fs/crypto/crypto.c

   1 /*
   2  * This contains encryption functions for per-file encryption.
   3  *
   4  * Copyright (C) 2015, Google, Inc.
   5  * Copyright (C) 2015, Motorola Mobility
   6  *
   7  * Written by Michael Halcrow, 2014.
   8  *
   9  * Filename encryption additions
  10  *      Uday Savagaonkar, 2014
  11  * Encryption policy handling additions
  12  *      Ildar Muslukhov, 2014
  13  * Add fscrypt_pullback_bio_page()
  14  *      Jaegeuk Kim, 2015.
  15  *
  16  * This has not yet undergone a rigorous security audit.
  17  *
  18  * The usage of AES-XTS should conform to recommendations in NIST
  19  * Special Publication 800-38E and IEEE P1619/D16.
  20  */
  21
  22 #include <linux/pagemap.h>
  23 #include <linux/mempool.h>
  24 #include <linux/module.h>
  25 #include <linux/scatterlist.h>
  26 #include <linux/ratelimit.h>
  27 #include <linux/bio.h>
  28 #include <linux/dcache.h>
  29 #include <linux/namei.h>
  30 #include <linux/fscrypto.h>
  31
  32 static unsigned int num_prealloc_crypto_pages = 32;
  33 static unsigned int num_prealloc_crypto_ctxs = 128;
  34
  35 module_param(num_prealloc_crypto_pages, uint, 0444);
  36 MODULE_PARM_DESC(num_prealloc_crypto_pages,
  37                 "Number of crypto pages to preallocate");
  38 module_param(num_prealloc_crypto_ctxs, uint, 0444);
  39 MODULE_PARM_DESC(num_prealloc_crypto_ctxs,
  40                 "Number of crypto contexts to preallocate");
  41
  42 static mempool_t *fscrypt_bounce_page_pool = NULL;
  43
  44 static LIST_HEAD(fscrypt_free_ctxs);
  45 static DEFINE_SPINLOCK(fscrypt_ctx_lock);
  46
  47 static struct workqueue_struct *fscrypt_read_workqueue;
  48 static DEFINE_MUTEX(fscrypt_init_mutex);
  49
  50 static struct kmem_cache *fscrypt_ctx_cachep;
  51 struct kmem_cache *fscrypt_info_cachep;
  52
  53 /**
  54  * fscrypt_release_ctx() - Releases an encryption context
  55  * @ctx: The encryption context to release.
  56  *
  57  * If the encryption context was allocated from the pre-allocated pool, returns
  58  * it to that pool. Else, frees it.
  59  *
  60  * If there's a bounce page in the context, this frees that.
  61  */
  62 void fscrypt_release_ctx(struct fscrypt_ctx *ctx)
  63 {
  64         unsigned long flags;
  65
  66         if (ctx->flags & FS_WRITE_PATH_FL && ctx->w.bounce_page) {
  67                 mempool_free(ctx->w.bounce_page, fscrypt_bounce_page_pool);
  68                 ctx->w.bounce_page = NULL;
  69         }
  70         ctx->w.control_page = NULL;
  71         if (ctx->flags & FS_CTX_REQUIRES_FREE_ENCRYPT_FL) {
  72                 kmem_cache_free(fscrypt_ctx_cachep, ctx);
  73         } else {
  74                 spin_lock_irqsave(&fscrypt_ctx_lock, flags);
  75                 list_add(&ctx->free_list, &fscrypt_free_ctxs);
  76                 spin_unlock_irqrestore(&fscrypt_ctx_lock, flags);
  77         }
  78 }
  79 EXPORT_SYMBOL(fscrypt_release_ctx);
  80
  81 /**
  82  * fscrypt_get_ctx() - Gets an encryption context
  83  * @inode:       The inode for which we are doing the crypto
  84  * @gfp_flags:   The gfp flag for memory allocation
  85  *
  86  * Allocates and initializes an encryption context.
