ovl: port to new mount api

We recently ported util-linux to the new mount api. Now the mount(8)
tool will by default use the new mount api. While trying hard to fall
back to the old mount api gracefully there are still cases where we run
into issues that are difficult to handle nicely.

Now with mount(8) and libmount supporting the new mount api I expect an
increase in the number of bug reports and issues we're going to see with
filesystems that don't yet support the new mount api. So it's time we
rectify this.

When ovl_fill_super() fails before setting sb->s_root, we need to cleanup
sb->s_fs_info.  The logic is a bit convoluted but tl;dr: If sget_fc() has
succeeded fc->s_fs_info will have been transferred to sb->s_fs_info.
So by the time ->fill_super()/ovl_fill_super() is called fc->s_fs_info
is NULL consequently fs_context->free() won't call ovl_free_fs().

If we fail before sb->s_root() is set then ->put_super() won't be called
which would call ovl_free_fs(). IOW, if we fail in ->fill_super() before
sb->s_root we have to clean it up.
Signed-off-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Amir Goldstein <amir73il@gmail.com>

fs/overlayfs/super.c

@@ -16,6 +16,7 @@
 #include <linux/posix_acl_xattr.h>
 #include <linux/exportfs.h>
 #include <linux/file.h>
+#include <linux/fs_context.h>
 #include <linux/fs_parser.h>
 #include "overlayfs.h"
 
@@ -253,7 +254,8 @@ static void ovl_put_super(struct super_block *sb)
 {
 	struct ovl_fs *ofs = sb->s_fs_info;
 
-	ovl_free_fs(ofs);
+	if (ofs)
+		ovl_free_fs(ofs);
 }
 
 /* Sync real dirty inodes in upper filesystem (if it exists) */
@@ -408,16 +410,17 @@ static int ovl_show_options(struct seq_file *m, struct dentry *dentry)
 	return 0;
 }
 
-static int ovl_remount(struct super_block *sb, int *flags, char *data)
+static int ovl_reconfigure(struct fs_context *fc)
 {
+	struct super_block *sb = fc->root->d_sb;
 	struct ovl_fs *ofs = sb->s_fs_info;
 	struct super_block *upper_sb;
 	int ret = 0;
 
-	if (!(*flags & SB_RDONLY) && ovl_force_readonly(ofs))
+	if (!(fc->sb_flags & SB_RDONLY) && ovl_force_readonly(ofs))
 		return -EROFS;
 
-	if (*flags & SB_RDONLY && !sb_rdonly(sb)) {
+	if (fc->sb_flags & SB_RDONLY && !sb_rdonly(sb)) {
 		upper_sb = ovl_upper_mnt(ofs)->mnt_sb;
 		if (ovl_should_sync(ofs)) {
 			down_read(&upper_sb->s_umount);
@@ -438,219 +441,151 @@ static const struct super_operations ovl_super_operations = {
 	.sync_fs	= ovl_sync_fs,
 	.statfs		= ovl_statfs,
 	.show_options	= ovl_show_options,
-	.remount_fs	= ovl_remount,
 };
 
 enum {
-	OPT_LOWERDIR,
-	OPT_UPPERDIR,
-	OPT_WORKDIR,
-	OPT_DEFAULT_PERMISSIONS,
-	OPT_REDIRECT_DIR_ON,
-	OPT_REDIRECT_DIR_OFF,
-	OPT_REDIRECT_DIR_FOLLOW,
-	OPT_REDIRECT_DIR_NOFOLLOW,
-	OPT_INDEX_ON,
-	OPT_INDEX_OFF,
-	OPT_UUID_ON,
-	OPT_UUID_OFF,
-	OPT_NFS_EXPORT_ON,
-	OPT_USERXATTR,
-	OPT_NFS_EXPORT_OFF,
-	OPT_XINO_ON,
-	OPT_XINO_OFF,
-	OPT_XINO_AUTO,
-	OPT_METACOPY_ON,
-	OPT_METACOPY_OFF,
-	OPT_VOLATILE,
-	OPT_ERR,
+	Opt_lowerdir,
+	Opt_upperdir,
+	Opt_workdir,
+	Opt_default_permissions,
+	Opt_redirect_dir,
+	Opt_index,
+	Opt_uuid,
+	Opt_nfs_export,
+	Opt_userxattr,
+	Opt_xino,
+	Opt_metacopy,
+	Opt_volatile,
 };
 
