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XROOTD-L  February 2006

XROOTD-L February 2006

Subject:

Re: xrootd redirection based on client's subnet

From:

Artem Trunov <[log in to unmask]>

Date:

3 Feb 2006 07:17:23 -0800 (PST)Fri, 3 Feb 2006 07:17:23 -0800 (PST)

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TEXT/PLAIN (134 lines)

Hi, Derek!

Thanks for all explanations! I am now trying to actually setup servers
for Alice.

Since this libTokenAuthzOfs library is replacing libXrdOfs in the
xrd.fslib directive , is it compatible with original?

I tried to compile xrootd (20060105-0311) with token support, but got the
following:

XrdTokenAuthzOfs.cc:8:25: TTokenAuthz.h: No such file or directory
XrdTokenAuthzOfs.cc: In member function `virtual int
   XrdTokenAuthzOfsFile::open(const char*, int, unsigned int, const
   XrdSecEntity*, const char*)':
XrdTokenAuthzOfs.cc:71: `TAuthzXMLreader' undeclared (first use this
function)

..etc...

For my very first tests, I can probably use production alien installation
at our site with it's token library, but I do need to be able to compile
xrootd with it for normal production installations...

Is this just packaging problems? Or there dependencies on ROOT?

Artem.


On Thu, 2 Feb 2006, Derek Feichtinger wrote:

> Hi, Artem
>
> On Thursday 02 February 2006 11.10, Artem Trunov wrote:
> > Hi, Derek!
> >
> > Thanks for detailed explanations! I now see that we indeed can't get away
> > with generic setup of xrootd clusters, and will have to run AliEn-enabled
> > version. It's not a big problem by itself, buth there is a complication -
> > we have to maintain authorization database on every leaf node - not a nice
> > thing...
>
> No, I was too unclear in my previous mail.
> The leaf nodes are completely generic. They all contain the same little policy
> file where keys per VO are defined and maybe some special rules, if required
> (you can slice of part of the namespace for a certain VO, etc). The
> authorization decision is taken by the catalog. The token you get contains
> everything that the xrootd needs to determine the access rights. The method
> just guarantees that the catalog's decision is safely forwarded to the
> xrootd.
>
> Conceptually, the catalog is the owner of all files in this method (however,
> we provided a possibility in the policy file, where local site policy can be
> enforced, since this is a requirement from some sites).
>
> >
> > If I understad you correctly, you prefere to avoid authorization on the
> > master, and push it to leaf nodes? What do you think about reverse
> > solution - authorization only on the master? This way the master is also
> > you authorization server,  and leaf nodes are generic...
>
> We want to avoid authentication on the redirector, because it is slow (and as
> a consequence, I cannot do full authorization, because this depends on prior
> authentication). The redirector should work in a way that it can redirect
> clients as fast as possible, leaving the grunt work to the leafs.
>
> For your approach, you would need to modify the xrootd protocol in a way that
> the redirector informs the leaf that your access is allowed, because your
> client is not proxied through the redirector to the leafs, but really makes
> an own connection to the leaf node: If you know the name of the file and on
> which leaf it resides, you can just go there directly without ever contacting
> the redirector. So, in the present system you need authen and authz on the
> leafs.
> I think this is ok, because the additional effort is then optimally
> distributed over the servers and you don't have a bottleneck in a centrally
> important machine.
>
> Cheers,
> Derek
>
>
> >
> > Artem.
> >
> > On Thu, 2 Feb 2006, Derek Feichtinger wrote:
> > > Hello, Artem
> > >
> > > > > we would be forced to run it on both redirectors and leaf nodes
> > > > > (awful).
> > > >
> > > > Could you please explain a bit more, since this contradicts to Andy's
> > > > answer. I.e. what will happen if Alien client carrying authz token
> > > > comes to a server w/o AliEn authz lib?
> > >
> > > Ok. In our current design, the client asks the xrootd for the LFN. The
> > > PFN is contained in the encrypted token from the catalog together with
> > > the permission information and the requester's certificate subject (the
> > > token can contain entries for multiple files). But the redirector needs
> > > to know the PFN in order to perform its duty, so it has to decrypt the
> > > token.
> > >
> > > xrootd gets the request as a normal URL:
> > > root://server/LFN?authz=encrypted-token&vo=VO-name
> > >
> > > This was done, so that even the names of the physical files are hidden
> > > from outside (and we wanted to have this in mainly to show what
> > > possibilities the method offers, also for the paper we presented at
> > > SC05). However, this forces us to decode the token already on the
> > > redirector.
> > > We could drop this hiding of the PFN, or we could think of a setup where
> > > we still perform the token decryption on the redirector, but without
> > > doing any authentication there. Authentication will then be done on the
> > > leaf node together with another token decryption. The token decryption is
> > > pretty fast (<10 ms).
> > > I think this would be a good solution.
> > >
> > > The whole mechanism has the advantage that it can be easily implemented
> > > for every catalog and that a single server can also easily work securely
> > > for a number of different VOs (the catalog and the storage elements just
> > > need to know each others public keys. That's the central part of the
> > > encryption) Here is a link to the SC05 paper, if you are interested:
> > >
> > > Paper: http://people.web.psi.ch/feichtinger/doc/authz.pdf
> > >
> > > (slides, somewhat flashy and ppt format):
> > > http://people.web.psi.ch/feichtinger/doc/Grid05_dfeich.ppt
> > >
> > >
> > > Cheers,
> > > Derek
>


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