Re: 2.6 nfsd troubles - stale filehandles

From: Neil Brown
Date: Wed Dec 03 2003 - 22:15:57 EST

On Wednesday December 3, fredrik@xxxxxxxxxxxxx wrote:
> So, I managed to do it now. The strange thing is, I had created an
> extra share of the home dirs for this test (I had "mount --bind"'ed it
> on /var/lib/nfs/nfstest), and only set subtree_check back on the test
> export, in an attempt to keep the normal parts of the system reliable
> while testing, but just doing that made the real export behave bad as
> well. It seems to run amok as soon as I have subtree_checking on only
> one export.

"mount --bind" certainly has a good chance of confusing nfsd.
If you --bind mount the root of the filesystem somewhere else and
export that, then the filehandles generated will be exactly the same
and nfsd cannot know whether a request is indented for one mountpoint
or the other.
When using --bind, it is best to give an 'fsid=' option in
/etc/exports so that nfsd can use that to differentiate the mount

> nfsd_dispatch: vers 3 proc 1
> nfsd: GETATTR(3) 36: 06000001 0000fe00 00000002 00023b44 00023957 00000000
> nfsd: fh_verify(36: 06000001 0000fe00 00000002 00023b44 00023957 00000000)
> nfsd_acceptable failed at c669a5c0 dc

This strongly suggests that nfsd thought that the user making the
request didn't have 'x' access to the parent of 'dc'. i.e. to /hannes.

> Some more info: I was root while causing this error, and the dir arch
> looks like this (from this filesystem's point of view, it is really my
> home dirs):
> rwxr-xr-x root root /
> rwx--x---+ hannes users /hannes
> rwxr-xr-x hannes users /hannes/dc

And if you are not exporting with no_root_squash, then the user does
not have 'x' access to hannes.

So if you haven't exported with 'no_root_squash', then this completely
makes sense. The nfs client is allowing root access (based on cached
data that some other local users recently accessed) but the server is
not allowing root access.
Arguably you should be getting "permission denied" rather than
"stale", but you certainly shouldn't expect it to work.

If, on the other hand, you have specified no_root_squash, then this is
still very strange.

What export options are you using?


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