 join_id;
 	u8 backup;
-	u8 reset_reason:4;
-	u8 reset_transient:1;
+	u8 reset_reason:4,
+	   reset_transient:1,
+	   csum_reqd:1;
 	u32 nonce;
 	u64 thmac;
 	u32 token;

net/mptcp/options.c

@@ -380,6 +380,7 @@ bool mptcp_syn_options(struct sock *sk, const struct sk_buff *skb,
 	subflow->snd_isn = TCP_SKB_CB(skb)->end_seq;
 	if (subflow->request_mptcp) {
 		opts->suboptions = OPTION_MPTCP_MPC_SYN;
+		opts->csum_reqd = mptcp_is_checksum_enabled(sock_net(sk));
 		*size = TCPOLEN_MPTCP_MPC_SYN;
 		return true;
 	} else if (subflow->request_join) {
@@ -435,6 +436,7 @@ static bool mptcp_established_options_mp(struct sock *sk, struct sk_buff *skb,
 					 struct mptcp_out_options *opts)
 {
 	struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(sk);
+	struct mptcp_sock *msk = mptcp_sk(subflow->conn);
 	struct mptcp_ext *mpext;
 	unsigned int data_len;
 
@@ -465,6 +467,7 @@ static bool mptcp_established_options_mp(struct sock *sk, struct sk_buff *skb,
 		opts->suboptions = OPTION_MPTCP_MPC_ACK;
 		opts->sndr_key = subflow->local_key;
 		opts->rcvr_key = subflow->remote_key;
+		opts->csum_reqd = READ_ONCE(msk->csum_enabled);
 
 		/* Section 3.1.
 		 * The MP_CAPABLE option is carried on the SYN, SYN/ACK, and ACK
@@ -789,6 +792,7 @@ bool mptcp_synack_options(const struct request_sock *req, unsigned int *size,
 	if (subflow_req->mp_capable) {
 		opts->suboptions = OPTION_MPTCP_MPC_SYNACK;
 		opts->sndr_key = subflow_req->local_key;
+		opts->csum_reqd = subflow_req->csum_reqd;
 		*size = TCPOLEN_MPTCP_MPC_SYNACK;
 		pr_debug("subflow_req=%p, local_key=%llu",
 			 subflow_req, subflow_req->local_key);
@@ -1123,7 +1127,7 @@ void mptcp_write_options(__be32 *ptr, const struct tcp_sock *tp,
 {
 	if ((OPTION_MPTCP_MPC_SYN | OPTION_MPTCP_MPC_SYNACK |
 	     OPTION_MPTCP_MPC_ACK) & opts->suboptions) {
-		u8 len;
+		u8 len, flag = MPTCP_CAP_HMAC_SHA256;
 
 		if (OPTION_MPTCP_MPC_SYN & opts->suboptions)
 			len = TCPOLEN_MPTCP_MPC_SYN;
@@ -1134,9 +1138,12 @@ void mptcp_write_options(__be32 *ptr, const struct tcp_sock *tp,
 		else
 			len = TCPOLEN_MPTCP_MPC_ACK;
 
+		if (opts->csum_reqd)
+			flag |= MPTCP_CAP_CHECKSUM_REQD;
+
 		*ptr++ = mptcp_option(MPTCPOPT_MP_CAPABLE, len,
 				      MPTCP_SUPPORTED_VERSION,
-				      MPTCP_CAP_HMAC_SHA256);
+				      flag);
 
 		if (!((OPTION_MPTCP_MPC_SYNACK | OPTION_MPTCP_MPC_ACK) &
 		    opts->suboptions))

net/mptcp/protocol.h

@@ -347,7 +347,8 @@ struct mptcp_subflow_request_sock {
 	struct	tcp_request_sock sk;
 	u16	mp_capable : 1,
 		mp_join : 1,
-		backup : 1;
+		backup : 1,
+		csum_reqd : 1;
 	u8	local_id;
 	u8	remote_id;
 	u64	local_key;

net/mptcp/subflow.c

@@ -108,6 +108,7 @@ 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->msk = NULL;
 	mptcp_token_init_request(req);
 }