  87  *
  88  * Return: An allocated and initialized encryption context on success; error
  89  * value or NULL otherwise.
  90  */
  91 struct fscrypt_ctx *fscrypt_get_ctx(struct inode *inode, gfp_t gfp_flags)
  92 {
  93         struct fscrypt_ctx *ctx = NULL;
  94         struct fscrypt_info *ci = inode->i_crypt_info;
  95         unsigned long flags;
  96
  97         if (ci == NULL)
  98                 return ERR_PTR(-ENOKEY);
  99
 100         /*
 101          * We first try getting the ctx from a free list because in
 102          * the common case the ctx will have an allocated and
 103          * initialized crypto tfm, so it's probably a worthwhile
 104          * optimization. For the bounce page, we first try getting it
 105          * from the kernel allocator because that's just about as fast
 106          * as getting it from a list and because a cache of free pages
 107          * should generally be a "last resort" option for a filesystem
 108          * to be able to do its job.
 109          */
 110         spin_lock_irqsave(&fscrypt_ctx_lock, flags);
 111         ctx = list_first_entry_or_null(&fscrypt_free_ctxs,
 112                                         struct fscrypt_ctx, free_list);
 113         if (ctx)
 114                 list_del(&ctx->free_list);
 115         spin_unlock_irqrestore(&fscrypt_ctx_lock, flags);
 116         if (!ctx) {
 117                 ctx = kmem_cache_zalloc(fscrypt_ctx_cachep, gfp_flags);
 118                 if (!ctx)
 119                         return ERR_PTR(-ENOMEM);
 120                 ctx->flags |= FS_CTX_REQUIRES_FREE_ENCRYPT_FL;
 121         } else {
 122                 ctx->flags &= ~FS_CTX_REQUIRES_FREE_ENCRYPT_FL;
 123         }
 124         ctx->flags &= ~FS_WRITE_PATH_FL;
 125         return ctx;
 126 }
 127 EXPORT_SYMBOL(fscrypt_get_ctx);
 128
 129 /**
 130  * page_crypt_complete() - completion callback for page crypto
 131  * @req: The asynchronous cipher request context
 132  * @res: The result of the cipher operation
 133  */
 134 static void page_crypt_complete(struct crypto_async_request *req, int res)
 135 {
 136         struct fscrypt_completion_result *ecr = req->data;
 137
 138         if (res == -EINPROGRESS)
 139                 return;
 140         ecr->res = res;
 141         complete(&ecr->completion);
 142 }
 143
 144 typedef enum {
 145         FS_DECRYPT = 0,
 146         FS_ENCRYPT,
 147 } fscrypt_direction_t;
 148
 149 static int do_page_crypto(struct inode *inode,
 150                         fscrypt_direction_t rw, pgoff_t index,
 151                         struct page *src_page, struct page *dest_page,
 152                         gfp_t gfp_flags)
 153 {
 154         struct {
 155                 __le64 index;
 156                 u8 padding[FS_XTS_TWEAK_SIZE - sizeof(__le64)];
 157         } xts_tweak;
 158         struct skcipher_request *req = NULL;
 159         DECLARE_FS_COMPLETION_RESULT(ecr);
 160         struct scatterlist dst, src;
 161         struct fscrypt_info *ci = inode->i_crypt_info;
 162         struct crypto_skcipher *tfm = ci->ci_ctfm;
 163         int res = 0;
 164
 165         req = skcipher_request_alloc(tfm, gfp_flags);
 166         if (!req) {
 167                 printk_ratelimited(KERN_ERR
 168                                 "%s: crypto_request_alloc() failed\n",
 169                                 __func__);
 170                 return -ENOMEM;
 171         }
 172
 173         skcipher_request_set_callback(
 174                 req, CRYPTO_TFM_REQ_MAY_BACKLOG | CRYPTO_TFM_REQ_MAY_SLEEP,
 175                 page_crypt_complete, &ecr);
 176
 177         BUILD_BUG_ON(sizeof(xts_tweak) != FS_XTS_TWEAK_SIZE);
