NFSD: Support write delegations in LAYOUTGET

JIRA: https://issues.redhat.com/browse/RHEL-53004

commit abc02e5
Author: Chuck Lever <chuck.lever@oracle.com>
Date:   Tue Jun 11 15:36:46 2024 -0400

    NFSD: Support write delegations in LAYOUTGET

    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>
    Cc: stable@vger.kernel.org # v6.6+
    Message-Id: 4E9C0D74-A06D-4DC3-A48A-73034DC40395@oracle.com
    Reviewed-by: Jeff Layton <jlayton@kernel.org>
    Reviewed-by: Christoph Hellwig <hch@lst.de>
    Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

Signed-off-by: Benjamin Coddington <bcodding@redhat.com>

Author: bcodding-rh

fs/nfsd/nfs4proc.c

@@ -2255,7 +2255,7 @@ 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:
@@ -2345,7 +2345,8 @@ 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;