Re: [PATCH] fix posix lock on NFS

[Trond Myklebust]

On Tue, 2006-01-03 at 15:09 -0500, Peter Staubach wrote:
> Matthew Wilcox wrote:
> >Mandatory locks aren't mandatory for other clients.
> >  
> >
> 
> So?
> 
> I guess that I don't understand this response.
> 
> The server is responsible for keeping itself from attempting to access
> a mandatory lock file.  The client is not responsible for doing so and
> trying to help the server is kind of a waste of time, mostly.
> 
> The mandatory lock mode bits really only come into play when attempting
> to read or write the file.  In this case, the system will automatically
> try to take a lock for the process, if that process does not already
> have a lock.  The server should prevent itself from trying to access
> files like this in order to avoid DoS attacks.
> 
> The NFS client does not support mandatory locking, mostly due to the
> possibility of DoS attacks and also due to the locking and NFS protocols
> not being sufficiently aware of each other.  NFSv4 can be used to address
> this latter problem, but probably not the former.
> 
> So, why deny lock requests for such files?  Especially on the client?

I agree, however that would have been a change in behaviour that would
have been hard to find time to test properly in an -rc6(?) release, so
we went for the quick and dirty fix.

Cheers,
  Trond

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