1 files changed, 44 insertions, 5 deletions

diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
index 4ebbb368fce8..1d538be87fa0 100644
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -45,6 +45,11 @@ module_param_named(index, ovl_index_def, bool, 0644);
 MODULE_PARM_DESC(ovl_index_def,
 		 "Default to on or off for the inodes index feature");
 
+static bool ovl_nfs_export_def = IS_ENABLED(CONFIG_OVERLAY_FS_NFS_EXPORT);
+module_param_named(nfs_export, ovl_nfs_export_def, bool, 0644);
+MODULE_PARM_DESC(ovl_nfs_export_def,
+		 "Default to on or off for the NFS export feature");
+
 static void ovl_entry_stack_free(struct ovl_entry *oe)
 {
 	unsigned int i;
@@ -342,6 +347,9 @@ static int ovl_show_options(struct seq_file *m, struct dentry *dentry)
 		seq_printf(m, ",redirect_dir=%s", ofs->config.redirect_mode);
 	if (ofs->config.index != ovl_index_def)
 		seq_printf(m, ",index=%s", ofs->config.index ? "on" : "off");
+	if (ofs->config.nfs_export != ovl_nfs_export_def)
+		seq_printf(m, ",nfs_export=%s", ofs->config.nfs_export ?
+						"on" : "off");
 	return 0;
 }
 
@@ -374,6 +382,8 @@ enum {
 	OPT_REDIRECT_DIR,
 	OPT_INDEX_ON,
 	OPT_INDEX_OFF,
+	OPT_NFS_EXPORT_ON,
+	OPT_NFS_EXPORT_OFF,
 	OPT_ERR,
 };
 
@@ -385,6 +395,8 @@ static const match_table_t ovl_tokens = {
 	{OPT_REDIRECT_DIR,		"redirect_dir=%s"},
 	{OPT_INDEX_ON,			"index=on"},
 	{OPT_INDEX_OFF,			"index=off"},
+	{OPT_NFS_EXPORT_ON,		"nfs_export=on"},
+	{OPT_NFS_EXPORT_OFF,		"nfs_export=off"},
 	{OPT_ERR,			NULL}
 };
 
@@ -491,6 +503,14 @@ static int ovl_parse_opt(char *opt, struct ovl_config *config)
 			config->index = false;
 			break;
 
+		case OPT_NFS_EXPORT_ON:
+			config->nfs_export = true;
+			break;
+
+		case OPT_NFS_EXPORT_OFF:
+			config->nfs_export = false;
+			break;
+
 		default:
 			pr_err("overlayfs: unrecognized mount option \"%s\" or missing value\n", p);
 			return -EINVAL;
@@ -696,13 +716,16 @@ static int ovl_lower_dir(const char *name, struct path *path,
 		*remote = true;
 
 	/*
-	 * The inodes index feature needs to encode and decode file
-	 * handles, so it requires that all layers support them.
+	 * The inodes index feature and NFS export need to encode and decode
+	 * file handles, so they require that all layers support them.
 	 */
-	if (ofs->config.index && ofs->config.upperdir &&
+	if ((ofs->config.nfs_export ||
+	     (ofs->config.index && ofs->config.upperdir)) &&
 	    !ovl_can_decode_fh(path->dentry->d_sb)) {
 		ofs->config.index = false;
-		pr_warn("overlayfs: fs on '%s' does not support file handles, falling back to index=off.\n", name);
+		ofs->config.nfs_export = false;
+		pr_warn("overlayfs: fs on '%s' does not support file handles, falling back to index=off,nfs_export=off.\n",
+			name);
 	}
 
 	return 0;
@@ -983,6 +1006,12 @@ static int ovl_make_workdir(struct ovl_fs *ofs, struct path *workpath)
 		pr_warn("overlayfs: upper fs does not support file handles, falling back to index=off.\n");
 	}
 
+	/* NFS export of r/w mount depends on index */
+	if (ofs->config.nfs_export && !ofs->config.index) {
+		pr_warn("overlayfs: NFS export requires \"index=on\", falling back to nfs_export=off.\n");
+		ofs->config.nfs_export = false;
+	}
+
 out:
 	mnt_drop_write(mnt);
 	return err;
@@ -1141,6 +1170,10 @@ static struct ovl_entry *ovl_get_lowerstack(struct super_block *sb,
 	} else if (!ofs->config.upperdir && stacklen == 1) {
 		pr_err("overlayfs: at least 2 lowerdir are needed while upperdir nonexistent\n");
 		goto out_err;
+	} else if (!ofs->config.upperdir && ofs->config.nfs_export &&
+		   ofs->config.redirect_follow) {
+		pr_warn("overlayfs: NFS export requires \"redirect_dir=nofollow\" on non-upper mount, falling back to nfs_export=off.\n");
+		ofs->config.nfs_export = false;
 	}
 
 	err = -ENOMEM;
@@ -1217,6 +1250,7 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
 		goto out_err;
 
 	ofs->config.index = ovl_index_def;
+	ofs->config.nfs_export = ovl_nfs_export_def;
 	err = ovl_parse_opt((char *) data, &ofs->config);
 	if (err)
 		goto out_err;
@@ -1277,8 +1311,13 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
 	}
 
 	/* Show index=off in /proc/mounts for forced r/o mount */
-	if (!ofs->indexdir)
+	if (!ofs->indexdir) {
 		ofs->config.index = false;
+		if (ofs->upper_mnt && ofs->config.nfs_export) {
+			pr_warn("overlayfs: NFS export requires an index dir, falling back to nfs_export=off.\n");
+			ofs->config.nfs_export = false;
+		}
+	}
 
 	/* Never override disk quota limits or use reserved space */
 	cap_lower(cred->cap_effective, CAP_SYS_RESOURCE);