diff --git a/include/net/mptcp.h b/include/net/mptcp.h
index 8f86c05ddbfd6..bd272c34b53c0 100644
--- a/include/net/mptcp.h
+++ b/include/net/mptcp.h
@@ -32,7 +32,8 @@ struct mptcp_ext {
 			mpc_map:1,
 			frozen:1,
 			reset_transient:1;
-	u8		reset_reason:4;
+	u8		reset_reason:4,
+			csum_reqd:1;
 };
 
 #define MPTCP_RM_IDS_MAX	8
diff --git a/net/mptcp/options.c b/net/mptcp/options.c
index b86777b2b505f..1f267b34d78ed 100644
--- a/net/mptcp/options.c
+++ b/net/mptcp/options.c
@@ -37,17 +37,31 @@ static void mptcp_parse_option(const struct sock *sk,
 	case MPTCPOPT_MP_CAPABLE:
 		/* strict size checking */
 		if (!(TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN)) {
-			if (skb->len > tcp_hdr(skb)->doff << 2)
+			if (skb->len > tcp_hdr(skb)->doff << 2) {
 				expected_opsize = TCPOLEN_MPTCP_MPC_ACK_DATA;
-			else
+			} else {
 				expected_opsize = TCPOLEN_MPTCP_MPC_ACK;
+			}
 		} else {
 			if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_ACK)
 				expected_opsize = TCPOLEN_MPTCP_MPC_SYNACK;
 			else
 				expected_opsize = TCPOLEN_MPTCP_MPC_SYN;
 		}
-		if (opsize != expected_opsize)
+
+		/* Cfr RFC 8684 Section 3.3.0:
+		 * If a checksum is present but its use had
+		 * not been negotiated in the MP_CAPABLE handshake, the receiver MUST
+		 * close the subflow with a RST, as it is not behaving as negotiated.
+		 * If a checksum is not present when its use has been negotiated, the
+		 * receiver MUST close the subflow with a RST, as it is considered
+		 * broken
+		 * We parse even option with mismatching csum presence, so that
+		 * later in subflow_data_ready we can trigger the reset.
+		 */
+		if (opsize != expected_opsize &&
+		    (expected_opsize != TCPOLEN_MPTCP_MPC_ACK_DATA ||
+		     opsize != TCPOLEN_MPTCP_MPC_ACK_DATA_CSUM))
 			break;
 
 		/* try to be gentle vs future versions on the initial syn */
@@ -69,11 +83,6 @@ static void mptcp_parse_option(const struct sock *sk,
 		 * host requires the use of checksums, checksums MUST be used.
 		 * In other words, the only way for checksums not to be used
 		 * is if both hosts in their SYNs set A=0."
-		 *
-		 * Section 3.3.0:
-		 * "If a checksum is not present when its use has been
-		 * negotiated, the receiver MUST close the subflow with a RST as
-		 * it is considered broken."
 		 */
 		mp_opt->csum_reqd = READ_ONCE(msk->csum_enabled);
 		if (flags & MPTCP_CAP_CHECKSUM_REQD)
@@ -88,7 +97,7 @@ static void mptcp_parse_option(const struct sock *sk,
 			mp_opt->rcvr_key = get_unaligned_be64(ptr);
 			ptr += 8;
 		}
-		if (opsize == TCPOLEN_MPTCP_MPC_ACK_DATA) {
+		if (opsize >= TCPOLEN_MPTCP_MPC_ACK_DATA) {
 			/* Section 3.1.:
 			 * "the data parameters in a MP_CAPABLE are semantically
 			 * equivalent to those in a DSS option and can be used
@@ -100,9 +109,14 @@ static void mptcp_parse_option(const struct sock *sk,
 			mp_opt->data_len = get_unaligned_be16(ptr);
 			ptr += 2;
 		}
-		pr_debug("MP_CAPABLE version=%x, flags=%x, optlen=%d sndr=%llu, rcvr=%llu len=%d",
+		if (opsize == TCPOLEN_MPTCP_MPC_ACK_DATA_CSUM) {
+			mp_opt->csum = (__force __sum16)get_unaligned_be16(ptr);
+			mp_opt->csum_reqd = 1;
+			ptr += 2;
+		}
+		pr_debug("MP_CAPABLE version=%x, flags=%x, optlen=%d sndr=%llu, rcvr=%llu len=%d csum=%u",
 			 version, flags, opsize, mp_opt->sndr_key,
-			 mp_opt->rcvr_key, mp_opt->data_len);
+			 mp_opt->rcvr_key, mp_opt->data_len, mp_opt->csum);
 		break;
 
 	case MPTCPOPT_MP_JOIN:
@@ -538,7 +552,9 @@ static void mptcp_write_data_fin(struct mptcp_subflow_context *subflow,
 		ext->data_len++;
 
 		/* the pseudo header has changed, update the csum accordingly */
-		csum_replace2(&ext->csum, htons(ext->data_len - 1), htons(ext->data_len));
+		if (ext->csum_reqd)
+			csum_replace2(&ext->csum, htons(ext->data_len - 1),
+				      htons(ext->data_len));
 	}
 }
 
@@ -1124,6 +1140,10 @@ void mptcp_incoming_options(struct sock *sk, struct sk_buff *skb)
 		}
 		mpext->data_len = mp_opt.data_len;
 		mpext->use_map = 1;
+		mpext->csum_reqd = mp_opt.csum_reqd;
+
+		if (mpext->csum_reqd)
+			mpext->csum = mp_opt.csum;
 	}
 }
 
diff --git a/net/mptcp/protocol.h b/net/mptcp/protocol.h
index b1d360a498a0e..c7cc9382bf779 100644
--- a/net/mptcp/protocol.h
+++ b/net/mptcp/protocol.h
@@ -68,6 +68,8 @@
 #define TCPOLEN_MPTCP_FASTCLOSE		12
 #define TCPOLEN_MPTCP_RST		4
 
+#define TCPOLEN_MPTCP_MPC_ACK_DATA_CSUM	(TCPOLEN_MPTCP_DSS_CHECKSUM + TCPOLEN_MPTCP_MPC_ACK_DATA)
+
 /* MPTCP MP_JOIN flags */
 #define MPTCPOPT_BACKUP		BIT(0)
 #define MPTCPOPT_HMAC_LEN	20
@@ -124,6 +126,7 @@ struct mptcp_options_received {
 	u64	data_seq;
 	u32	subflow_seq;
 	u16	data_len;
+	__sum16	csum;
 	u16	mp_capable : 1,
 		mp_join : 1,
 		fastclose : 1,