netdev - [PATCH net-next 1/3] tcp: fix __tcp_close() to only send RST when required

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Message-ID: <20250903084720.1168904-2-edumazet@google.com>
Date: Wed,  3 Sep 2025 08:47:18 +0000
From: Eric Dumazet <edumazet@...gle.com>
To: "David S . Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, 
	Paolo Abeni <pabeni@...hat.com>, Neal Cardwell <ncardwell@...gle.com>
Cc: Simon Horman <horms@...nel.org>, Kuniyuki Iwashima <kuniyu@...gle.com>, netdev@...r.kernel.org, 
	eric.dumazet@...il.com, Eric Dumazet <edumazet@...gle.com>
Subject: [PATCH net-next 1/3] tcp: fix __tcp_close() to only send RST when required

If the receive queue contains payload that was already
received, __tcp_close() can send an unexpected RST.

Refine the code to take tp->copied_seq into account,
as we already do in tcp recvmsg().

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: Eric Dumazet <edumazet@...gle.com>
---
 net/ipv4/tcp.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 40b774b4f587..39eb03f6d07f 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -3099,8 +3099,8 @@ bool tcp_check_oom(const struct sock *sk, int shift)
 
 void __tcp_close(struct sock *sk, long timeout)
 {
+	bool data_was_unread = false;
 	struct sk_buff *skb;
-	int data_was_unread = 0;
 	int state;
 
 	WRITE_ONCE(sk->sk_shutdown, SHUTDOWN_MASK);
@@ -3119,11 +3119,12 @@ void __tcp_close(struct sock *sk, long timeout)
 	 *  reader process may not have drained the data yet!
 	 */
 	while ((skb = __skb_dequeue(&sk->sk_receive_queue)) != NULL) {
-		u32 len = TCP_SKB_CB(skb)->end_seq - TCP_SKB_CB(skb)->seq;
+		u32 end_seq = TCP_SKB_CB(skb)->end_seq;
 
 		if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN)
-			len--;
-		data_was_unread += len;
+			end_seq--;
+		if (after(end_seq, tcp_sk(sk)->copied_seq))
+			data_was_unread = true;
 		__kfree_skb(skb);
 	}
 
-- 
2.51.0.338.gd7d06c2dae-goog