Re: [RFC PATCH 0/3] nfsd: close potential race between open and setting delegation

[Jeff Layton <jlayton@kernel.org>]

On Mon, 2022-07-18 at 17:18 -0400, J. Bruce Fields wrote:
> On Thu, Jul 14, 2022 at 11:28:16AM -0400, Jeff Layton wrote:
> > Here's a first stab at a patchset to close a potential race when setting
> > a delegation on a file. Between the point where we open the file and
> > where we set the delegation, another task or client could unlink or
> > rename the dentry. If that occurs, we shouldn't hand out a delegation
> > in the open response, but we don't prevent that today.
> > 
> > The basic idea here is to re-do the lookup after setting the delegation.
> > If the resulting dentry is not the one we have in the open, then we can
> > reject handing out a delegation.
> 
> I have this distinct memory of actually doing that before.
> 
> But looking through the git history all I find is 4335723e8e9f "nfsd4:
> fix delegation-unlink/rename race", from 2014, which claims to fix a
> similar-sounding race in a different way.
> 
> How are you reproducing this?
> 
> --b.
> 

I'm not at all, so far. This race is entirely theoretical. Probably we
could reproduce it by introducing some artificial delays or something.

> > 
> > Only lightly tested, so this is an RFC for now.
> > 
> > Jeff Layton (3): nfsd: drop fh argument from alloc_init_deleg nfsd:
> > rework arguments to nfs4_set_delegation nfsd: vet the opened dentry
> > after setting a delegation
> > 
> >  fs/nfsd/nfs4state.c | 65
> >  ++++++++++++++++++++++++++++++++++++++------- 1 file changed, 55
> >  insertions(+), 10 deletions(-)
> > 
> > -- 2.36.1

-- 
Jeff Layton <jlayton@kernel.org>