Merge branch 'mptcp-fix-duplicate-data-handling'

Matthieu Baerts says:

====================
mptcp: fix duplicate data handling

In some cases, the subflow-level's copied_seq counter was incorrectly
increased, leading to an unexpected subflow reset.

Patch 1/2 fixes the RCVPRUNED MIB counter that was attached to the wrong
event since its introduction in v5.14, backported to v5.11.

Patch 2/2 fixes the copied_seq counter issues, is present since v5.10.
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
====================

Link: https://patch.msgid.link/20240731-upstream-net-20240731-mptcp-dup-data-v1-0-bde833fa628a@kernel.orgSigned-off-by: Paolo Abeni <pabeni@redhat.com>

net/mptcp/protocol.c

@@ -350,8 +350,10 @@ static bool __mptcp_move_skb(struct mptcp_sock *msk, struct sock *ssk,
 	skb_orphan(skb);
 
 	/* try to fetch required memory from subflow */
-	if (!mptcp_rmem_schedule(sk, ssk, skb->truesize))
+	if (!mptcp_rmem_schedule(sk, ssk, skb->truesize)) {
+		MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_RCVPRUNED);
 		goto drop;
+	}
 
 	has_rxtstamp = TCP_SKB_CB(skb)->has_rxtstamp;
 
@@ -844,10 +846,8 @@ void mptcp_data_ready(struct sock *sk, struct sock *ssk)
 		sk_rbuf = ssk_rbuf;
 
 	/* over limit? can't append more skbs to msk, Also, no need to wake-up*/
-	if (__mptcp_rmem(sk) > sk_rbuf) {
-		MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_RCVPRUNED);
+	if (__mptcp_rmem(sk) > sk_rbuf)
 		return;
-	}
 
 	/* Wake-up the reader only for in-sequence data */
 	mptcp_data_lock(sk);

net/mptcp/subflow.c

@@ -1230,14 +1230,22 @@ static void mptcp_subflow_discard_data(struct sock *ssk, struct sk_buff *skb,
 {
 	struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(ssk);
 	bool fin = TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN;
-	u32 incr;
+	struct tcp_sock *tp = tcp_sk(ssk);
+	u32 offset, incr, avail_len;
 
-	incr = limit >= skb->len ? skb->len + fin : limit;
+	offset = tp->copied_seq - TCP_SKB_CB(skb)->seq;
+	if (WARN_ON_ONCE(offset > skb->len))
+		goto out;
+
+	avail_len = skb->len - offset;
+	incr = limit >= avail_len ? avail_len + fin : limit;
 
-	pr_debug("discarding=%d len=%d seq=%d", incr, skb->len,
-		 subflow->map_subflow_seq);
+	pr_debug("discarding=%d len=%d offset=%d seq=%d", incr, skb->len,
+		 offset, subflow->map_subflow_seq);
 	MPTCP_INC_STATS(sock_net(ssk), MPTCP_MIB_DUPDATA);
 	tcp_sk(ssk)->copied_seq += incr;
+
+out:
 	if (!before(tcp_sk(ssk)->copied_seq, TCP_SKB_CB(skb)->end_seq))
 		sk_eat_skb(ssk, skb);
 	if (mptcp_subflow_get_map_offset(subflow) >= subflow->map_data_len)