restrict ssh access

[Valeriu Mutu]

On Fri, Apr 25, 2008 at 07:50:47PM +0000, D Hill wrote:
> On Fri, 25 Apr 2008 at 14:30 -0500, pauls at utdallas.edu confabulated:
> 
>> --On Friday, April 25, 2008 16:41:07 +0000 D Hill <d.hill at yournetplus.com> 
>> wrote:
>> 
>>> On Fri, 25 Apr 2008 at 09:30 -0700, cswiger at mac.com confabulated:
>>> 
>>>> On Apr 25, 2008, at 6:46 AM, Geert Geurts wrote:
>>>>> I've got a server running a ssh server, I want to enable ssh for the use
>>>>> of sftp by a group of users, and limit their ssh access to just allow
>>>>> running passwd so they can change their default password. What whould be
>>>>> the best/easiest way to acomplish this, or something similiar?
>>>> 
>>>> I wonder what would happen if you gave them a shell of 
>>>> "/usr/bin/passwd"...?
>>>> :-)
>>> 
>>> That should work. I just tested. When an ssh connection is made, it 
>>> executes
>>> passwd. As soon as the password is changed, the ssh connection was closed:
>>> 
>>>    %ssh -l asdf 192.168.1.50
>>>    Password:
>>>    ...
>>>    Changing local password for asdf
>>>    Old Password:
>>>    New Password:
>>>    Retype New Password:
>>>    Connection to 192.168.1.50 closed.
>> 
>> Should make for some fascinating experiences with sftp.  :-)
> 
> I believe the connecton would just close. Somehow I missed that sftp part :-(

Indeed, the connection closes. It looks like the SSH server relies on a valid login shell program to run the SFTP server. 

Anyway, may I suggest using ACL?

You'll have to add the 'acls' option in fstab and do a reboot.

After that, put those users in a group and deny that group all the permissions (r,w,x) on all executables on the system.
Set r-x permissions on their _login shell_ (i.e /bin/csh, /bin/sh etc.) and /usr/bin/passwd executable.

It worked for me.

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-- 
Valeriu Mutu