[Pvfs2-developers] Batch create in sys-symlink.sm

[Walter Ligon]

up until now it has been the user's prerogative to create files with as 
many dfiles as he wants - I assume a user is limited to some max by the 
configuration (is he?) but that could be large - so he could allocate 
100 dfiles and only use 2 (if he only uses 1 the stuffing will come into 
play).  I'm open to discussion of how to deal with that in terms of 
interface and such.  If we need that we can work on a way to do it.

Over the last year I've found David & Nick to be very thorough in trying 
to design so that users can only do what they are supposed to do.  It 
may be that it really isn't that bid a deal if users can allocate extra 
object - as long as they can't link anything to them.  I fully suspect 
that we can improve beyond the basic level of security we are working on 
now and we can discuss that.  What I'm saying is I'm not sure how 
important this bulk-create issue really is - but there are ways to deal 
with it.

Walt

Rob Ross wrote:
> 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