ovl: fix mount option checks for nfs_export with no upperdir

Without upperdir mount option, there is no index dir and the dependency
checks nfs_export => index for mount options parsing are incorrect.

Allow the combination nfs_export=on,index=off with no upperdir and move
the check for dependency redirect_dir=nofollow for non-upper mount case
to mount options parsing.

Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

fs/overlayfs/super.c

@@ -580,12 +580,19 @@ static int ovl_parse_opt(char *opt, struct ovl_config *config)
 		}
 	}
 
-	/* Workdir is useless in non-upper mount */
-	if (!config->upperdir && config->workdir) {
-		pr_info("option \"workdir=%s\" is useless in a non-upper mount, ignore\n",
-			config->workdir);
-		kfree(config->workdir);
-		config->workdir = NULL;
+	/* Workdir/index are useless in non-upper mount */
+	if (!config->upperdir) {
+		if (config->workdir) {
+			pr_info("option \"workdir=%s\" is useless in a non-upper mount, ignore\n",
+				config->workdir);
+			kfree(config->workdir);
+			config->workdir = NULL;
+		}
+		if (config->index && index_opt) {
+			pr_info("option \"index=on\" is useless in a non-upper mount, ignore\n");
+			index_opt = false;
+		}
+		config->index = false;
 	}
 
 	err = ovl_parse_redirect_mode(config, config->redirect_mode);
@@ -622,11 +629,13 @@ static int ovl_parse_opt(char *opt, struct ovl_config *config)
 
 	/* Resolve nfs_export -> index dependency */
 	if (config->nfs_export && !config->index) {
-		if (nfs_export_opt && index_opt) {
+		if (!config->upperdir && config->redirect_follow) {
+			pr_info("NFS export requires \"redirect_dir=nofollow\" on non-upper mount, falling back to nfs_export=off.\n");
+			config->nfs_export = false;
+		} else if (nfs_export_opt && index_opt) {
 			pr_err("conflicting options: nfs_export=on,index=off\n");
 			return -EINVAL;
-		}
-		if (index_opt) {
+		} else if (index_opt) {
 			/*
 			 * There was an explicit index=off that resulted
 			 * in this conflict.
@@ -1603,10 +1612,6 @@ static struct ovl_entry *ovl_get_lowerstack(struct super_block *sb,
 	if (!ofs->config.upperdir && numlower == 1) {
 		pr_err("at least 2 lowerdir are needed while upperdir nonexistent\n");
 		return ERR_PTR(-EINVAL);
-	} else if (!ofs->config.upperdir && ofs->config.nfs_export &&
-		   ofs->config.redirect_follow) {
-		pr_warn("NFS export requires \"redirect_dir=nofollow\" on non-upper mount, falling back to nfs_export=off.\n");
-		ofs->config.nfs_export = false;
 	}
 
 	stack = kcalloc(numlower, sizeof(struct path), GFP_KERNEL);