text: // SPDX-License-Identifier: GPL-2.0-only
  /*
   *
   * Copyright (C) 2011 Novell Inc.
   */
  
  #include <uapi/linux/magic.h>
  #include <linux/fs.h>
  #include <linux/namei.h>
  #include <linux/xattr.h>
  #include <linux/mount.h>
  #include <linux/parser.h>
  #include <linux/module.h>
  #include <linux/statfs.h>
  #include <linux/seq_file.h>
  #include <linux/posix_acl_xattr.h>
  #include <linux/exportfs.h>
  #include "overlayfs.h"
  
  MODULE_AUTHOR("Miklos Szeredi <miklos@szeredi.hu>");
  MODULE_DESCRIPTION("Overlay filesystem");
  MODULE_LICENSE("GPL");
  
  
  struct ovl_dir_cache;
  
  #define OVL_MAX_STACK 500
  
  static bool ovl_redirect_dir_def = IS_ENABLED(CONFIG_OVERLAY_FS_REDIRECT_DIR);
  module_param_named(redirect_dir, ovl_redirect_dir_def, bool, 0644);
  MODULE_PARM_DESC(redirect_dir,
  		 "Default to on or off for the redirect_dir feature");
  
  static bool ovl_redirect_always_follow =
  	IS_ENABLED(CONFIG_OVERLAY_FS_REDIRECT_ALWAYS_FOLLOW);
  module_param_named(redirect_always_follow, ovl_redirect_always_follow,
  		   bool, 0644);
  MODULE_PARM_DESC(redirect_always_follow,
  		 "Follow redirects even if redirect_dir feature is turned off");
  
  static bool ovl_index_def = IS_ENABLED(CONFIG_OVERLAY_FS_INDEX);
  module_param_named(index, ovl_index_def, bool, 0644);
  MODULE_PARM_DESC(index,
  		 "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(nfs_export,
  		 "Default to on or off for the NFS export feature");
  
  static bool ovl_xino_auto_def = IS_ENABLED(CONFIG_OVERLAY_FS_XINO_AUTO);
  module_param_named(xino_auto, ovl_xino_auto_def, bool, 0644);
  MODULE_PARM_DESC(xino_auto,
  		 "Auto enable xino feature");
  
  static void ovl_entry_stack_free(struct ovl_entry *oe)
  {
  	unsigned int i;
  
  	for (i = 0; i < oe->numlower; i++)
  		dput(oe->lowerstack[i].dentry);
  }
  
  static bool ovl_metacopy_def = IS_ENABLED(CONFIG_OVERLAY_FS_METACOPY);
  module_param_named(metacopy, ovl_metacopy_def, bool, 0644);
  MODULE_PARM_DESC(metacopy,
  		 "Default to on or off for the metadata only copy up feature");
  
  static void ovl_dentry_release(struct dentry *dentry)
  {
  	struct ovl_entry *oe = dentry->d_fsdata;
  
  	if (oe) {
  		ovl_entry_stack_free(oe);
  		kfree_rcu(oe, rcu);
  	}
  }
  
  static struct dentry *ovl_d_real(struct dentry *dentry,
  				 const struct inode *inode)
  {
  	struct dentry *real;
  
  	/* It's an overlay file */
  	if (inode && d_inode(dentry) == inode)
  		return dentry;
  
  	if (!d_is_reg(dentry)) {
  		if (!inode || inode == d_inode(dentry))
  			return dentry;
  		goto bug;
  	}
  
  	real = ovl_dentry_upper(dentry);
  	if (real && (inode == d_inode(real)))
  		return real;
  
  	if (real && !inode && ovl_has_upperdata(d_inode(dentry)))
  		return real;
  
  	real = ovl_dentry_lowerdata(dentry);
  	if (!real)
  		goto bug;
  
  	/* Handle recursion */
  	real = d_real(real, inode);
  
  	if (!inode || inode == d_inode(real))
  		return real;
  bug:
  	WARN(1, "ovl_d_real(%pd4, %s:%lu): real dentry not found\n", dentry,
  	     inode ? inode->i_sb->s_id : "NULL", inode ? inode->i_ino : 0);
  	return dentry;
  }
  
  static int ovl_dentry_revalidate(struct dentry *dentry, unsigned int flags)
  {
  	struct ovl_entry *oe = dentry->d_fsdata;
  	unsigned int i;
  	int ret = 1;
  
  	for (i = 0; i < oe->numlower; i++) {
  		struct dentry *d = oe->lowerstack[i].dentry;
  
  		if (d->d_flags & DCACHE_OP_REVALIDATE) {
  			ret = d->d_op->d_revalidate(d, flags);
  			if (ret < 0)
  				return ret;
  			if (!ret) {
  				if (!(flags & LOOKUP_RCU))
  					d_invalidate(d);
  				return -ESTALE;
  			}
  		}
  	}
  	return 1;
  }
  
  static int ovl_dentry_weak_revalidate(struct dentry *dentry, unsigned int flags)
  {
  	struct ovl_entry *oe = dentry->d_fsdata;
  	unsigned int i;
  	int ret = 1;
  
  	for (i = 0; i < oe->numlower; i++) {
  		struct dentry *d = oe->lowerstack[i].dentry;
  
  		if (d->d_flags & DCACHE_OP_WEAK_REVALIDATE) {
  			ret = d->d_op->d_weak_revalidate(d, flags);
  			if (ret <= 0)
  				break;
  		}
  	}
  	return ret;
  }
  
  static const struct dentry_operations ovl_dentry_operations = {
  	.d_release = ovl_dentry_release,
  	.d_real = ovl_d_real,
  };
  
  static const struct dentry_operations ovl_reval_dentry_operations = {
  	.d_release = ovl_dentry_release,
  	.d_real = ovl_d_real,
  	.d_revalidate = ovl_dentry_revalidate,
  	.d_weak_revalidate = ovl_dentry_weak_revalidate,
  };
  
  static struct kmem_cache *ovl_inode_cachep;
  
  static struct inode *ovl_alloc_inode(struct super_block *sb)
  {
  	struct ovl_inode *oi = kmem_cache_alloc(ovl_inode_cachep, GFP_KERNEL);
  
  	if (!oi)
  		return NULL;
  
  	oi->cache = NULL;
  	oi->redirect = NULL;
  	oi->version = 0;
  	oi->flags = 0;
  	oi->__upperdentry = NULL;
  	oi->lower = NULL;
  	oi->lowerdata = NULL;
  	mutex_init(&oi->lock);
  
  	return &oi->vfs_inode;
  }
  
  static void ovl_free_inode(struct inode *inode)
  {
  	struct ovl_inode *oi = OVL_I(inode);
  
  	kfree(oi->redirect);
  	mutex_destroy(&oi->lock);
  	kmem_cache_free(ovl_inode_cachep, oi);
  }
  
  static void ovl_destroy_inode(struct inode *inode)
  {
  	struct ovl_inode *oi = OVL_I(inode);
  
  	dput(oi->__upperdentry);
  	iput(oi->lower);
  	if (S_ISDIR(inode->i_mode))
  		ovl_dir_cache_free(inode);
  	else
  		iput(oi->lowerdata);
  }
  
