fs/ecryptfs/mmap.c

   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  */
  47 struct 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  */
  65 static int ecryptfs_writepage(struct page *page, struct writeback_control *wbc)
  66 {
  67         int rc;
  68
  69         /*
  70          * Refuse to write the page out if we are called from reclaim context
  71          * since our writepage() path may potentially allocate memory when
  72          * calling into the lower fs vfs_write() which may in turn invoke
  73          * us again.
  74          */
  75         if (current->flags & PF_MEMALLOC) {
  76                 redirty_page_for_writepage(wbc, page);
  77                 rc = 0;
  78                 goto out;
  79         }
  80
  81         rc = ecryptfs_encrypt_page(page);
  82         if (rc) {
  83                 ecryptfs_printk(KERN_WARNING, "Error encrypting "
  84                                 "page (upper index [0x%.16lx])\n", page->index);
  85                 ClearPageUptodate(page);
  86                 goto out;
  87         }
  88         SetPageUptodate(page);
  89 out:
  90         unlock_page(page);
  91         return rc;
  92 }
  93
  94 static void strip_xattr_flag(char *page_virt,
  95                              struct ecryptfs_crypt_stat *crypt_stat)
  96 {
  97         if (crypt_stat->flags & ECRYPTFS_METADATA_IN_XATTR) {
  98                 size_t written;
  99
 100                 crypt_stat->flags &= ~ECRYPTFS_METADATA_IN_XATTR;
 101                 ecryptfs_write_crypt_stat_flags(page_virt, crypt_stat,
 102                                                 &written);
 103                 crypt_stat->flags |= ECRYPTFS_METADATA_IN_XATTR;
 104         }
 105 }
 106
 107 /**
 108  *   Header Extent:
 109  *     Octets 0-7:        Unencrypted file size (big-endian)
 110  *     Octets 8-15:       eCryptfs special marker
 111  *     Octets 16-19:      Flags
 112  *      Octet 16:         File format version number (between 0 and 255)
 113  *      Octets 17-18:     Reserved
 114  *      Octet 19:         Bit 1 (lsb): Reserved
 115  *                        Bit 2: Encrypted?
 116  *                        Bits 3-8: Reserved
 117  *     Octets 20-23:      Header extent size (big-endian)
 118  *     Octets 24-25:      Number of header extents at front of file
 119  *                        (big-endian)
 120  *     Octet  26:         Begin RFC 2440 authentication token packet set
 121  */
 122
 123 /**
 124  * ecryptfs_copy_up_encrypted_with_header
 125  * @page: Sort of a ``virtual'' representation of the encrypted lower
 126  *        file. The actual lower file does not have the metadata in
 127  *        the header. This is locked.
 128  * @crypt_stat: The eCryptfs inode's cryptographic context
 129  *
 130  * The ``view'' is the version of the file that userspace winds up
 131  * seeing, with the header information inserted.
 132  */
 133 static int
 134 ecryptfs_copy_up_encrypted_with_header(struct page *page,
 135                                        struct ecryptfs_crypt_stat *crypt_stat)
 136 {
 137         loff_t extent_num_in_page = 0;
 138         loff_t num_extents_per_page = (PAGE_CACHE_SIZE
 139                                        / crypt_stat->extent_size);
 140         int rc = 0;
 141
 142         while (extent_num_in_page < num_extents_per_page) {
 143                 loff_t view_extent_num = ((((loff_t)page->index)
 144                                            * num_extents_per_page)
 145                                           + extent_num_in_page);
 146                 size_t num_header_extents_at_front =
 147                         (crypt_stat->metadata_size / crypt_stat->extent_size);
 148
 149                 if (view_extent_num < num_header_extents_at_front) {
 150                         /* This is a header extent */
 151                         char *page_virt;
 152
 153                         page_virt = kmap_atomic(page, KM_USER0);
 154                         memset(page_virt, 0, PAGE_CACHE_SIZE);
 155                         /* TODO: Support more than one header extent */
 156                         if (view_extent_num == 0) {
 157                                 size_t written;
 158
 159                                 rc = ecryptfs_read_xattr_region(
 160                                         page_virt, page->mapping->host);
 161                                 strip_xattr_flag(page_virt + 16, crypt_stat);
 162                                 ecryptfs_write_header_metadata(page_virt + 20,
 163                                                                crypt_stat,
