/*
   *
   * Copyright (C) 2011 Novell Inc.
   *
   * This program is free software; you can redistribute it and/or modify it
   * under the terms of the GNU General Public License version 2 as published by
   * the Free Software Foundation.
   */
  
  #include <linux/fs.h>
  #include <linux/namei.h>
  #include <linux/xattr.h>
  #include <linux/security.h>
  #include <linux/mount.h>
  #include <linux/slab.h>
  #include <linux/parser.h>
  #include <linux/module.h>
  #include <linux/cred.h>
  #include <linux/sched.h>
  #include <linux/statfs.h>
  #include <linux/seq_file.h>
  #include "overlayfs.h"
  
  MODULE_AUTHOR("Miklos Szeredi <miklos@szeredi.hu>");
  MODULE_DESCRIPTION("Overlay filesystem");
  MODULE_LICENSE("GPL");
  
  #define OVERLAYFS_SUPER_MAGIC 0x794c764f
  
  struct ovl_config {
  	char *lowerdir;
  	char *upperdir;
  };
  
  /* private information held for overlayfs's superblock */
  struct ovl_fs {
  	struct vfsmount *upper_mnt;
  	struct vfsmount *lower_mnt;
  	long lower_namelen;
  	/* pathnames of lower and upper dirs, for show_options */
  	struct ovl_config config;
  };
  
  /* private information held for every overlayfs dentry */
  struct ovl_entry {
  	/*
  	 * Keep "double reference" on upper dentries, so that
  	 * d_delete() doesn't think it's OK to reset d_inode to NULL.
  	 */
  	struct dentry *__upperdentry;
  	struct dentry *lowerdentry;
  	union {
  		struct {
  			u64 version;
  			bool opaque;
  		};
  		struct rcu_head rcu;
  	};
  };
  
  const char *ovl_whiteout_xattr = "trusted.overlay.whiteout";
  const char *ovl_opaque_xattr = "trusted.overlay.opaque";
  
  
  enum ovl_path_type ovl_path_type(struct dentry *dentry)
  {
  	struct ovl_entry *oe = dentry->d_fsdata;
  
  	if (oe->__upperdentry) {
  		if (oe->lowerdentry && S_ISDIR(dentry->d_inode->i_mode))
  			return OVL_PATH_MERGE;
  		else
  			return OVL_PATH_UPPER;
  	} else {
  		return OVL_PATH_LOWER;
  	}
  }
  
  static struct dentry *ovl_upperdentry_dereference(struct ovl_entry *oe)
  {
  	struct dentry *upperdentry = ACCESS_ONCE(oe->__upperdentry);
  	smp_read_barrier_depends();
  	return upperdentry;
  }
  
  void ovl_path_upper(struct dentry *dentry, struct path *path)
  {
  	struct ovl_fs *ofs = dentry->d_sb->s_fs_info;
  	struct ovl_entry *oe = dentry->d_fsdata;
  
  	path->mnt = ofs->upper_mnt;
  	path->dentry = ovl_upperdentry_dereference(oe);
  }
  
  void ovl_path_lower(struct dentry *dentry, struct path *path)
  {
  	struct ovl_fs *ofs = dentry->d_sb->s_fs_info;
  	struct ovl_entry *oe = dentry->d_fsdata;
  
  	path->mnt = ofs->lower_mnt;
  	path->dentry = oe->lowerdentry;
  }
  
  enum ovl_path_type ovl_path_real(struct dentry *dentry, struct path *path)
  {
  
  	enum ovl_path_type type = ovl_path_type(dentry);
  
  	if (type == OVL_PATH_LOWER)
  		ovl_path_lower(dentry, path);
  	else
  		ovl_path_upper(dentry, path);
  
  	return type;
  }
  
  struct dentry *ovl_dentry_upper(struct dentry *dentry)
  {
  	struct ovl_entry *oe = dentry->d_fsdata;
  
  	return ovl_upperdentry_dereference(oe);
  }
  
  struct dentry *ovl_dentry_lower(struct dentry *dentry)
  {
  	struct ovl_entry *oe = dentry->d_fsdata;
  
