/**
   * eCryptfs: Linux filesystem encryption layer
   * This is where eCryptfs coordinates the symmetric encryption and
   * decryption of the file data as it passes between the lower
   * encrypted file and the upper decrypted file.
   *
   * Copyright (C) 1997-2003 Erez Zadok
   * Copyright (C) 2001-2003 Stony Brook University

   * Copyright (C) 2004-2007 International Business Machines Corp.

   *   Author(s): Michael A. Halcrow <mahalcro@us.ibm.com>
   *
   * This program is free software; you can redistribute it and/or
   * modify it under the terms of the GNU General Public License as
   * published by the Free Software Foundation; either version 2 of the
   * License, or (at your option) any later version.
   *
   * This program is distributed in the hope that it will be useful, but
   * WITHOUT ANY WARRANTY; without even the implied warranty of
   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   * General Public License for more details.
   *
   * You should have received a copy of the GNU General Public License
   * along with this program; if not, write to the Free Software
   * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA
   * 02111-1307, USA.
   */
  
  #include <linux/pagemap.h>
  #include <linux/writeback.h>
  #include <linux/page-flags.h>
  #include <linux/mount.h>
  #include <linux/file.h>
  #include <linux/crypto.h>
  #include <linux/scatterlist.h>

  #include <linux/slab.h>

  #include <asm/unaligned.h>

  #include "ecryptfs_kernel.h"

  /**

   * ecryptfs_get_locked_page

   *
   * Get one page from cache or lower f/s, return error otherwise.
   *

   * Returns locked and up-to-date page (if ok), with increased

   * refcnt.
   */

  struct page *ecryptfs_get_locked_page(struct inode *inode, loff_t index)

  {

  	struct page *page = read_mapping_page(inode->i_mapping, index, NULL);

  	if (!IS_ERR(page))
  		lock_page(page);
  	return page;

  }

  /**

   * ecryptfs_writepage
   * @page: Page that is locked before this call is made
   *
   * Returns zero on success; non-zero otherwise
   */
  static int ecryptfs_writepage(struct page *page, struct writeback_control *wbc)
  {

  	int rc;

  	/*
  	 * Refuse to write the page out if we are called from reclaim context
  	 * since our writepage() path may potentially allocate memory when
  	 * calling into the lower fs vfs_write() which may in turn invoke
  	 * us again.
  	 */
  	if (current->flags & PF_MEMALLOC) {
  		redirty_page_for_writepage(wbc, page);
  		rc = 0;
  		goto out;
  	}

  	rc = ecryptfs_encrypt_page(page);

  	if (rc) {
  		ecryptfs_printk(KERN_WARNING, "Error encrypting "

  				"page (upper index [0x%.16lx])
  ", page->index);

  		ClearPageUptodate(page);
  		goto out;
  	}
  	SetPageUptodate(page);

  out:

  	unlock_page(page);

  	return rc;
  }

  static void strip_xattr_flag(char *page_virt,
  			     struct ecryptfs_crypt_stat *crypt_stat)
  {
  	if (crypt_stat->flags & ECRYPTFS_METADATA_IN_XATTR) {
  		size_t written;
  
  		crypt_stat->flags &= ~ECRYPTFS_METADATA_IN_XATTR;
  		ecryptfs_write_crypt_stat_flags(page_virt, crypt_stat,
  						&written);
  		crypt_stat->flags |= ECRYPTFS_METADATA_IN_XATTR;
  	}
  }

  /**

   *   Header Extent:
   *     Octets 0-7:        Unencrypted file size (big-endian)
   *     Octets 8-15:       eCryptfs special marker
   *     Octets 16-19:      Flags
   *      Octet 16:         File format version number (between 0 and 255)
   *      Octets 17-18:     Reserved
   *      Octet 19:         Bit 1 (lsb): Reserved
   *                        Bit 2: Encrypted?
   *                        Bits 3-8: Reserved
   *     Octets 20-23:      Header extent size (big-endian)
   *     Octets 24-25:      Number of header extents at front of file
   *                        (big-endian)
   *     Octet  26:         Begin RFC 2440 authentication token packet set
   */

