[Sugar-devel] Sugar-Server enhancement
Tony Anderson
tony_anderson at usa.net
Sun Apr 17 04:14:11 EDT 2016
Hi, Manash
After sending the previous e-mail, I got thinking the following
situation. An admin goes to a deployment which reports a problem. Each
of the deployments
for that admin has the schoolserver address 172.18.96.1. This is the
case for the three schools in Rwanda and also for the three schools in
the Philippines.
Will your technique work to register multiple servers with the same IP?
Tony
On 04/17/2016 03:17 PM, Manash Raja wrote:
> Regarding SSH. I think I have found a good solution. (I have tested
> it.) Thanks @Tony for telling where exactly the problem occurs.
>
> Commit :
> https://github.com/sugarlabs/sugar/pull/679/commits/930726741744ebdf6d464b84b31210aa0897124a
> Commit message : ds-backup works independently on its own by using
> priave/public key pair and ignoring known_hosts by setting
> 'StrictHostKeyChecking no'. Problem might arise when other
> applications or user try to connect ssh to server without using
> private/public key. In that case known_hosts should be maintained to
> avoid conflict. Eg scenario: Client ssh into xsce1 on server_address
> say schoolserver id1 of xsce1 stored at known_hosts. Client tries for
> ssh into xsce2 with same server_address (schoolserver) id2 of xsce2
> does not match with id1. Hence error. Solution: If registration is
> successful, we know that we have correct server_address of the xsce,
> hence we take its identification using 'ssh-keyscan -H -t ecdsa
> server_address' and add it to known_hosts. So when ssh is initiated,
> the id of the xsce server is found along with its server_address.
> It removes the use of "ssh-keygen -R" and hence will be more secured.
> It might happen that multiple identification for a particular
> server_address is present in the known_hosts file as "schoolserver" is
> mostly used as the server address. But ssh will take the one that matches.
>
>
> On Sun, Apr 17, 2016 at 7:27 AM, Tony Anderson <tony_anderson at usa.net
> <mailto:tony_anderson at usa.net>> wrote:
>
> In the current backup system, the only involvement of the user is
> to register. The ds-backup script uses the serial-number of the
> XO. The 'known_host' check must pass in order for this to work.
> Normally, this is not a problem because a given deployed XO only
> ever sees one server. It is usually only a problem for the person
> setting up multiple deployments (or multiple servers).
>
> Adam Holt apparently contemplates setting up multiple Raspberry Pi
> size servers with an SD card for content at a single deployment. I
> believe that this environment will not support backup and so there
> would be no need to register (except possibly for ejabberd - I
> haven't looked at that in years). Possibly HaitiOS should not
> execute the ds_backup script. However, if the script fails there
> is consequence. What will be required is that each server on a
> single network have a unique name to support access by
> url:http://schoolserver1, http://schoolserver2, ....
>
> I assume 10.105.57.97 is the IP address of the server. In the
> server setup, the server is set as the network gateway and
> provides dns translation from
> server name to IP. This works with one school server per network
> (the norm). In the special case of multiple school servers, one
> should supply DHCP services and be the gateway. The other school
> servers would need fixed IP addresses. Currently, the school
> server is set up as 172.18.96.1 with a netmask of 255.255.224.0.
> In this scheme, other school servers could be given fixed
> addresses such as 172.18.126.1, 172.18.126.2, .... I have attached
> the relevant information from the school server: /etc/dchpd-xs.conf.
>
> Naturally, you can save the IP address if that is more convenient.
>
> The logic of the situation is that a user should keep its Journal
> backup on a single school server. The current ds_backup would take
> duplicate the same backup on each server. I suppose Sugar could be
> modified to specify backup to a designated school server. The
> proposed backup would fragment the Journal objects since it would
> assume that objects have been backed up and so not make copies on
> alternate school servers.
>
> I am sure in Adam's scenario, the SD cards will not afford
> complete backups from multiple laptops on each SD card. Most
> likely, there would have to be a dedicated server for backup with
> an essentially empty card.
>
> On your third question, system adminstrators use ssh. This is not
> a problem because access is by password. The server is set up for
> ssh xsce-admin at schoolserver
>
> Once logged in, an adminstrator can su to root. This requires two
> independent passwords to authenticate.
>
> Tony
>
>
> On 04/17/2016 05:24 AM, Manash Raja wrote:
>> Hi,
>>
>> Here are some updates.*
>>
>> ssh:* I found from the source code for ds-backup provided by
>> James http://dev.laptop.org/git/users/quozl/ds-backup/ and while
>> searching along the lines of Tony (/The script stores and
>> retrieves using sftp with authentication by public/private key./)
>> that communication by ds-backup is done using this command:
>> /usr/bin/ssh -o "PasswordAuthentication no" -o
>> "StrictHostKeyChecking no" -i ~/.sugar/default/owner.key -l
>> serial_number server_address
>>
>> as you all know that ~/.sugar/default/owner.key is the private
>> key for ~/.sugar/default/owner.key.pub public key. The public key
>> is sent to the server at the time of registration. The server
>> adds this public key to
>> /library/users/serial_number/.ssh/authorized_keys .
>>
>> I understand that ds-backup don't care about the .ssh/known_hosts
>> on the client side due to "StrictHostKeyChecking no" even though
>> the file is getting populated.
