linux/fs/ecryptfs/mmap.c
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   1/**
   2 * eCryptfs: Linux filesystem encryption layer
   3 * This is where eCryptfs coordinates the symmetric encryption and
   4 * decryption of the file data as it passes between the lower
   5 * encrypted file and the upper decrypted file.
   6 *
   7 * Copyright (C) 1997-2003 Erez Zadok
   8 * Copyright (C) 2001-2003 Stony Brook University
   9 * Copyright (C) 2004-2007 International Business Machines Corp.
  10 *   Author(s): Michael A. Halcrow <mahalcro@us.ibm.com>
  11 *
  12 * This program is free software; you can redistribute it and/or
  13 * modify it under the terms of the GNU General Public License as
  14 * published by the Free Software Foundation; either version 2 of the
  15 * License, or (at your option) any later version.
  16 *
  17 * This program is distributed in the hope that it will be useful, but
  18 * WITHOUT ANY WARRANTY; without even the implied warranty of
  19 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  20 * General Public License for more details.
  21 *
  22 * You should have received a copy of the GNU General Public License
  23 * along with this program; if not, write to the Free Software
  24 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA
  25 * 02111-1307, USA.
  26 */
  27
  28#include <linux/pagemap.h>
  29#include <linux/writeback.h>
  30#include <linux/page-flags.h>
  31#include <linux/mount.h>
  32#include <linux/file.h>
  33#include <linux/crypto.h>
  34#include <linux/scatterlist.h>
  35#include <linux/slab.h>
  36#include <asm/unaligned.h>
  37#include "ecryptfs_kernel.h"
  38
  39/**
  40 * ecryptfs_get_locked_page
  41 *
  42 * Get one page from cache or lower f/s, return error otherwise.
  43 *
  44 * Returns locked and up-to-date page (if ok), with increased
  45 * refcnt.
  46 */
  47struct page *ecryptfs_get_locked_page(struct inode *inode, loff_t index)
  48{
  49        struct page *page = read_mapping_page(inode->i_mapping, index, NULL);
  50        if (!IS_ERR(page))
  51                lock_page(page);
  52        return page;
  53}
  54
  55/**
  56 * ecryptfs_writepage
  57 * @page: Page that is locked before this call is made
  58 *
  59 * Returns zero on success; non-zero otherwise
  60 *
  61 * This is where we encrypt the data and pass the encrypted data to
  62 * the lower filesystem.  In OpenPGP-compatible mode, we operate on
  63 * entire underlying packets.
  64 */
  65static int ecryptfs_writepage(struct page *page, struct writeback_control *wbc)
  66{
  67        int rc;
  68
  69        rc = ecryptfs_encrypt_page(page);
  70        if (rc) {
  71                ecryptfs_printk(KERN_WARNING, "Error encrypting "
  72                                "page (upper index [0x%.16lx])\n", page->index);
  73                ClearPageUptodate(page);
  74                goto out;
  75        }
  76        SetPageUptodate(page);
  77out:
  78        unlock_page(page);
  79        return rc;
  80}
  81
  82static void strip_xattr_flag(char *page_virt,
  83                             struct ecryptfs_crypt_stat *crypt_stat)
  84{
  85        if (crypt_stat->flags & ECRYPTFS_METADATA_IN_XATTR) {
  86                size_t written;
  87
  88                crypt_stat->flags &= ~ECRYPTFS_METADATA_IN_XATTR;
  89                ecryptfs_write_crypt_stat_flags(page_virt, crypt_stat,
  90                                                &written);
  91                crypt_stat->flags |= ECRYPTFS_METADATA_IN_XATTR;
  92        }
  93}
  94
  95/**
  96 *   Header Extent:
  97 *     Octets 0-7:        Unencrypted file size (big-endian)
  98 *     Octets 8-15:       eCryptfs special marker
  99 *     Octets 16-19:      Flags
 100 *      Octet 16:         File format version number (between 0 and 255)
 101 *      Octets 17-18:     Reserved
 102 *      Octet 19:         Bit 1 (lsb): Reserved
 103 *                        Bit 2: Encrypted?
