NFS-bug or not ?

[Mikhail E. Zakharov]

> On May 12, 2004, at 3:31 AM, Mikhail E. Zakharov wrote:
> > When playing with NFS under FreeBSD, I've noticed something strange.
> > You know it's impossible to export 2 directories of the same file 
> > system on the server to the 1 nfs-client:
> > server# cat /etc/exports
> > /usr/c client
> > /usr/d client
> > server# killall -HUP mountd
> > server# showmount -e
> > /usr/c                             Everyone
> >
> > There is no /usr/d exported. And we got errors in /var/log/messages:
> > mountd[377]: can't change attributes for /usr/d
> > mountd[377]: bad exports list line /usr/d
> 
> Please refer to _Managing NFS and NIS_, O'Reilly, p92:
> 
> "2. You cannot export any subdirectory of an exported filesystem unless 
> the
>   subdirectory is on a different physical device.
> 
>   3. You cannot export any parent directory of an exported filesystem 
> unless
>   the parent is on a different physical device."
> 
> Basicly, NFS exports work on a per-filesystem basis, although one can 
> use symbolic links to achieve results similar to what you are trying to 
> do by exporting different subdirectories of the same filesystem.
> 
> There's a more extensive writeup about this here:
> 
> http://www.pkix.net/~chuck/doc/NFS/article.html
 
> > But it's possible(!) to fool mountd when using the -network key.
> > Let's try to export /usr/a as read-only system for the whole network, 
> > and /usr/b writable for one host, and not readable for other. NB! Our 
> > NFS-client (192.168.12.98) is from 192.168.0.0/16 network. See this 
> > example:
> [ ... ]
> > When we mounted them on client. Let's make additional tests:
> > client# echo "something stupid" > /mnt/test.txt
> > client# echo "something stupid1" > /mnt1/test1.txt
> > client# cat /mnt/test.txt
> > something stupid
> > client# cat /mnt1/test1.txt
> > something stupid1
> >
> > Oh, my God! Both of the exported directories are writable.
> 
> If you export one filesystem ro to an entire subnet, and then also 
> export the same filesystem rw to a specific machine, the machine 
> granted r/w permissions can write to that filesystem, yes.  That's by 
> design.

Ok, Per-filesystem basis explains everything. Thaks!
 
> If some other machine could write to the filesystem, or if you choose 
> to export two different filesystems with different permissions, that 
> would indicate a problem...
> 
> -- 
> -Chuck
> 
>