  
  /**

   * ecryptfs_copy_up_encrypted_with_header
   * @page: Sort of a ``virtual'' representation of the encrypted lower
   *        file. The actual lower file does not have the metadata in
   *        the header. This is locked.
   * @crypt_stat: The eCryptfs inode's cryptographic context
   *
   * The ``view'' is the version of the file that userspace winds up
   * seeing, with the header information inserted.
   */
  static int
  ecryptfs_copy_up_encrypted_with_header(struct page *page,
  				       struct ecryptfs_crypt_stat *crypt_stat)
  {
  	loff_t extent_num_in_page = 0;
  	loff_t num_extents_per_page = (PAGE_CACHE_SIZE
  				       / crypt_stat->extent_size);
  	int rc = 0;
  
  	while (extent_num_in_page < num_extents_per_page) {

  		loff_t view_extent_num = ((((loff_t)page->index)
  					   * num_extents_per_page)

  					  + extent_num_in_page);

  		size_t num_header_extents_at_front =

  			(crypt_stat->metadata_size / crypt_stat->extent_size);

  		if (view_extent_num < num_header_extents_at_front) {

  			/* This is a header extent */
  			char *page_virt;
  
  			page_virt = kmap_atomic(page, KM_USER0);
  			memset(page_virt, 0, PAGE_CACHE_SIZE);
  			/* TODO: Support more than one header extent */
  			if (view_extent_num == 0) {

  				size_t written;

  				rc = ecryptfs_read_xattr_region(
  					page_virt, page->mapping->host);

  				strip_xattr_flag(page_virt + 16, crypt_stat);

  				ecryptfs_write_header_metadata(page_virt + 20,
  							       crypt_stat,
  							       &written);

  			}
  			kunmap_atomic(page_virt, KM_USER0);
  			flush_dcache_page(page);
  			if (rc) {

  				printk(KERN_ERR "%s: Error reading xattr "

  				       "region; rc = [%d]
  ", __func__, rc);

  				goto out;
  			}

  		} else {
  			/* This is an encrypted data extent */
  			loff_t lower_offset =

  				((view_extent_num * crypt_stat->extent_size)

  				 - crypt_stat->metadata_size);

  
  			rc = ecryptfs_read_lower_page_segment(
  				page, (lower_offset >> PAGE_CACHE_SHIFT),
  				(lower_offset & ~PAGE_CACHE_MASK),
  				crypt_stat->extent_size, page->mapping->host);
  			if (rc) {
  				printk(KERN_ERR "%s: Error attempting to read "
  				       "extent at offset [%lld] in the lower "

  				       "file; rc = [%d]
  ", __func__,

  				       lower_offset, rc);
  				goto out;
  			}
  		}
  		extent_num_in_page++;
  	}
  out:
  	return rc;
  }
  
  /**

   * ecryptfs_readpage

   * @file: An eCryptfs file
   * @page: Page from eCryptfs inode mapping into which to stick the read data

   *
   * Read in a page, decrypting if necessary.
   *
   * Returns zero on success; non-zero on error.
   */
  static int ecryptfs_readpage(struct file *file, struct page *page)
  {

  	struct ecryptfs_crypt_stat *crypt_stat =

  		&ecryptfs_inode_to_private(page->mapping->host)->crypt_stat;

  	int rc = 0;

  	if (!crypt_stat || !(crypt_stat->flags & ECRYPTFS_ENCRYPTED)) {

  		rc = ecryptfs_read_lower_page_segment(page, page->index, 0,
  						      PAGE_CACHE_SIZE,
  						      page->mapping->host);

  	} else if (crypt_stat->flags & ECRYPTFS_VIEW_AS_ENCRYPTED) {
  		if (crypt_stat->flags & ECRYPTFS_METADATA_IN_XATTR) {

  			rc = ecryptfs_copy_up_encrypted_with_header(page,
  								    crypt_stat);
  			if (rc) {
  				printk(KERN_ERR "%s: Error attempting to copy "
  				       "the encrypted content from the lower "
  				       "file whilst inserting the metadata "
  				       "from the xattr into the header; rc = "

  				       "[%d]
  ", __func__, rc);

  				goto out;

  			}

  		} else {

  			rc = ecryptfs_read_lower_page_segment(
  				page, page->index, 0, PAGE_CACHE_SIZE,
  				page->mapping->host);

  			if (rc) {
  				printk(KERN_ERR "Error reading page; rc = "
  				       "[%d]
  ", rc);
  				goto out;
  			}
  		}

