Confusion on SSH and PAM

[Rakhesh Sasidharan]

CyberLeo Kitsana wrote:

> Rakhesh Sasidharan wrote:
>> Any ideas or nudges in the right direction as to why this is happening?
>> Looks like I've understood the interaction between SSH and PAM wrong
>> here, so would appreciate some enlightenment.
>
> According to my understanding of the SSH protocol, you're continually
> asked because an authentication failure is not a fatal error.
>
> When authenticating an SSH session, a list of mutually supported methods
> is compiled (public-key, challenge-response, S/Key,
> keyboard-interactive, plaintext) and the client cycles through the list
> based on what it thinks is most likely to work.
>
> It's perfectly acceptable for a client to attempt password
> authentication before public-key, or even interleave them. All the
> server can do is say yay or nay to an attempt with a restricted method,
> because it cannot know if the next attempt may utilize an allowed method.
>
> After the requisite three or five failed attempts (depending on the
> server config), it may send a general failure code (too many failed
> attempts) and disconnect the client at it's discretion.

Here's another oddity I encountered today.

If "PermitRootLogin" is set to "forced-commands-only", my understanding is 
the SSHD will permit root logins if a command to be executed is given. But 
that doesn't seem to be the case in practice! I have keys setup for root 
to login, but instead of letting me in with those keys, SSHD ignores them, 
passes me to PAM for password prompting (three times) and the denies me 
out! Very strange.

I even setup a "Match User" clause for root and specified a command to 
run. Still, SSHD refuses to let me in with/ without key and for a specific 
command.

Regards,
 				- Rakhesh
                                 http://rakhesh.net/