SSH client for Win10 hangs sometimes

[ngugcx]

Troubleshooting steps
https://github.com/PowerShell/Win32-OpenSSH/wiki/Troubleshooting-Steps

Terminal issue? please go through wiki
https://github.com/PowerShell/Win32-OpenSSH/wiki/TTY-PTY-support-in-Windows-OpenSSH

Please answer the following

"OpenSSH for Windows" version
((Get-Item (Get-Command sshd).Source).VersionInfo.FileVersion)

Server OperatingSystem
((Get-ItemProperty "HKLM:\SOFTWARE\Microsoft\Windows nt\CurrentVersion\" -Name ProductName).ProductName)

Client OperatingSystem
Win10

What is failing
Sometimes SSH get hung when connecting to Ubuntu 16.04 64bit.
ssh -V
OpenSSH_for_Windows_7.6p1, LibreSSL 2.6.4

I got the debug trace with -vvv:
ssh.txt

Expected output
don't hang

Actual output
hang

[alexv1n]

I'm having a similar issue. Executing ssh.exe user@ip.address -- echo -n "" just hangs sometimes.

When it does hang, it happens at syncio_close() (in contrib\win32\win32compat\termio.c) at line 263 (WaitForSingleObject):

	if (pio->read_details.pending) {
		/*
		Terminate the read thread at the below situations:
		1. For console - the read thread is blocked by the while loop on raw mode
		2. Function ReadFile on Win7 machine dees not return when no content to read in non-interactive mode.
		*/
		if (FILETYPE(pio) == FILE_TYPE_CHAR && (IsWin7OrLess() || in_raw_mode))
			TerminateThread(pio->read_overlapped.hEvent, 0);
		else
			WaitForSingleObject(pio->read_overlapped.hEvent, INFINITE);
	}

Sometimes hitting Enter in terminal unblocks ssh.exe and it exits successfully.

Also, if I run ssh user@server -- echo -n "" <NUL it blocks 100% of the time.

I have tried code from #1338 but it doesn't fix the issue. This seems like a different bug, probably closely related to #874 but it seems the issue is not confined to Win7 only. It happens on Win10 as well.

[manojampalam]

@alexv1n can you try out patched binaries from @NoMoreFood in this thread - #1338

You would just need the updated version of ssh.exe.

[alexv1n]

I did say that I tried that and it didn't help

[Tyriar]

I'm seeing this as well, sometimes ssh <host> uname -sm hangs:

The window has been like this for 10+ minutes:

Pressing enter after that long:

Version info:

C:\Users\daimms.REDMOND>ssh -V
OpenSSH_for_Windows_7.7p1, LibreSSL 2.6.5

Windows 10 1903 18875.1000 (Insiders)

[bobvandevijver]

Seems this might be a low-level Windows issue, as I'm hitting something similar with kitty: cyd01/KiTTY#22

[NoMoreFood]

@Tyriar Can you please try the version 8.0 binaries (and verify using ssh -V that you're actually using version 8.0 binaries, as you did with 7.7). Thanks!

[Tyriar]

Still hanging sometimes:

[NoMoreFood]

@Tyriar, alright I'll try to take a look and see if I can repro it. What's the purpose of wrapping the execution in a command prompt?

[Tyriar]

@NoMoreFood it might not make a difference but that's how we hit the bug initially

[AHelper]

FYI, I have been getting hangs on OpenSSH_for_Windows_7.9p1, LibreSSL 2.6.5. I pulled the latest and still get hangs:

PS C:\Users\user\Downloads\OpenSSH-Win64> .\ssh.exe -V
OpenSSH_for_Windows_8.0p1, LibreSSL 2.6.5
PS C:\Users\user\Downloads\OpenSSH-Win64> .\ssh.exe -vvv -E log2.txt -i .\id_rsa test@10.9.73.34 date
Tue Jul  9 18:50:29 UTC 2019
PS C:\Users\user\Downloads\OpenSSH-Win64> .\ssh.exe -vvvvvv -E log3.txt -i .\id_rsa test@10.9.73.34 date
                <<< Hung, enter pressed
Tue Jul  9 18:39:21 UTC 2019
PS C:\Users\user\Downloads\OpenSSH-Win64> .\ssh.exe -vvv -E log4.txt -i .\id_rsa test@10.9.73.34 date
Tue Jul  9 18:50:29 UTC 2019
                <<< Hung, enter pressed
PS C:\Users\user\Downloads\OpenSSH-Win64>

I find that running with -vvv alone masks the problem. Logging to file with -E allows the hang again. I annotated the logs where they stopped at the time they hung.

Now, this is about a 1-in-10 chance. I get different odds (more frequent) against an OpenSSH_7.9p1, OpenSSL 1.1.1b 26 Feb 2019 (Alpine 3.9) server.

Windows 10 Enterprise 1709 16299.1217
ssh: OpenSSH_for_Windows_8.0p1, LibreSSL 2.6.5
sshd: OpenSSH_7.4p1 Debian-10+deb9u6, OpenSSL 1.0.2s 28 May 2019

log3.txt
log4.txt

Let me know if there's anything I should test out.