[PATCH mptcp-next v6 6/6] mptcp: copy subflow's tos/tclass to msk on accept

From: Geliang Tang <[email protected]>

When a new MPTCP socket is accepted, copy the tos (and rcv_tos for IPv4)
or tclass (and rcv_flowinfo for IPv6) from the first subflow to the
newly-created msk.

This mirrors what plain TCP does in tcp_v4_syn_recv_sock() and
tcp_v6_syn_recv_sock(), where these values are copied from the incoming
skb to the accepted socket.

Without this, MP_JOIN subflows created later would inherit tos/tclass=0
from the msk and lose the peer's reflected value, causing inconsistent
traffic class behavior.

Signed-off-by: Geliang Tang <[email protected]>
---
 net/mptcp/protocol.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index c2762d74f29d..f18af725e8e2 100644
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -3756,6 +3756,22 @@ struct sock *mptcp_sk_clone_init(const struct sock *sk,
 #endif
 		mptcp_copy_ip_options(nsk, sk);
 
+	if (ssk->sk_family == AF_INET) {
+		inet_sk(nsk)->rcv_tos = inet_sk(ssk)->rcv_tos;
+		__ip_sock_set_tos(nsk, inet_sk(ssk)->tos);
+	}
+#if IS_ENABLED(CONFIG_MPTCP_IPV6)
+	else if (ssk->sk_family == AF_INET6 &&
+		 ipv6_addr_v4mapped(&ssk->sk_v6_daddr)) {
+		inet_sk(nsk)->rcv_tos = inet_sk(ssk)->rcv_tos;
+		__ip_sock_set_tos(nsk, inet_sk(ssk)->tos);
+		inet6_sk(nsk)->rcv_flowinfo = 0;
+	} else if (ssk->sk_family == AF_INET6) {
+		inet6_sk(nsk)->rcv_flowinfo = inet6_sk(ssk)->rcv_flowinfo;
+		__ip6_sock_set_tclass(nsk, inet6_sk(ssk)->tclass);
+	}
+#endif
+
 	msk = mptcp_sk(nsk);
 	WRITE_ONCE(msk->local_key, subflow_req->local_key);
 	WRITE_ONCE(msk->token, subflow_req->token);
-- 
2.53.0