-static const match_table_t ovl_tokens = {
-	{OPT_LOWERDIR,			"lowerdir=%s"},
-	{OPT_UPPERDIR,			"upperdir=%s"},
-	{OPT_WORKDIR,			"workdir=%s"},
-	{OPT_DEFAULT_PERMISSIONS,	"default_permissions"},
-	{OPT_REDIRECT_DIR_ON,		"redirect_dir=on"},
-	{OPT_REDIRECT_DIR_OFF,		"redirect_dir=off"},
-	{OPT_REDIRECT_DIR_FOLLOW,	"redirect_dir=follow"},
-	{OPT_REDIRECT_DIR_NOFOLLOW,	"redirect_dir=nofollow"},
-	{OPT_INDEX_ON,			"index=on"},
-	{OPT_INDEX_OFF,			"index=off"},
-	{OPT_USERXATTR,			"userxattr"},
-	{OPT_UUID_ON,			"uuid=on"},
-	{OPT_UUID_OFF,			"uuid=off"},
-	{OPT_NFS_EXPORT_ON,		"nfs_export=on"},
-	{OPT_NFS_EXPORT_OFF,		"nfs_export=off"},
-	{OPT_XINO_ON,			"xino=on"},
-	{OPT_XINO_OFF,			"xino=off"},
-	{OPT_XINO_AUTO,			"xino=auto"},
-	{OPT_METACOPY_ON,		"metacopy=on"},
-	{OPT_METACOPY_OFF,		"metacopy=off"},
-	{OPT_VOLATILE,			"volatile"},
-	{OPT_ERR,			NULL}
+static const struct constant_table ovl_parameter_bool[] = {
+	{ "on",		true  },
+	{ "off",	false },
+	{}
 };
 
-static char *ovl_next_opt(char **s)
-{
-	char *sbegin = *s;
-	char *p;
-
-	if (sbegin == NULL)
-		return NULL;
+static const struct fs_parameter_spec ovl_parameter_spec[] = {
+	fsparam_string("lowerdir",          Opt_lowerdir),
+	fsparam_string("upperdir",          Opt_upperdir),
+	fsparam_string("workdir",           Opt_workdir),
+	fsparam_flag("default_permissions", Opt_default_permissions),
+	fsparam_enum("redirect_dir",        Opt_redirect_dir, ovl_parameter_redirect_dir),
+	fsparam_enum("index",               Opt_index, ovl_parameter_bool),
+	fsparam_enum("uuid",                Opt_uuid, ovl_parameter_bool),
+	fsparam_enum("nfs_export",          Opt_nfs_export, ovl_parameter_bool),
+	fsparam_flag("userxattr",           Opt_userxattr),
+	fsparam_enum("xino",                Opt_xino, ovl_parameter_xino),
+	fsparam_enum("metacopy",            Opt_metacopy, ovl_parameter_bool),
+	fsparam_flag("volatile",            Opt_volatile),
+	{}
+};
 
-	for (p = sbegin; *p; p++) {
-		if (*p == '\\') {
-			p++;
-			if (!*p)
-				break;
-		} else if (*p == ',') {
-			*p = '\0';
-			*s = p + 1;
-			return sbegin;
-		}
-	}
-	*s = NULL;
-	return sbegin;
-}
+struct ovl_fs_context {
+	struct ovl_opt_set set;
+};
 