 164                                                                &written);
 165                         }
 166                         kunmap_atomic(page_virt, KM_USER0);
 167                         flush_dcache_page(page);
 168                         if (rc) {
 169                                 printk(KERN_ERR "%s: Error reading xattr "
 170                                        "region; rc = [%d]\n", __func__, rc);
 171                                 goto out;
 172                         }
 173                 } else {
 174                         /* This is an encrypted data extent */
 175                         loff_t lower_offset =
 176                                 ((view_extent_num * crypt_stat->extent_size)
 177                                  - crypt_stat->metadata_size);
 178
 179                         rc = ecryptfs_read_lower_page_segment(
 180                                 page, (lower_offset >> PAGE_CACHE_SHIFT),
 181                                 (lower_offset & ~PAGE_CACHE_MASK),
 182                                 crypt_stat->extent_size, page->mapping->host);
 183                         if (rc) {
 184                                 printk(KERN_ERR "%s: Error attempting to read "
 185                                        "extent at offset [%lld] in the lower "
 186                                        "file; rc = [%d]\n", __func__,
 187                                        lower_offset, rc);
 188                                 goto out;
 189                         }
 190                 }
 191                 extent_num_in_page++;
 192         }
 193 out:
 194         return rc;
 195 }
 196
 197 /**
 198  * ecryptfs_readpage
 199  * @file: An eCryptfs file
 200  * @page: Page from eCryptfs inode mapping into which to stick the read data
 201  *
 202  * Read in a page, decrypting if necessary.
 203  *
 204  * Returns zero on success; non-zero on error.
 205  */
 206 static int ecryptfs_readpage(struct file *file, struct page *page)
 207 {
 208         struct ecryptfs_crypt_stat *crypt_stat =
 209                 &ecryptfs_inode_to_private(page->mapping->host)->crypt_stat;
 210         int rc = 0;
 211
 212         if (!crypt_stat || !(crypt_stat->flags & ECRYPTFS_ENCRYPTED)) {
 213                 rc = ecryptfs_read_lower_page_segment(page, page->index, 0,
 214                                                       PAGE_CACHE_SIZE,
 215                                                       page->mapping->host);
 216         } else if (crypt_stat->flags & ECRYPTFS_VIEW_AS_ENCRYPTED) {
 217                 if (crypt_stat->flags & ECRYPTFS_METADATA_IN_XATTR) {
 218                         rc = ecryptfs_copy_up_encrypted_with_header(page,
 219                                                                     crypt_stat);
 220                         if (rc) {
 221                                 printk(KERN_ERR "%s: Error attempting to copy "
 222                                        "the encrypted content from the lower "
 223                                        "file whilst inserting the metadata "
 224                                        "from the xattr into the header; rc = "
 225                                        "[%d]\n", __func__, rc);
 226                                 goto out;
 227                         }
 228
 229                 } else {
 230                         rc = ecryptfs_read_lower_page_segment(
 231                                 page, page->index, 0, PAGE_CACHE_SIZE,
 232                                 page->mapping->host);
 233                         if (rc) {
 234                                 printk(KERN_ERR "Error reading page; rc = "
 235                                        "[%d]\n", rc);
 236                                 goto out;
 237                         }
 238                 }
 239         } else {
 240                 rc = ecryptfs_decrypt_page(page);
 241                 if (rc) {
 242                         ecryptfs_printk(KERN_ERR, "Error decrypting page; "
 243                                         "rc = [%d]\n", rc);
 244                         goto out;
 245                 }
 246         }
 247 out:
 248         if (rc)
 249                 ClearPageUptodate(page);
 250         else
 251                 SetPageUptodate(page);
 252         ecryptfs_printk(KERN_DEBUG, "Unlocking page with index = [0x%.16lx]\n",
 253                         page->index);
 254         unlock_page(page);
 255         return rc;
 256 }
 257
 258 /**
 259  * Called with lower inode mutex held.