 178         xts_tweak.index = cpu_to_le64(index);
 179         memset(xts_tweak.padding, 0, sizeof(xts_tweak.padding));
 180
 181         sg_init_table(&dst, 1);
 182         sg_set_page(&dst, dest_page, PAGE_SIZE, 0);
 183         sg_init_table(&src, 1);
 184         sg_set_page(&src, src_page, PAGE_SIZE, 0);
 185         skcipher_request_set_crypt(req, &src, &dst, PAGE_SIZE, &xts_tweak);
 186         if (rw == FS_DECRYPT)
 187                 res = crypto_skcipher_decrypt(req);
 188         else
 189                 res = crypto_skcipher_encrypt(req);
 190         if (res == -EINPROGRESS || res == -EBUSY) {
 191                 BUG_ON(req->base.data != &ecr);
 192                 wait_for_completion(&ecr.completion);
 193                 res = ecr.res;
 194         }
 195         skcipher_request_free(req);
 196         if (res) {
 197                 printk_ratelimited(KERN_ERR
 198                         "%s: crypto_skcipher_encrypt() returned %d\n",
 199                         __func__, res);
 200                 return res;
 201         }
 202         return 0;
 203 }
 204
 205 static struct page *alloc_bounce_page(struct fscrypt_ctx *ctx, gfp_t gfp_flags)
 206 {
 207         ctx->w.bounce_page = mempool_alloc(fscrypt_bounce_page_pool, gfp_flags);
 208         if (ctx->w.bounce_page == NULL)
 209                 return ERR_PTR(-ENOMEM);
 210         ctx->flags |= FS_WRITE_PATH_FL;
 211         return ctx->w.bounce_page;
 212 }
 213
 214 /**
 215  * fscypt_encrypt_page() - Encrypts a page
 216  * @inode:          The inode for which the encryption should take place
 217  * @plaintext_page: The page to encrypt. Must be locked.
 218  * @gfp_flags:      The gfp flag for memory allocation
 219  *
 220  * Allocates a ciphertext page and encrypts plaintext_page into it using the ctx
 221  * encryption context.
 222  *
 223  * Called on the page write path.  The caller must call
 224  * fscrypt_restore_control_page() on the returned ciphertext page to
 225  * release the bounce buffer and the encryption context.
 226  *
 227  * Return: An allocated page with the encrypted content on success. Else, an
 228  * error value or NULL.
 229  */
 230 struct page *fscrypt_encrypt_page(struct inode *inode,
 231                                 struct page *plaintext_page, gfp_t gfp_flags)
 232 {
 233         struct fscrypt_ctx *ctx;
 234         struct page *ciphertext_page = NULL;
 235         int err;
 236
 237         BUG_ON(!PageLocked(plaintext_page));
 238
 239         ctx = fscrypt_get_ctx(inode, gfp_flags);
 240         if (IS_ERR(ctx))
 241                 return (struct page *)ctx;
 242
 243         /* The encryption operation will require a bounce page. */
 244         ciphertext_page = alloc_bounce_page(ctx, gfp_flags);
 245         if (IS_ERR(ciphertext_page))
 246                 goto errout;
 247
 248         ctx->w.control_page = plaintext_page;
 249         err = do_page_crypto(inode, FS_ENCRYPT, plaintext_page->index,
 250                                         plaintext_page, ciphertext_page,
 251                                         gfp_flags);
 252         if (err) {
 253                 ciphertext_page = ERR_PTR(err);
 254                 goto errout;
 255         }
 256         SetPagePrivate(ciphertext_page);
 257         set_page_private(ciphertext_page, (unsigned long)ctx);
 258         lock_page(ciphertext_page);
 259         return ciphertext_page;
 260
 261 errout:
 262         fscrypt_release_ctx(ctx);
 263         return ciphertext_page;
 264 }
 265 EXPORT_SYMBOL(fscrypt_encrypt_page);
 266
 267 /**
 268  * f2crypt_decrypt_page() - Decrypts a page in-place
 269  * @page: The page to decrypt. Must be locked.
