ovl: store and show the user provided lowerdir mount option

We are about to add new mount options for adding lowerdir one by one,
but those mount options will not support escaping.

For the existing case, where lowerdir mount option is provided as a colon
separated list, store the user provided (possibly escaped) string and
display it as is when showing the lowerdir mount option.

Signed-off-by: Amir Goldstein <amir73il@gmail.com>

Author: amir73il

fs/overlayfs/params.c

@@ -332,12 +332,18 @@ static int ovl_parse_param_upperdir(const char *name, struct fs_context *fc,
 	return 0;
 }
 
-static void ovl_parse_param_drop_lowerdir(struct ovl_fs_context *ctx)
+static void ovl_reset_lowerdirs(struct ovl_fs_context *ctx)
 {
-	for (size_t nr = 0; nr < ctx->nr; nr++) {
-		path_put(&ctx->lower[nr].path);
-		kfree(ctx->lower[nr].name);
-		ctx->lower[nr].name = NULL;
+	struct ovl_fs_context_layer *l = ctx->lower;
+
+	// Reset old user provided lowerdir string
+	kfree(ctx->lowerdir_all);
+	ctx->lowerdir_all = NULL;
+
+	for (size_t nr = 0; nr < ctx->nr; nr++, l++) {
+		path_put(&l->path);
+		kfree(l->name);
+		l->name = NULL;
 	}
 	ctx->nr = 0;
 	ctx->nr_data = 0;
@@ -366,7 +372,7 @@ static int ovl_parse_param_lowerdir(const char *name, struct fs_context *fc)
 	 */
 
 	/* drop all existing lower layers */
-	ovl_parse_param_drop_lowerdir(ctx);
+	ovl_reset_lowerdirs(ctx);
 
 	if (!*name)
 		return 0;
@@ -376,6 +382,11 @@ static int ovl_parse_param_lowerdir(const char *name, struct fs_context *fc)
 		return -EINVAL;
 	}
 
+	// Store user provided lowerdir string to show in mount options
+	ctx->lowerdir_all = kstrdup(name, GFP_KERNEL);
+	if (!ctx->lowerdir_all)
+		return -ENOMEM;
+
 	dup = kstrdup(name, GFP_KERNEL);
 	if (!dup)
 		return -ENOMEM;
@@ -448,7 +459,7 @@ static int ovl_parse_param_lowerdir(const char *name, struct fs_context *fc)
 	return 0;
 
 out_put:
-	ovl_parse_param_drop_lowerdir(ctx);
+	ovl_reset_lowerdirs(ctx);
 
 out_err:
 	kfree(dup);
@@ -554,7 +565,7 @@ static int ovl_get_tree(struct fs_context *fc)
 
 static inline void ovl_fs_context_free(struct ovl_fs_context *ctx)
 {
-	ovl_parse_param_drop_lowerdir(ctx);
+	ovl_reset_lowerdirs(ctx);
 	path_put(&ctx->upper);
 	path_put(&ctx->work);
 	kfree(ctx->lower);
@@ -870,24 +881,13 @@ int ovl_show_options(struct seq_file *m, struct dentry *dentry)
 {
 	struct super_block *sb = dentry->d_sb;
 	struct ovl_fs *ofs = OVL_FS(sb);
-	size_t nr, nr_merged_lower = ofs->numlayer - ofs->numdatalayer;
+	char **lowerdirs = ofs->config.lowerdirs;
 
 	/*
-	 * lowerdirs[] starts from offset 1, then
-	 * >= 0 regular lower layers prefixed with : and
-	 * >= 0 data-only lower layers prefixed with ::
-	 *
-	 * we need to escase comma and space like seq_show_option() does and
-	 * we also need to escape the colon separator from lowerdir paths.
+	 * lowerdirs[0] holds the colon separated list that user provided
+	 * with lowerdir mount option.
 	 */
-	seq_puts(m, ",lowerdir=");
-	for (nr = 1; nr < ofs->numlayer; nr++) {
-		if (nr > 1)
-			seq_putc(m, ':');
-		if (nr >= nr_merged_lower)
-			seq_putc(m, ':');
-		seq_escape(m, ofs->config.lowerdirs[nr], ":, \t\n\\");
-	}
+	seq_show_option(m, "lowerdir", lowerdirs[0]);
 	if (ofs->config.upperdir) {
 		seq_show_option(m, "upperdir", ofs->config.upperdir);
 		seq_show_option(m, "workdir", ofs->config.workdir);

fs/overlayfs/params.h

@@ -32,6 +32,7 @@ struct ovl_fs_context {
 	size_t nr_data;
 	struct ovl_opt_set set;
 	struct ovl_fs_context_layer *lower;
+	char *lowerdir_all; /* user provided lowerdir string */
 };
 
 int ovl_init_fs_context(struct fs_context *fc);

fs/overlayfs/super.c

@@ -1328,8 +1328,11 @@ int ovl_fill_super(struct super_block *sb, struct fs_context *fc)
 	ofs->layers = layers;
 	/*
 	 * Layer 0 is reserved for upper even if there's no upper.
-	 * For consistency, config.lowerdirs[0] is NULL.
+	 * config.lowerdirs[0] is used for storing the user provided colon
+	 * separated lowerdir string.
 	 */
+	ofs->config.lowerdirs[0] = ctx->lowerdir_all;
+	ctx->lowerdir_all = NULL;
 	ofs->numlayer = 1;
 
 	sb->s_stack_depth = 0;