/*
   *
   * 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/slab.h>
  #include <linux/xattr.h>
  #include "overlayfs.h"
  
  static int ovl_copy_up_last(struct dentry *dentry, struct iattr *attr,
  			    bool no_data)
  {
  	int err;
  	struct dentry *parent;
  	struct kstat stat;
  	struct path lowerpath;
  
  	parent = dget_parent(dentry);
  	err = ovl_copy_up(parent);
  	if (err)
  		goto out_dput_parent;
  
  	ovl_path_lower(dentry, &lowerpath);
  	err = vfs_getattr(&lowerpath, &stat);
  	if (err)
  		goto out_dput_parent;
  
  	if (no_data)
  		stat.size = 0;
  
  	err = ovl_copy_up_one(parent, dentry, &lowerpath, &stat, attr);
  
  out_dput_parent:
  	dput(parent);
  	return err;
  }
  
  int ovl_setattr(struct dentry *dentry, struct iattr *attr)
  {
  	int err;
  	struct dentry *upperdentry;
  
  	err = ovl_want_write(dentry);
  	if (err)
  		goto out;
  
  	upperdentry = ovl_dentry_upper(dentry);
  	if (upperdentry) {
  		mutex_lock(&upperdentry->d_inode->i_mutex);
  		err = notify_change(upperdentry, attr, NULL);
  		mutex_unlock(&upperdentry->d_inode->i_mutex);
  	} else {
  		err = ovl_copy_up_last(dentry, attr, false);
  	}
  	ovl_drop_write(dentry);
  out:
  	return err;
  }
  
  static int ovl_getattr(struct vfsmount *mnt, struct dentry *dentry,
  			 struct kstat *stat)
  {
  	struct path realpath;
  
  	ovl_path_real(dentry, &realpath);
  	return vfs_getattr(&realpath, stat);
  }
  
  int ovl_permission(struct inode *inode, int mask)
  {
  	struct ovl_entry *oe;
  	struct dentry *alias = NULL;
  	struct inode *realinode;
  	struct dentry *realdentry;
  	bool is_upper;
  	int err;
  
  	if (S_ISDIR(inode->i_mode)) {
  		oe = inode->i_private;
  	} else if (mask & MAY_NOT_BLOCK) {
  		return -ECHILD;
  	} else {
  		/*
  		 * For non-directories find an alias and get the info
  		 * from there.
  		 */
  		alias = d_find_any_alias(inode);
  		if (WARN_ON(!alias))
  			return -ENOENT;
  
  		oe = alias->d_fsdata;
  	}
  
  	realdentry = ovl_entry_real(oe, &is_upper);
  
  	/* Careful in RCU walk mode */
  	realinode = ACCESS_ONCE(realdentry->d_inode);
  	if (!realinode) {
  		WARN_ON(!(mask & MAY_NOT_BLOCK));
  		err = -ENOENT;
  		goto out_dput;
  	}
  
  	if (mask & MAY_WRITE) {
  		umode_t mode = realinode->i_mode;
  
  		/*
  		 * Writes will always be redirected to upper layer, so
  		 * ignore lower layer being read-only.
  		 *
  		 * If the overlay itself is read-only then proceed
  		 * with the permission check, don't return EROFS.
  		 * This will only happen if this is the lower layer of
  		 * another overlayfs.
  		 *
  		 * If upper fs becomes read-only after the overlay was
  		 * constructed return EROFS to prevent modification of
  		 * upper layer.
  		 */
  		err = -EROFS;
  		if (is_upper && !IS_RDONLY(inode) && IS_RDONLY(realinode) &&
  		    (S_ISREG(mode) || S_ISDIR(mode) || S_ISLNK(mode)))
  			goto out_dput;
  	}
  
  	err = __inode_permission(realinode, mask);
  out_dput:
  	dput(alias);
  	return err;
  }
  
  
  struct ovl_link_data {
  	struct dentry *realdentry;
  	void *cookie;
  };
  
  static void *ovl_follow_link(struct dentry *dentry, struct nameidata *nd)
  {
  	void *ret;
  	struct dentry *realdentry;
  	struct inode *realinode;
  
  	realdentry = ovl_dentry_real(dentry);
  	realinode = realdentry->d_inode;
  
