Re: [PATCH v2] NFSD: Support write delegations in LAYOUTGET

[Christoph Hellwig <hch@lst.de>]

On Tue, Jun 11, 2024 at 03:36:46PM -0400, cel@kernel.org wrote:
> From: Chuck Lever <chuck.lever@oracle.com>
> 
> I noticed LAYOUTGET(LAYOUTIOMODE4_RW) returning NFS4ERR_ACCESS
> unexpectedly. The NFS client had created a file with mode 0444, and
> the server had returned a write delegation on the OPEN(CREATE). The
> client was requesting a RW layout using the write delegation stateid
> so that it could flush file modifications.
> 
> Creating a read-only file does not seem to be problematic for
> NFSv4.1 without pNFS, so I began looking at NFSD's implementation of
> LAYOUTGET.
> 
> The failure was because fh_verify() was doing a permission check as
> part of verifying the FH presented during the LAYOUTGET. It uses the
> loga_iomode value to specify the @accmode argument to fh_verify().
> fh_verify(MAY_WRITE) on a file whose mode is 0444 fails with -EACCES.
> 
> To permit LAYOUT* operations in this case, add OWNER_OVERRIDE when
> checking the access permission of the incoming file handle for
> LAYOUTGET and LAYOUTCOMMIT.

This looks reasonable to me:

Reviewed-by: Christoph Hellwig <hch@lst.de>