  static void ovl_free_fs(struct ovl_fs *ofs)
  {
  	unsigned i;
  
  	iput(ofs->indexdir_trap);
  	iput(ofs->workdir_trap);
  	iput(ofs->upperdir_trap);
  	dput(ofs->indexdir);
  	dput(ofs->workdir);
  	if (ofs->workdir_locked)
  		ovl_inuse_unlock(ofs->workbasedir);
  	dput(ofs->workbasedir);
  	if (ofs->upperdir_locked)
  		ovl_inuse_unlock(ofs->upper_mnt->mnt_root);
  	mntput(ofs->upper_mnt);
  	for (i = 0; i < ofs->numlower; i++) {
  		iput(ofs->lower_layers[i].trap);
  		mntput(ofs->lower_layers[i].mnt);
  	}
  	for (i = 0; i < ofs->numlowerfs; i++)
  		free_anon_bdev(ofs->lower_fs[i].pseudo_dev);
  	kfree(ofs->lower_layers);
  	kfree(ofs->lower_fs);
  
  	kfree(ofs->config.lowerdir);
  	kfree(ofs->config.upperdir);
  	kfree(ofs->config.workdir);
  	kfree(ofs->config.redirect_mode);
  	if (ofs->creator_cred)
  		put_cred(ofs->creator_cred);
  	kfree(ofs);
  }
  
  static void ovl_put_super(struct super_block *sb)
  {
  	struct ovl_fs *ofs = sb->s_fs_info;
  
  	ovl_free_fs(ofs);
  }
  
  /* Sync real dirty inodes in upper filesystem (if it exists) */
  static int ovl_sync_fs(struct super_block *sb, int wait)
  {
  	struct ovl_fs *ofs = sb->s_fs_info;
  	struct super_block *upper_sb;
  	int ret;
  
  	if (!ofs->upper_mnt)
  		return 0;
  
  	/*
  	 * If this is a sync(2) call or an emergency sync, all the super blocks
  	 * will be iterated, including upper_sb, so no need to do anything.
  	 *
  	 * If this is a syncfs(2) call, then we do need to call
  	 * sync_filesystem() on upper_sb, but enough if we do it when being
  	 * called with wait == 1.
  	 */
  	if (!wait)
  		return 0;
  
  	upper_sb = ofs->upper_mnt->mnt_sb;
  
  	down_read(&upper_sb->s_umount);
  	ret = sync_filesystem(upper_sb);
  	up_read(&upper_sb->s_umount);
  
  	return ret;
  }
  
  /**
   * ovl_statfs
   * @sb: The overlayfs super block
   * @buf: The struct kstatfs to fill in with stats
   *
   * Get the filesystem statistics.  As writes always target the upper layer
   * filesystem pass the statfs to the upper filesystem (if it exists)
   */
  static int ovl_statfs(struct dentry *dentry, struct kstatfs *buf)
  {
  	struct ovl_fs *ofs = dentry->d_sb->s_fs_info;
  	struct dentry *root_dentry = dentry->d_sb->s_root;
  	struct path path;
  	int err;
  
  	ovl_path_real(root_dentry, &path);
  
  	err = vfs_statfs(&path, buf);
  	if (!err) {
  		buf->f_namelen = ofs->namelen;
  		buf->f_type = OVERLAYFS_SUPER_MAGIC;
  	}
  
  	return err;
  }
  
  /* Will this overlay be forced to mount/remount ro? */
  static bool ovl_force_readonly(struct ovl_fs *ofs)
  {
  	return (!ofs->upper_mnt || !ofs->workdir);
  }
  
  static const char *ovl_redirect_mode_def(void)
  {
  	return ovl_redirect_dir_def ? "on" : "off";
  }
  
  enum {
  	OVL_XINO_OFF,
  	OVL_XINO_AUTO,
  	OVL_XINO_ON,
  };
  
  static const char * const ovl_xino_str[] = {
  	"off",
  	"auto",
  	"on",
  };
  
  static inline int ovl_xino_def(void)
  {
  	return ovl_xino_auto_def ? OVL_XINO_AUTO : OVL_XINO_OFF;
  }
  
  /**
   * ovl_show_options
   *
   * Prints the mount options for a given superblock.
   * Returns zero; does not fail.
   */
  static int ovl_show_options(struct seq_file *m, struct dentry *dentry)
  {
  	struct super_block *sb = dentry->d_sb;
  	struct ovl_fs *ofs = sb->s_fs_info;
  
  	seq_show_option(m, "lowerdir", ofs->config.lowerdir);
  	if (ofs->config.upperdir) {
  		seq_show_option(m, "upperdir", ofs->config.upperdir);
  		seq_show_option(m, "workdir", ofs->config.workdir);
  	}
  	if (ofs->config.default_permissions)
  		seq_puts(m, ",default_permissions");
  	if (strcmp(ofs->config.redirect_mode, ovl_redirect_mode_def()) != 0)
  		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");
  	if (ofs->config.xino != ovl_xino_def())
  		seq_printf(m, ",xino=%s", ovl_xino_str[ofs->config.xino]);
  	if (ofs->config.metacopy != ovl_metacopy_def)
  		seq_printf(m, ",metacopy=%s",
  			   ofs->config.metacopy ? "on" : "off");
  	return 0;
  }
  
  static int ovl_remount(struct super_block *sb, int *flags, char *data)
  {
  	struct ovl_fs *ofs = sb->s_fs_info;
  
  	if (!(*flags & SB_RDONLY) && ovl_force_readonly(ofs))
  		return -EROFS;
  
  	return 0;
  }
  
  static const struct super_operations ovl_super_operations = {
  	.alloc_inode	= ovl_alloc_inode,
  	.free_inode	= ovl_free_inode,
  	.destroy_inode	= ovl_destroy_inode,
  	.drop_inode	= generic_delete_inode,
  	.put_super	= ovl_put_super,
  	.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,
  	OPT_INDEX_ON,
  	OPT_INDEX_OFF,
  	OPT_NFS_EXPORT_ON,
  	OPT_NFS_EXPORT_OFF,
  	OPT_XINO_ON,
  	OPT_XINO_OFF,
  	OPT_XINO_AUTO,
  	OPT_METACOPY_ON,
  	OPT_METACOPY_OFF,
  	OPT_ERR,
  };
  
  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,		"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_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_ERR,			NULL}
  };
  
  static char *ovl_next_opt(char **s)
  {
  	char *sbegin = *s;
  	char *p;
  
  	if (sbegin == NULL)
  		return NULL;
  