  	if (WARN_ON(!realinode->i_op->follow_link))
  		return ERR_PTR(-EPERM);
  
  	ret = realinode->i_op->follow_link(realdentry, nd);
  	if (IS_ERR(ret))
  		return ret;
  
  	if (realinode->i_op->put_link) {
  		struct ovl_link_data *data;
  
  		data = kmalloc(sizeof(struct ovl_link_data), GFP_KERNEL);
  		if (!data) {
  			realinode->i_op->put_link(realdentry, nd, ret);
  			return ERR_PTR(-ENOMEM);
  		}
  		data->realdentry = realdentry;
  		data->cookie = ret;
  
  		return data;
  	} else {
  		return NULL;
  	}
  }
  
  static void ovl_put_link(struct dentry *dentry, struct nameidata *nd, void *c)
  {
  	struct inode *realinode;
  	struct ovl_link_data *data = c;
  
  	if (!data)
  		return;
  
  	realinode = data->realdentry->d_inode;
  	realinode->i_op->put_link(data->realdentry, nd, data->cookie);
  	kfree(data);
  }
  
  static int ovl_readlink(struct dentry *dentry, char __user *buf, int bufsiz)
  {
  	struct path realpath;
  	struct inode *realinode;
  
  	ovl_path_real(dentry, &realpath);
  	realinode = realpath.dentry->d_inode;
  
  	if (!realinode->i_op->readlink)
  		return -EINVAL;
  
  	touch_atime(&realpath);
  
  	return realinode->i_op->readlink(realpath.dentry, buf, bufsiz);
  }
  
  
  static bool ovl_is_private_xattr(const char *name)
  {

  	return strncmp(name, OVL_XATTR_PRE_NAME, OVL_XATTR_PRE_LEN) == 0;

  }
  
  int ovl_setxattr(struct dentry *dentry, const char *name,
  		 const void *value, size_t size, int flags)
  {
  	int err;
  	struct dentry *upperdentry;
  
  	err = ovl_want_write(dentry);
  	if (err)
  		goto out;
  
  	err = -EPERM;
  	if (ovl_is_private_xattr(name))
  		goto out_drop_write;
  
  	err = ovl_copy_up(dentry);
  	if (err)
  		goto out_drop_write;
  
  	upperdentry = ovl_dentry_upper(dentry);
  	err = vfs_setxattr(upperdentry, name, value, size, flags);
  
  out_drop_write:
  	ovl_drop_write(dentry);
  out:
  	return err;
  }

  static bool ovl_need_xattr_filter(struct dentry *dentry,
  				  enum ovl_path_type type)
  {

  	if ((type & (__OVL_PATH_PURE | __OVL_PATH_UPPER)) == __OVL_PATH_UPPER)
  		return S_ISDIR(dentry->d_inode->i_mode);
  	else
  		return false;

  }

  ssize_t ovl_getxattr(struct dentry *dentry, const char *name,
  		     void *value, size_t size)
  {

  	struct path realpath;
  	enum ovl_path_type type = ovl_path_real(dentry, &realpath);
  
  	if (ovl_need_xattr_filter(dentry, type) && ovl_is_private_xattr(name))

  		return -ENODATA;

  	return vfs_getxattr(realpath.dentry, name, value, size);

  }
  
  ssize_t ovl_listxattr(struct dentry *dentry, char *list, size_t size)
  {

  	struct path realpath;
  	enum ovl_path_type type = ovl_path_real(dentry, &realpath);

  	ssize_t res;
  	int off;

  	res = vfs_listxattr(realpath.dentry, list, size);

  	if (res <= 0 || size == 0)
  		return res;

  	if (!ovl_need_xattr_filter(dentry, type))

  		return res;
  
  	/* filter out private xattrs */
  	for (off = 0; off < res;) {
  		char *s = list + off;
  		size_t slen = strlen(s) + 1;
  