 270  *
 271  * Decrypts page in-place using the ctx encryption context.
 272  *
 273  * Called from the read completion callback.
 274  *
 275  * Return: Zero on success, non-zero otherwise.
 276  */
 277 int fscrypt_decrypt_page(struct page *page)
 278 {
 279         BUG_ON(!PageLocked(page));
 280
 281         return do_page_crypto(page->mapping->host,
 282                         FS_DECRYPT, page->index, page, page, GFP_NOFS);
 283 }
 284 EXPORT_SYMBOL(fscrypt_decrypt_page);
 285
 286 int fscrypt_zeroout_range(struct inode *inode, pgoff_t lblk,
 287                                 sector_t pblk, unsigned int len)
 288 {
 289         struct fscrypt_ctx *ctx;
 290         struct page *ciphertext_page = NULL;
 291         struct bio *bio;
 292         int ret, err = 0;
 293
 294         BUG_ON(inode->i_sb->s_blocksize != PAGE_SIZE);
 295
 296         ctx = fscrypt_get_ctx(inode, GFP_NOFS);
 297         if (IS_ERR(ctx))
 298                 return PTR_ERR(ctx);
 299
 300         ciphertext_page = alloc_bounce_page(ctx, GFP_NOWAIT);
 301         if (IS_ERR(ciphertext_page)) {
 302                 err = PTR_ERR(ciphertext_page);
 303                 goto errout;
 304         }
 305
 306         while (len--) {
 307                 err = do_page_crypto(inode, FS_ENCRYPT, lblk,
 308                                         ZERO_PAGE(0), ciphertext_page,
 309                                         GFP_NOFS);
 310                 if (err)
 311                         goto errout;
 312
 313                 bio = bio_alloc(GFP_NOWAIT, 1);
 314                 if (!bio) {
 315                         err = -ENOMEM;
 316                         goto errout;
 317                 }
 318                 bio->bi_bdev = inode->i_sb->s_bdev;
 319                 bio->bi_iter.bi_sector =
 320                         pblk << (inode->i_sb->s_blocksize_bits - 9);
 321                 bio_set_op_attrs(bio, REQ_OP_WRITE, 0);
 322                 ret = bio_add_page(bio, ciphertext_page,
 323                                         inode->i_sb->s_blocksize, 0);
 324                 if (ret != inode->i_sb->s_blocksize) {
 325                         /* should never happen! */
 326                         WARN_ON(1);
 327                         bio_put(bio);
 328                         err = -EIO;
 329                         goto errout;
 330                 }
 331                 err = submit_bio_wait(bio);
 332                 if ((err == 0) && bio->bi_error)
 333                         err = -EIO;
 334                 bio_put(bio);
 335                 if (err)
 336                         goto errout;
 337                 lblk++;
 338                 pblk++;
 339         }
 340         err = 0;
 341 errout:
 342         fscrypt_release_ctx(ctx);
 343         return err;
 344 }
 345 EXPORT_SYMBOL(fscrypt_zeroout_range);
 346
 347 /*
 348  * Validate dentries for encrypted directories to make sure we aren't
 349  * potentially caching stale data after a key has been added or
 350  * removed.
 351  */
 352 static int fscrypt_d_revalidate(struct dentry *dentry, unsigned int flags)
 353 {
 354         struct dentry *dir;
 355         int dir_has_key, cached_with_key;
 356
 357         if (flags & LOOKUP_RCU)
 358                 return -ECHILD;
 359
 360         dir = dget_parent(dentry);
 361         if (!d_inode(dir)->i_sb->s_cop->is_encrypted(d_inode(dir))) {
 362                 dput(dir);
 363                 return 0;
 364         }
 365
 366         /* this should eventually be an flag in d_flags */
 367         spin_lock(&dentry->d_lock);
 368         cached_with_key = dentry->d_flags & DCACHE_ENCRYPTED_WITH_KEY;
 369         spin_unlock(&dentry->d_lock);
 370         dir_has_key = (d_inode(dir)->i_crypt_info != NULL);
 371         dput(dir);
 372
 373         /*
 374          * If the dentry was cached without the key, and it is a
 375          * negative dentry, it might be a valid name.  We can't check
 376          * if the key has since been made available due to locking
 377          * reasons, so we fail the validation so ext4_lookup() can do
 378          * this check.