 104 *                        Bits 3-8: Reserved
 105 *     Octets 20-23:      Header extent size (big-endian)
 106 *     Octets 24-25:      Number of header extents at front of file
 107 *                        (big-endian)
 108 *     Octet  26:         Begin RFC 2440 authentication token packet set
 109 */
 110
 111/**
 112 * ecryptfs_copy_up_encrypted_with_header
 113 * @page: Sort of a ``virtual'' representation of the encrypted lower
 114 *        file. The actual lower file does not have the metadata in
 115 *        the header. This is locked.
 116 * @crypt_stat: The eCryptfs inode's cryptographic context
 117 *
 118 * The ``view'' is the version of the file that userspace winds up
 119 * seeing, with the header information inserted.
 120 */
 121static int
 122ecryptfs_copy_up_encrypted_with_header(struct page *page,
 123                                       struct ecryptfs_crypt_stat *crypt_stat)
 124{
 125        loff_t extent_num_in_page = 0;
 126        loff_t num_extents_per_page = (PAGE_CACHE_SIZE
 127                                       / crypt_stat->extent_size);
 128        int rc = 0;
 129
 130        while (extent_num_in_page < num_extents_per_page) {
 131                loff_t view_extent_num = ((((loff_t)page->index)
 132                                           * num_extents_per_page)
 133                                          + extent_num_in_page);
 134                size_t num_header_extents_at_front =
 135                        (crypt_stat->metadata_size / crypt_stat->extent_size);
 136
 137                if (view_extent_num < num_header_extents_at_front) {
 138                        /* This is a header extent */
 139                        char *page_virt;
 140
 141                        page_virt = kmap_atomic(page);
 142                        memset(page_virt, 0, PAGE_CACHE_SIZE);
 143                        /* TODO: Support more than one header extent */
 144                        if (view_extent_num == 0) {
 145                                size_t written;
 146
 147                                rc = ecryptfs_read_xattr_region(
 148                                        page_virt, page->mapping->host);
 149                                strip_xattr_flag(page_virt + 16, crypt_stat);
 150                                ecryptfs_write_header_metadata(page_virt + 20,
 151                                                               crypt_stat,
 152                                                               &written);
 153                        }
 154                        kunmap_atomic(page_virt);
 155                        flush_dcache_page(page);
 156                        if (rc) {
 157                                printk(KERN_ERR "%s: Error reading xattr "
 158                                       "region; rc = [%d]\n", __func__, rc);
 159                                goto out;
 160                        }
 161                } else {
 162                        /* This is an encrypted data extent */
 163                        loff_t lower_offset =
 164                                ((view_extent_num * crypt_stat->extent_size)
 165                                 - crypt_stat->metadata_size);
 166
 167                        rc = ecryptfs_read_lower_page_segment(
 168                                page, (lower_offset >> PAGE_CACHE_SHIFT),
 169                                (lower_offset & ~PAGE_CACHE_MASK),
 170                                crypt_stat->extent_size, page->mapping->host);
 171                        if (rc) {
 172                                printk(KERN_ERR "%s: Error attempting to read "
 173                                       "extent at offset [%lld] in the lower "
 174                                       "file; rc = [%d]\n", __func__,
 175                                       lower_offset, rc);
 176                                goto out;
 177                        }
 178                }
 179                extent_num_in_page++;
 180        }
 181out:
 182        return rc;
 183}
 184
 185/**
 186 * ecryptfs_readpage
 187 * @file: An eCryptfs file
 188 * @page: Page from eCryptfs inode mapping into which to stick the read data
 189 *
 190 * Read in a page, decrypting if necessary.
 191 *
 192 * Returns zero on success; non-zero on error.