 260  */
 261 static int fill_zeros_to_end_of_page(struct page *page, unsigned int to)
 262 {
 263         struct inode *inode = page->mapping->host;
 264         int end_byte_in_page;
 265
 266         if ((i_size_read(inode) / PAGE_CACHE_SIZE) != page->index)
 267                 goto out;
 268         end_byte_in_page = i_size_read(inode) % PAGE_CACHE_SIZE;
 269         if (to > end_byte_in_page)
 270                 end_byte_in_page = to;
 271         zero_user_segment(page, end_byte_in_page, PAGE_CACHE_SIZE);
 272 out:
 273         return 0;
 274 }
 275
 276 /**
 277  * ecryptfs_write_begin
 278  * @file: The eCryptfs file
 279  * @mapping: The eCryptfs object
 280  * @pos: The file offset at which to start writing
 281  * @len: Length of the write
 282  * @flags: Various flags
 283  * @pagep: Pointer to return the page
 284  * @fsdata: Pointer to return fs data (unused)
 285  *
 286  * This function must zero any hole we create
 287  *
 288  * Returns zero on success; non-zero otherwise
 289  */
 290 static int ecryptfs_write_begin(struct file *file,
 291                         struct address_space *mapping,
 292                         loff_t pos, unsigned len, unsigned flags,
 293                         struct page **pagep, void **fsdata)
 294 {
 295         pgoff_t index = pos >> PAGE_CACHE_SHIFT;
 296         struct page *page;
 297         loff_t prev_page_end_size;
 298         int rc = 0;
 299
 300         page = grab_cache_page_write_begin(mapping, index, flags);
 301         if (!page)
 302                 return -ENOMEM;
 303         *pagep = page;
 304
 305         prev_page_end_size = ((loff_t)index << PAGE_CACHE_SHIFT);
 306         if (!PageUptodate(page)) {
 307                 struct ecryptfs_crypt_stat *crypt_stat =
 308                         &ecryptfs_inode_to_private(mapping->host)->crypt_stat;
 309
 310                 if (!(crypt_stat->flags & ECRYPTFS_ENCRYPTED)) {
 311                         rc = ecryptfs_read_lower_page_segment(
 312                                 page, index, 0, PAGE_CACHE_SIZE, mapping->host);
 313                         if (rc) {
 314                                 printk(KERN_ERR "%s: Error attemping to read "
 315                                        "lower page segment; rc = [%d]\n",
 316                                        __func__, rc);
 317                                 ClearPageUptodate(page);
 318                                 goto out;
 319                         } else
 320                                 SetPageUptodate(page);
 321                 } else if (crypt_stat->flags & ECRYPTFS_VIEW_AS_ENCRYPTED) {
 322                         if (crypt_stat->flags & ECRYPTFS_METADATA_IN_XATTR) {
 323                                 rc = ecryptfs_copy_up_encrypted_with_header(
 324                                         page, crypt_stat);
 325                                 if (rc) {
 326                                         printk(KERN_ERR "%s: Error attempting "
 327                                                "to copy the encrypted content "
 328                                                "from the lower file whilst "
 329                                                "inserting the metadata from "
 330                                                "the xattr into the header; rc "
 331                                                "= [%d]\n", __func__, rc);
 332                                         ClearPageUptodate(page);
 333                                         goto out;
 334                                 }
 335                                 SetPageUptodate(page);
 336                         } else {
 337                                 rc = ecryptfs_read_lower_page_segment(
 338                                         page, index, 0, PAGE_CACHE_SIZE,
 339                                         mapping->host);
 340                                 if (rc) {
 341                                         printk(KERN_ERR "%s: Error reading "
 342                                                "page; rc = [%d]\n",
 343                                                __func__, rc);
 344                                         ClearPageUptodate(page);
 345                                         goto out;
 346                                 }
 347                                 SetPageUptodate(page);
 348                         }
 349                 } else {
 350                         if (prev_page_end_size
 351                             >= i_size_read(page->mapping->host)) {
 352                                 zero_user(page, 0, PAGE_CACHE_SIZE);
 353                         } else {
 354                                 rc = ecryptfs_decrypt_page(page);
 355                                 if (rc) {
 356                                         printk(KERN_ERR "%s: Error decrypting "
 357                                                "page at index [%ld]; "
 358                                                "rc = [%d]\n",
 359                                                __func__, page->index, rc);
 360                                         ClearPageUptodate(page);
 361                                         goto out;
 362                                 }
 363                         }
 364                         SetPageUptodate(page);
 365                 }
 366         }
 367         /* If creating a page or more of holes, zero them out via truncate.