  	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;
  }
  
  static int ovl_parse_redirect_mode(struct ovl_config *config, const char *mode)
  {
  	if (strcmp(mode, "on") == 0) {
  		config->redirect_dir = true;
  		/*
  		 * Does not make sense to have redirect creation without
  		 * redirect following.
  		 */
  		config->redirect_follow = true;
  	} else if (strcmp(mode, "follow") == 0) {
  		config->redirect_follow = true;
  	} else if (strcmp(mode, "off") == 0) {
  		if (ovl_redirect_always_follow)
  			config->redirect_follow = true;
  	} else if (strcmp(mode, "nofollow") != 0) {
  		pr_err("overlayfs: bad mount option \"redirect_dir=%s\"\n",
  		       mode);
  		return -EINVAL;
  	}
  
  	return 0;
  }
  
  static int ovl_parse_opt(char *opt, struct ovl_config *config)
  {
  	char *p;
  	int err;
  	bool metacopy_opt = false, redirect_opt = false;
  
  	config->redirect_mode = kstrdup(ovl_redirect_mode_def(), GFP_KERNEL);
  	if (!config->redirect_mode)
  		return -ENOMEM;
  
  	while ((p = ovl_next_opt(&opt)) != NULL) {
  		int token;
  		substring_t args[MAX_OPT_ARGS];
  
  		if (!*p)
  			continue;
  
  		token = match_token(p, ovl_tokens, args);
  		switch (token) {
  		case OPT_UPPERDIR:
  			kfree(config->upperdir);
  			config->upperdir = match_strdup(&args[0]);
  			if (!config->upperdir)
  				return -ENOMEM;
  			break;
  
  		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:
  			kfree(config->redirect_mode);
  			config->redirect_mode = match_strdup(&args[0]);
  			if (!config->redirect_mode)
  				return -ENOMEM;
  			redirect_opt = true;
  			break;
  
  		case OPT_INDEX_ON:
  			config->index = true;
  			break;
  
  		case OPT_INDEX_OFF:
  			config->index = false;
  			break;
  
  		case OPT_NFS_EXPORT_ON:
  			config->nfs_export = true;
  			break;
  
  		case OPT_NFS_EXPORT_OFF:
  			config->nfs_export = false;
  			break;
  
  		case OPT_XINO_ON:
  			config->xino = OVL_XINO_ON;
  			break;
  
  		case OPT_XINO_OFF:
  			config->xino = OVL_XINO_OFF;
  			break;
  
  		case OPT_XINO_AUTO:
  			config->xino = OVL_XINO_AUTO;
  			break;
  
  		case OPT_METACOPY_ON:
  			config->metacopy = true;
  			metacopy_opt = true;
  			break;
  
  		case OPT_METACOPY_OFF:
  			config->metacopy = false;
  			break;
  
  		default:
  			pr_err("overlayfs: unrecognized mount option \"%s\" or missing value\n", p);
  			return -EINVAL;
  		}
  	}
  
  	/* Workdir is useless in non-upper mount */
  	if (!config->upperdir && config->workdir) {
  		pr_info("overlayfs: option \"workdir=%s\" is useless in a non-upper mount, ignore\n",
  			config->workdir);
  		kfree(config->workdir);
  		config->workdir = NULL;
  	}
  
  	err = ovl_parse_redirect_mode(config, config->redirect_mode);
  	if (err)
  		return err;
  
  	/*
  	 * This is to make the logic below simpler.  It doesn't make any other
  	 * difference, since config->redirect_dir is only used for upper.
  	 */
  	if (!config->upperdir && config->redirect_follow)
  		config->redirect_dir = true;
  
  	/* Resolve metacopy -> redirect_dir dependency */
  	if (config->metacopy && !config->redirect_dir) {
  		if (metacopy_opt && redirect_opt) {
  			pr_err("overlayfs: conflicting options: metacopy=on,redirect_dir=%s\n",
  			       config->redirect_mode);
  			return -EINVAL;
  		}
  		if (redirect_opt) {
  			/*
  			 * There was an explicit redirect_dir=... that resulted
  			 * in this conflict.
  			 */
  			pr_info("overlayfs: disabling metacopy due to redirect_dir=%s\n",
  				config->redirect_mode);
  			config->metacopy = false;
  		} else {
  			/* Automatically enable redirect otherwise. */
  			config->redirect_follow = config->redirect_dir = true;
  		}
  	}
  
  	return 0;
  }
  
  #define OVL_WORKDIR_NAME "work"
  #define OVL_INDEXDIR_NAME "index"
  
  static struct dentry *ovl_workdir_create(struct ovl_fs *ofs,
  					 const char *name, bool persist)
  {
  	struct inode *dir =  ofs->workbasedir->d_inode;
  	struct vfsmount *mnt = ofs->upper_mnt;
  	struct dentry *work;
  	int err;
  	bool retried = false;
  	bool locked = false;
  
  	inode_lock_nested(dir, I_MUTEX_PARENT);
  	locked = true;
  
  retry:
  	work = lookup_one_len(name, ofs->workbasedir, strlen(name));
  
  	if (!IS_ERR(work)) {
  		struct iattr attr = {
  			.ia_valid = ATTR_MODE,
  			.ia_mode = S_IFDIR | 0,
  		};
  
  		if (work->d_inode) {
  			err = -EEXIST;
  			if (retried)
  				goto out_dput;
  
  			if (persist)
  				goto out_unlock;
  
  			retried = true;
  			ovl_workdir_cleanup(dir, mnt, work, 0);
  			dput(work);
  			goto retry;
  		}
  
  		work = ovl_create_real(dir, work, OVL_CATTR(attr.ia_mode));
  		err = PTR_ERR(work);
  		if (IS_ERR(work))
  			goto out_err;
  
  		/*
  		 * Try to remove POSIX ACL xattrs from workdir.  We are good if:
  		 *
  		 * a) success (there was a POSIX ACL xattr and was removed)
  		 * b) -ENODATA (there was no POSIX ACL xattr)
  		 * c) -EOPNOTSUPP (POSIX ACL xattrs are not supported)
  		 *
  		 * There are various other error values that could effectively
  		 * mean that the xattr doesn't exist (e.g. -ERANGE is returned
  		 * if the xattr name is too long), but the set of filesystems
  		 * allowed as upper are limited to "normal" ones, where checking
  		 * for the above two errors is sufficient.
  		 */
  		err = vfs_removexattr(work, XATTR_NAME_POSIX_ACL_DEFAULT);
  		if (err && err != -ENODATA && err != -EOPNOTSUPP)
  			goto out_dput;
  
  		err = vfs_removexattr(work, XATTR_NAME_POSIX_ACL_ACCESS);
  		if (err && err != -ENODATA && err != -EOPNOTSUPP)
  			goto out_dput;
  
