How to prevent NFS writes by unknown users

[Andre Albsmeier <Andre.Albsmeier@xxxxxxxxxxxxxxx>]

Hi,

how can I prevent an NFS exported filesystem to be written by users
that are not known by the server? My problem is: I export a filesystem
/people to some PCs running PCNFS on our network. Users there typically
have homedirectories which contain a directoy pub that is 1777 so
that others can write there. However, if you don't pass a username
to PCNFS you are logged in as nobody (uid -2) and can still write to
the pub directories. As a result there are files created that have a
very high uids:

-rw-rw-r--  1 4294967294  andre  1115 Feb 17 10:04 test

This confuses quotacheck which runs endlessly (see also my PR 2325).

A solution could be to prevent that uids that are unknown by the server
are not allowed to write to the fs. Or, to prevent special uids to
write the fs. I have checked the exports manpage but have no idea
how this could be done..

Any help is greatly appreciated...

Thanks
	-Andre