 379          *
 380          * We also fail the validation if the dentry was created with
 381          * the key present, but we no longer have the key, or vice versa.
 382          */
 383         if ((!cached_with_key && d_is_negative(dentry)) ||
 384                         (!cached_with_key && dir_has_key) ||
 385                         (cached_with_key && !dir_has_key))
 386                 return 0;
 387         return 1;
 388 }
 389
 390 const struct dentry_operations fscrypt_d_ops = {
 391         .d_revalidate = fscrypt_d_revalidate,
 392 };
 393 EXPORT_SYMBOL(fscrypt_d_ops);
 394
 395 /*
 396  * Call fscrypt_decrypt_page on every single page, reusing the encryption
 397  * context.
 398  */
 399 static void completion_pages(struct work_struct *work)
 400 {
 401         struct fscrypt_ctx *ctx =
 402                 container_of(work, struct fscrypt_ctx, r.work);
 403         struct bio *bio = ctx->r.bio;
 404         struct bio_vec *bv;
 405         int i;
 406
 407         bio_for_each_segment_all(bv, bio, i) {
 408                 struct page *page = bv->bv_page;
 409                 int ret = fscrypt_decrypt_page(page);
 410
 411                 if (ret) {
 412                         WARN_ON_ONCE(1);
 413                         SetPageError(page);
 414                 } else {
 415                         SetPageUptodate(page);
 416                 }
 417                 unlock_page(page);
 418         }
 419         fscrypt_release_ctx(ctx);
 420         bio_put(bio);
 421 }
 422
 423 void fscrypt_decrypt_bio_pages(struct fscrypt_ctx *ctx, struct bio *bio)
 424 {
 425         INIT_WORK(&ctx->r.work, completion_pages);
 426         ctx->r.bio = bio;
 427         queue_work(fscrypt_read_workqueue, &ctx->r.work);
 428 }
 429 EXPORT_SYMBOL(fscrypt_decrypt_bio_pages);
 430
 431 void fscrypt_pullback_bio_page(struct page **page, bool restore)
 432 {
 433         struct fscrypt_ctx *ctx;
 434         struct page *bounce_page;
 435
 436         /* The bounce data pages are unmapped. */
 437         if ((*page)->mapping)
 438                 return;
 439
 440         /* The bounce data page is unmapped. */
 441         bounce_page = *page;
 442         ctx = (struct fscrypt_ctx *)page_private(bounce_page);
 443
 444         /* restore control page */
 445         *page = ctx->w.control_page;
 446
 447         if (restore)
 448                 fscrypt_restore_control_page(bounce_page);
 449 }
 450 EXPORT_SYMBOL(fscrypt_pullback_bio_page);
 451
 452 void fscrypt_restore_control_page(struct page *page)
 453 {
 454         struct fscrypt_ctx *ctx;
 455
 456         ctx = (struct fscrypt_ctx *)page_private(page);
 457         set_page_private(page, (unsigned long)NULL);
 458         ClearPagePrivate(page);
 459         unlock_page(page);
 460         fscrypt_release_ctx(ctx);
 461 }
 462 EXPORT_SYMBOL(fscrypt_restore_control_page);
 463
 464 static void fscrypt_destroy(void)
 465 {
 466         struct fscrypt_ctx *pos, *n;
 467
 468         list_for_each_entry_safe(pos, n, &fscrypt_free_ctxs, free_list)
 469                 kmem_cache_free(fscrypt_ctx_cachep, pos);
 470         INIT_LIST_HEAD(&fscrypt_free_ctxs);
 471         mempool_destroy(fscrypt_bounce_page_pool);
 472         fscrypt_bounce_page_pool = NULL;
 473 }
 474
 475 /**
 476  * fscrypt_initialize() - allocate major buffers for fs encryption.