-static int ovl_parse_opt(char *opt, struct ovl_config *config,
-			 struct ovl_opt_set *set)
+static int ovl_parse_param(struct fs_context *fc, struct fs_parameter *param)
 {
 	int err = 0;
-	int token;
-	substring_t args[MAX_OPT_ARGS];
+	struct fs_parse_result result;
+	struct ovl_fs *ofs = fc->s_fs_info;
+	struct ovl_config *config = &ofs->config;
+	struct ovl_fs_context *ctx = fc->fs_private;
+	char *dup;
+	int opt;
 
-	if (!*opt)
+	/*
+	 * On remount overlayfs has always ignored all mount options no
+	 * matter if malformed or not so for backwards compatibility we
+	 * do the same here.
+	 */
+	if (fc->purpose == FS_CONTEXT_FOR_RECONFIGURE)
 		return 0;
 
-	token = match_token(opt, ovl_tokens, args);
-	switch (token) {
-	case OPT_UPPERDIR:
-		kfree(config->upperdir);
-		config->upperdir = match_strdup(&args[0]);
-		if (!config->upperdir)
-			return -ENOMEM;
-		break;
+	opt = fs_parse(fc, ovl_parameter_spec, param, &result);
+	if (opt < 0)
+		return opt;
 
-	case OPT_LOWERDIR:
-		kfree(config->lowerdir);
-		config->lowerdir = match_strdup(&args[0]);
-		if (!config->lowerdir)
-			return -ENOMEM;
-		break;
-
-	case OPT_WORKDIR:
-		kfree(config->workdir);
-		config->workdir = match_strdup(&args[0]);
-		if (!config->workdir)
-			return -ENOMEM;
-		break;
-
-	case OPT_DEFAULT_PERMISSIONS:
-		config->default_permissions = true;
-		break;
-
-	case OPT_REDIRECT_DIR_ON:
-		config->redirect_mode = OVL_REDIRECT_ON;
-		set->redirect = true;
-		break;
-
-	case OPT_REDIRECT_DIR_OFF:
-		config->redirect_mode = ovl_redirect_always_follow ?
-			OVL_REDIRECT_FOLLOW :
-			OVL_REDIRECT_NOFOLLOW;
-		set->redirect = true;
-		break;
-
-	case OPT_REDIRECT_DIR_FOLLOW:
-		config->redirect_mode = OVL_REDIRECT_FOLLOW;
-		set->redirect = true;
-		break;
-
-	case OPT_REDIRECT_DIR_NOFOLLOW:
-		config->redirect_mode = OVL_REDIRECT_NOFOLLOW;
-		set->redirect = true;
-		break;
-
-	case OPT_INDEX_ON:
-		config->index = true;
-		set->index = true;
-		break;
+	switch (opt) {
+	case Opt_lowerdir:
+		dup = kstrdup(param->string, GFP_KERNEL);
+		if (!dup) {
+			err = -ENOMEM;
+			break;
+		}
 
-	case OPT_INDEX_OFF:
-		config->index = false;
-		set->index = true;
+		kfree(config->lowerdir);
+		config->lowerdir = dup;
 		break;
+	case Opt_upperdir:
+		dup = kstrdup(param->string, GFP_KERNEL);
+		if (!dup) {
+			err = -ENOMEM;
+			break;
+		}
 
-	case OPT_UUID_ON:
-		config->uuid = true;
+		kfree(config->upperdir);
+		config->upperdir = dup;
 		break;
+	case Opt_workdir:
+		dup = kstrdup(param->string, GFP_KERNEL);
+		if (!dup) {
+			err = -ENOMEM;
+			break;
+		}
 
