[PATCH 6.6.y 1/3] mptcp: introduce the mptcp_init_skb helper

[Sasha Levin <sashal@kernel.org>]

From: Paolo Abeni <pabeni@redhat.com>

[ Upstream commit 9a0afe0db46720ce1a009c7dac168aa0584bd732 ]

Factor out all the skb initialization step in a new helper and
use it. Note that this change moves the MPTCP CB initialization
earlier: we can do such step as soon as the skb leaves the
subflow socket receive queues.

Reviewed-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Reviewed-by: Geliang Tang <geliang@kernel.org>
Tested-by: Geliang Tang <geliang@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Link: https://patch.msgid.link/20250927-net-next-mptcp-rcv-path-imp-v1-4-5da266aa9c1a@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Stable-dep-of: 50c2d91c5dfa ("mptcp: do not drop partial packets")
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 net/mptcp/protocol.c | 50 ++++++++++++++++++++++++--------------------
 1 file changed, 27 insertions(+), 23 deletions(-)

diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index aed6c04c7de67..1c30bb369498a 100644
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -323,7 +323,7 @@ static void mptcp_data_queue_ofo(struct mptcp_sock *msk, struct sk_buff *skb)
 	mptcp_set_owner_r(skb, sk);
 }
 
-static bool mptcp_rmem_schedule(struct sock *sk, struct sock *ssk, int size)
+static bool mptcp_rmem_schedule(struct sock *sk, int size)
 {
 	struct mptcp_sock *msk = mptcp_sk(sk);
 	int amt, amount;
@@ -341,27 +341,11 @@ static bool mptcp_rmem_schedule(struct sock *sk, struct sock *ssk, int size)
 	return true;
 }
 
-static bool __mptcp_move_skb(struct mptcp_sock *msk, struct sock *ssk,
-			     struct sk_buff *skb, unsigned int offset,
-			     size_t copy_len)
+static void mptcp_init_skb(struct sock *ssk, struct sk_buff *skb, int offset,
+			   int copy_len)
 {
-	struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(ssk);
-	struct sock *sk = (struct sock *)msk;
-	struct sk_buff *tail;
-	bool has_rxtstamp;
-
-	__skb_unlink(skb, &ssk->sk_receive_queue);
-
-	skb_ext_reset(skb);
-	skb_orphan(skb);
-
-	/* try to fetch required memory from subflow */
-	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;
+	const struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(ssk);
+	bool has_rxtstamp = TCP_SKB_CB(skb)->has_rxtstamp;
 
 	/* the skb map_seq accounts for the skb offset:
 	 * mptcp_subflow_get_mapped_dsn() is based on the current tp->copied_seq
@@ -373,6 +357,25 @@ static bool __mptcp_move_skb(struct mptcp_sock *msk, struct sock *ssk,
 	MPTCP_SKB_CB(skb)->has_rxtstamp = has_rxtstamp;
 	MPTCP_SKB_CB(skb)->cant_coalesce = 0;
 
+	__skb_unlink(skb, &ssk->sk_receive_queue);
+
+	skb_ext_reset(skb);
+	skb_dst_drop(skb);
+}
+
+static bool __mptcp_move_skb(struct sock *sk, struct sk_buff *skb)
+{
+	u64 copy_len = MPTCP_SKB_CB(skb)->end_seq - MPTCP_SKB_CB(skb)->map_seq;
+	struct mptcp_sock *msk = mptcp_sk(sk);
+	struct sk_buff *tail;
+
+	/* try to fetch required memory from subflow */
+	if (!mptcp_rmem_schedule(sk, skb->truesize)) {
+		MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_RCVPRUNED);
+		mptcp_drop(sk, skb);
+		return false;
+	}
+
 	if (MPTCP_SKB_CB(skb)->map_seq == msk->ack_seq) {
 		/* in sequence */
 		msk->bytes_received += copy_len;
@@ -393,7 +396,6 @@ static bool __mptcp_move_skb(struct mptcp_sock *msk, struct sock *ssk,
 	 * will retransmit as needed, if needed.
 	 */
 	MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_DUPDATA);
-drop:
 	mptcp_drop(sk, skb);
 	return false;
 }
@@ -720,7 +722,9 @@ static bool __mptcp_move_skbs_from_subflow(struct mptcp_sock *msk,
 			if (tp->urg_data)
 				done = true;
 
-			if (__mptcp_move_skb(msk, ssk, skb, offset, len))
+			mptcp_init_skb(ssk, skb, offset, len);
+			skb_orphan(skb);
+			if (__mptcp_move_skb(sk, skb))
 				moved += len;
 			seq += len;
 
-- 
2.53.0