openssh unix dev - Oct 2023 - Host name lookup failure using hostbased authentication

There is a nasty problem when using hostbased authentication:

[thomas at sarkovy ~]$ journalctl -l -f | grep -Fe 'sshd['
Okt 22 15:20:54 sarkovy sshd[35034]: userauth_hostbased mismatch: client 
sends htpc.koeller.dyndns.org, but we resolve 192.168.0.2 to 192.168.0.2
Okt 22 15:20:54 sarkovy sshd[35034]: Connection closed by authenticating 
user thomas 192.168.0.2 port 36284 [preauth]
^C

Note that hostname/address lookups work in either direction:

[thomas at sarkovy ~]$ host htpc.koeller.dyndns.org
htpc.koeller.dyndns.org has address 192.168.0.2
htpc.koeller.dyndns.org has IPv6 address fd46:1ffa:d8e0::2
[thomas at sarkovy ~]$ host 192.168.0.2
2.0.168.192.in-addr.arpa domain name pointer htpc.koeller.dyndns.org.

What's wrong here?

Thomas

On Mon, 23 Oct 2023 at 00:43, Thomas K?ller <thomas at koeller.dyndns.org>
wrote:
> There is a nasty problem when using hostbased authentication:
Suggestions:
 - "host" does DNS lookups, but is your system's nsswitch.conf or
equivalent actually configured to use DNS?
 - have you turned off DNS lookups in sshd with "UseDNS no" in
sshd_config?
 - you could try setting "HostbasedUsesNameFromPacketOnly yes" in
sshd_config.

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Darren Tucker (dtucker at dtucker.net)
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