netdev - [PATCH] tcp: Reset tcp connections in SYN-SENT state

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Date:   Mon,  5 Apr 2021 22:32:42 +0530
From:   Manoj Basapathi <manojbm@...eaurora.org>
To:     netdev@...r.kernel.org
Cc:     jgarzik@...ox.com, avem@...emloft.net, shemminger@...tta.com,
        linville@...driver.com, mkubecek@...e.cz, kuba@...nel.org,
        bpf@...earbox.net, dsahern@...il.com, kubakici@...pl,
        sharathv@....qualcomm.com, ssaha@....qualcomm.com,
        vidulak@....qualcomm.com, manojbm@....qualcomm.com,
        subashab@...cinc.com, rpavan@....qualcomm.com,
        Manoj Basapathi <manojbm@...eaurora.org>,
        Sauvik Saha <ssaha@...eaurora.org>
Subject: [PATCH] tcp: Reset tcp connections in SYN-SENT state

Userspace sends tcp connection (sock) destroy on network switch
i.e switching the default network of the device between multiple
networks(Cellular/Wifi/Ethernet).

Kernel though doesn't send reset for the connections in SYN-SENT state
and these connections continue to remain.
Even as per RFC 793, there is no hard rule to not send RST on ABORT in
this state.

Modify tcp_abort and tcp_disconnect behavior to send RST for connections
in syn-sent state to avoid lingering connections on network switch.

Signed-off-by: Manoj Basapathi <manojbm@...eaurora.org>
Signed-off-by: Sauvik Saha <ssaha@...eaurora.org>
---
 net/ipv4/tcp.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index e14fd0c50c10..627a472161fb 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -2888,7 +2888,7 @@ static inline bool tcp_need_reset(int state)
 {
 	return (1 << state) &
 	       (TCPF_ESTABLISHED | TCPF_CLOSE_WAIT | TCPF_FIN_WAIT1 |
-		TCPF_FIN_WAIT2 | TCPF_SYN_RECV);
+		TCPF_FIN_WAIT2 | TCPF_SYN_RECV | TCPF_SYN_SENT);
 }
 
 static void tcp_rtx_queue_purge(struct sock *sk)
@@ -2954,8 +2954,7 @@ int tcp_disconnect(struct sock *sk, int flags)
 		 */
 		tcp_send_active_reset(sk, gfp_any());
 		sk->sk_err = ECONNRESET;
-	} else if (old_state == TCP_SYN_SENT)
-		sk->sk_err = ECONNRESET;
+	}
 
 	tcp_clear_xmit_timers(sk);
 	__skb_queue_purge(&sk->sk_receive_queue);
-- 
2.29.0