[PATCH mptcp-next v5 1/8] mptcp: track and update contiguous data status

[Geliang Tang <geliangtang@gmail.com>]

This patch added a new member last_retrans_seq in mptcp_subflow_context
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.

Suggested-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Geliang Tang <geliangtang@gmail.com>
---
 net/mptcp/protocol.c |  6 ++++++
 net/mptcp/protocol.h |  8 ++++++++
 net/mptcp/subflow.c  | 12 ++++++------
 3 files changed, 20 insertions(+), 6 deletions(-)

diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index f8ad049d6941..cf8cccfefb51 100644
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -729,6 +729,9 @@ void mptcp_data_ready(struct sock *sk, struct sock *ssk)
 	if (unlikely(subflow->disposable))
 		return;
 
+	if (!subflow->last_retrans_seq || mptcp_is_data_contiguous(ssk))
+		subflow->last_retrans_seq = tcp_sk(ssk)->snd_una - 1;
+
 	ssk_rbuf = READ_ONCE(ssk->sk_rcvbuf);
 	sk_rbuf = READ_ONCE(sk->sk_rcvbuf);
 	if (unlikely(ssk_rbuf > sk_rbuf))
@@ -2415,6 +2418,7 @@ static void mptcp_check_fastclose(struct mptcp_sock *msk)
 static void __mptcp_retrans(struct sock *sk)
 {
 	struct mptcp_sock *msk = mptcp_sk(sk);
+	struct mptcp_subflow_context *subflow;
 	struct mptcp_sendmsg_info info = {};
 	struct mptcp_data_frag *dfrag;
 	size_t copied = 0;
@@ -2464,6 +2468,8 @@ 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);
+		subflow = mptcp_subflow_ctx(ssk);
+		subflow->last_retrans_seq = tcp_sk(ssk)->snd_nxt;
 	}
 
 	release_sock(ssk);
diff --git a/net/mptcp/protocol.h b/net/mptcp/protocol.h
index 7379ab580a7e..e090a9244f8b 100644
--- a/net/mptcp/protocol.h
+++ b/net/mptcp/protocol.h
@@ -416,6 +416,7 @@ struct mptcp_subflow_context {
 	u32	map_data_len;
 	__wsum	map_data_csum;
 	u32	map_csum_len;
+	u32	last_retrans_seq;
 	u32	request_mptcp : 1,  /* send MP_CAPABLE */
 		request_join : 1,   /* send MP_JOIN */
 		request_bkup : 1,
@@ -625,6 +626,13 @@ static inline bool mptcp_has_another_subflow(struct sock *ssk)
 	return false;
 }
 
+static inline bool mptcp_is_data_contiguous(struct sock *ssk)
+{
+	struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(ssk);
+
+	return before(subflow->last_retrans_seq, tcp_sk(ssk)->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 6172f380dfb7..a8f46a48feb1 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(ssk)) {
+			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