scattered thoughts on connection sharing

[mark.yagnatinsky at barclays.com]

Not sure what the standard etiquette around these parts is for how long to wait for a reply but I thought it might be faster than this...
Or did I breach etiquette in my original email?
If so, I'd appreciate someone explicitly telling me "your email was bad and you should feel bad"
I cope poorly with radio silence.

Thanks in advance for any reply at all,
Mark.

-----Original Message-----
From: Yagnatinsky, Mark : IT (NYK) 
Sent: Monday, July 15, 2024 12:47 PM
To: openssh-unix-dev at mindrot.org
Subject: scattered thoughts on connection sharing

Resending, got blocked last time.

I have a few things I'd like to say about the (seriously nifty) connection sharing feature of OpenSSH and I'm not sure if the convention here is to use one email thread per distinct thing or just stuff everything into one email.
I decided to combine them because splitting is much easier than combining.

Thing 1: This is the main thing that motivated me to write this email.
I'm on Windows 10 and I'm using the SSH client that comes bundled with Git for Windows, which I believe is basically the Cygwin port.  (Or is it??) I found bug 1278 in the issue tracker: https://bugzilla.mindrot.org/show_bug.cgi?id=1278
It appears it has been fixed a few years ago, and the version I'm on is much newer than that, but it still doesn't work for me.
Do you need more details to reproduce this or do you folks have a windows install to test this on?

Thing 2: It appears that "ssh -M localhost" does NOT attempt to start a "master" session, and the -M is silently ignored because no control path is mentioned.  I'd think that this should be a fatal error, just like passing -S without giving a path.  Instead, nothing is said, not even with -vvv.

Thing 3: Related to the previous point: is there any philosophical reason why there's no bundled default for the control path if none is given, or is this simply one of those things that no one ever got around to doing?
The analogous feature in PuTTY/plink (and also IntelliJ) Just Works, so coming from those clients this feels like ssh(1) needs micromanaging.

Thing 4: Are there any widespread conventions on where these socket files go, or does everyone pretty much do their own ad-hoc thing?

Thing 5: Is there any way to tell the ssh client "try to connect using path/to/my-ctl.socket, and if it doesn't work, then exit with an error code"?
I originally had a long rant written here how -O check is not suitable because it has a TOCTOU issue.
Namely, the persist timeout could expire after the check but before trying to connect.
But it turns out that merely checking resets the timer, so this is not likely to be an issue in practice after all.
I still wish I didn't have to use it because it means I have to launch an extra process, which is very slow on our laptops for some reason.
(Only for Cygwin-ish things. native windows processes launch quickly)


There might have been a Thing 6 but if so I can't recall it right this moment, so.

That's all for now,
Mark.
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