  		BUG_ON(off + slen > res);
  
  		if (ovl_is_private_xattr(s)) {
  			res -= slen;
  			memmove(s, s + slen, res - off);
  		} else {
  			off += slen;
  		}
  	}
  
  	return res;
  }
  
  int ovl_removexattr(struct dentry *dentry, const char *name)
  {
  	int err;
  	struct path realpath;

  	enum ovl_path_type type = ovl_path_real(dentry, &realpath);

  
  	err = ovl_want_write(dentry);
  	if (err)
  		goto out;

  	err = -ENODATA;
  	if (ovl_need_xattr_filter(dentry, type) && ovl_is_private_xattr(name))

  		goto out_drop_write;

  	if (!OVL_TYPE_UPPER(type)) {

  		err = vfs_getxattr(realpath.dentry, name, NULL, 0);
  		if (err < 0)
  			goto out_drop_write;
  
  		err = ovl_copy_up(dentry);
  		if (err)
  			goto out_drop_write;
  
  		ovl_path_upper(dentry, &realpath);
  	}
  
  	err = vfs_removexattr(realpath.dentry, name);
  out_drop_write:
  	ovl_drop_write(dentry);
  out:
  	return err;
  }
  
  static bool ovl_open_need_copy_up(int flags, enum ovl_path_type type,
  				  struct dentry *realdentry)
  {

  	if (OVL_TYPE_UPPER(type))

  		return false;
  
  	if (special_file(realdentry->d_inode->i_mode))
  		return false;
  
  	if (!(OPEN_FMODE(flags) & FMODE_WRITE) && !(flags & O_TRUNC))
  		return false;
  
  	return true;
  }

  struct inode *ovl_d_select_inode(struct dentry *dentry, unsigned file_flags)

  {
  	int err;
  	struct path realpath;
  	enum ovl_path_type type;

  	if (d_is_dir(dentry))
  		return d_backing_inode(dentry);

  	type = ovl_path_real(dentry, &realpath);

  	if (ovl_open_need_copy_up(file_flags, type, realpath.dentry)) {

  		err = ovl_want_write(dentry);
  		if (err)

  			return ERR_PTR(err);

  		if (file_flags & O_TRUNC)

  			err = ovl_copy_up_last(dentry, NULL, true);
  		else
  			err = ovl_copy_up(dentry);

  		ovl_drop_write(dentry);

  		if (err)

  			return ERR_PTR(err);

  
  		ovl_path_upper(dentry, &realpath);
  	}

  	return d_backing_inode(realpath.dentry);

  }
  
  static const struct inode_operations ovl_file_inode_operations = {
  	.setattr	= ovl_setattr,
  	.permission	= ovl_permission,
  	.getattr	= ovl_getattr,
  	.setxattr	= ovl_setxattr,
  	.getxattr	= ovl_getxattr,
  	.listxattr	= ovl_listxattr,
  	.removexattr	= ovl_removexattr,

  };
  
  static const struct inode_operations ovl_symlink_inode_operations = {
  	.setattr	= ovl_setattr,
  	.follow_link	= ovl_follow_link,
  	.put_link	= ovl_put_link,
  	.readlink	= ovl_readlink,
  	.getattr	= ovl_getattr,
  	.setxattr	= ovl_setxattr,
  	.getxattr	= ovl_getxattr,
  	.listxattr	= ovl_listxattr,
  	.removexattr	= ovl_removexattr,
  };
  
  struct inode *ovl_new_inode(struct super_block *sb, umode_t mode,
  			    struct ovl_entry *oe)
  {
  	struct inode *inode;
  
  	inode = new_inode(sb);
  	if (!inode)
  		return NULL;
  
  	mode &= S_IFMT;
  
  	inode->i_ino = get_next_ino();
  	inode->i_mode = mode;
  	inode->i_flags |= S_NOATIME | S_NOCMTIME;
  
  	switch (mode) {
  	case S_IFDIR:
  		inode->i_private = oe;
  		inode->i_op = &ovl_dir_inode_operations;
  		inode->i_fop = &ovl_dir_operations;
  		break;
  
  	case S_IFLNK:
  		inode->i_op = &ovl_symlink_inode_operations;
  		break;
  
  	case S_IFREG:
  	case S_IFSOCK:
  	case S_IFBLK:
  	case S_IFCHR:
  	case S_IFIFO:
  		inode->i_op = &ovl_file_inode_operations;
  		break;
  
  	default:
  		WARN(1, "illegal file type: %i
  ", mode);
  		iput(inode);
  		inode = NULL;
  	}
  
  	return inode;

  }