/**
 * 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
 *
 * 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_writepage(struct page *page, struct writeback_control *wbc)
{
        int rc;

        rc = ecryptfs_encrypt_page(page);
        if (rc) {
                ecryptfs_printk(KERN_WARNING, "Error encrypting "
                                "page (upper index [0x%.16lx])\n", 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);
                        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);
                        flush_dcache_page(page);
                        if (rc) {
                                printk(KERN_ERR "%s: Error reading xattr "
                                       "region; rc = [%d]\n", __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]\n", __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]\n", __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]\n", rc);
                                goto out;
                        }
                }
        } else {
                rc = ecryptfs_decrypt_page(page);
                if (rc) {
                        ecryptfs_printk(KERN_ERR, "Error decrypting page; "
                                        "rc = [%d]\n", rc);
                        goto out;
                }
        }
out:
        if (rc)
                ClearPageUptodate(page);
        else
                SetPageUptodate(page);
        ecryptfs_printk(KERN_DEBUG, "Unlocking page with index = [0x%.16lx]\n",
                        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]\n",
                                       __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]\n", __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]\n",
                                               __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);
                                SetPageUptodate(page);
                        } else if (len < PAGE_CACHE_SIZE) {
                                rc = ecryptfs_decrypt_page(page);
                                if (rc) {
                                        printk(KERN_ERR "%s: Error decrypting "
                                               "page at index [%ld]; "
                                               "rc = [%d]\n",
                                               __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]\n", __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]\n", __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\n");
                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\n");
                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]\n", 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)
 */
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;

        ecryptfs_printk(KERN_DEBUG, "Calling fill_zeros_to_end_of_page"
                        "(page w/ index = [0x%.16lx], to = [%d])\n", 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;
        }
        if (!PageUptodate(page)) {
                if (copied < PAGE_CACHE_SIZE) {
                        rc = 0;
                        goto out;
                }
                SetPageUptodate(page);
        }
        /* 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]\n", index);
                goto out;
        }
        rc = ecryptfs_encrypt_page(page);
        if (rc) {
                ecryptfs_printk(KERN_WARNING, "Error encrypting page (upper "
                                "index [0x%.16lx])\n", index);
                goto out;
        }
        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]\n",
                        (unsigned long long)i_size_read(ecryptfs_inode));
        }
        rc = ecryptfs_write_inode_size_to_metadata(ecryptfs_inode);
        if (rc)
                printk(KERN_ERR "Error writing inode size to metadata; "
                       "rc = [%d]\n", rc);
        else
                rc = copied;
out:
        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,
};