  	return oe->lowerdentry;
  }
  
  struct dentry *ovl_dentry_real(struct dentry *dentry)
  {
  	struct ovl_entry *oe = dentry->d_fsdata;
  	struct dentry *realdentry;
  
  	realdentry = ovl_upperdentry_dereference(oe);
  	if (!realdentry)
  		realdentry = oe->lowerdentry;
  
  	return realdentry;
  }
  
  struct dentry *ovl_entry_real(struct ovl_entry *oe, bool *is_upper)
  {
  	struct dentry *realdentry;
  
  	realdentry = ovl_upperdentry_dereference(oe);
  	if (realdentry) {
  		*is_upper = true;
  	} else {
  		realdentry = oe->lowerdentry;
  		*is_upper = false;
  	}
  	return realdentry;
  }
  
  bool ovl_dentry_is_opaque(struct dentry *dentry)
  {
  	struct ovl_entry *oe = dentry->d_fsdata;
  	return oe->opaque;
  }
  
  void ovl_dentry_set_opaque(struct dentry *dentry, bool opaque)
  {
  	struct ovl_entry *oe = dentry->d_fsdata;
  	oe->opaque = opaque;
  }
  
  void ovl_dentry_update(struct dentry *dentry, struct dentry *upperdentry)
  {
  	struct ovl_entry *oe = dentry->d_fsdata;
  
  	WARN_ON(!mutex_is_locked(&upperdentry->d_parent->d_inode->i_mutex));
  	WARN_ON(oe->__upperdentry);
  	BUG_ON(!upperdentry->d_inode);
  	smp_wmb();
  	oe->__upperdentry = dget(upperdentry);
  }
  
  void ovl_dentry_version_inc(struct dentry *dentry)
  {
  	struct ovl_entry *oe = dentry->d_fsdata;
  
  	WARN_ON(!mutex_is_locked(&dentry->d_inode->i_mutex));
  	oe->version++;
  }
  
  u64 ovl_dentry_version_get(struct dentry *dentry)
  {
  	struct ovl_entry *oe = dentry->d_fsdata;
  
  	WARN_ON(!mutex_is_locked(&dentry->d_inode->i_mutex));
  	return oe->version;
  }
  
  bool ovl_is_whiteout(struct dentry *dentry)
  {
  	int res;
  	char val;
  
  	if (!dentry)
  		return false;
  	if (!dentry->d_inode)
  		return false;
  	if (!S_ISLNK(dentry->d_inode->i_mode))
  		return false;
  
  	res = vfs_getxattr(dentry, ovl_whiteout_xattr, &val, 1);
  	if (res == 1 && val == 'y')
  		return true;
  
  	return false;
  }
  
  static bool ovl_is_opaquedir(struct dentry *dentry)
  {
  	int res;
  	char val;
  
  	if (!S_ISDIR(dentry->d_inode->i_mode))
  		return false;
  
  	res = vfs_getxattr(dentry, ovl_opaque_xattr, &val, 1);
  	if (res == 1 && val == 'y')
  		return true;
  
  	return false;
  }
  
  static void ovl_entry_free(struct rcu_head *head)
  {
  	struct ovl_entry *oe = container_of(head, struct ovl_entry, rcu);
  	kfree(oe);
  }
  
  static void ovl_dentry_release(struct dentry *dentry)
  {
  	struct ovl_entry *oe = dentry->d_fsdata;
  
  	if (oe) {
  		dput(oe->__upperdentry);
  		dput(oe->__upperdentry);
  		dput(oe->lowerdentry);
  		call_rcu(&oe->rcu, ovl_entry_free);
  	}
  }
  
  const struct dentry_operations ovl_dentry_operations = {
  	.d_release = ovl_dentry_release,
  };
  
  static struct ovl_entry *ovl_alloc_entry(void)
  {
  	return kzalloc(sizeof(struct ovl_entry), GFP_KERNEL);
  }
  
  static inline struct dentry *ovl_lookup_real(struct dentry *dir,
  					     struct qstr *name)
  {
  	struct dentry *dentry;
  