  		/* Clear any inherited mode bits */
  		inode_lock(work->d_inode);
  		err = notify_change(work, &attr, NULL);
  		inode_unlock(work->d_inode);
  		if (err)
  			goto out_dput;
  	} else {
  		err = PTR_ERR(work);
  		goto out_err;
  	}
  out_unlock:
  	if (locked)
  		inode_unlock(dir);
  
  	return work;
  
  out_dput:
  	dput(work);
  out_err:
  	pr_warn("overlayfs: failed to create directory %s/%s (errno: %i); mounting read-only\n",
  		ofs->config.workdir, name, -err);
  	work = NULL;
  	goto out_unlock;
  }
  
  static void ovl_unescape(char *s)
  {
  	char *d = s;
  
  	for (;; s++, d++) {
  		if (*s == '\\')
  			s++;
  		*d = *s;
  		if (!*s)
  			break;
  	}
  }
  
  static int ovl_mount_dir_noesc(const char *name, struct path *path)
  {
  	int err = -EINVAL;
  
  	if (!*name) {
  		pr_err("overlayfs: empty lowerdir\n");
  		goto out;
  	}
  	err = kern_path(name, LOOKUP_FOLLOW, path);
  	if (err) {
  		pr_err("overlayfs: failed to resolve '%s': %i\n", name, err);
  		goto out;
  	}
  	err = -EINVAL;
  	if (ovl_dentry_weird(path->dentry)) {
  		pr_err("overlayfs: filesystem on '%s' not supported\n", name);
  		goto out_put;
  	}
  	if (!d_is_dir(path->dentry)) {
  		pr_err("overlayfs: '%s' not a directory\n", name);
  		goto out_put;
  	}
  	return 0;
  
  out_put:
  	path_put_init(path);
  out:
  	return err;
  }
  
  static int ovl_mount_dir(const char *name, struct path *path)
  {
  	int err = -ENOMEM;
  	char *tmp = kstrdup(name, GFP_KERNEL);
  
  	if (tmp) {
  		ovl_unescape(tmp);
  		err = ovl_mount_dir_noesc(tmp, path);
  
  		if (!err)
  			if (ovl_dentry_remote(path->dentry)) {
  				pr_err("overlayfs: filesystem on '%s' not supported as upperdir\n",
  				       tmp);
  				path_put_init(path);
  				err = -EINVAL;
  			}
  		kfree(tmp);
  	}
  	return err;
  }
  
  static int ovl_check_namelen(struct path *path, struct ovl_fs *ofs,
  			     const char *name)
  {
  	struct kstatfs statfs;
  	int err = vfs_statfs(path, &statfs);
  
  	if (err)
  		pr_err("overlayfs: statfs failed on '%s'\n", name);
  	else
  		ofs->namelen = max(ofs->namelen, statfs.f_namelen);
  
  	return err;
  }
  
  static int ovl_lower_dir(const char *name, struct path *path,
  			 struct ovl_fs *ofs, int *stack_depth, bool *remote)
  {
  	int fh_type;
  	int err;
  
  	err = ovl_mount_dir_noesc(name, path);
  	if (err)
  		goto out;
  
  	err = ovl_check_namelen(path, ofs, name);
  	if (err)
  		goto out_put;
  
  	*stack_depth = max(*stack_depth, path->mnt->mnt_sb->s_stack_depth);
  
  	if (ovl_dentry_remote(path->dentry))
  		*remote = true;
  
  	/*
  	 * The inodes index feature and NFS export need to encode and decode
  	 * file handles, so they require that all layers support them.
  	 */
  	fh_type = ovl_can_decode_fh(path->dentry->d_sb);
  	if ((ofs->config.nfs_export ||
  	     (ofs->config.index && ofs->config.upperdir)) && !fh_type) {
  		ofs->config.index = false;
  		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);
  	}
  
  	/* Check if lower fs has 32bit inode numbers */
  	if (fh_type != FILEID_INO32_GEN)
  		ofs->xino_bits = 0;
  
  	return 0;
  
  out_put:
  	path_put_init(path);
  out:
  	return err;
  }
  
  /* Workdir should not be subdir of upperdir and vice versa */
  static bool ovl_workdir_ok(struct dentry *workdir, struct dentry *upperdir)
  {
  	bool ok = false;
  
  	if (workdir != upperdir) {
  		ok = (lock_rename(workdir, upperdir) == NULL);
  		unlock_rename(workdir, upperdir);
  	}
  	return ok;
  }
  
  static unsigned int ovl_split_lowerdirs(char *str)
  {
  	unsigned int ctr = 1;
  	char *s, *d;
  
  	for (s = d = str;; s++, d++) {
  		if (*s == '\\') {
  			s++;
  		} else if (*s == ':') {
  			*d = '\0';
  			ctr++;
  			continue;
  		}
  		*d = *s;
  		if (!*s)
  			break;
  	}
  	return ctr;
  }
  
  static int __maybe_unused
  ovl_posix_acl_xattr_get(const struct xattr_handler *handler,
  			struct dentry *dentry, struct inode *inode,
  			const char *name, void *buffer, size_t size)
  {
  	return ovl_xattr_get(dentry, inode, handler->name, buffer, size);
  }
  
  static int __maybe_unused
  ovl_posix_acl_xattr_set(const struct xattr_handler *handler,
  			struct dentry *dentry, struct inode *inode,
  			const char *name, const void *value,
  			size_t size, int flags)
  {
  	struct dentry *workdir = ovl_workdir(dentry);
  	struct inode *realinode = ovl_inode_real(inode);
  	struct posix_acl *acl = NULL;
  	int err;
  
  	/* Check that everything is OK before copy-up */
  	if (value) {
  		acl = posix_acl_from_xattr(&init_user_ns, value, size);
  		if (IS_ERR(acl))
  			return PTR_ERR(acl);
  	}
  	err = -EOPNOTSUPP;
  	if (!IS_POSIXACL(d_inode(workdir)))
  		goto out_acl_release;
  	if (!realinode->i_op->set_acl)
  		goto out_acl_release;
  	if (handler->flags == ACL_TYPE_DEFAULT && !S_ISDIR(inode->i_mode)) {
  		err = acl ? -EACCES : 0;
  		goto out_acl_release;
  	}
  	err = -EPERM;
  	if (!inode_owner_or_capable(inode))
  		goto out_acl_release;
  
  	posix_acl_release(acl);
  
  	/*
  	 * Check if sgid bit needs to be cleared (actual setacl operation will
  	 * be done with mounter's capabilities and so that won't do it for us).
  	 */
  	if (unlikely(inode->i_mode & S_ISGID) &&
  	    handler->flags == ACL_TYPE_ACCESS &&
  	    !in_group_p(inode->i_gid) &&
  	    !capable_wrt_inode_uidgid(inode, CAP_FSETID)) {
  		struct iattr iattr = { .ia_valid = ATTR_KILL_SGID };
  
  		err = ovl_setattr(dentry, &iattr);
  		if (err)
  			return err;
  	}
  
  	err = ovl_xattr_set(dentry, inode, handler->name, value, size, flags);
  	if (!err)
  		ovl_copyattr(ovl_inode_real(inode), inode);
  
  	return err;
  
  out_acl_release:
  	posix_acl_release(acl);
  	return err;
  }
  
  static int ovl_own_xattr_get(const struct xattr_handler *handler,
  			     struct dentry *dentry, struct inode *inode,
  			     const char *name, void *buffer, size_t size)
  {
  	return -EOPNOTSUPP;
  }
  
  static int ovl_own_xattr_set(const struct xattr_handler *handler,
  			     struct dentry *dentry, struct inode *inode,
  			     const char *name, const void *value,
  			     size_t size, int flags)
  {
  	return -EOPNOTSUPP;
  }
  
  static int ovl_other_xattr_get(const struct xattr_handler *handler,
  			       struct dentry *dentry, struct inode *inode,
  			       const char *name, void *buffer, size_t size)
  {
  	return ovl_xattr_get(dentry, inode, name, buffer, size);
  }
  