 193 */
 194static int ecryptfs_readpage(struct file *file, struct page *page)
 195{
 196        struct ecryptfs_crypt_stat *crypt_stat =
 197                &ecryptfs_inode_to_private(page->mapping->host)->crypt_stat;
 198        int rc = 0;
 199
 200        if (!crypt_stat || !(crypt_stat->flags & ECRYPTFS_ENCRYPTED)) {
 201                rc = ecryptfs_read_lower_page_segment(page, page->index, 0,
 202                                                      PAGE_CACHE_SIZE,
 203                                                      page->mapping->host);
 204        } else if (crypt_stat->flags & ECRYPTFS_VIEW_AS_ENCRYPTED) {
 205                if (crypt_stat->flags & ECRYPTFS_METADATA_IN_XATTR) {
 206                        rc = ecryptfs_copy_up_encrypted_with_header(page,
 207                                                                    crypt_stat);
 208                        if (rc) {
 209                                printk(KERN_ERR "%s: Error attempting to copy "
 210                                       "the encrypted content from the lower "
 211                                       "file whilst inserting the metadata "
 212                                       "from the xattr into the header; rc = "
 213                                       "[%d]\n", __func__, rc);
 214                                goto out;
 215                        }
 216
 217                } else {
 218                        rc = ecryptfs_read_lower_page_segment(
 219                                page, page->index, 0, PAGE_CACHE_SIZE,
 220                                page->mapping->host);
 221                        if (rc) {
 222                                printk(KERN_ERR "Error reading page; rc = "
 223                                       "[%d]\n", rc);
 224                                goto out;
 225                        }
 226                }
 227        } else {
 228                rc = ecryptfs_decrypt_page(page);
 229                if (rc) {
 230                        ecryptfs_printk(KERN_ERR, "Error decrypting page; "
 231                                        "rc = [%d]\n", rc);
 232                        goto out;
 233                }
 234        }
 235out:
 236        if (rc)
 237                ClearPageUptodate(page);
 238        else
 239                SetPageUptodate(page);
 240        ecryptfs_printk(KERN_DEBUG, "Unlocking page with index = [0x%.16lx]\n",
 241                        page->index);
 242        unlock_page(page);
 243        return rc;
 244}
 245
 246/**
 247 * Called with lower inode mutex held.
 248 */
 249static int fill_zeros_to_end_of_page(struct page *page, unsigned int to)
 250{
 251        struct inode *inode = page->mapping->host;
 252        int end_byte_in_page;
 253
 254        if ((i_size_read(inode) / PAGE_CACHE_SIZE) != page->index)
 255                goto out;
 256        end_byte_in_page = i_size_read(inode) % PAGE_CACHE_SIZE;
 257        if (to > end_byte_in_page)
 258                end_byte_in_page = to;
 259        zero_user_segment(page, end_byte_in_page, PAGE_CACHE_SIZE);
 260out:
 261        return 0;
 262}
 263
 264/**
 265 * ecryptfs_write_begin
 266 * @file: The eCryptfs file
 267 * @mapping: The eCryptfs object
 268 * @pos: The file offset at which to start writing
 269 * @len: Length of the write
 270 * @flags: Various flags
 271 * @pagep: Pointer to return the page
 272 * @fsdata: Pointer to return fs data (unused)
 273 *
 274 * This function must zero any hole we create
 275 *
 276 * Returns zero on success; non-zero otherwise
 277 */
 278static int ecryptfs_write_begin(struct file *file,
 279                        struct address_space *mapping,
 280                        loff_t pos, unsigned len, unsigned flags,
 281                        struct page **pagep, void **fsdata)
 282{
 283        pgoff_t index = pos >> PAGE_CACHE_SHIFT;
 284        struct page *page;
 285        loff_t prev_page_end_size;
 286        int rc = 0;
 287
 288        page = grab_cache_page_write_begin(mapping, index, flags);
 289        if (!page)
 290                return -ENOMEM;
 291        *pagep = page;
 292
 293        prev_page_end_size = ((loff_t)index << PAGE_CACHE_SHIFT);
 294        if (!PageUptodate(page)) {
 295                struct ecryptfs_crypt_stat *crypt_stat =
 296                        &ecryptfs_inode_to_private(mapping->host)->crypt_stat;
 297
 298                if (!(crypt_stat->flags & ECRYPTFS_ENCRYPTED)) {
 299                        rc = ecryptfs_read_lower_page_segment(
 300                                page, index, 0, PAGE_CACHE_SIZE, mapping->host);
 301                        if (rc) {