  	mutex_lock(&dir->d_inode->i_mutex);
  	dentry = lookup_one_len(name->name, dir, name->len);
  	mutex_unlock(&dir->d_inode->i_mutex);
  
  	if (IS_ERR(dentry)) {
  		if (PTR_ERR(dentry) == -ENOENT)
  			dentry = NULL;
  	} else if (!dentry->d_inode) {
  		dput(dentry);
  		dentry = NULL;
  	}
  	return dentry;
  }
  
  static int ovl_do_lookup(struct dentry *dentry)
  {
  	struct ovl_entry *oe;
  	struct dentry *upperdir;
  	struct dentry *lowerdir;
  	struct dentry *upperdentry = NULL;
  	struct dentry *lowerdentry = NULL;
  	struct inode *inode = NULL;
  	int err;
  
  	err = -ENOMEM;
  	oe = ovl_alloc_entry();
  	if (!oe)
  		goto out;
  
  	upperdir = ovl_dentry_upper(dentry->d_parent);
  	lowerdir = ovl_dentry_lower(dentry->d_parent);
  
  	if (upperdir) {
  		upperdentry = ovl_lookup_real(upperdir, &dentry->d_name);
  		err = PTR_ERR(upperdentry);
  		if (IS_ERR(upperdentry))
  			goto out_put_dir;
  
  		if (lowerdir && upperdentry &&
  		    (S_ISLNK(upperdentry->d_inode->i_mode) ||
  		     S_ISDIR(upperdentry->d_inode->i_mode))) {
  			const struct cred *old_cred;
  			struct cred *override_cred;
  
  			err = -ENOMEM;
  			override_cred = prepare_creds();
  			if (!override_cred)
  				goto out_dput_upper;
  
  			/* CAP_SYS_ADMIN needed for getxattr */
  			cap_raise(override_cred->cap_effective, CAP_SYS_ADMIN);
  			old_cred = override_creds(override_cred);
  
  			if (ovl_is_opaquedir(upperdentry)) {
  				oe->opaque = true;
  			} else if (ovl_is_whiteout(upperdentry)) {
  				dput(upperdentry);
  				upperdentry = NULL;
  				oe->opaque = true;
  			}
  			revert_creds(old_cred);
  			put_cred(override_cred);
  		}
  	}
  	if (lowerdir && !oe->opaque) {
  		lowerdentry = ovl_lookup_real(lowerdir, &dentry->d_name);
  		err = PTR_ERR(lowerdentry);
  		if (IS_ERR(lowerdentry))
  			goto out_dput_upper;
  	}
  
  	if (lowerdentry && upperdentry &&
  	    (!S_ISDIR(upperdentry->d_inode->i_mode) ||
  	     !S_ISDIR(lowerdentry->d_inode->i_mode))) {
  		dput(lowerdentry);
  		lowerdentry = NULL;
  		oe->opaque = true;
  	}
  
  	if (lowerdentry || upperdentry) {
  		struct dentry *realdentry;
  
  		realdentry = upperdentry ? upperdentry : lowerdentry;
  		err = -ENOMEM;
  		inode = ovl_new_inode(dentry->d_sb, realdentry->d_inode->i_mode,
  				      oe);
  		if (!inode)
  			goto out_dput;
  		ovl_copyattr(realdentry->d_inode, inode);
  	}
  
  	if (upperdentry)
  		oe->__upperdentry = dget(upperdentry);
  
  	if (lowerdentry)
  		oe->lowerdentry = lowerdentry;
  
  	dentry->d_fsdata = oe;
  	dentry->d_op = &ovl_dentry_operations;
  	d_add(dentry, inode);
  
  	return 0;
  
  out_dput:
  	dput(lowerdentry);
  out_dput_upper:
  	dput(upperdentry);
  out_put_dir:
  	kfree(oe);
  out:
  	return err;
  }
  
  struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
  			  unsigned int flags)
  {
  	int err = ovl_do_lookup(dentry);
  
  	if (err)
  		return ERR_PTR(err);
  
  	return NULL;
  }
  
  struct file *ovl_path_open(struct path *path, int flags)
  {
  	return dentry_open(path, flags, current_cred());
  }
  
