NFSD: Return NFS4ERR_FILE_OPEN only when renaming over an open file

RFC 8881 Section 18.26.4 paragraphs 1 - 3 tell us that RENAME should
return NFS4ERR_FILE_OPEN only when the target object is a file that
is currently open. If the target is a directory, some other status
must be returned.

Generally I expect that a delegation recall will be triggered in
some of these circumstances. In other cases, the VFS might return
-EBUSY for other reasons, and NFSD has to ensure that errno does
not leak to clients as a status code that is not permitted by spec.

There are some error flows where the target dentry hasn't been
found yet. The default value for @type therefore is S_IFDIR to return
an alternate status code in those cases.

Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

fs/nfsd/vfs.c

@@ -1794,16 +1794,27 @@ nfsd_has_cached_files(struct dentry *dentry)
 	return ret;
 }
 
-/*
- * Rename a file
- * N.B. After this call _both_ ffhp and tfhp need an fh_put
+/**
+ * nfsd_rename - rename a directory entry
+ * @rqstp: RPC transaction context
+ * @ffhp: the file handle of parent directory containing the entry to be renamed
+ * @fname: the filename of directory entry to be renamed
+ * @flen: the length of @fname in octets
+ * @tfhp: the file handle of parent directory to contain the renamed entry
+ * @tname: the filename of the new entry
+ * @tlen: the length of @tlen in octets
+ *
+ * After this call _both_ ffhp and tfhp need an fh_put.
+ *
+ * Returns a generic NFS status code in network byte-order.
  */
 __be32
 nfsd_rename(struct svc_rqst *rqstp, struct svc_fh *ffhp, char *fname, int flen,
 			    struct svc_fh *tfhp, char *tname, int tlen)
 {
 	struct dentry	*fdentry, *tdentry, *odentry, *ndentry, *trap;
 	struct inode	*fdir, *tdir;
+	int		type = S_IFDIR;
 	__be32		err;
 	int		host_err;
 	bool		close_cached = false;
@@ -1861,11 +1872,14 @@ nfsd_rename(struct svc_rqst *rqstp, struct svc_fh *ffhp, char *fname, int flen,
 	host_err = -EINVAL;
 	if (odentry == trap)
 		goto out_dput_old;
+	type = d_inode(odentry)->i_mode & S_IFMT;
 
 	ndentry = lookup_one_len(tname, tdentry, tlen);
 	host_err = PTR_ERR(ndentry);
 	if (IS_ERR(ndentry))
 		goto out_dput_old;
+	if (d_inode(ndentry))
+		type = d_inode(ndentry)->i_mode & S_IFMT;
 	host_err = -ENOTEMPTY;
 	if (ndentry == trap)
 		goto out_dput_new;
@@ -1903,7 +1917,18 @@ nfsd_rename(struct svc_rqst *rqstp, struct svc_fh *ffhp, char *fname, int flen,
  out_dput_old:
 	dput(odentry);
  out_nfserr:
-	err = nfserrno(host_err);
+	if (host_err == -EBUSY) {
+		/*
+		 * See RFC 8881 Section 18.26.4 para 1-3: NFSv4 RENAME
+		 * wants a status unique to the object type.
+		 */
+		if (type != S_IFDIR)
+			err = nfserr_file_open;
+		else
+			err = nfserr_acces;
+	} else {
+		err = nfserrno(host_err);
+	}
 
 	if (!close_cached) {
 		fh_fill_post_attrs(ffhp);