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Allow userok@ip_good, Deny userok@any_other_ip and Allow *@*

Posted on 2010-08-25
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Last Modified: 2013-11-17
Is it possible? I'm running sshd on Aix6.1

Scenario:
ALLOW only access from: userok@ip_good
DENY access from userok@*
and
ALLOW acces from *@*

Thanks
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Question by:sminfo
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Accepted Solution

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arnold earned 1000 total points
ID: 33521779
I've not used AIX, but do not think it is possible.
You can use the hosts.allow/hosts.deny if your SSH has tcp_wrappers to deny based on IP.

If sshd with tcp_wrappers handles the user@ip,
The other issue is that deny supersedes allows such that an entry in Allow userok@ip_good will be ignored because of the entry in DENY: sshd:userok@*  

I've not tested whether username@ is even an option which seems rather problemativ as it will be a nightmare to track down. i.e. user is active everywhere except the user can not connect.
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Assisted Solution

by:woolmilkporc
woolmilkporc earned 1000 total points
ID: 33521801
Hello again,
I fear this will not be feasible.
All "DenyUsers user@host" directives in sshd_config are processed before the "Allow..." directives, and once a user's access is denied it will not be granted back to them depending on a particular host.
wmp
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Author Comment

by:sminfo
ID: 33522281
Hi wmp and arnold,

The fact is I have a user 'userok' who uses to connect all my servers and run certain commands via sshd. I want to block access in my servers  from userok@* but let only access to sshd to userok@ip_good. :-)
Am I asking too much? I've searched a lot but can find a solution to make this possible.
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Expert Comment

by:woolmilkporc
ID: 33522424
I think we understood your question and we answered it: No, it is not possible to achieve what you desire.
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Expert Comment

by:arnold
ID: 33522523
You are trying to combine two separate functions into working in tandem.
I.e. TCP based access list (tcp_wrappers) allows access control to SSHD.
You can use the hosts.allow and hosts.deny to deny sshd:all and in the hosts.allow add the SSHD: IPrange, ips, etc. that you want to allow.

The SSH level restriction for user and group access will handle that side using AllowGroups, AllowUsers, DenyGroups, DenyUsers will process the deny first.

The problem is you seemingly want to limit access of a specific user to a specific IP.

An option you could have is to replace the shell configured for userok.
instead of /bin/bash, you could have an intermediary shell which is a script that will check whether the user is connecting from ip_good by checking the SSH_client env source. If it is, the script runs bash. If it is not, the script exits which will terminate the ssh session.

You would need to add this overlay/wrapper script on every system as well as modify the userok /etc/passwd entry if it is not centrally managed using NIS, NIS+, LDAP, etc.
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