  	} else {

  		rc = ecryptfs_decrypt_page(page);

  		if (rc) {

  			ecryptfs_printk(KERN_ERR, "Error decrypting page; "
  					"rc = [%d]
  ", rc);
  			goto out;
  		}
  	}

  out:

  	if (rc)
  		ClearPageUptodate(page);
  	else
  		SetPageUptodate(page);

  	ecryptfs_printk(KERN_DEBUG, "Unlocking page with index = [0x%.16lx]
  ",

  			page->index);
  	unlock_page(page);
  	return rc;
  }

  /**
   * Called with lower inode mutex held.
   */

  static int fill_zeros_to_end_of_page(struct page *page, unsigned int to)
  {
  	struct inode *inode = page->mapping->host;
  	int end_byte_in_page;

  	if ((i_size_read(inode) / PAGE_CACHE_SIZE) != page->index)
  		goto out;
  	end_byte_in_page = i_size_read(inode) % PAGE_CACHE_SIZE;
  	if (to > end_byte_in_page)
  		end_byte_in_page = to;

  	zero_user_segment(page, end_byte_in_page, PAGE_CACHE_SIZE);

  out:

  	return 0;

  }

  /**

   * ecryptfs_write_begin

   * @file: The eCryptfs file

   * @mapping: The eCryptfs object
   * @pos: The file offset at which to start writing
   * @len: Length of the write
   * @flags: Various flags
   * @pagep: Pointer to return the page
   * @fsdata: Pointer to return fs data (unused)

   *
   * This function must zero any hole we create
   *
   * Returns zero on success; non-zero otherwise
   */

  static int ecryptfs_write_begin(struct file *file,
  			struct address_space *mapping,
  			loff_t pos, unsigned len, unsigned flags,
  			struct page **pagep, void **fsdata)

  {

  	pgoff_t index = pos >> PAGE_CACHE_SHIFT;
  	struct page *page;

  	loff_t prev_page_end_size;

  	int rc = 0;

  	page = grab_cache_page_write_begin(mapping, index, flags);

  	if (!page)
  		return -ENOMEM;
  	*pagep = page;

  	prev_page_end_size = ((loff_t)index << PAGE_CACHE_SHIFT);

  	if (!PageUptodate(page)) {

  		struct ecryptfs_crypt_stat *crypt_stat =

  			&ecryptfs_inode_to_private(mapping->host)->crypt_stat;

  		if (!(crypt_stat->flags & ECRYPTFS_ENCRYPTED)) {

  			rc = ecryptfs_read_lower_page_segment(

  				page, index, 0, PAGE_CACHE_SIZE, mapping->host);

  			if (rc) {
  				printk(KERN_ERR "%s: Error attemping to read "
  				       "lower page segment; rc = [%d]
  ",

  				       __func__, rc);

  				ClearPageUptodate(page);
  				goto out;
  			} else
  				SetPageUptodate(page);
  		} else if (crypt_stat->flags & ECRYPTFS_VIEW_AS_ENCRYPTED) {
  			if (crypt_stat->flags & ECRYPTFS_METADATA_IN_XATTR) {
  				rc = ecryptfs_copy_up_encrypted_with_header(
  					page, crypt_stat);
  				if (rc) {
  					printk(KERN_ERR "%s: Error attempting "
  					       "to copy the encrypted content "
  					       "from the lower file whilst "
  					       "inserting the metadata from "
  					       "the xattr into the header; rc "

  					       "= [%d]
  ", __func__, rc);

  					ClearPageUptodate(page);
  					goto out;
  				}
  				SetPageUptodate(page);
  			} else {
  				rc = ecryptfs_read_lower_page_segment(

  					page, index, 0, PAGE_CACHE_SIZE,
  					mapping->host);

  				if (rc) {
  					printk(KERN_ERR "%s: Error reading "
  					       "page; rc = [%d]
  ",

  					       __func__, rc);

  					ClearPageUptodate(page);
  					goto out;
  				}
  				SetPageUptodate(page);
  			}
  		} else {

  			if (prev_page_end_size
  			    >= i_size_read(page->mapping->host)) {
  				zero_user(page, 0, PAGE_CACHE_SIZE);
  			} else {
  				rc = ecryptfs_decrypt_page(page);
  				if (rc) {
  					printk(KERN_ERR "%s: Error decrypting "
  					       "page at index [%ld]; "
  					       "rc = [%d]
  ",
  					       __func__, page->index, rc);
  					ClearPageUptodate(page);
  					goto out;
  				}

