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

[Jeff Layton <jlayton@kernel.org>]

On Tue, 2024-06-11 at 15:36 -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.
> 
> Cc: Christoph Hellwig <hch@lst.de>
> X-Cc: stable@vger.kernel.org # v6.6+
> Message-Id: 4E9C0D74-A06D-4DC3-A48A-73034DC40395@oracle.com
> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
> ---
>  fs/nfsd/nfs4proc.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/nfsd/nfs4proc.c b/fs/nfsd/nfs4proc.c
> index 46bd20fe5c0f..2e39cf2e502a 100644
> --- a/fs/nfsd/nfs4proc.c
> +++ b/fs/nfsd/nfs4proc.c
> @@ -2269,7 +2269,7 @@ nfsd4_layoutget(struct svc_rqst *rqstp,
>  	const struct nfsd4_layout_ops *ops;
>  	struct nfs4_layout_stateid *ls;
>  	__be32 nfserr;
> -	int accmode = NFSD_MAY_READ_IF_EXEC;
> +	int accmode = NFSD_MAY_READ_IF_EXEC |
> NFSD_MAY_OWNER_OVERRIDE;
>  
>  	switch (lgp->lg_seg.iomode) {
>  	case IOMODE_READ:
> @@ -2359,7 +2359,8 @@ nfsd4_layoutcommit(struct svc_rqst *rqstp,
>  	struct nfs4_layout_stateid *ls;
>  	__be32 nfserr;
>  
> -	nfserr = fh_verify(rqstp, current_fh, 0, NFSD_MAY_WRITE);
> +	nfserr = fh_verify(rqstp, current_fh, 0,
> +			   NFSD_MAY_WRITE |
> NFSD_MAY_OWNER_OVERRIDE);
>  	if (nfserr)
>  		goto out;
>  

Reviewed-by: Jeff Layton <jlayton@kernel.org>