  static int ovl_other_xattr_set(const struct xattr_handler *handler,
  			       struct dentry *dentry, struct inode *inode,
  			       const char *name, const void *value,
  			       size_t size, int flags)
  {
  	return ovl_xattr_set(dentry, inode, name, value, size, flags);
  }
  
  static const struct xattr_handler __maybe_unused
  ovl_posix_acl_access_xattr_handler = {
  	.name = XATTR_NAME_POSIX_ACL_ACCESS,
  	.flags = ACL_TYPE_ACCESS,
  	.get = ovl_posix_acl_xattr_get,
  	.set = ovl_posix_acl_xattr_set,
  };
  
  static const struct xattr_handler __maybe_unused
  ovl_posix_acl_default_xattr_handler = {
  	.name = XATTR_NAME_POSIX_ACL_DEFAULT,
  	.flags = ACL_TYPE_DEFAULT,
  	.get = ovl_posix_acl_xattr_get,
  	.set = ovl_posix_acl_xattr_set,
  };
  
  static const struct xattr_handler ovl_own_xattr_handler = {
  	.prefix	= OVL_XATTR_PREFIX,
  	.get = ovl_own_xattr_get,
  	.set = ovl_own_xattr_set,
  };
  
  static const struct xattr_handler ovl_other_xattr_handler = {
  	.prefix	= "", /* catch all */
  	.get = ovl_other_xattr_get,
  	.set = ovl_other_xattr_set,
  };
  
  static const struct xattr_handler *ovl_xattr_handlers[] = {
  #ifdef CONFIG_FS_POSIX_ACL
  	&ovl_posix_acl_access_xattr_handler,
  	&ovl_posix_acl_default_xattr_handler,
  #endif
  	&ovl_own_xattr_handler,
  	&ovl_other_xattr_handler,
  	NULL
  };
  
  static int ovl_setup_trap(struct super_block *sb, struct dentry *dir,
  			  struct inode **ptrap, const char *name)
  {
  	struct inode *trap;
  	int err;
  
  	trap = ovl_get_trap_inode(sb, dir);
  	err = PTR_ERR_OR_ZERO(trap);
  	if (err) {
  		if (err == -ELOOP)
  			pr_err("overlayfs: conflicting %s path\n", name);
  		return err;
  	}
  
  	*ptrap = trap;
  	return 0;
  }
  
  static int ovl_get_upper(struct super_block *sb, struct ovl_fs *ofs,
  			 struct path *upperpath)
  {
  	struct vfsmount *upper_mnt;
  	int err;
  
  	err = ovl_mount_dir(ofs->config.upperdir, upperpath);
  	if (err)
  		goto out;
  
  	/* Upper fs should not be r/o */
  	if (sb_rdonly(upperpath->mnt->mnt_sb)) {
  		pr_err("overlayfs: upper fs is r/o, try multi-lower layers mount\n");
  		err = -EINVAL;
  		goto out;
  	}
  
  	err = ovl_check_namelen(upperpath, ofs, ofs->config.upperdir);
  	if (err)
  		goto out;
  
  	err = ovl_setup_trap(sb, upperpath->dentry, &ofs->upperdir_trap,
  			     "upperdir");
  	if (err)
  		goto out;
  
  	upper_mnt = clone_private_mount(upperpath);
  	err = PTR_ERR(upper_mnt);
  	if (IS_ERR(upper_mnt)) {
  		pr_err("overlayfs: failed to clone upperpath\n");
  		goto out;
  	}
  
  	/* Don't inherit atime flags */
  	upper_mnt->mnt_flags &= ~(MNT_NOATIME | MNT_NODIRATIME | MNT_RELATIME);
  	ofs->upper_mnt = upper_mnt;
  
  	err = -EBUSY;
  	if (ovl_inuse_trylock(ofs->upper_mnt->mnt_root)) {
  		ofs->upperdir_locked = true;
  	} else if (ofs->config.index) {
  		pr_err("overlayfs: upperdir is in-use by another mount, mount with '-o index=off' to override exclusive upperdir protection.\n");
  		goto out;
  	} else {
  		pr_warn("overlayfs: upperdir is in-use by another mount, accessing files from both mounts will result in undefined behavior.\n");
  	}
  
  	err = 0;
  out:
  	return err;
  }
  
  static int ovl_make_workdir(struct super_block *sb, struct ovl_fs *ofs,
  			    struct path *workpath)
  {
  	struct vfsmount *mnt = ofs->upper_mnt;
  	struct dentry *temp;
  	int fh_type;
  	int err;
  
  	err = mnt_want_write(mnt);
  	if (err)
  		return err;
  
  	ofs->workdir = ovl_workdir_create(ofs, OVL_WORKDIR_NAME, false);
  	if (!ofs->workdir)
  		goto out;
  
  	err = ovl_setup_trap(sb, ofs->workdir, &ofs->workdir_trap, "workdir");
  	if (err)
  		goto out;
  
  	/*
  	 * Upper should support d_type, else whiteouts are visible.  Given
  	 * workdir and upper are on same fs, we can do iterate_dir() on
  	 * workdir. This check requires successful creation of workdir in
  	 * previous step.
  	 */
  	err = ovl_check_d_type_supported(workpath);
  	if (err < 0)
  		goto out;
  
  	/*
  	 * We allowed this configuration and don't want to break users over
  	 * kernel upgrade. So warn instead of erroring out.
  	 */
  	if (!err)
  		pr_warn("overlayfs: upper fs needs to support d_type.\n");
  
  	/* Check if upper/work fs supports O_TMPFILE */
  	temp = ovl_do_tmpfile(ofs->workdir, S_IFREG | 0);
  	ofs->tmpfile = !IS_ERR(temp);
  	if (ofs->tmpfile)
  		dput(temp);
  	else
  		pr_warn("overlayfs: upper fs does not support tmpfile.\n");
  
  	/*
  	 * Check if upper/work fs supports trusted.overlay.* xattr
  	 */
  	err = ovl_do_setxattr(ofs->workdir, OVL_XATTR_OPAQUE, "0", 1, 0);
  	if (err) {
  		ofs->noxattr = true;
  		ofs->config.index = false;
  		ofs->config.metacopy = false;
  		pr_warn("overlayfs: upper fs does not support xattr, falling back to index=off and metacopy=off.\n");
  		err = 0;
  	} else {
  		vfs_removexattr(ofs->workdir, OVL_XATTR_OPAQUE);
  	}
  
  	/* Check if upper/work fs supports file handles */
  	fh_type = ovl_can_decode_fh(ofs->workdir->d_sb);
  	if (ofs->config.index && !fh_type) {
  		ofs->config.index = false;
  		pr_warn("overlayfs: upper fs does not support file handles, falling back to index=off.\n");
  	}
  
  	/* Check if upper fs has 32bit inode numbers */
  	if (fh_type != FILEID_INO32_GEN)
  		ofs->xino_bits = 0;
  