  static void ovl_put_super(struct super_block *sb)
  {
  	struct ovl_fs *ufs = sb->s_fs_info;
  
  	if (!(sb->s_flags & MS_RDONLY))
  		mnt_drop_write(ufs->upper_mnt);
  
  	mntput(ufs->upper_mnt);
  	mntput(ufs->lower_mnt);
  
  	kfree(ufs->config.lowerdir);
  	kfree(ufs->config.upperdir);
  	kfree(ufs);
  }
  
  static int ovl_remount_fs(struct super_block *sb, int *flagsp, char *data)
  {
  	int flags = *flagsp;
  	struct ovl_fs *ufs = sb->s_fs_info;
  
  	/* When remounting rw or ro, we need to adjust the write access to the
  	 * upper fs.
  	 */
  	if (((flags ^ sb->s_flags) & MS_RDONLY) == 0)
  		/* No change to readonly status */
  		return 0;
  
  	if (flags & MS_RDONLY) {
  		mnt_drop_write(ufs->upper_mnt);
  		return 0;
  	} else
  		return mnt_want_write(ufs->upper_mnt);
  }
  
  /**
   * 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 same filesystem.
   */
  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_upper(root_dentry, &path);
  
  	err = vfs_statfs(&path, buf);
  	if (!err) {
  		buf->f_namelen = max(buf->f_namelen, ofs->lower_namelen);
  		buf->f_type = OVERLAYFS_SUPER_MAGIC;
  	}
  
  	return err;
  }
  
  /**
   * 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 *ufs = sb->s_fs_info;
  
  	seq_printf(m, ",lowerdir=%s", ufs->config.lowerdir);
  	seq_printf(m, ",upperdir=%s", ufs->config.upperdir);
  	return 0;
  }
  
  static const struct super_operations ovl_super_operations = {
  	.put_super	= ovl_put_super,
  	.remount_fs	= ovl_remount_fs,
  	.statfs		= ovl_statfs,
  	.show_options	= ovl_show_options,
  };
  
  enum {
  	OPT_LOWERDIR,
  	OPT_UPPERDIR,
  	OPT_ERR,
  };
  
  static const match_table_t ovl_tokens = {
  	{OPT_LOWERDIR,			"lowerdir=%s"},
  	{OPT_UPPERDIR,			"upperdir=%s"},
  	{OPT_ERR,			NULL}
  };
  
  static int ovl_parse_opt(char *opt, struct ovl_config *config)
  {
  	char *p;
  
  	config->upperdir = NULL;
  	config->lowerdir = NULL;
  
  	while ((p = strsep(&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;
  
  		default:
  			return -EINVAL;
  		}
  	}
  	return 0;
  }
  
  static int ovl_fill_super(struct super_block *sb, void *data, int silent)
  {
  	struct path lowerpath;
  	struct path upperpath;
  	struct inode *root_inode;
  	struct dentry *root_dentry;
  	struct ovl_entry *oe;
  	struct ovl_fs *ufs;
  	struct kstatfs statfs;
  	int err;
  
  	err = -ENOMEM;
  	ufs = kmalloc(sizeof(struct ovl_fs), GFP_KERNEL);
  	if (!ufs)
  		goto out;
  
  	err = ovl_parse_opt((char *) data, &ufs->config);
  	if (err)
  		goto out_free_ufs;
  
  	err = -EINVAL;
  	if (!ufs->config.upperdir || !ufs->config.lowerdir) {
  		pr_err("overlayfs: missing upperdir or lowerdir
  ");
  		goto out_free_config;
  	}
  
  	oe = ovl_alloc_entry();
  	if (oe == NULL)
  		goto out_free_config;
  
  	err = kern_path(ufs->config.upperdir, LOOKUP_FOLLOW, &upperpath);
  	if (err)
  		goto out_free_oe;
  
  	err = kern_path(ufs->config.lowerdir, LOOKUP_FOLLOW, &lowerpath);
  	if (err)
  		goto out_put_upperpath;
  
  	err = -ENOTDIR;
  	if (!S_ISDIR(upperpath.dentry->d_inode->i_mode) ||
  	    !S_ISDIR(lowerpath.dentry->d_inode->i_mode))
  		goto out_put_lowerpath;
  
