[PATCH mptcp-next v3 1/8] mptcp: add mptcp_is_data_contiguous helper

[Geliang Tang <geliangtang@gmail.com>]

This patch added a new member last_retrans_seq in the msk to track the
last retransmitting sequence number.

Add a new helper named mptcp_is_data_contiguous() to check whether the
data is contiguous on a subflow.

When a bad checksum is detected and a single contiguous subflow is in
use, don't send RST + MP_FAIL, send data_ack + MP_FAIL instead.

Signed-off-by: Geliang Tang <geliangtang@gmail.com>
---
 net/mptcp/protocol.c |  3 +++
 net/mptcp/protocol.h |  6 ++++++
 net/mptcp/subflow.c  | 12 ++++++------
 3 files changed, 15 insertions(+), 6 deletions(-)

diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index ff574d62073f..71a5427609a9 100644
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -2464,6 +2464,7 @@ static void __mptcp_retrans(struct sock *sk)
 		dfrag->already_sent = max(dfrag->already_sent, info.sent);
 		tcp_push(ssk, 0, info.mss_now, tcp_sk(ssk)->nonagle,
 			 info.size_goal);
+		msk->last_retrans_seq = dfrag->data_seq;
 	}
 
 	release_sock(ssk);
@@ -2889,6 +2890,7 @@ struct sock *mptcp_sk_clone(const struct sock *sk,
 	msk->snd_una = msk->write_seq;
 	msk->wnd_end = msk->snd_nxt + req->rsk_rcv_wnd;
 	msk->setsockopt_seq = mptcp_sk(sk)->setsockopt_seq;
+	msk->last_retrans_seq = subflow_req->idsn - 1;
 
 	if (mp_opt->suboptions & OPTIONS_MPTCP_MPC) {
 		msk->can_ack = true;
@@ -3145,6 +3147,7 @@ void mptcp_finish_connect(struct sock *ssk)
 	WRITE_ONCE(msk->rcv_wnd_sent, ack_seq);
 	WRITE_ONCE(msk->can_ack, 1);
 	WRITE_ONCE(msk->snd_una, msk->write_seq);
+	WRITE_ONCE(msk->last_retrans_seq, subflow->idsn - 1);
 
 	mptcp_pm_new_connection(msk, ssk, 0);
 
diff --git a/net/mptcp/protocol.h b/net/mptcp/protocol.h
index d516fb6578cc..eb3473d128d4 100644
--- a/net/mptcp/protocol.h
+++ b/net/mptcp/protocol.h
@@ -227,6 +227,7 @@ struct mptcp_sock {
 	u64		ack_seq;
 	u64		rcv_wnd_sent;
 	u64		rcv_data_fin_seq;
+	u64		last_retrans_seq;
 	int		wmem_reserved;
 	struct sock	*last_snd;
 	int		snd_burst;
@@ -625,6 +626,11 @@ static inline bool mptcp_has_another_subflow(struct sock *ssk)
 	return false;
 }
 
+static inline bool mptcp_is_data_contiguous(struct mptcp_sock *msk)
+{
+	return before64(msk->last_retrans_seq, msk->snd_una);
+}
+
 void __init mptcp_proto_init(void);
 #if IS_ENABLED(CONFIG_MPTCP_IPV6)
 int __init mptcp_proto_v6_init(void);
diff --git a/net/mptcp/subflow.c b/net/mptcp/subflow.c
index 1de7ce883c37..b07803ed3053 100644
--- a/net/mptcp/subflow.c
+++ b/net/mptcp/subflow.c
@@ -1166,15 +1166,15 @@ static bool subflow_check_data_avail(struct sock *ssk)
 fallback:
 	/* RFC 8684 section 3.7. */
 	if (subflow->send_mp_fail) {
-		if (mptcp_has_another_subflow(ssk)) {
+		if (mptcp_has_another_subflow(ssk) || !mptcp_is_data_contiguous(msk)) {
+			ssk->sk_err = EBADMSG;
+			tcp_set_state(ssk, TCP_CLOSE);
+			subflow->reset_transient = 0;
+			subflow->reset_reason = MPTCP_RST_EMIDDLEBOX;
+			tcp_send_active_reset(ssk, GFP_ATOMIC);
 			while ((skb = skb_peek(&ssk->sk_receive_queue)))
 				sk_eat_skb(ssk, skb);
 		}
-		ssk->sk_err = EBADMSG;
-		tcp_set_state(ssk, TCP_CLOSE);
-		subflow->reset_transient = 0;
-		subflow->reset_reason = MPTCP_RST_EMIDDLEBOX;
-		tcp_send_active_reset(ssk, GFP_ATOMIC);
 		WRITE_ONCE(subflow->data_avail, 0);
 		return true;
 	}
-- 
2.31.1