  	/* 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;
  }
  
  static int ovl_get_workdir(struct super_block *sb, struct ovl_fs *ofs,
  			   struct path *upperpath)
  {
  	int err;
  	struct path workpath = { };
  
  	err = ovl_mount_dir(ofs->config.workdir, &workpath);
  	if (err)
  		goto out;
  
  	err = -EINVAL;
  	if (upperpath->mnt != workpath.mnt) {
  		pr_err("overlayfs: workdir and upperdir must reside under the same mount\n");
  		goto out;
  	}
  	if (!ovl_workdir_ok(workpath.dentry, upperpath->dentry)) {
  		pr_err("overlayfs: workdir and upperdir must be separate subtrees\n");
  		goto out;
  	}
  
  	ofs->workbasedir = dget(workpath.dentry);
  
  	err = -EBUSY;
  	if (ovl_inuse_trylock(ofs->workbasedir)) {
  		ofs->workdir_locked = true;
  	} else if (ofs->config.index) {
  		pr_err("overlayfs: workdir is in-use by another mount, mount with '-o index=off' to override exclusive workdir protection.\n");
  		goto out;
  	} else {
  		pr_warn("overlayfs: workdir is in-use by another mount, accessing files from both mounts will result in undefined behavior.\n");
  	}
  
  	err = ovl_make_workdir(sb, ofs, &workpath);
  
  out:
  	path_put(&workpath);
  
  	return err;
  }
  
  static int ovl_get_indexdir(struct super_block *sb, struct ovl_fs *ofs,
  			    struct ovl_entry *oe, struct path *upperpath)
  {
  	struct vfsmount *mnt = ofs->upper_mnt;
  	int err;
  
  	err = mnt_want_write(mnt);
  	if (err)
  		return err;
  
  	/* Verify lower root is upper root origin */
  	err = ovl_verify_origin(upperpath->dentry, oe->lowerstack[0].dentry,
  				true);
  	if (err) {
  		pr_err("overlayfs: failed to verify upper root origin\n");
  		goto out;
  	}
  
  	ofs->indexdir = ovl_workdir_create(ofs, OVL_INDEXDIR_NAME, true);
  	if (ofs->indexdir) {
  		err = ovl_setup_trap(sb, ofs->indexdir, &ofs->indexdir_trap,
  				     "indexdir");
  		if (err)
  			goto out;
  
  		/*
  		 * Verify upper root is exclusively associated with index dir.
  		 * Older kernels stored upper fh in "trusted.overlay.origin"
  		 * xattr. If that xattr exists, verify that it is a match to
  		 * upper dir file handle. In any case, verify or set xattr
  		 * "trusted.overlay.upper" to indicate that index may have
  		 * directory entries.
  		 */
  		if (ovl_check_origin_xattr(ofs->indexdir)) {
  			err = ovl_verify_set_fh(ofs->indexdir, OVL_XATTR_ORIGIN,
  						upperpath->dentry, true, false);
  			if (err)
  				pr_err("overlayfs: failed to verify index dir 'origin' xattr\n");
  		}
  		err = ovl_verify_upper(ofs->indexdir, upperpath->dentry, true);
  		if (err)
  			pr_err("overlayfs: failed to verify index dir 'upper' xattr\n");
  
  		/* Cleanup bad/stale/orphan index entries */
  		if (!err)
  			err = ovl_indexdir_cleanup(ofs);
  	}
  	if (err || !ofs->indexdir)
  		pr_warn("overlayfs: try deleting index dir or mounting with '-o index=off' to disable inodes index.\n");
  
  out:
  	mnt_drop_write(mnt);
  	return err;
  }
  
  static bool ovl_lower_uuid_ok(struct ovl_fs *ofs, const uuid_t *uuid)
  {
  	unsigned int i;
  
  	if (!ofs->config.nfs_export && !(ofs->config.index && ofs->upper_mnt))
  		return true;
  
  	for (i = 0; i < ofs->numlowerfs; i++) {
  		/*
  		 * We use uuid to associate an overlay lower file handle with a
  		 * lower layer, so we can accept lower fs with null uuid as long
  		 * as all lower layers with null uuid are on the same fs.
  		 */
  		if (uuid_equal(&ofs->lower_fs[i].sb->s_uuid, uuid))
  			return false;
  	}
  	return true;
  }
  
  /* Get a unique fsid for the layer */
  static int ovl_get_fsid(struct ovl_fs *ofs, const struct path *path)
  {
  	struct super_block *sb = path->mnt->mnt_sb;
  	unsigned int i;
  	dev_t dev;
  	int err;
  
  	/* fsid 0 is reserved for upper fs even with non upper overlay */
  	if (ofs->upper_mnt && ofs->upper_mnt->mnt_sb == sb)
  		return 0;
  
  	for (i = 0; i < ofs->numlowerfs; i++) {
  		if (ofs->lower_fs[i].sb == sb)
  			return i + 1;
  	}
  
  	if (!ovl_lower_uuid_ok(ofs, &sb->s_uuid)) {
  		ofs->config.index = false;
  		ofs->config.nfs_export = false;
  		pr_warn("overlayfs: %s uuid detected in lower fs '%pd2', falling back to index=off,nfs_export=off.\n",
  			uuid_is_null(&sb->s_uuid) ? "null" : "conflicting",
  			path->dentry);
  	}
  
  	err = get_anon_bdev(&dev);
  	if (err) {
  		pr_err("overlayfs: failed to get anonymous bdev for lowerpath\n");
  		return err;
  	}
  
  	ofs->lower_fs[ofs->numlowerfs].sb = sb;
  	ofs->lower_fs[ofs->numlowerfs].pseudo_dev = dev;
  	ofs->numlowerfs++;
  
  	return ofs->numlowerfs;
  }
  
  static int ovl_get_lower_layers(struct super_block *sb, struct ovl_fs *ofs,
  				struct path *stack, unsigned int numlower)
  {
  	int err;
  	unsigned int i;
  
  	err = -ENOMEM;
  	ofs->lower_layers = kcalloc(numlower, sizeof(struct ovl_layer),
  				    GFP_KERNEL);
  	if (ofs->lower_layers == NULL)
  		goto out;
  
  	ofs->lower_fs = kcalloc(numlower, sizeof(struct ovl_sb),
  				GFP_KERNEL);
  	if (ofs->lower_fs == NULL)
  		goto out;
  
  	for (i = 0; i < numlower; i++) {
  		struct vfsmount *mnt;
  		struct inode *trap;
  		int fsid;
  
  		err = fsid = ovl_get_fsid(ofs, &stack[i]);
  		if (err < 0)
  			goto out;
  
  		err = -EBUSY;
  		if (ovl_is_inuse(stack[i].dentry)) {
  			pr_err("overlayfs: lowerdir is in-use as upperdir/workdir\n");
  			goto out;
  		}
  
  		err = ovl_setup_trap(sb, stack[i].dentry, &trap, "lowerdir");
  		if (err)
  			goto out;
  
  		mnt = clone_private_mount(&stack[i]);
  		err = PTR_ERR(mnt);
  		if (IS_ERR(mnt)) {
  			pr_err("overlayfs: failed to clone lowerpath\n");
  			iput(trap);
  			goto out;
  		}
  
