Re: NFS FAQ updates

["J. Bruce Fields" <bfields@fieldses.org>]

On Sun, Mar 13, 2005 at 05:10:11PM -0500, Trond Myklebust wrote:
> The subtree_check option attempts to decide whether or not a file lies
> within an exported subtree. If you turn it off, then people can
> theoretically try to guess filehandles and gain access to the files
> (assuming the access permissions on the file itself allow that).

I wouldn't put too much emphasis on that "theoretically".  The root
directory on all my ext2/3 filesystems has inode number 2, and as far as
I can tell guessing the rest of the rest of the filehandle just comes
down to guessing the root device, which on my machines is always
/dev/hdaN for some very small N.  Add a few more for people with scsi
and so on, and I bet you could cover most linux NFS servers with a dozen
guesses.  Now just lookup and readdir down to wherever you want.  Am I
missing anything here?

If the administrator tightened down directory permissions a bit, you'll
be forced to guess filehandles for objects deeper in the filesystem,
which may be a little harder.  I wouldn't count on it.

--b.


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