 368          * Note, this will increase i_size. */
 369         if (index != 0) {
 370                 if (prev_page_end_size > i_size_read(page->mapping->host)) {
 371                         rc = ecryptfs_truncate(file->f_path.dentry,
 372                                                prev_page_end_size);
 373                         if (rc) {
 374                                 printk(KERN_ERR "%s: Error on attempt to "
 375                                        "truncate to (higher) offset [%lld];"
 376                                        " rc = [%d]\n", __func__,
 377                                        prev_page_end_size, rc);
 378                                 goto out;
 379                         }
 380                 }
 381         }
 382         /* Writing to a new page, and creating a small hole from start
 383          * of page?  Zero it out. */
 384         if ((i_size_read(mapping->host) == prev_page_end_size)
 385             && (pos != 0))
 386                 zero_user(page, 0, PAGE_CACHE_SIZE);
 387 out:
 388         if (unlikely(rc)) {
 389                 unlock_page(page);
 390                 page_cache_release(page);
 391                 *pagep = NULL;
 392         }
 393         return rc;
 394 }
 395
 396 /**
 397  * ecryptfs_write_inode_size_to_header
 398  *
 399  * Writes the lower file size to the first 8 bytes of the header.
 400  *
 401  * Returns zero on success; non-zero on error.
 402  */
 403 static int ecryptfs_write_inode_size_to_header(struct inode *ecryptfs_inode)
 404 {
 405         char *file_size_virt;
 406         int rc;
 407
 408         file_size_virt = kmalloc(sizeof(u64), GFP_KERNEL);
 409         if (!file_size_virt) {
 410                 rc = -ENOMEM;
 411                 goto out;
 412         }
 413         put_unaligned_be64(i_size_read(ecryptfs_inode), file_size_virt);
 414         rc = ecryptfs_write_lower(ecryptfs_inode, file_size_virt, 0,
 415                                   sizeof(u64));
 416         kfree(file_size_virt);
 417         if (rc < 0)
 418                 printk(KERN_ERR "%s: Error writing file size to header; "
 419                        "rc = [%d]\n", __func__, rc);
 420         else
 421                 rc = 0;
 422 out:
 423         return rc;
 424 }
 425
 426 struct kmem_cache *ecryptfs_xattr_cache;
 427
 428 static int ecryptfs_write_inode_size_to_xattr(struct inode *ecryptfs_inode)
 429 {
 430         ssize_t size;
 431         void *xattr_virt;
 432         struct dentry *lower_dentry =
 433                 ecryptfs_inode_to_private(ecryptfs_inode)->lower_file->f_dentry;
 434         struct inode *lower_inode = lower_dentry->d_inode;
 435         int rc;
 436
 437         if (!lower_inode->i_op->getxattr || !lower_inode->i_op->setxattr) {
 438                 printk(KERN_WARNING
 439                        "No support for setting xattr in lower filesystem\n");
 440                 rc = -ENOSYS;
 441                 goto out;
 442         }
 443         xattr_virt = kmem_cache_alloc(ecryptfs_xattr_cache, GFP_KERNEL);
 444         if (!xattr_virt) {
 445                 printk(KERN_ERR "Out of memory whilst attempting to write "
 446                        "inode size to xattr\n");
 447                 rc = -ENOMEM;
 448                 goto out;
 449         }
 450         mutex_lock(&lower_inode->i_mutex);
 451         size = lower_inode->i_op->getxattr(lower_dentry, ECRYPTFS_XATTR_NAME,
 452                                            xattr_virt, PAGE_CACHE_SIZE);
 453         if (size < 0)
 454                 size = 8;
 455         put_unaligned_be64(i_size_read(ecryptfs_inode), xattr_virt);
 456         rc = lower_inode->i_op->setxattr(lower_dentry, ECRYPTFS_XATTR_NAME,
 457                                          xattr_virt, size, 0);
 458         mutex_unlock(&lower_inode->i_mutex);
 459         if (rc)
 460                 printk(KERN_ERR "Error whilst attempting to write inode size "
 461                        "to lower file xattr; rc = [%d]\n", rc);
 462         kmem_cache_free(ecryptfs_xattr_cache, xattr_virt);
 463 out:
 464         return rc;
 465 }
 466
 467 int ecryptfs_write_inode_size_to_metadata(struct inode *ecryptfs_inode)
 468 {
 469         struct ecryptfs_crypt_stat *crypt_stat;