  		/*
  		 * Make lower layers R/O.  That way fchmod/fchown on lower file
  		 * will fail instead of modifying lower fs.
  		 */
  		mnt->mnt_flags |= MNT_READONLY | MNT_NOATIME;
  
  		ofs->lower_layers[ofs->numlower].trap = trap;
  
  		/*
  		 * If any lower mount is nosuid, force the ovl sb to also
  		 * be nosuid.
  		 */
  		if (mnt->mnt_flags & MNT_NOSUID)
  			sb->s_iflags |= SB_I_NOSUID;
  
  		ofs->lower_layers[ofs->numlower].mnt = mnt;
  		ofs->lower_layers[ofs->numlower].idx = i + 1;
  		ofs->lower_layers[ofs->numlower].fsid = fsid;
  		if (fsid) {
  			ofs->lower_layers[ofs->numlower].fs =
  				&ofs->lower_fs[fsid - 1];
  		}
  		ofs->numlower++;
  	}
  
  	/*
  	 * When all layers on same fs, overlay can use real inode numbers.
  	 * With mount option "xino=on", mounter declares that there are enough
  	 * free high bits in underlying fs to hold the unique fsid.
  	 * If overlayfs does encounter underlying inodes using the high xino
  	 * bits reserved for fsid, it emits a warning and uses the original
  	 * inode number.
  	 */
  	if (!ofs->numlowerfs || (ofs->numlowerfs == 1 && !ofs->upper_mnt)) {
  		ofs->xino_bits = 0;
  		ofs->config.xino = OVL_XINO_OFF;
  	} else if (ofs->config.xino == OVL_XINO_ON && !ofs->xino_bits) {
  		/*
  		 * This is a roundup of number of bits needed for numlowerfs+1
  		 * (i.e. ilog2(numlowerfs+1 - 1) + 1). fsid 0 is reserved for
  		 * upper fs even with non upper overlay.
  		 */
  		BUILD_BUG_ON(ilog2(OVL_MAX_STACK) > 31);
  		ofs->xino_bits = ilog2(ofs->numlowerfs) + 1;
  	}
  
  	if (ofs->xino_bits) {
  		pr_info("overlayfs: \"xino\" feature enabled using %d upper inode bits.\n",
  			ofs->xino_bits);
  	}
  
  	err = 0;
  out:
  	return err;
  }
  
  static struct ovl_entry *ovl_get_lowerstack(struct super_block *sb,
  					    struct ovl_fs *ofs)
  {
  	int err;
  	char *lowertmp, *lower;
  	struct path *stack = NULL;
  	unsigned int stacklen, numlower = 0, i;
  	bool remote = false;
  	struct ovl_entry *oe;
  
  	err = -ENOMEM;
  	lowertmp = kstrdup(ofs->config.lowerdir, GFP_KERNEL);
  	if (!lowertmp)
  		goto out_err;
  
  	err = -EINVAL;
  	stacklen = ovl_split_lowerdirs(lowertmp);
  	if (stacklen > OVL_MAX_STACK) {
  		pr_err("overlayfs: too many lower directories, limit is %d\n",
  		       OVL_MAX_STACK);
  		goto out_err;
  	} 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;
  	stack = kcalloc(stacklen, sizeof(struct path), GFP_KERNEL);
  	if (!stack)
  		goto out_err;
  
  	err = -EINVAL;
  	lower = lowertmp;
  	for (numlower = 0; numlower < stacklen; numlower++) {
  		err = ovl_lower_dir(lower, &stack[numlower], ofs,
  				    &sb->s_stack_depth, &remote);
  		if (err)
  			goto out_err;
  
  		lower = strchr(lower, '\0') + 1;
  	}
  
  	err = -EINVAL;
  	sb->s_stack_depth++;
  	if (sb->s_stack_depth > FILESYSTEM_MAX_STACK_DEPTH) {
  		pr_err("overlayfs: maximum fs stacking depth exceeded\n");
  		goto out_err;
  	}
  
  	err = ovl_get_lower_layers(sb, ofs, stack, numlower);
  	if (err)
  		goto out_err;
  
  	err = -ENOMEM;
  	oe = ovl_alloc_entry(numlower);
  	if (!oe)
  		goto out_err;
  
  	for (i = 0; i < numlower; i++) {
  		oe->lowerstack[i].dentry = dget(stack[i].dentry);
  		oe->lowerstack[i].layer = &ofs->lower_layers[i];
  	}
  
  	if (remote)
  		sb->s_d_op = &ovl_reval_dentry_operations;
  	else
  		sb->s_d_op = &ovl_dentry_operations;
  
  out:
  	for (i = 0; i < numlower; i++)
  		path_put(&stack[i]);
  	kfree(stack);
  	kfree(lowertmp);
  
  	return oe;
  
  out_err:
  	oe = ERR_PTR(err);
  	goto out;
  }
  
  /*
   * Check if this layer root is a descendant of:
   * - another layer of this overlayfs instance
   * - upper/work dir of any overlayfs instance
   */
  static int ovl_check_layer(struct super_block *sb, struct dentry *dentry,
  			   const char *name)
  {
  	struct dentry *next = dentry, *parent;
  	int err = 0;
  
  	if (!dentry)
  		return 0;
  
  	parent = dget_parent(next);
  
  	/* Walk back ancestors to root (inclusive) looking for traps */
  	while (!err && parent != next) {
  		if (ovl_is_inuse(parent)) {
  			err = -EBUSY;
  			pr_err("overlayfs: %s path overlapping in-use upperdir/workdir\n",
  			       name);
  		} else if (ovl_lookup_trap_inode(sb, parent)) {
  			err = -ELOOP;
  			pr_err("overlayfs: overlapping %s path\n", name);
  		}
  		next = parent;
  		parent = dget_parent(next);
  		dput(next);
  	}
  
  	dput(parent);
  
  	return err;
  }
  
  /*
   * Check if any of the layers or work dirs overlap.
   */
  static int ovl_check_overlapping_layers(struct super_block *sb,
  					struct ovl_fs *ofs)
  {
  	int i, err;
  
  	if (ofs->upper_mnt) {
  		err = ovl_check_layer(sb, ofs->upper_mnt->mnt_root, "upperdir");
  		if (err)
  			return err;
  