  			}

  			SetPageUptodate(page);

  		}

  	}

  	/* If creating a page or more of holes, zero them out via truncate.
  	 * Note, this will increase i_size. */

  	if (index != 0) {

  		if (prev_page_end_size > i_size_read(page->mapping->host)) {

  			rc = ecryptfs_truncate(file->f_path.dentry,

  					       prev_page_end_size);

  			if (rc) {

  				printk(KERN_ERR "%s: Error on attempt to "

  				       "truncate to (higher) offset [%lld];"

  				       " rc = [%d]
  ", __func__,

  				       prev_page_end_size, rc);

  				goto out;
  			}

  		}

  	}

  	/* Writing to a new page, and creating a small hole from start
  	 * of page?  Zero it out. */

  	if ((i_size_read(mapping->host) == prev_page_end_size)
  	    && (pos != 0))

  		zero_user(page, 0, PAGE_CACHE_SIZE);

  out:

  	if (unlikely(rc)) {
  		unlock_page(page);
  		page_cache_release(page);
  		*pagep = NULL;
  	}

  	return rc;
  }

  /**
   * ecryptfs_write_inode_size_to_header
   *
   * Writes the lower file size to the first 8 bytes of the header.
   *
   * Returns zero on success; non-zero on error.
   */

  static int ecryptfs_write_inode_size_to_header(struct inode *ecryptfs_inode)

  {

  	char *file_size_virt;
  	int rc;

  	file_size_virt = kmalloc(sizeof(u64), GFP_KERNEL);
  	if (!file_size_virt) {
  		rc = -ENOMEM;

  		goto out;
  	}

  	put_unaligned_be64(i_size_read(ecryptfs_inode), file_size_virt);

  	rc = ecryptfs_write_lower(ecryptfs_inode, file_size_virt, 0,
  				  sizeof(u64));
  	kfree(file_size_virt);

  	if (rc < 0)

  		printk(KERN_ERR "%s: Error writing file size to header; "

  		       "rc = [%d]
  ", __func__, rc);

  	else
  		rc = 0;

  out:
  	return rc;
  }

  struct kmem_cache *ecryptfs_xattr_cache;
  
  static int ecryptfs_write_inode_size_to_xattr(struct inode *ecryptfs_inode)

  {
  	ssize_t size;
  	void *xattr_virt;

  	struct dentry *lower_dentry =
  		ecryptfs_inode_to_private(ecryptfs_inode)->lower_file->f_dentry;
  	struct inode *lower_inode = lower_dentry->d_inode;

  	int rc;

  	if (!lower_inode->i_op->getxattr || !lower_inode->i_op->setxattr) {
  		printk(KERN_WARNING
  		       "No support for setting xattr in lower filesystem
  ");
  		rc = -ENOSYS;
  		goto out;
  	}

  	xattr_virt = kmem_cache_alloc(ecryptfs_xattr_cache, GFP_KERNEL);
  	if (!xattr_virt) {
  		printk(KERN_ERR "Out of memory whilst attempting to write "
  		       "inode size to xattr
  ");
  		rc = -ENOMEM;
  		goto out;
  	}

  	mutex_lock(&lower_inode->i_mutex);
  	size = lower_inode->i_op->getxattr(lower_dentry, ECRYPTFS_XATTR_NAME,
  					   xattr_virt, PAGE_CACHE_SIZE);

  	if (size < 0)
  		size = 8;

  	put_unaligned_be64(i_size_read(ecryptfs_inode), xattr_virt);

  	rc = lower_inode->i_op->setxattr(lower_dentry, ECRYPTFS_XATTR_NAME,
  					 xattr_virt, size, 0);
  	mutex_unlock(&lower_inode->i_mutex);

  	if (rc)
  		printk(KERN_ERR "Error whilst attempting to write inode size "
  		       "to lower file xattr; rc = [%d]
  ", rc);
  	kmem_cache_free(ecryptfs_xattr_cache, xattr_virt);
  out:
  	return rc;
  }

  int ecryptfs_write_inode_size_to_metadata(struct inode *ecryptfs_inode)

