openssh bugs - Mar 2022 - [Bug 3406] New: RSA key authentication doesn't work with enabled GSSAPIKeyExchange: sign_and_send_pubkey: internal error: initial hostkey not recorded

https://bugzilla.mindrot.org/show_bug.cgi?id=3406

            Bug ID: 3406
           Summary: RSA key authentication doesn't work with enabled
                    GSSAPIKeyExchange: sign_and_send_pubkey: internal
                    error: initial hostkey not recorded
           Product: Portable OpenSSH
           Version: 8.9p1
          Hardware: Other
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P5
         Component: Kerberos support
          Assignee: unassigned-bugs at mindrot.org
          Reporter: robert.kulyassa at gmail.com

I've set up an openssh server to use GSSAPI authentication (too), it
all worked last week, I was able to login with password, ssh key or
kerberos ticket, all the 3 worked fine. Today I updated the ssh server
(8.8p1 -> 8.9p1), the kerberos and password auth still work, but when I
try to use key authentication I get this:

sign_and_send_pubkey: internal error: initial hostkey not recorded

If I disable the GSSAPIKeyExchange then it works again (kerberos and
password auth works in both case).



The environment:
client and server side are almost the same, Ubuntu 22.04 client and
server:
openssh version: 8.9p1 (and earlier when it worked: 8.8p1)

sshd_config (almost default, just enabled the GSSAPIAuthentication)

Include /etc/ssh/sshd_config.d/*.conf # <- nothing here
LogLevel INFO
KbdInteractiveAuthentication no
GSSAPIAuthentication yes
GSSAPIKeyExchange yes
UsePAM yes
X11Forwarding yes
PrintMotd no
AcceptEnv LANG LC_*
Subsystem sftp  /usr/lib/openssh/sftp-server


ps: May it be related to the "stricter UpdateHostkey signature
verification logic" what I see in the 8.9 release notes?
https://www.openssh.com/txt/release-8.9

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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 attach a full debug trace from the server. It's hard to tell
what has gone wrong from just the error message.

Also:
> GSSAPIKeyExchange yes
This is a third-party patch to OpenSSH. It's fairly likely that this is
causing the problem.

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--- Comment #2 from Damien Miller <djm at mindrot.org> ---
specifically, the gssapi-kex patch probably needs something like:
> if (ssh->kex->initial_hostkey == NULL)
>         hostbound = 0;
added after the first "if" statement near the start of
sshconnect2.c:sign_and_send_pubkey()

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--- Comment #3 from qji <robert.kulyassa at gmail.com> ---
Created attachment 3582
  --> https://bugzilla.mindrot.org/attachment.cgi?id=3582&action=edit
sshd_debug3_log_key_auth_failed.txt

Here is a sshd debug3 log showing the output the same time I ran the
"ssh localadmin at myserver" command on my client.

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--- Comment #4 from qji <robert.kulyassa at gmail.com> ---
Created attachment 3583
  --> https://bugzilla.mindrot.org/attachment.cgi?id=3583&action=edit
ssh_client_debug3_log_key_auth_failed.txt

And here is the client log (ssh -vvv) for the same event (but a
different session)

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--- Comment #5 from Damien Miller <djm at mindrot.org> ---
Comment on attachment 3583
  --> https://bugzilla.mindrot.org/attachment.cgi?id=3583
ssh_client_debug3_log_key_auth_failed.txt

thanks - yes, this is the 3rd-party gssapi-kex modification causing
this. It needs a tweak like the one I described above

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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> ---
problem not in OpenSSH code but in a third-party patch

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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 bugs from openssh-9.1 release cycle

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Colin Watson <cjwatson at debian.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |cjwatson at debian.org

--- Comment #8 from Colin Watson <cjwatson at debian.org> ---
Belatedly, I just wanted to say that I've committed a fix for this to
Debian's openssh git repository
(https://salsa.debian.org/ssh-team/openssh/-/commit/7d291bb6319611a01dfa0f56fd161db11547320f),
so that should deal with this problem for Debian, Ubuntu, and friends
once it trickles down.

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