  		/*
  		 * Checking workbasedir avoids hitting ovl_is_inuse(parent) of
  		 * this instance and covers overlapping work and index dirs,
  		 * unless work or index dir have been moved since created inside
  		 * workbasedir.  In that case, we already have their traps in
  		 * inode cache and we will catch that case on lookup.
  		 */
  		err = ovl_check_layer(sb, ofs->workbasedir, "workdir");
  		if (err)
  			return err;
  	}
  
  	for (i = 0; i < ofs->numlower; i++) {
  		err = ovl_check_layer(sb, ofs->lower_layers[i].mnt->mnt_root,
  				      "lowerdir");
  		if (err)
  			return err;
  	}
  
  	return 0;
  }
  
  static int ovl_fill_super(struct super_block *sb, void *data, int silent)
  {
  	struct path upperpath = { };
  	struct dentry *root_dentry;
  	struct ovl_entry *oe;
  	struct ovl_fs *ofs;
  	struct cred *cred;
  	int err;
  
  	err = -ENOMEM;
  	ofs = kzalloc(sizeof(struct ovl_fs), GFP_KERNEL);
  	if (!ofs)
  		goto out;
  
  	ofs->creator_cred = cred = prepare_creds();
  	if (!cred)
  		goto out_err;
  
  	ofs->config.index = ovl_index_def;
  	ofs->config.nfs_export = ovl_nfs_export_def;
  	ofs->config.xino = ovl_xino_def();
  	ofs->config.metacopy = ovl_metacopy_def;
  	err = ovl_parse_opt((char *) data, &ofs->config);
  	if (err)
  		goto out_err;
  
  	err = -EINVAL;
  	if (!ofs->config.lowerdir) {
  		if (!silent)
  			pr_err("overlayfs: missing 'lowerdir'\n");
  		goto out_err;
  	}
  
  	sb->s_stack_depth = 0;
  	sb->s_maxbytes = MAX_LFS_FILESIZE;
  	/* Assume underlaying fs uses 32bit inodes unless proven otherwise */
  	if (ofs->config.xino != OVL_XINO_OFF)
  		ofs->xino_bits = BITS_PER_LONG - 32;
  
  	/* alloc/destroy_inode needed for setting up traps in inode cache */
  	sb->s_op = &ovl_super_operations;
  
  	if (ofs->config.upperdir) {
  		if (!ofs->config.workdir) {
  			pr_err("overlayfs: missing 'workdir'\n");
  			goto out_err;
  		}
  
  		err = ovl_get_upper(sb, ofs, &upperpath);
  		if (err)
  			goto out_err;
  
  		err = ovl_get_workdir(sb, ofs, &upperpath);
  		if (err)
  			goto out_err;
  
  		if (!ofs->workdir)
  			sb->s_flags |= SB_RDONLY;
  
  		/*
  		 * If the upper mount is nosuid, force the ovl sb to also
  		 * be nosuid.
  		 */
  		if (ofs->upper_mnt->mnt_flags & MNT_NOSUID)
  			sb->s_iflags |= SB_I_NOSUID;
  
  		sb->s_stack_depth = ofs->upper_mnt->mnt_sb->s_stack_depth;
  		sb->s_time_gran = ofs->upper_mnt->mnt_sb->s_time_gran;
  
  	}
  	oe = ovl_get_lowerstack(sb, ofs);
  	err = PTR_ERR(oe);
  	if (IS_ERR(oe))
  		goto out_err;
  
  	/* If the upper fs is nonexistent, we mark overlayfs r/o too */
  	if (!ofs->upper_mnt)
  		sb->s_flags |= SB_RDONLY;
  
  	if (!(ovl_force_readonly(ofs)) && ofs->config.index) {
  		err = ovl_get_indexdir(sb, ofs, oe, &upperpath);
  		if (err)
  			goto out_free_oe;
  
  		/* Force r/o mount with no index dir */
  		if (!ofs->indexdir) {
  			dput(ofs->workdir);
  			ofs->workdir = NULL;
  			sb->s_flags |= SB_RDONLY;
  		}
  
  	}
  
  	err = ovl_check_overlapping_layers(sb, ofs);
  	if (err)
  		goto out_free_oe;
  
  	/* Show index=off in /proc/mounts for forced r/o mount */
  	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;
  		}
  	}
  
  	if (ofs->config.metacopy && ofs->config.nfs_export) {
  		pr_warn("overlayfs: NFS export is not supported with metadata only copy up, falling back to nfs_export=off.\n");
  		ofs->config.nfs_export = false;
  	}
  
  	if (ofs->config.nfs_export)
  		sb->s_export_op = &ovl_export_operations;
  
  	/* Never override disk quota limits or use reserved space */
  	cap_lower(cred->cap_effective, CAP_SYS_RESOURCE);
  
  	sb->s_magic = OVERLAYFS_SUPER_MAGIC;
  	sb->s_xattr = ovl_xattr_handlers;
  	sb->s_fs_info = ofs;
  	sb->s_flags |= SB_POSIXACL;
  
  	err = -ENOMEM;
  	root_dentry = d_make_root(ovl_new_inode(sb, S_IFDIR, 0));
  	if (!root_dentry)
  		goto out_free_oe;
  
  	root_dentry->d_fsdata = oe;
  
  	mntput(upperpath.mnt);
  	if (upperpath.dentry) {
  		ovl_dentry_set_upper_alias(root_dentry);
  		if (ovl_is_impuredir(upperpath.dentry))
  			ovl_set_flag(OVL_IMPURE, d_inode(root_dentry));
  	}
  
  	/* Root is always merge -> can have whiteouts */
  	ovl_set_flag(OVL_WHITEOUTS, d_inode(root_dentry));
  	ovl_dentry_set_flag(OVL_E_CONNECTED, root_dentry);
  	ovl_set_upperdata(d_inode(root_dentry));
  	ovl_inode_init(d_inode(root_dentry), upperpath.dentry,
  		       ovl_dentry_lower(root_dentry), NULL);
  
  	sb->s_root = root_dentry;
  
  	return 0;
  
  out_free_oe:
  	ovl_entry_stack_free(oe);
  	kfree(oe);
  out_err:
  	path_put(&upperpath);
  	ovl_free_fs(ofs);
  out:
  	return err;
  }
  
  static struct dentry *ovl_mount(struct file_system_type *fs_type, int flags,
  				const char *dev_name, void *raw_data)
  {
  	return mount_nodev(fs_type, flags, raw_data, ovl_fill_super);
  }
  
  static struct file_system_type ovl_fs_type = {
  	.owner		= THIS_MODULE,
  	.name		= "overlay",
  	.mount		= ovl_mount,
  	.kill_sb	= kill_anon_super,
  	.fs_flags	= FS_USERNS_MOUNT,
  };
  MODULE_ALIAS_FS("overlay");
  
  static void ovl_inode_init_once(void *foo)
  {
  	struct ovl_inode *oi = foo;
  
  	inode_init_once(&oi->vfs_inode);
  }
  
  static int __init ovl_init(void)
  {
  	int err;
  
  	ovl_inode_cachep = kmem_cache_create("ovl_inode",
  					     sizeof(struct ovl_inode), 0,
  					     (SLAB_RECLAIM_ACCOUNT|
  					      SLAB_MEM_SPREAD|SLAB_ACCOUNT),
  					     ovl_inode_init_once);
  	if (ovl_inode_cachep == NULL)
  		return -ENOMEM;
  
  	err = register_filesystem(&ovl_fs_type);
  	if (err)
  		kmem_cache_destroy(ovl_inode_cachep);
  
  	return err;
  }
  
  static void __exit ovl_exit(void)
  {
  	unregister_filesystem(&ovl_fs_type);
  
  	/*
  	 * Make sure all delayed rcu free inodes are flushed before we
  	 * destroy cache.
  	 */
  	rcu_barrier();
  	kmem_cache_destroy(ovl_inode_cachep);
  
  }
  
  module_init(ovl_init);
  module_exit(ovl_exit);
  