 477  *
 478  * We only call this when we start accessing encrypted files, since it
 479  * results in memory getting allocated that wouldn't otherwise be used.
 480  *
 481  * Return: Zero on success, non-zero otherwise.
 482  */
 483 int fscrypt_initialize(void)
 484 {
 485         int i, res = -ENOMEM;
 486
 487         mutex_lock(&fscrypt_init_mutex);
 488         if (fscrypt_bounce_page_pool)
 489                 goto already_initialized;
 490
 491         for (i = 0; i < num_prealloc_crypto_ctxs; i++) {
 492                 struct fscrypt_ctx *ctx;
 493
 494                 ctx = kmem_cache_zalloc(fscrypt_ctx_cachep, GFP_NOFS);
 495                 if (!ctx)
 496                         goto fail;
 497                 list_add(&ctx->free_list, &fscrypt_free_ctxs);
 498         }
 499
 500         fscrypt_bounce_page_pool =
 501                 mempool_create_page_pool(num_prealloc_crypto_pages, 0);
 502         if (!fscrypt_bounce_page_pool)
 503                 goto fail;
 504
 505 already_initialized:
 506         mutex_unlock(&fscrypt_init_mutex);
 507         return 0;
 508 fail:
 509         fscrypt_destroy();
 510         mutex_unlock(&fscrypt_init_mutex);
 511         return res;
 512 }
 513 EXPORT_SYMBOL(fscrypt_initialize);
 514
 515 /**
 516  * fscrypt_init() - Set up for fs encryption.
 517  */
 518 static int __init fscrypt_init(void)
 519 {
 520         /*
 521          * Use an unbound workqueue to allow bios to be decrypted in parallel
 522          * even when they happen to complete on the same CPU.  This sacrifices
 523          * locality, but it's worthwhile since decryption is CPU-intensive.
 524          *
 525          * Also use a high-priority workqueue to prioritize decryption work,
 526          * which blocks reads from completing, over regular application tasks.
 527          */
 528         fscrypt_read_workqueue = alloc_workqueue("fscrypt_read_queue",
 529                                                  WQ_UNBOUND | WQ_HIGHPRI,
 530                                                  num_online_cpus());
 531         if (!fscrypt_read_workqueue)
 532                 goto fail;
 533
 534         fscrypt_ctx_cachep = KMEM_CACHE(fscrypt_ctx, SLAB_RECLAIM_ACCOUNT);
 535         if (!fscrypt_ctx_cachep)
 536                 goto fail_free_queue;
 537
 538         fscrypt_info_cachep = KMEM_CACHE(fscrypt_info, SLAB_RECLAIM_ACCOUNT);
 539         if (!fscrypt_info_cachep)
 540                 goto fail_free_ctx;
 541
 542         return 0;
 543
 544 fail_free_ctx:
 545         kmem_cache_destroy(fscrypt_ctx_cachep);
 546 fail_free_queue:
 547         destroy_workqueue(fscrypt_read_workqueue);
 548 fail:
 549         return -ENOMEM;
 550 }
 551 module_init(fscrypt_init)
 552
 553 /**
 554  * fscrypt_exit() - Shutdown the fs encryption system
 555  */
 556 static void __exit fscrypt_exit(void)
 557 {
 558         fscrypt_destroy();
 559
 560         if (fscrypt_read_workqueue)
 561                 destroy_workqueue(fscrypt_read_workqueue);
 562         kmem_cache_destroy(fscrypt_ctx_cachep);
 563         kmem_cache_destroy(fscrypt_info_cachep);
 564 }
 565 module_exit(fscrypt_exit);
 566
 567 MODULE_LICENSE("GPL");