>>
>> So the ssh command is concerned of mainly the public/private key
>> pair, serial and the server address. If we know the serial of the
>> laptop that is registered with a server we can connect
>> successfully with it using the above command. But it might fail
>> using a normal ssh command due to known_host conflict. If we
>> assume that all the server communication (sftp and rsync) will
>> occur using private/public keys, then we don't even need to do
>> "ssh-keygen -R hostame" or "rm ~/.ssh/known_hosts" I guess.
>> The issue might have been caused when wrong serial was used to
>> connect to a server which do not have it registered. Which has
>> now been fixed in the patch by retaining the serial for previous
>> registrations.
>>
>> I have tested that we can add to .ssh/config
>> Host custom_server_name
>> HostName 10.105.57.97
>> PasswordAuthentication no
>> StrictHostKeyChecking no
>> IdentityFile ~/.sugar/default/owner.key
>> User <serial>
>>
>> and it works by simply calling : ssh custom_server_name
>> So we can work upon it.
>> A few doubts:
>>
>> 1. What should be used in custom_server_name?
>> 2. How do we expect our codes to sftp or rsync with server?
>> ds-backup will run properly in backup if we keep setting the
>> proper serial. But other than that no application does sftp
>> or rsync to server, so we can define the proper way now.
>> 3. How do we expect a human user to use ssh? the longer command
>> or .ssh/config based command? or simply ssh user at server with
>> constant modifications to known_hosts.
>>
>>
>> *XSCE vs XS*:
>>
>> The patch I built uses relies on xs-authserver which is absent in
>> xs. I really want to add support for XS for this feature. And I
>> discussed on #schoolserver to know if there is any other way to
>> get idmgr database info on client side. XS doesn't seem to
>> support it well enough. I have identified a way to solve this
>> issues by modifying "registration-server" and "idmanager.py"
>> scripts of idmgr.
>>
>> @Jerry
>>
>> I'm concerned with backwards compatibility, the original
>> 'schoolserver'(XS)
>> based on CentOS-6 doesn't offer the xs-authserver service,
>> hence why I
>> mentioned it. I would not want to break a deployment where
>> the older server
>> version is used.
>>
>> It would not break deployment, as Tony mentioned. The maximum
>> harm that can be caused is to have multiple registrations for a
>> single laptop in XS due to inability of XS to provide list of
>> registered laptops to the client.
>>
>> A few doubts:
>>
>> 1. Rough percentage of XS against XSCE out there?
>> 2. Scope of modifying idmgr? I am still looking for alternatives
>> in XS that doesn't need server side modification but till
>> then I really want to know what are the steps if we finally
>> need to modify to establish a clear implementation.
>> 3. Even without XS support, the patch solves the issue of taking
>> the load out of teachers, just that same backup path cannot
>> be ensured if serial keeps changing. Hence, is this a
>> significant issue to need a server modification? As if not,
>> then we can move on and wait until the XS catches up.
>>
>> @Tony, certainly as you said things can be reorganized starting
>> from now in small steps so that future features can easily fall
>> into place. This registration feature may change a component here
>> and there (like idmgr) but in the progress it might provide a
>> cleaner and better framework for server related features. (LDAP
>> being one of them).
>>
>> Thanks.
>>
>>
>> On Sat, Apr 16, 2016 at 7:56 AM, Tony Anderson
>> <tony_anderson at usa.net <mailto:tony_anderson at usa.net>> wrote:
>>
>> The operative code on the school server is
>> /usr/libexec/create_user. What Manash describes
>> is apparently using the db setup by idmgr to list the
>> registered laptops. I don't think you will
>> break compatibility.
>>
>> What I hope we can look at is implementing LDAP as a central
>> authentication for all of the services which
>> require a user name, password. Of the top of my head -
>> Moodle, Khan Academy Lite, OwnCloud, and Elgg.
>>
>> My brief experience with OwnCloud is that it is a shell
>> requiring a lot of configuration. I would be interested if TK has
>> actually deployed it and, if so, how he uses it. I don't know
>> of any one else who is using it at the moment.
>>
>> Tony
>>
>>
>> On 04/16/2016 10:05 AM, Jerry Vonau wrote:
>>
>>
>> On April 15, 2016 at 6:56 PM Manash Raja
>> <mpdmanash at gmail.com <mailto:mpdmanash at gmail.com>> wrote:
>>
>>
>> @Jerry,
>> I haven't modified anything for this feature on the
>> server side. I found
>> that it uses both idmgr and xs-authserver. But the
>> 5000 port is used by
>> xs-authserver to display a list of registered
>> laptops. I didn't enable it
>> myself, it was there. All I did was to setup my
>> server according to the
>> instructions and enabled the "XO register" feature
>> from the admin page.
>>
>> I'm concerned with backwards compatibility, the original
>> 'schoolserver'(XS)
>> based on CentOS-6 doesn't offer the xs-authserver
>> service, hence why I
>> mentioned it. I would not want to break a deployment
>> where the older server
>> version is used.
>>
>>
>> @Tony,
>> Can you tell me how ownCloud is supported by XSCE? I
>> saw it in the
>> services
>> ready to be enabled. So can we not move the storage
>> location of
>> /library/user/<some_id> inside or account based user
>> directories to the
>> cloud storage locations.
>>
>> Thanks
>>
>> The ownCloud service is not enabled out of the box, same
>> as the
>> 'xo-services'. You can enable it and play around, figure
>> out how and where
>> the users' data is stored. Either idmgr or ownCloud could
>> be altered to
>> suit the need. Here it would be safe to rely on
>> xs-authserver's information
>> as there is no existing implementation of owncloud in
>> previous releases of
>> the server software. I can help push the server-side PR's
>> through.
>>
>>
>> Jerry
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