  	err = vfs_statfs(&lowerpath, &statfs);
  	if (err) {
  		pr_err("overlayfs: statfs failed on lowerpath
  ");
  		goto out_put_lowerpath;
  	}
  	ufs->lower_namelen = statfs.f_namelen;
  
  	sb->s_stack_depth = max(upperpath.mnt->mnt_sb->s_stack_depth,
  				lowerpath.mnt->mnt_sb->s_stack_depth) + 1;
  
  	err = -EINVAL;
  	if (sb->s_stack_depth > FILESYSTEM_MAX_STACK_DEPTH) {
  		pr_err("overlayfs: maximum fs stacking depth exceeded
  ");
  		goto out_put_lowerpath;
  	}
  
  
  	ufs->upper_mnt = clone_private_mount(&upperpath);
  	err = PTR_ERR(ufs->upper_mnt);
  	if (IS_ERR(ufs->upper_mnt)) {
  		pr_err("overlayfs: failed to clone upperpath
  ");
  		goto out_put_lowerpath;
  	}
  
  	ufs->lower_mnt = clone_private_mount(&lowerpath);
  	err = PTR_ERR(ufs->lower_mnt);
  	if (IS_ERR(ufs->lower_mnt)) {
  		pr_err("overlayfs: failed to clone lowerpath
  ");
  		goto out_put_upper_mnt;
  	}
  
  	/*
  	 * Make lower_mnt R/O.  That way fchmod/fchown on lower file
  	 * will fail instead of modifying lower fs.
  	 */
  	ufs->lower_mnt->mnt_flags |= MNT_READONLY;
  
  	/* If the upper fs is r/o, we mark overlayfs r/o too */
  	if (ufs->upper_mnt->mnt_sb->s_flags & MS_RDONLY)
  		sb->s_flags |= MS_RDONLY;
  
  	if (!(sb->s_flags & MS_RDONLY)) {
  		err = mnt_want_write(ufs->upper_mnt);
  		if (err)
  			goto out_put_lower_mnt;
  	}
  
  	err = -ENOMEM;
  	root_inode = ovl_new_inode(sb, S_IFDIR, oe);
  	if (!root_inode)
  		goto out_drop_write;
  
  	root_dentry = d_make_root(root_inode);
  	if (!root_dentry)
  		goto out_drop_write;
  
  	mntput(upperpath.mnt);
  	mntput(lowerpath.mnt);
  
  	oe->__upperdentry = dget(upperpath.dentry);
  	oe->lowerdentry = lowerpath.dentry;
  
  	root_dentry->d_fsdata = oe;
  	root_dentry->d_op = &ovl_dentry_operations;
  
  	sb->s_magic = OVERLAYFS_SUPER_MAGIC;
  	sb->s_op = &ovl_super_operations;
  	sb->s_root = root_dentry;
  	sb->s_fs_info = ufs;
  
  	return 0;
  
  out_drop_write:
  	if (!(sb->s_flags & MS_RDONLY))
  		mnt_drop_write(ufs->upper_mnt);
  out_put_lower_mnt:
  	mntput(ufs->lower_mnt);
  out_put_upper_mnt:
  	mntput(ufs->upper_mnt);
  out_put_lowerpath:
  	path_put(&lowerpath);
  out_put_upperpath:
  	path_put(&upperpath);
  out_free_oe:
  	kfree(oe);
  out_free_config:
  	kfree(ufs->config.lowerdir);
  	kfree(ufs->config.upperdir);
  out_free_ufs:
  	kfree(ufs);
  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		= "overlayfs",
  	.mount		= ovl_mount,
  	.kill_sb	= kill_anon_super,
  };
  MODULE_ALIAS_FS("overlayfs");
  
  static int __init ovl_init(void)
  {
  	return register_filesystem(&ovl_fs_type);
  }
  
  static void __exit ovl_exit(void)
  {
  	unregister_filesystem(&ovl_fs_type);
  }
  
  module_init(ovl_init);
  module_exit(ovl_exit);