 302                                printk(KERN_ERR "%s: Error attemping to read "
 303                                       "lower page segment; rc = [%d]\n",
 304                                       __func__, rc);
 305                                ClearPageUptodate(page);
 306                                goto out;
 307                        } else
 308                                SetPageUptodate(page);
 309                } else if (crypt_stat->flags & ECRYPTFS_VIEW_AS_ENCRYPTED) {
 310                        if (crypt_stat->flags & ECRYPTFS_METADATA_IN_XATTR) {
 311                                rc = ecryptfs_copy_up_encrypted_with_header(
 312                                        page, crypt_stat);
 313                                if (rc) {
 314                                        printk(KERN_ERR "%s: Error attempting "
 315                                               "to copy the encrypted content "
 316                                               "from the lower file whilst "
 317                                               "inserting the metadata from "
 318                                               "the xattr into the header; rc "
 319                                               "= [%d]\n", __func__, rc);
 320                                        ClearPageUptodate(page);
 321                                        goto out;
 322                                }
 323                                SetPageUptodate(page);
 324                        } else {
 325                                rc = ecryptfs_read_lower_page_segment(
 326                                        page, index, 0, PAGE_CACHE_SIZE,
 327                                        mapping->host);
 328                                if (rc) {
 329                                        printk(KERN_ERR "%s: Error reading "
 330                                               "page; rc = [%d]\n",
 331                                               __func__, rc);
 332                                        ClearPageUptodate(page);
 333                                        goto out;
 334                                }
 335                                SetPageUptodate(page);
 336                        }
 337                } else {
 338                        if (prev_page_end_size
 339                            >= i_size_read(page->mapping->host)) {
 340                                zero_user(page, 0, PAGE_CACHE_SIZE);
 341                                SetPageUptodate(page);
 342                        } else if (len < PAGE_CACHE_SIZE) {
 343                                rc = ecryptfs_decrypt_page(page);
 344                                if (rc) {
 345                                        printk(KERN_ERR "%s: Error decrypting "
 346                                               "page at index [%ld]; "
 347                                               "rc = [%d]\n",
 348                                               __func__, page->index, rc);
 349                                        ClearPageUptodate(page);
 350                                        goto out;
 351                                }
 352                                SetPageUptodate(page);
 353                        }
 354                }
 355        }
 356        /* If creating a page or more of holes, zero them out via truncate.
 357         * Note, this will increase i_size. */
 358        if (index != 0) {
 359                if (prev_page_end_size > i_size_read(page->mapping->host)) {
 360                        rc = ecryptfs_truncate(file->f_path.dentry,
 361                                               prev_page_end_size);
 362                        if (rc) {
 363                                printk(KERN_ERR "%s: Error on attempt to "
 364                                       "truncate to (higher) offset [%lld];"
 365                                       " rc = [%d]\n", __func__,
 366                                       prev_page_end_size, rc);
 367                                goto out;
 368                        }
 369                }
 370        }
 371        /* Writing to a new page, and creating a small hole from start
 372         * of page?  Zero it out. */
 373        if ((i_size_read(mapping->host) == prev_page_end_size)
 374            && (pos != 0))
 375                zero_user(page, 0, PAGE_CACHE_SIZE);
 376out:
 377        if (unlikely(rc)) {
 378                unlock_page(page);
 379                page_cache_release(page);
 380                *pagep = NULL;
 381        }
 382        return rc;
 383}
 384
 385/**
 386 * ecryptfs_write_inode_size_to_header
 387 *
 388 * Writes the lower file size to the first 8 bytes of the header.
