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

[bfields@fieldses.org (J. Bruce Fields)]

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.

> 
> 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