tcp: rstreason: handle timewait cases in the receive path

There are two possible cases where TCP layer can send an RST. Since they
happen in the same place, I think using one independent reason is enough
to identify this special situation.

Signed-off-by: Jason Xing <kernelxing@tencent.com>
Link: https://lore.kernel.org/r/20240510122502.27850-5-kerneljasonxing@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

include/net/rstreason.h

@@ -15,6 +15,7 @@
 	FN(TCP_FLAGS)			\
 	FN(TCP_OLD_ACK)			\
 	FN(TCP_ABORT_ON_DATA)		\
+	FN(TCP_TIMEWAIT_SOCKET)		\
 	FN(MPTCP_RST_EUNSPEC)		\
 	FN(MPTCP_RST_EMPTCP)		\
 	FN(MPTCP_RST_ERESOURCE)		\
@@ -72,6 +73,10 @@ enum sk_rst_reason {
 	 */
 	SK_RST_REASON_TCP_ABORT_ON_DATA,
 
+	/* Here start with the independent reasons */
+	/** @SK_RST_REASON_TCP_TIMEWAIT_SOCKET: happen on the timewait socket */
+	SK_RST_REASON_TCP_TIMEWAIT_SOCKET,
+
 	/* Copy from include/uapi/linux/mptcp.h.
 	 * These reset fields will not be changed since they adhere to
 	 * RFC 8684. So do not touch them. I'm going to list each definition

net/ipv4/tcp_ipv4.c

@@ -2427,7 +2427,7 @@ int tcp_v4_rcv(struct sk_buff *skb)
 		tcp_v4_timewait_ack(sk, skb);
 		break;
 	case TCP_TW_RST:
-		tcp_v4_send_reset(sk, skb, sk_rst_convert_drop_reason(drop_reason));
+		tcp_v4_send_reset(sk, skb, SK_RST_REASON_TCP_TIMEWAIT_SOCKET);
 		inet_twsk_deschedule_put(inet_twsk(sk));
 		goto discard_it;
 	case TCP_TW_SUCCESS:;

net/ipv6/tcp_ipv6.c

@@ -1999,7 +1999,7 @@ INDIRECT_CALLABLE_SCOPE int tcp_v6_rcv(struct sk_buff *skb)
 		tcp_v6_timewait_ack(sk, skb);
 		break;
 	case TCP_TW_RST:
-		tcp_v6_send_reset(sk, skb, sk_rst_convert_drop_reason(drop_reason));
+		tcp_v6_send_reset(sk, skb, SK_RST_REASON_TCP_TIMEWAIT_SOCKET);
 		inet_twsk_deschedule_put(inet_twsk(sk));
 		goto discard_it;
 	case TCP_TW_SUCCESS: