/*
   *
   * 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/file.h>
  #include <linux/splice.h>
  #include <linux/xattr.h>
  #include <linux/security.h>
  #include <linux/uaccess.h>
  #include <linux/sched.h>
  #include <linux/namei.h>
  #include "overlayfs.h"
  
  #define OVL_COPY_UP_CHUNK_SIZE (1 << 20)
  
  int ovl_copy_xattr(struct dentry *old, struct dentry *new)
  {
  	ssize_t list_size, size, value_size = 0;
  	char *buf, *name, *value = NULL;
  	int uninitialized_var(error);
  	size_t slen;
  
  	if (!old->d_inode->i_op->getxattr ||
  	    !new->d_inode->i_op->getxattr)
  		return 0;
  
  	list_size = vfs_listxattr(old, NULL, 0);
  	if (list_size <= 0) {
  		if (list_size == -EOPNOTSUPP)
  			return 0;
  		return list_size;
  	}
  
  	buf = kzalloc(list_size, GFP_KERNEL);
  	if (!buf)
  		return -ENOMEM;
  
  	list_size = vfs_listxattr(old, buf, list_size);
  	if (list_size <= 0) {
  		error = list_size;
  		goto out;
  	}
  
  	for (name = buf; list_size; name += slen) {
  		slen = strnlen(name, list_size) + 1;
  
  		/* underlying fs providing us with an broken xattr list? */
  		if (WARN_ON(slen > list_size)) {
  			error = -EIO;
  			break;
  		}
  		list_size -= slen;
  
  		if (ovl_is_private_xattr(name))
  			continue;
  retry:
  		size = vfs_getxattr(old, name, value, value_size);
  		if (size == -ERANGE)
  			size = vfs_getxattr(old, name, NULL, 0);
  
  		if (size < 0) {
  			error = size;
  			break;
  		}
  
  		if (size > value_size) {
  			void *new;
  
  			new = krealloc(value, size, GFP_KERNEL);
  			if (!new) {
  				error = -ENOMEM;
  				break;
  			}
  			value = new;
  			value_size = size;
  			goto retry;
  		}
  
  		error = vfs_setxattr(new, name, value, size, 0);
  		if (error)
  			break;
  	}
  	kfree(value);
  out:
  	kfree(buf);
  	return error;
  }
  
  static int ovl_copy_up_data(struct path *old, struct path *new, loff_t len)
  {
  	struct file *old_file;
  	struct file *new_file;
  	loff_t old_pos = 0;
  	loff_t new_pos = 0;
  	int error = 0;
  
  	if (len == 0)
  		return 0;
  
  	old_file = ovl_path_open(old, O_LARGEFILE | O_RDONLY);
  	if (IS_ERR(old_file))
  		return PTR_ERR(old_file);
  
  	new_file = ovl_path_open(new, O_LARGEFILE | O_WRONLY);
  	if (IS_ERR(new_file)) {
  		error = PTR_ERR(new_file);
  		goto out_fput;
  	}
  
  	/* FIXME: copy up sparse files efficiently */
  	while (len) {
  		size_t this_len = OVL_COPY_UP_CHUNK_SIZE;
  		long bytes;
  
  		if (len < this_len)
  			this_len = len;
  
  		if (signal_pending_state(TASK_KILLABLE, current)) {
  			error = -EINTR;
  			break;
  		}
  
  		bytes = do_splice_direct(old_file, &old_pos,
  					 new_file, &new_pos,
  					 this_len, SPLICE_F_MOVE);
  		if (bytes <= 0) {
  			error = bytes;
  			break;
  		}
  		WARN_ON(old_pos != new_pos);
  
  		len -= bytes;
  	}
  
  	if (!error)
  		error = vfs_fsync(new_file, 0);
  	fput(new_file);
  out_fput:
  	fput(old_file);
  	return error;
  }
  
  static char *ovl_read_symlink(struct dentry *realdentry)
  {
  	int res;
  	char *buf;
  	struct inode *inode = realdentry->d_inode;
  	mm_segment_t old_fs;
  
  	res = -EINVAL;
  	if (!inode->i_op->readlink)
  		goto err;
  
  	res = -ENOMEM;
  	buf = (char *) __get_free_page(GFP_KERNEL);
  	if (!buf)
  		goto err;
  
  	old_fs = get_fs();
  	set_fs(get_ds());
  	/* The cast to a user pointer is valid due to the set_fs() */
  	res = inode->i_op->readlink(realdentry,
  				    (char __user *)buf, PAGE_SIZE - 1);
  	set_fs(old_fs);
  	if (res < 0) {
  		free_page((unsigned long) buf);
  		goto err;
  	}
  	buf[res] = '\0';
  
  	return buf;
  
  err:
  	return ERR_PTR(res);
  }
  
  static int ovl_set_timestamps(struct dentry *upperdentry, struct kstat *stat)
  {
  	struct iattr attr = {
  		.ia_valid =
  		     ATTR_ATIME | ATTR_MTIME | ATTR_ATIME_SET | ATTR_MTIME_SET,
  		.ia_atime = stat->atime,
  		.ia_mtime = stat->mtime,
  	};
  
  	return notify_change(upperdentry, &attr, NULL);
  }
  
  int ovl_set_attr(struct dentry *upperdentry, struct kstat *stat)
  {
  	int err = 0;
  
  	if (!S_ISLNK(stat->mode)) {
  		struct iattr attr = {
  			.ia_valid = ATTR_MODE,
  			.ia_mode = stat->mode,
  		};
  		err = notify_change(upperdentry, &attr, NULL);
  	}
  	if (!err) {
  		struct iattr attr = {
  			.ia_valid = ATTR_UID | ATTR_GID,
  			.ia_uid = stat->uid,
  			.ia_gid = stat->gid,
  		};
  		err = notify_change(upperdentry, &attr, NULL);
  	}
  	if (!err)
  		ovl_set_timestamps(upperdentry, stat);
  
  	return err;
  }
  
  static int ovl_copy_up_locked(struct dentry *workdir, struct dentry *upperdir,
  			      struct dentry *dentry, struct path *lowerpath,
  			      struct kstat *stat, const char *link)
  {
  	struct inode *wdir = workdir->d_inode;
  	struct inode *udir = upperdir->d_inode;
  	struct dentry *newdentry = NULL;
  	struct dentry *upper = NULL;
  	umode_t mode = stat->mode;
  	int err;
  
  	newdentry = ovl_lookup_temp(workdir, dentry);
  	err = PTR_ERR(newdentry);
  	if (IS_ERR(newdentry))
  		goto out;
  
  	upper = lookup_one_len(dentry->d_name.name, upperdir,
  			       dentry->d_name.len);
  	err = PTR_ERR(upper);
  	if (IS_ERR(upper))
  		goto out1;
  
  	/* Can't properly set mode on creation because of the umask */
  	stat->mode &= S_IFMT;
  	err = ovl_create_real(wdir, newdentry, stat, link, NULL, true);
  	stat->mode = mode;
  	if (err)
  		goto out2;
  
  	if (S_ISREG(stat->mode)) {
  		struct path upperpath;
  		ovl_path_upper(dentry, &upperpath);
  		BUG_ON(upperpath.dentry != NULL);
  		upperpath.dentry = newdentry;
  
  		err = ovl_copy_up_data(lowerpath, &upperpath, stat->size);
  		if (err)
  			goto out_cleanup;
  	}
  
  	err = ovl_copy_xattr(lowerpath->dentry, newdentry);
  	if (err)
  		goto out_cleanup;
  
  	mutex_lock(&newdentry->d_inode->i_mutex);
  	err = ovl_set_attr(newdentry, stat);
  	mutex_unlock(&newdentry->d_inode->i_mutex);
  	if (err)
  		goto out_cleanup;
  
  	err = ovl_do_rename(wdir, newdentry, udir, upper, 0);
  	if (err)
  		goto out_cleanup;
  
  	ovl_dentry_update(dentry, newdentry);
  	newdentry = NULL;
  