 389 *
 390 * Returns zero on success; non-zero on error.
 391 */
 392static int ecryptfs_write_inode_size_to_header(struct inode *ecryptfs_inode)
 393{
 394        char *file_size_virt;
 395        int rc;
 396
 397        file_size_virt = kmalloc(sizeof(u64), GFP_KERNEL);
 398        if (!file_size_virt) {
 399                rc = -ENOMEM;
 400                goto out;
 401        }
 402        put_unaligned_be64(i_size_read(ecryptfs_inode), file_size_virt);
 403        rc = ecryptfs_write_lower(ecryptfs_inode, file_size_virt, 0,
 404                                  sizeof(u64));
 405        kfree(file_size_virt);
 406        if (rc < 0)
 407                printk(KERN_ERR "%s: Error writing file size to header; "
 408                       "rc = [%d]\n", __func__, rc);
 409        else
 410                rc = 0;
 411out:
 412        return rc;
 413}
 414
 415struct kmem_cache *ecryptfs_xattr_cache;
 416
 417static int ecryptfs_write_inode_size_to_xattr(struct inode *ecryptfs_inode)
 418{
 419        ssize_t size;
 420        void *xattr_virt;
 421        struct dentry *lower_dentry =
 422                ecryptfs_inode_to_private(ecryptfs_inode)->lower_file->f_dentry;
 423        struct inode *lower_inode = lower_dentry->d_inode;
 424        int rc;
 425
 426        if (!lower_inode->i_op->getxattr || !lower_inode->i_op->setxattr) {
 427                printk(KERN_WARNING
 428                       "No support for setting xattr in lower filesystem\n");
 429                rc = -ENOSYS;
 430                goto out;
 431        }
 432        xattr_virt = kmem_cache_alloc(ecryptfs_xattr_cache, GFP_KERNEL);
 433        if (!xattr_virt) {
 434                printk(KERN_ERR "Out of memory whilst attempting to write "
 435                       "inode size to xattr\n");
 436                rc = -ENOMEM;
 437                goto out;
 438        }
 439        mutex_lock(&lower_inode->i_mutex);
 440        size = lower_inode->i_op->getxattr(lower_dentry, ECRYPTFS_XATTR_NAME,
 441                                           xattr_virt, PAGE_CACHE_SIZE);
 442        if (size < 0)
 443                size = 8;
 444        put_unaligned_be64(i_size_read(ecryptfs_inode), xattr_virt);
 445        rc = lower_inode->i_op->setxattr(lower_dentry, ECRYPTFS_XATTR_NAME,
 446                                         xattr_virt, size, 0);
 447        mutex_unlock(&lower_inode->i_mutex);
 448        if (rc)
 449                printk(KERN_ERR "Error whilst attempting to write inode size "
 450                       "to lower file xattr; rc = [%d]\n", rc);
 451        kmem_cache_free(ecryptfs_xattr_cache, xattr_virt);
 452out:
 453        return rc;
 454}
 455
 456int ecryptfs_write_inode_size_to_metadata(struct inode *ecryptfs_inode)
 457{
 458        struct ecryptfs_crypt_stat *crypt_stat;
 459
 460        crypt_stat = &ecryptfs_inode_to_private(ecryptfs_inode)->crypt_stat;
 461        BUG_ON(!(crypt_stat->flags & ECRYPTFS_ENCRYPTED));
 462        if (crypt_stat->flags & ECRYPTFS_METADATA_IN_XATTR)
 463                return ecryptfs_write_inode_size_to_xattr(ecryptfs_inode);
 464        else
 465                return ecryptfs_write_inode_size_to_header(ecryptfs_inode);
 466}
 467
 468/**
 469 * ecryptfs_write_end
 470 * @file: The eCryptfs file object
 471 * @mapping: The eCryptfs object
 472 * @pos: The file position
 473 * @len: The length of the data (unused)
 474 * @copied: The amount of data copied
 475 * @page: The eCryptfs page
 476 * @fsdata: The fsdata (unused)
 477 */
 478static int ecryptfs_write_end(struct file *file,
 479                        struct address_space *mapping,