 470
 471         crypt_stat = &ecryptfs_inode_to_private(ecryptfs_inode)->crypt_stat;
 472         BUG_ON(!(crypt_stat->flags & ECRYPTFS_ENCRYPTED));
 473         if (crypt_stat->flags & ECRYPTFS_METADATA_IN_XATTR)
 474                 return ecryptfs_write_inode_size_to_xattr(ecryptfs_inode);
 475         else
 476                 return ecryptfs_write_inode_size_to_header(ecryptfs_inode);
 477 }
 478
 479 /**
 480  * ecryptfs_write_end
 481  * @file: The eCryptfs file object
 482  * @mapping: The eCryptfs object
 483  * @pos: The file position
 484  * @len: The length of the data (unused)
 485  * @copied: The amount of data copied
 486  * @page: The eCryptfs page
 487  * @fsdata: The fsdata (unused)
 488  */
 489 static int ecryptfs_write_end(struct file *file,
 490                         struct address_space *mapping,
 491                         loff_t pos, unsigned len, unsigned copied,
 492                         struct page *page, void *fsdata)
 493 {
 494         pgoff_t index = pos >> PAGE_CACHE_SHIFT;
 495         unsigned from = pos & (PAGE_CACHE_SIZE - 1);
 496         unsigned to = from + copied;
 497         struct inode *ecryptfs_inode = mapping->host;
 498         struct ecryptfs_crypt_stat *crypt_stat =
 499                 &ecryptfs_inode_to_private(ecryptfs_inode)->crypt_stat;
 500         int rc;
 501         int need_unlock_page = 1;
 502
 503         ecryptfs_printk(KERN_DEBUG, "Calling fill_zeros_to_end_of_page"
 504                         "(page w/ index = [0x%.16lx], to = [%d])\n", index, to);
 505         if (!(crypt_stat->flags & ECRYPTFS_ENCRYPTED)) {
 506                 rc = ecryptfs_write_lower_page_segment(ecryptfs_inode, page, 0,
 507                                                        to);
 508                 if (!rc) {
 509                         rc = copied;
 510                         fsstack_copy_inode_size(ecryptfs_inode,
 511                                 ecryptfs_inode_to_lower(ecryptfs_inode));
 512                 }
 513                 goto out;
 514         }
 515         /* Fills in zeros if 'to' goes beyond inode size */
 516         rc = fill_zeros_to_end_of_page(page, to);
 517         if (rc) {
 518                 ecryptfs_printk(KERN_WARNING, "Error attempting to fill "
 519                         "zeros in page with index = [0x%.16lx]\n", index);
 520                 goto out;
 521         }
 522         set_page_dirty(page);
 523         unlock_page(page);
 524         need_unlock_page = 0;
 525         if (pos + copied > i_size_read(ecryptfs_inode)) {
 526                 i_size_write(ecryptfs_inode, pos + copied);
 527                 ecryptfs_printk(KERN_DEBUG, "Expanded file size to "
 528                         "[0x%.16llx]\n",
 529                         (unsigned long long)i_size_read(ecryptfs_inode));
 530                 balance_dirty_pages_ratelimited(mapping);
 531                 rc = ecryptfs_write_inode_size_to_metadata(ecryptfs_inode);
 532                 if (rc) {
 533                         printk(KERN_ERR "Error writing inode size to metadata; "
 534                                "rc = [%d]\n", rc);
 535                         goto out;
 536                 }
 537         }
 538         rc = copied;
 539 out:
 540         if (need_unlock_page)
 541                 unlock_page(page);
 542         page_cache_release(page);
 543         return rc;
 544 }
 545
 546 static sector_t ecryptfs_bmap(struct address_space *mapping, sector_t block)
 547 {
 548         int rc = 0;
 549         struct inode *inode;
 550         struct inode *lower_inode;
 551
 552         inode = (struct inode *)mapping->host;
 553         lower_inode = ecryptfs_inode_to_lower(inode);
 554         if (lower_inode->i_mapping->a_ops->bmap)
 555                 rc = lower_inode->i_mapping->a_ops->bmap(lower_inode->i_mapping,
 556                                                          block);
 557         return rc;
 558 }
 559
 560 const struct address_space_operations ecryptfs_aops = {
 561         .writepage = ecryptfs_writepage,
 562         .readpage = ecryptfs_readpage,
 563         .write_begin = ecryptfs_write_begin,
 564         .write_end = ecryptfs_write_end,
 565         .bmap = ecryptfs_bmap,
 566 };