  	/*
  	 * Non-directores become opaque when copied up.
  	 */
  	if (!S_ISDIR(stat->mode))
  		ovl_dentry_set_opaque(dentry, true);
  out2:
  	dput(upper);
  out1:
  	dput(newdentry);
  out:
  	return err;
  
  out_cleanup:
  	ovl_cleanup(wdir, newdentry);
  	goto out2;
  }
  
  /*
   * Copy up a single dentry
   *
   * Directory renames only allowed on "pure upper" (already created on
   * upper filesystem, never copied up).  Directories which are on lower or
   * are merged may not be renamed.  For these -EXDEV is returned and
   * userspace has to deal with it.  This means, when copying up a
   * directory we can rely on it and ancestors being stable.
   *
   * Non-directory renames start with copy up of source if necessary.  The
   * actual rename will only proceed once the copy up was successful.  Copy
   * up uses upper parent i_mutex for exclusion.  Since rename can change
   * d_parent it is possible that the copy up will lock the old parent.  At
   * that point the file will have already been copied up anyway.
   */
  int ovl_copy_up_one(struct dentry *parent, struct dentry *dentry,
  		    struct path *lowerpath, struct kstat *stat)
  {
  	struct dentry *workdir = ovl_workdir(dentry);
  	int err;
  	struct kstat pstat;
  	struct path parentpath;
  	struct dentry *upperdir;
  	struct dentry *upperdentry;
  	const struct cred *old_cred;
  	struct cred *override_cred;
  	char *link = NULL;
  
  	if (WARN_ON(!workdir))
  		return -EROFS;
  
  	ovl_path_upper(parent, &parentpath);
  	upperdir = parentpath.dentry;
  
  	err = vfs_getattr(&parentpath, &pstat);
  	if (err)
  		return err;
  
  	if (S_ISLNK(stat->mode)) {
  		link = ovl_read_symlink(lowerpath->dentry);
  		if (IS_ERR(link))
  			return PTR_ERR(link);
  	}
  
  	err = -ENOMEM;
  	override_cred = prepare_creds();
  	if (!override_cred)
  		goto out_free_link;
  
  	override_cred->fsuid = stat->uid;
  	override_cred->fsgid = stat->gid;
  	/*
  	 * CAP_SYS_ADMIN for copying up extended attributes
  	 * CAP_DAC_OVERRIDE for create
  	 * CAP_FOWNER for chmod, timestamp update
  	 * CAP_FSETID for chmod
  	 * CAP_CHOWN for chown
  	 * CAP_MKNOD for mknod
  	 */
  	cap_raise(override_cred->cap_effective, CAP_SYS_ADMIN);
  	cap_raise(override_cred->cap_effective, CAP_DAC_OVERRIDE);
  	cap_raise(override_cred->cap_effective, CAP_FOWNER);
  	cap_raise(override_cred->cap_effective, CAP_FSETID);
  	cap_raise(override_cred->cap_effective, CAP_CHOWN);
  	cap_raise(override_cred->cap_effective, CAP_MKNOD);
  	old_cred = override_creds(override_cred);
  
  	err = -EIO;
  	if (lock_rename(workdir, upperdir) != NULL) {
  		pr_err("overlayfs: failed to lock workdir+upperdir
  ");
  		goto out_unlock;
  	}
  	upperdentry = ovl_dentry_upper(dentry);
  	if (upperdentry) {
  		/* Raced with another copy-up?  Nothing to do, then... */
  		err = 0;
  		goto out_unlock;
  	}
  
  	err = ovl_copy_up_locked(workdir, upperdir, dentry, lowerpath,
  				 stat, link);
  	if (!err) {
  		/* Restore timestamps on parent (best effort) */
  		ovl_set_timestamps(upperdir, &pstat);
  	}
  out_unlock:
  	unlock_rename(workdir, upperdir);
  	revert_creds(old_cred);
  	put_cred(override_cred);
  
  out_free_link:
  	if (link)
  		free_page((unsigned long) link);
  
  	return err;
  }
  
  int ovl_copy_up(struct dentry *dentry)
  {
  	int err;
  
  	err = 0;
  	while (!err) {
  		struct dentry *next;
  		struct dentry *parent;
  		struct path lowerpath;
  		struct kstat stat;
  		enum ovl_path_type type = ovl_path_type(dentry);
  
  		if (OVL_TYPE_UPPER(type))
  			break;
  
  		next = dget(dentry);
  		/* find the topmost dentry not yet copied up */
  		for (;;) {
  			parent = dget_parent(next);
  
  			type = ovl_path_type(parent);
  			if (OVL_TYPE_UPPER(type))
  				break;
  
  			dput(next);
  			next = parent;
  		}
  
  		ovl_path_lower(next, &lowerpath);
  		err = vfs_getattr(&lowerpath, &stat);
  		if (!err)
  			err = ovl_copy_up_one(parent, next, &lowerpath, &stat);
  
  		dput(parent);
  		dput(next);
  	}
  
  	return err;
  }