  {
  	struct ecryptfs_crypt_stat *crypt_stat;

  	crypt_stat = &ecryptfs_inode_to_private(ecryptfs_inode)->crypt_stat;

  	BUG_ON(!(crypt_stat->flags & ECRYPTFS_ENCRYPTED));

  	if (crypt_stat->flags & ECRYPTFS_METADATA_IN_XATTR)

  		return ecryptfs_write_inode_size_to_xattr(ecryptfs_inode);

  	else

  		return ecryptfs_write_inode_size_to_header(ecryptfs_inode);

  }

  /**

   * ecryptfs_write_end

   * @file: The eCryptfs file object

   * @mapping: The eCryptfs object
   * @pos: The file position
   * @len: The length of the data (unused)
   * @copied: The amount of data copied

   * @page: The eCryptfs page

   * @fsdata: The fsdata (unused)

   *
   * This is where we encrypt the data and pass the encrypted data to
   * the lower filesystem.  In OpenPGP-compatible mode, we operate on
   * entire underlying packets.
   */

  static int ecryptfs_write_end(struct file *file,
  			struct address_space *mapping,
  			loff_t pos, unsigned len, unsigned copied,
  			struct page *page, void *fsdata)

  {

  	pgoff_t index = pos >> PAGE_CACHE_SHIFT;
  	unsigned from = pos & (PAGE_CACHE_SIZE - 1);
  	unsigned to = from + copied;
  	struct inode *ecryptfs_inode = mapping->host;

  	struct ecryptfs_crypt_stat *crypt_stat =

  		&ecryptfs_inode_to_private(ecryptfs_inode)->crypt_stat;

  	int rc;

  	int need_unlock_page = 1;

  	ecryptfs_printk(KERN_DEBUG, "Calling fill_zeros_to_end_of_page"

  			"(page w/ index = [0x%.16lx], to = [%d])
  ", index, to);

  	if (!(crypt_stat->flags & ECRYPTFS_ENCRYPTED)) {
  		rc = ecryptfs_write_lower_page_segment(ecryptfs_inode, page, 0,
  						       to);
  		if (!rc) {
  			rc = copied;
  			fsstack_copy_inode_size(ecryptfs_inode,
  				ecryptfs_inode_to_lower(ecryptfs_inode));
  		}
  		goto out;
  	}

  	/* Fills in zeros if 'to' goes beyond inode size */

  	rc = fill_zeros_to_end_of_page(page, to);
  	if (rc) {
  		ecryptfs_printk(KERN_WARNING, "Error attempting to fill "

  			"zeros in page with index = [0x%.16lx]
  ", index);

  		goto out;
  	}

  	set_page_dirty(page);
  	unlock_page(page);
  	need_unlock_page = 0;

  	if (pos + copied > i_size_read(ecryptfs_inode)) {
  		i_size_write(ecryptfs_inode, pos + copied);

  		ecryptfs_printk(KERN_DEBUG, "Expanded file size to "

  			"[0x%.16llx]
  ",
  			(unsigned long long)i_size_read(ecryptfs_inode));

  		balance_dirty_pages_ratelimited(mapping);
  		rc = ecryptfs_write_inode_size_to_metadata(ecryptfs_inode);
  		if (rc) {
  			printk(KERN_ERR "Error writing inode size to metadata; "
  			       "rc = [%d]
  ", rc);
  			goto out;
  		}

  	}

  	rc = copied;

  out:

  	if (need_unlock_page)
  		unlock_page(page);

  	page_cache_release(page);

  	return rc;
  }

  static sector_t ecryptfs_bmap(struct address_space *mapping, sector_t block)
  {
  	int rc = 0;
  	struct inode *inode;
  	struct inode *lower_inode;
  
  	inode = (struct inode *)mapping->host;
  	lower_inode = ecryptfs_inode_to_lower(inode);
  	if (lower_inode->i_mapping->a_ops->bmap)
  		rc = lower_inode->i_mapping->a_ops->bmap(lower_inode->i_mapping,
  							 block);
  	return rc;
  }

  const struct address_space_operations ecryptfs_aops = {

  	.writepage = ecryptfs_writepage,
  	.readpage = ecryptfs_readpage,

  	.write_begin = ecryptfs_write_begin,
  	.write_end = ecryptfs_write_end,

  	.bmap = ecryptfs_bmap,

  };