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Message-ID: <0100018dae3b46a4-ccc76b81-1814-421b-a81c-d00436297c10-000000@email.amazonses.com>
Date: Thu, 15 Feb 2024 19:25:36 +0000
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lMessage-ID: <26062 DOT 25778 DOT 563913 DOT 671336 AT gargle DOT gargle DOT HOWL>
To: cygwin AT cygwin DOT com
Subject: ssh over stunnel hangs on second connection
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From: cygwin--- via Cygwin <cygwin AT cygwin DOT com>
Reply-To: cygwin AT kosowsky DOT org
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Sender: "Cygwin" <cygwin-bounces+archive-cygwin=delorie DOT com AT cygwin DOT com>

I am using Cygwin stunnel 5.71 on Windows 11 to connect to 'ssh' into my Ubuntu
server over 'stunnel'.

- The first time I ssh via stunnel it works fine The second time, I
- try to connect, it hangs with 'ssh -v' showing only the initial
  local steps of connection:

	OpenSSH_9.5p1, OpenSSL 3.0.12 24 Oct 2023
	debug1: Reading configuration data /home/myuser/.ssh/config
	debug1: Reading configuration data /etc/ssh_config
	debug1: Connecting to localhost [::1] port 2222.
	debug1: Connection established.
	debug1: identity file /home/myuser/.ssh/id_rsa type 0
	debug1: identity file /home/myuser/.ssh/id_rsa-cert type -1
	debug1: identity file /home/myuser/.ssh/id_ecdsa type -1
	debug1: identity file /home/myuser/.ssh/id_ecdsa-cert type -1
	debug1: identity file /home/myuser/.ssh/id_ecdsa_sk type -1
	debug1: identity file /home/myuser/.ssh/id_ecdsa_sk-cert type -1
	debug1: identity file /home/myuser/.ssh/id_ed25519 type -1
	debug1: identity file /home/myuser/.ssh/id_ed25519-cert type -1
	debug1: identity file /home/myuser/.ssh/id_ed25519_sk type -1
	debug1: identity file /home/myuser/.ssh/id_ed25519_sk-cert type -1
	debug1: identity file /home/myuser/.ssh/id_xmss type -1
	debug1: identity file /home/myuser/.ssh/id_xmss-cert type -1
	debug1: identity file /home/myuser/.ssh/id_dsa type -1
	debug1: identity file /home/myuser/.ssh/id_dsa-cert type -1
	debug1: Local version string SSH-2.0-OpenSSH_9.5

  and '/var/log/stunnel' on the Cygwin client failing early:

    LOG7[main]: Found 1 ready file descriptor(s)
	LOG7[main]: FD=4 events=0x1 revents=0x0
	LOG7[main]: FD=8 events=0x1 revents=0x1
	LOG7[main]: FD=10 events=0x1 revents=0x0
	LOG7[main]: Service [ssh] accepted (FD=3) from ::1:52718


- If I connect a *third* (or more times), 'ssh -v' hangs with the same
  output as above, but there is *no* additional logging in
  '/var/log/stunnel' on the client.


It thus is acting as if 'stunnel' on the Cygwin client itself somehow
hangs/becomes unresponsive early in the second 'ssh' connection
attempt.

Note that the client '/usr/bin/stunnel/ process continues to run so it
doesn't crash.

Killing and relaunching /usr/bin/stunnel restarts the situation
allowing me to ssh-over-stunel OK on the first attempt but again
hanging on the 2nd and subsequent 'ssh' attempts

Also, the 'stunnel' server on Ubuntu continues to run throughout since
I can continue to ssh-over-stunnel into it from other machines.

It doesn't *seem* to be a firewall problem, since it connects fine the
first time. Nor does it seem to be a network or 'stunnel' server
problem.

Any ideas on why this is happening?


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