 480                        loff_t pos, unsigned len, unsigned copied,
 481                        struct page *page, void *fsdata)
 482{
 483        pgoff_t index = pos >> PAGE_CACHE_SHIFT;
 484        unsigned from = pos & (PAGE_CACHE_SIZE - 1);
 485        unsigned to = from + copied;
 486        struct inode *ecryptfs_inode = mapping->host;
 487        struct ecryptfs_crypt_stat *crypt_stat =
 488                &ecryptfs_inode_to_private(ecryptfs_inode)->crypt_stat;
 489        int rc;
 490
 491        ecryptfs_printk(KERN_DEBUG, "Calling fill_zeros_to_end_of_page"
 492                        "(page w/ index = [0x%.16lx], to = [%d])\n", index, to);
 493        if (!(crypt_stat->flags & ECRYPTFS_ENCRYPTED)) {
 494                rc = ecryptfs_write_lower_page_segment(ecryptfs_inode, page, 0,
 495                                                       to);
 496                if (!rc) {
 497                        rc = copied;
 498                        fsstack_copy_inode_size(ecryptfs_inode,
 499                                ecryptfs_inode_to_lower(ecryptfs_inode));
 500                }
 501                goto out;
 502        }
 503        if (!PageUptodate(page)) {
 504                if (copied < PAGE_CACHE_SIZE) {
 505                        rc = 0;
 506                        goto out;
 507                }
 508                SetPageUptodate(page);
 509        }
 510        /* Fills in zeros if 'to' goes beyond inode size */
 511        rc = fill_zeros_to_end_of_page(page, to);
 512        if (rc) {
 513                ecryptfs_printk(KERN_WARNING, "Error attempting to fill "
 514                        "zeros in page with index = [0x%.16lx]\n", index);
 515                goto out;
 516        }
 517        rc = ecryptfs_encrypt_page(page);
 518        if (rc) {
 519                ecryptfs_printk(KERN_WARNING, "Error encrypting page (upper "
 520                                "index [0x%.16lx])\n", index);
 521                goto out;
 522        }
 523        if (pos + copied > i_size_read(ecryptfs_inode)) {
 524                i_size_write(ecryptfs_inode, pos + copied);
 525                ecryptfs_printk(KERN_DEBUG, "Expanded file size to "
 526                        "[0x%.16llx]\n",
 527                        (unsigned long long)i_size_read(ecryptfs_inode));
 528        }
 529        rc = ecryptfs_write_inode_size_to_metadata(ecryptfs_inode);
 530        if (rc)
 531                printk(KERN_ERR "Error writing inode size to metadata; "
 532                       "rc = [%d]\n", rc);
 533        else
 534                rc = copied;
 535out:
 536        unlock_page(page);
 537        page_cache_release(page);
 538        return rc;
 539}
 540
 541static sector_t ecryptfs_bmap(struct address_space *mapping, sector_t block)
 542{
 543        int rc = 0;
 544        struct inode *inode;
 545        struct inode *lower_inode;
 546
 547        inode = (struct inode *)mapping->host;
 548        lower_inode = ecryptfs_inode_to_lower(inode);
 549        if (lower_inode->i_mapping->a_ops->bmap)
 550                rc = lower_inode->i_mapping->a_ops->bmap(lower_inode->i_mapping,
 551                                                         block);
 552        return rc;
 553}
 554
 555const struct address_space_operations ecryptfs_aops = {
 556        .writepage = ecryptfs_writepage,
 557        .readpage = ecryptfs_readpage,
 558        .write_begin = ecryptfs_write_begin,
 559        .write_end = ecryptfs_write_end,
 560        .bmap = ecryptfs_bmap,
 561};
 562
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