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/dcache.h>
  28 #include <linux/namei.h>
  29 #include <crypto/aes.h>
  30 #include "fscrypt_private.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 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_CTX_HAS_BOUNCE_BUFFER_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(const 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_CTX_HAS_BOUNCE_BUFFER_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 int fscrypt_do_page_crypto(const struct inode *inode, fscrypt_direction_t rw,
 145                            u64 lblk_num, struct page *src_page,
 146                            struct page *dest_page, unsigned int len,
 147                            unsigned int offs, gfp_t gfp_flags)
 148 {
 149         struct {
 150                 __le64 index;
 151                 u8 padding[FS_IV_SIZE - sizeof(__le64)];
 152         } iv;
 153         struct skcipher_request *req = NULL;
 154         DECLARE_FS_COMPLETION_RESULT(ecr);
 155         struct scatterlist dst, src;
 156         struct fscrypt_info *ci = inode->i_crypt_info;
 157         struct crypto_skcipher *tfm = ci->ci_ctfm;
 158         int res = 0;
 159
 160         BUG_ON(len == 0);
 161
 162         BUILD_BUG_ON(sizeof(iv) != FS_IV_SIZE);
 163         BUILD_BUG_ON(AES_BLOCK_SIZE != FS_IV_SIZE);
 164         iv.index = cpu_to_le64(lblk_num);
 165         memset(iv.padding, 0, sizeof(iv.padding));
 166
 167         if (ci->ci_essiv_tfm != NULL) {
 168                 crypto_cipher_encrypt_one(ci->ci_essiv_tfm, (u8 *)&iv,
 169                                           (u8 *)&iv);
 170         }
 171
 172         req = skcipher_request_alloc(tfm, gfp_flags);
 173         if (!req) {
 174                 printk_ratelimited(KERN_ERR
 175                                 "%s: crypto_request_alloc() failed\n",
 176                                 __func__);
 177                 return -ENOMEM;
 178         }
 179
 180         skcipher_request_set_callback(
 181                 req, CRYPTO_TFM_REQ_MAY_BACKLOG | CRYPTO_TFM_REQ_MAY_SLEEP,
 182                 page_crypt_complete, &ecr);
 183
 184         sg_init_table(&dst, 1);
 185         sg_set_page(&dst, dest_page, len, offs);
 186         sg_init_table(&src, 1);
 187         sg_set_page(&src, src_page, len, offs);
 188         skcipher_request_set_crypt(req, &src, &dst, len, &iv);
 189         if (rw == FS_DECRYPT)
 190                 res = crypto_skcipher_decrypt(req);
 191         else
 192                 res = crypto_skcipher_encrypt(req);
 193         if (res == -EINPROGRESS || res == -EBUSY) {
 194                 BUG_ON(req->base.data != &ecr);
 195                 wait_for_completion(&ecr.completion);
 196                 res = ecr.res;
 197         }
 198         skcipher_request_free(req);
 199         if (res) {
 200                 printk_ratelimited(KERN_ERR
 201                         "%s: crypto_skcipher_encrypt() returned %d\n",
 202                         __func__, res);
 203                 return res;
 204         }
 205         return 0;
 206 }
 207
 208 struct page *fscrypt_alloc_bounce_page(struct fscrypt_ctx *ctx,
 209                                        gfp_t gfp_flags)
 210 {
 211         ctx->w.bounce_page = mempool_alloc(fscrypt_bounce_page_pool, gfp_flags);
 212         if (ctx->w.bounce_page == NULL)
 213                 return ERR_PTR(-ENOMEM);
 214         ctx->flags |= FS_CTX_HAS_BOUNCE_BUFFER_FL;
 215         return ctx->w.bounce_page;
 216 }
 217
 218 /**
 219  * fscypt_encrypt_page() - Encrypts a page
 220  * @inode:     The inode for which the encryption should take place
 221  * @page:      The page to encrypt. Must be locked for bounce-page
 222  *             encryption.
 223  * @len:       Length of data to encrypt in @page and encrypted
 224  *             data in returned page.
 225  * @offs:      Offset of data within @page and returned
 226  *             page holding encrypted data.
 227  * @lblk_num:  Logical block number. This must be unique for multiple
 228  *             calls with same inode, except when overwriting
 229  *             previously written data.
 230  * @gfp_flags: The gfp flag for memory allocation
 231  *
 232  * Encrypts @page using the ctx encryption context. Performs encryption
 233  * either in-place or into a newly allocated bounce page.
 234  * Called on the page write path.
 235  *
 236  * Bounce page allocation is the default.
 237  * In this case, the contents of @page are encrypted and stored in an
 238  * allocated bounce page. @page has to be locked and the caller must call
 239  * fscrypt_restore_control_page() on the returned ciphertext page to
 240  * release the bounce buffer and the encryption context.
 241  *
 242  * In-place encryption is used by setting the FS_CFLG_OWN_PAGES flag in
 243  * fscrypt_operations. Here, the input-page is returned with its content
 244  * encrypted.
 245  *
 246  * Return: A page with the encrypted content on success. Else, an
 247  * error value or NULL.
