On Jun 25, 2009, at 9:45 AM, Nicholas Mills wrote:
Rob -
You're absolutely correct. The capabilities are trusted and can only
come from servers. If a client gets a hold of one it's assumed that
some server determined the client had a need for the capability.
Servers are able to create capabilities for themselves that allow
them to do anything.
Everyone -
Right now I haven't had a need to differentiate between client and
server requests. However, in the case of batch create I'd really
like to prevent a client from having access to this capability. For
the moment the only client state machine to use batch create is sys-
symlink, and even then the state machine only creates one handle.
Walt suggested perhaps limiting clients to a single create by use of
some sort of differentiator in the capability. This would avoid the
need to change how PVFS is working today, but means you'd have to do a
little parameter checking; how awkward would that be? Seems to me you
might want to similarly be restricting the *types* of objects that a
client could create, if you're going to try to minimize the potential
damage from this particular call. Since clients would only be using
this to create a symlink object (if I understand the earlier
discussion correctly), you could limit clients to only creating
symlink objects and only one at a time.
Otherwise a client might be able to use this facility to create a
metadata object, populate it with something that makes it look like it
should have permission to access the associated datafiles, and then
point at some datafiles it would like to access? I dunno the bigger
picture, so I don't know if you have already handled this possibility
in some other way...
Ok, so all that leads me to agree that you don't ideally want clients
to be given permission to use this operation :).
Above all I want everyone to know that I'm very open to suggestion.
Of course I realize that in the future new client state machines
could make use of the batch create request. But for now, at least,
only the servers have a legitimate need for this request.
Now that I'm looking at this, why aren't you equally worried about a
user using the new create request and specifying some ridiculously
large num_dfiles_req? Doesn't that have the same problem with respect
to resource consumption?
Rob
_______________________________________________
Pvfs2-developers mailing list
Pvfs2-developers@beowulf-underground.org
http://www.beowulf-underground.org/mailman/listinfo/pvfs2-developers
