openssh bugs - Jun 2020 - [Bug 3187] New: 'unknown error' reported on local network if internet not available

https://bugzilla.mindrot.org/show_bug.cgi?id=3187

            Bug ID: 3187
           Summary: 'unknown error' reported on local network if
internet
                    not available
           Product: Portable OpenSSH
           Version: 8.3p1
          Hardware: 68k
                OS: Mac OS X
            Status: NEW
          Severity: normal
          Priority: P5
         Component: ssh
          Assignee: unassigned-bugs at mindrot.org
          Reporter: cjames at emolecules.com

I'm running a VirtualBox on a Mac (Catalina) which listens on
192.168.77.6. Normally "ssh user at 192.168.77.6" works. "ssh
user at host.domain.com" also works, where "host.domain.com" is
defined in
/etc/hosts as 192.168.77.6. Now turn off WiFi so there's no internet
connectivity. The first command, "ssh user at 192.168.77.6" still
works.
But "ssh user at host.domain.com" fails with the message "ssh:
connect to
host hostname.domain.com port 22: Undefined error: 0". If I then turn
on networking via BlueTooth through an iPhone (172.20.10.5), ssh works
again. It feels like a DNS problem: DNS fails, and rather than
continuing to use /etc/hosts, it just gives an error. This makes it
impossible to use ssh for local networks when the Mac has no internet
available.

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Damien Miller <djm at mindrot.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |djm at mindrot.org

--- Comment #1 from Damien Miller <djm at mindrot.org> ---
Please capture the debugging output of a failing ssh execution and
attach it to this bug. You can run "ssh -vvv user at host"

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--- Comment #2 from Craig James <cjames at emolecules.com> ---
 $ ssh -vvv user at host.domain.com
OpenSSH_8.1p1, LibreSSL 2.7.3
debug1: Reading configuration data /Users/cjames/.ssh/config
debug1: /Users/cjames/.ssh/config line 46: Applying options for
host.domain.com
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: /etc/ssh/ssh_config line 47: Applying options for *
debug1: Connecting to host.domain.com port 22.
ssh: connect to host host.domain.com port 22: Undefined error: 0

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--- Comment #3 from Damien Miller <djm at mindrot.org> ---
I can't replicate this with OpenSSH 8.2 or HEAD. It looks like you have
some configuration in ~/ssh/config that might be relevant - what is in
there?

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--- Comment #4 from Craig James <cjames at emolecules.com> ---
The relevant entry from my ~/.ssh/config file is:

Host v-application.emolecules.com
  User emi
  IdentityFile ~/.ssh/vagrant

The file ~/.ssh/vagrant is an RSA private key file.

The host "v-application.emolecules.com" is defined in my Macintosh
/etc/hosts file as:

$ grep v-application.emolecules.com /etc/hosts
192.168.77.6  v-application.emolecules.com

Hope that helps.

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--- Comment #5 from Damien Miller <djm at mindrot.org> ---
I can't replicate this using OpenSSH 8.3p1 on my available Mac
hardware:

Darwin djm-mba 19.5.0 Darwin Kernel Version 19.5.0: Tue May 26 20:41:44
PDT 2020; root:xnu-6153.121.2~2/RELEASE_X86_64 x86_64

However I don't see anything that could have caused this bug to be
fixed between 8.1 and 8.3p1. Are you using the OpenSSH that Apple ships
or one you've compiled yourself? (manually or via macports/brew etc)

If you are using the Apple version, I suggest trying to reproduce the
problem using a locally built OpenSSH to exclude any modifications they
may have made.

Otherwise, I recommend capturing a syscall trace from ssh to see where
it is going wrong. See
https://stackoverflow.com/questions/31045575/how-to-trace-system-calls-of-a-program-in-mac-os-x
for some hints here

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Damien Miller <djm at mindrot.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |WORKSFORME
             Status|NEW                         |RESOLVED

--- Comment #6 from Damien Miller <djm at mindrot.org> ---
I'm not able to reproduce this. Please reopen if you can reproduce this
using stock OpenSSH built from source.

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Damien Miller <djm at mindrot.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|RESOLVED                    |CLOSED

--- Comment #7 from Damien Miller <djm at mindrot.org> ---
closing resolved bugs as of 8.6p1 release

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