tailscale ssh doesn't work with the macOS sandbox app

[maisem]

What is the issue?

$ /Applications/Tailscale.app/Contents/MacOS/Tailscale ssh ws-1
Pseudo-terminal will not be allocated because stdin is not a terminal.
kex_exchange_identification: Connection closed by remote host
Connection closed by UNKNOWN port 65535

Steps to reproduce

Run /Applications/Tailscale.app/Contents/MacOS/Tailscale ssh <host> on any macOS machine, where <host> is any Tailscale node.

Are there any recent changes that introduced the issue?

No response

OS

macOS

OS version

12.2.1

Tailscale version

1.24

Bug report

No response

[bradfitz]

It's likely this just won't work in the App Store version.

We might have to detect that version and said, "Sorry, use a different macOS version."

/cc @nickoneill @crawshaw

[bradfitz]

As of #4531 it's better, but still not great. See the tcsetattr error and inability to
hit Ctrl-D, for instance:

    bradfitz@laptop ~ % tailscale.app ssh foo@bar
    tcsetattr: Operation not permitted
    # Authentication checked with Tailscale SSH.
    # Time since last authentication: 1h13m22s
    foo@bar:~$ ^D
    ^D
    ^D

[mayakacz]

I think you are saying that macOS won't work as the server you SSH to, but it should still work fine as the client you SSH from. (Or are you saying the client will not work?)

[bradfitz]

MacOS with Tailscale wrapper client won't work well. Bad enough to be embarrassing and will invite tons of dup bugs we'll be unable to do anything about.

MacOS with system ssh client is fine. We just don't get the magic host key checking bit yet.

[mihaip]

I looked into this a bit. The tcsetattr: Operation not permitted is due to not being able to set the tty in raw mode at https://github.com/openssh/openssh-portable/blob/2dc328023f60212cd29504fc05d849133ae47355/sshtty.c#L93.

I thought that this was maybe due to the ssh process not inheriting some permissions, so I tried doing this directly in the ssh.go CLI command (via termios.Raw), but that got the same permission error.

Looking at the console, there is a Sandbox: ssh(10318) deny(1) file-ioctl /dev/ttys001 line (tcsetattr is implemented in terms of ioctl), which suggests that this is indeed a sandbox limitation.

Looking at the default sandbox profile for apps (/System/Library/Sandbox/Profiles/application.sb), there are a few places where file-ioctl is allowed: (allow file-read* file-write* file-ioctl (literal "/dev/ptmx")) and something relating to application groups that I don't think is relevant.

Can we perhaps use /dev/ptmx (which can be put into raw mode) and connect it to stdin?

This may also be something for @nickoneill to bring up at the next WWDC. I can also try to make a self-contained sample and see if Quinn or someone else from Apple in their forums has ideas.

[mihaip]

Posted https://developer.apple.com/forums/thread/709444 on Apple's forums.