-	case OPT_UUID_OFF:
-		config->uuid = false;
+		kfree(config->workdir);
+		config->workdir = dup;
 		break;
-
-	case OPT_NFS_EXPORT_ON:
-		config->nfs_export = true;
-		set->nfs_export = true;
+	case Opt_default_permissions:
+		config->default_permissions = true;
 		break;
-
-	case OPT_NFS_EXPORT_OFF:
-		config->nfs_export = false;
-		set->nfs_export = true;
+	case Opt_redirect_dir:
+		config->redirect_mode = result.uint_32;
+		if (config->redirect_mode == OVL_REDIRECT_OFF) {
+			config->redirect_mode = ovl_redirect_always_follow ?
+						OVL_REDIRECT_FOLLOW :
+						OVL_REDIRECT_NOFOLLOW;
+		}
+		ctx->set.redirect = true;
 		break;
-
-	case OPT_XINO_ON:
-		config->xino = OVL_XINO_ON;
+	case Opt_index:
+		config->index = result.uint_32;
+		ctx->set.index = true;
 		break;
-
-	case OPT_XINO_OFF:
-		config->xino = OVL_XINO_OFF;
+	case Opt_uuid:
+		config->uuid = result.uint_32;
 		break;
-
-	case OPT_XINO_AUTO:
-		config->xino = OVL_XINO_AUTO;
+	case Opt_nfs_export:
+		config->nfs_export = result.uint_32;
+		ctx->set.nfs_export = true;
 		break;
-
-	case OPT_METACOPY_ON:
-		config->metacopy = true;
-		set->metacopy = true;
+	case Opt_xino:
+		config->xino = result.uint_32;
 		break;
-
-	case OPT_METACOPY_OFF:
-		config->metacopy = false;
-		set->metacopy = true;
+	case Opt_metacopy:
+		config->metacopy = result.uint_32;
+		ctx->set.metacopy = true;
 		break;
-
-	case OPT_VOLATILE:
+	case Opt_volatile:
 		config->ovl_volatile = true;
 		break;
-
-	case OPT_USERXATTR:
+	case Opt_userxattr:
 		config->userxattr = true;
 		break;
-
 	default:
 		pr_err("unrecognized mount option \"%s\" or missing value\n",
-		       opt);
+		       param->key);
 		return -EINVAL;
 	}
 
 	return err;
 }
 
-static int ovl_parse_options(char *opt, struct ovl_config *config)
+static int ovl_fs_params_verify(const struct ovl_fs_context *ctx,
+				struct ovl_config *config)
 {
-	char *p;
-	int err;
-	struct ovl_opt_set set = {};
-
-	while ((p = ovl_next_opt(&opt)) != NULL) {
-		err = ovl_parse_opt(p, config, &set);
-		if (err)
-			return err;
-	}
+	struct ovl_opt_set set = ctx->set;
 
 	/* Workdir/index are useless in non-upper mount */
 	if (!config->upperdir) {
@@ -1958,12 +1893,13 @@ static struct dentry *ovl_get_root(struct super_block *sb,
 	return root;
 }
 
-static int ovl_fill_super(struct super_block *sb, void *data, int silent)
+static int ovl_fill_super(struct super_block *sb, struct fs_context *fc)
 {
-	struct path upperpath = { };
+	struct ovl_fs *ofs = sb->s_fs_info;
+	struct ovl_fs_context *ctx = fc->fs_private;
+	struct path upperpath = {};
 	struct dentry *root_dentry;
 	struct ovl_entry *oe;
-	struct ovl_fs *ofs;
 	struct ovl_layer *layers;
 	struct cred *cred;
 	char *splitlower = NULL;
@@ -1971,34 +1907,23 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
 	int err;
 
 	err = -EIO;
-	if (WARN_ON(sb->s_user_ns != current_user_ns()))
-		goto out;
+	if (WARN_ON(fc->user_ns != current_user_ns()))
+		goto out_err;
 
 	sb->s_d_op = &ovl_dentry_operations;
 
-	err = -ENOMEM;
-	ofs = kzalloc(sizeof(struct ovl_fs), GFP_KERNEL);
-	if (!ofs)
-		goto out;
-
 	err = -ENOMEM;
 	ofs->creator_cred = cred = prepare_creds();
 	if (!cred)
 		goto out_err;
 
