[Bug 191218] mountd: can't change attributes for XXXXXXX: Invalid radix node head, rn: 0 0xXXXXXXXXXXXXXXX; can still mount path

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=191218

--- Comment #5 from yaneurabeya at gmail.com ---
(In reply to Xin LI from comment #4)
> (In reply to yaneurabeya from comment #3)
> > (In reply to Xin LI from comment #2)
> > > Exporting subdirectories of a mountpoint is problematic and this is a well
> > > known limitation of the protocol.  I don't consider this as a security issue
> > > because the administrator is supposed to know what they are doing.
> > 
> > The security concern was over the fact that mountd is clearly reporting an
> > error in the code, but hiding the fact that it's actually an error; unless
> > the administrator is looking for errors from mountd, they have absolutely
> > _no_ idea that the path is actually exported.
> 
> mountd have (correctly) reported that it was unable to change the export
> attributes, we could, of course, use better error message, but if the
> administrator chooses to ignore error messages, there is nothing we can do
> with it.
> 
> Also, exporting subdirectories just plain doesn't work because the NFS
> client can still request anything in the mountpoint.  Properly implemented
> client does not allow it but an attacker do not have to use a properly
> implemented one.  This is well known and relying on this security model is
> just plain wrong.

I forgot to include the fact that localhost:/tmp/bar was mounted to /mnt ; this
was implied in my reproduction steps.

/tmp/foo and /tmp/bar are two distinct paths. Why is /tmp/foo being exported if
it's not showing up in showmount -e?

Yes, I know that I've been playing in Linux for a little too long (9 months),
and looking back I'm not using the prescribed syntax for exports(5), but I
expected the code to not export /tmp/bar and it did.

(posing the question differently) As a sysadmin/support engineer, how could I
understand that mountd has actually exported the directory if the tools that
should be doing this (showmount -e) don't print out anything meaningful?

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