[Bug 3657] New: AuthenticationMethods any apparently not possible after previous non-any assignment

[bugzilla-daemon at mindrot.org]

https://bugzilla.mindrot.org/show_bug.cgi?id=3657

            Bug ID: 3657
           Summary: AuthenticationMethods any apparently not possible
                    after previous non-any assignment
           Product: Portable OpenSSH
           Version: 8.7p1
          Hardware: Other
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P5
         Component: sshd
          Assignee: unassigned-bugs at mindrot.org
          Reporter: krunoslav.sever at desy.de

Put this into sshd_config:

AuthenticationMethods password
Match User root
  AuthenticationMethods any

This fails for

# ssh -V
OpenSSH_8.9p1 Ubuntu-3ubuntu0.6, OpenSSL 3.0.2 15 Mar 2022
# sshd -T
/etc/ssh/sshd_config line 124: "any" must appear alone in
AuthenticationMethods

It is okay for e.g.

# ssh -V
OpenSSH_8.2p1 Ubuntu-4ubuntu0.11, OpenSSL 1.1.1f  31 Mar 2020

I think I have narrowed it down to the code change in commit a10f929d1,
between 8.6 and 8.7:

servconf.c:process_server_config_line_depth(...)
  case sAuthenticationMethods:
    ...

The code, before and after this change, rejects "any" if
options->num_auth_methods>0.

The working code ensures this to be 0 at the start of the loop with a
surrounding if, so this does not trigger.

The changed code misses the surrounding if.

It may be that the old code resets the num_auth_count before processing
the config line and the new code does not.

But this seems to be a solid starting point.

Best
  Kruno

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