-	ofs->config.redirect_mode = ovl_redirect_mode_def();
-	ofs->config.index = ovl_index_def;
-	ofs->config.uuid = true;
-	ofs->config.nfs_export = ovl_nfs_export_def;
-	ofs->config.xino = ovl_xino_def();
-	ofs->config.metacopy = ovl_metacopy_def;
-	err = ovl_parse_options((char *) data, &ofs->config);
+	err = ovl_fs_params_verify(ctx, &ofs->config);
 	if (err)
 		goto out_err;
 
 	err = -EINVAL;
 	if (!ofs->config.lowerdir) {
-		if (!silent)
+		if (!(fc->sb_flags & SB_SILENT))
 			pr_err("missing 'lowerdir'\n");
 		goto out_err;
 	}
@@ -2143,25 +2068,88 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
 out_free_oe:
 	ovl_free_entry(oe);
 out_err:
-	kfree(splitlower);
-	path_put(&upperpath);
 	ovl_free_fs(ofs);
-out:
+	sb->s_fs_info = NULL;
 	return err;
 }
 
-static struct dentry *ovl_mount(struct file_system_type *fs_type, int flags,
-				const char *dev_name, void *raw_data)
+static int ovl_get_tree(struct fs_context *fc)
 {
-	return mount_nodev(fs_type, flags, raw_data, ovl_fill_super);
+	return get_tree_nodev(fc, ovl_fill_super);
+}
+
+static inline void ovl_fs_context_free(struct ovl_fs_context *ctx)
+{
+	kfree(ctx);
+}
+
+static void ovl_free(struct fs_context *fc)
+{
+	struct ovl_fs *ofs = fc->s_fs_info;
+	struct ovl_fs_context *ctx = fc->fs_private;
+
+	/*
+	 * ofs is stored in the fs_context when it is initialized.
+	 * ofs is transferred to the superblock on a successful mount,
+	 * but if an error occurs before the transfer we have to free
+	 * it here.
+	 */
+	if (ofs)
+		ovl_free_fs(ofs);
+
+	if (ctx)
+		ovl_fs_context_free(ctx);
+}
+
+static const struct fs_context_operations ovl_context_ops = {
+	.parse_param = ovl_parse_param,
+	.get_tree    = ovl_get_tree,
+	.reconfigure = ovl_reconfigure,
+	.free        = ovl_free,
+};
+
+/*
+ * This is called during fsopen() and will record the user namespace of
+ * the caller in fc->user_ns since we've raised FS_USERNS_MOUNT. We'll
+ * need it when we actually create the superblock to verify that the
+ * process creating the superblock is in the same user namespace as
+ * process that called fsopen().
+ */
+static int ovl_init_fs_context(struct fs_context *fc)
+{
+	struct ovl_fs_context *ctx;
+	struct ovl_fs *ofs;
+
+	ctx = kzalloc(sizeof(*ctx), GFP_KERNEL_ACCOUNT);
+	if (!ctx)
+		return -ENOMEM;
+
+	ofs = kzalloc(sizeof(struct ovl_fs), GFP_KERNEL);
+	if (!ofs) {
+		ovl_fs_context_free(ctx);
+		return -ENOMEM;
+	}
+
+	ofs->config.redirect_mode = ovl_redirect_mode_def();
+	ofs->config.index	= ovl_index_def;
+	ofs->config.uuid	= true;
+	ofs->config.nfs_export	= ovl_nfs_export_def;
+	ofs->config.xino	= ovl_xino_def();
+	ofs->config.metacopy	= ovl_metacopy_def;
+
+	fc->s_fs_info		= ofs;
+	fc->fs_private		= ctx;
+	fc->ops			= &ovl_context_ops;
+	return 0;
 }
 
 static struct file_system_type ovl_fs_type = {
-	.owner		= THIS_MODULE,
-	.name		= "overlay",
-	.fs_flags	= FS_USERNS_MOUNT,
-	.mount		= ovl_mount,
-	.kill_sb	= kill_anon_super,
+	.owner			= THIS_MODULE,
+	.name			= "overlay",
+	.init_fs_context	= ovl_init_fs_context,
+	.parameters		= ovl_parameter_spec,
+	.fs_flags		= FS_USERNS_MOUNT,
+	.kill_sb		= kill_anon_super,
 };
 MODULE_ALIAS_FS("overlay");