 248  */
 249 struct page *fscrypt_encrypt_page(const struct inode *inode,
 250                                 struct page *page,
 251                                 unsigned int len,
 252                                 unsigned int offs,
 253                                 u64 lblk_num, gfp_t gfp_flags)
 254
 255 {
 256         struct fscrypt_ctx *ctx;
 257         struct page *ciphertext_page = page;
 258         int err;
 259
 260         BUG_ON(len % FS_CRYPTO_BLOCK_SIZE != 0);
 261
 262         if (inode->i_sb->s_cop->flags & FS_CFLG_OWN_PAGES) {
 263                 /* with inplace-encryption we just encrypt the page */
 264                 err = fscrypt_do_page_crypto(inode, FS_ENCRYPT, lblk_num, page,
 265                                              ciphertext_page, len, offs,
 266                                              gfp_flags);
 267                 if (err)
 268                         return ERR_PTR(err);
 269
 270                 return ciphertext_page;
 271         }
 272
 273         BUG_ON(!PageLocked(page));
 274
 275         ctx = fscrypt_get_ctx(inode, gfp_flags);
 276         if (IS_ERR(ctx))
 277                 return (struct page *)ctx;
 278
 279         /* The encryption operation will require a bounce page. */
 280         ciphertext_page = fscrypt_alloc_bounce_page(ctx, gfp_flags);
 281         if (IS_ERR(ciphertext_page))
 282                 goto errout;
 283
 284         ctx->w.control_page = page;
 285         err = fscrypt_do_page_crypto(inode, FS_ENCRYPT, lblk_num,
 286                                      page, ciphertext_page, len, offs,
 287                                      gfp_flags);
 288         if (err) {
 289                 ciphertext_page = ERR_PTR(err);
 290                 goto errout;
 291         }
 292         SetPagePrivate(ciphertext_page);
 293         set_page_private(ciphertext_page, (unsigned long)ctx);
 294         lock_page(ciphertext_page);
 295         return ciphertext_page;
 296
 297 errout:
 298         fscrypt_release_ctx(ctx);
 299         return ciphertext_page;
 300 }
 301 EXPORT_SYMBOL(fscrypt_encrypt_page);
 302
 303 /**
 304  * fscrypt_decrypt_page() - Decrypts a page in-place
 305  * @inode:     The corresponding inode for the page to decrypt.
 306  * @page:      The page to decrypt. Must be locked in case
 307  *             it is a writeback page (FS_CFLG_OWN_PAGES unset).
 308  * @len:       Number of bytes in @page to be decrypted.
 309  * @offs:      Start of data in @page.
 310  * @lblk_num:  Logical block number.
 311  *
 312  * Decrypts page in-place using the ctx encryption context.
 313  *
 314  * Called from the read completion callback.
 315  *
 316  * Return: Zero on success, non-zero otherwise.
 317  */
 318 int fscrypt_decrypt_page(const struct inode *inode, struct page *page,
 319                         unsigned int len, unsigned int offs, u64 lblk_num)
 320 {
 321         if (!(inode->i_sb->s_cop->flags & FS_CFLG_OWN_PAGES))
 322                 BUG_ON(!PageLocked(page));
 323
 324         return fscrypt_do_page_crypto(inode, FS_DECRYPT, lblk_num, page, page,
 325                                       len, offs, GFP_NOFS);
 326 }
 327 EXPORT_SYMBOL(fscrypt_decrypt_page);
 328
 329 /*
 330  * Validate dentries for encrypted directories to make sure we aren't
 331  * potentially caching stale data after a key has been added or
 332  * removed.
 333  */
 334 static int fscrypt_d_revalidate(struct dentry *dentry, unsigned int flags)
 335 {
 336         struct dentry *dir;
 337         int dir_has_key, cached_with_key;
 338
 339         if (flags & LOOKUP_RCU)
 340                 return -ECHILD;
 341
 342         dir = dget_parent(dentry);
 343         if (!d_inode(dir)->i_sb->s_cop->is_encrypted(d_inode(dir))) {
 344                 dput(dir);
 345                 return 0;
 346         }
 347
 348         /* this should eventually be an flag in d_flags */
 349         spin_lock(&dentry->d_lock);
 350         cached_with_key = dentry->d_flags & DCACHE_ENCRYPTED_WITH_KEY;
 351         spin_unlock(&dentry->d_lock);
 352         dir_has_key = (d_inode(dir)->i_crypt_info != NULL);
 353         dput(dir);
 354
 355         /*
 356          * If the dentry was cached without the key, and it is a
 357          * negative dentry, it might be a valid name.  We can't check
 358          * if the key has since been made available due to locking
 359          * reasons, so we fail the validation so ext4_lookup() can do
 360          * this check.
 361          *
 362          * We also fail the validation if the dentry was created with
 363          * the key present, but we no longer have the key, or vice versa.
 364          */
 365         if ((!cached_with_key && d_is_negative(dentry)) ||
 366                         (!cached_with_key && dir_has_key) ||
 367                         (cached_with_key && !dir_has_key))
 368                 return 0;
 369         return 1;
 370 }
 371
 372 const struct dentry_operations fscrypt_d_ops = {
 373         .d_revalidate = fscrypt_d_revalidate,
 374 };
 375 EXPORT_SYMBOL(fscrypt_d_ops);
 376
 377 void fscrypt_restore_control_page(struct page *page)
 378 {
 379         struct fscrypt_ctx *ctx;
 380
 381         ctx = (struct fscrypt_ctx *)page_private(page);
 382         set_page_private(page, (unsigned long)NULL);
 383         ClearPagePrivate(page);
 384         unlock_page(page);
 385         fscrypt_release_ctx(ctx);
 386 }
 387 EXPORT_SYMBOL(fscrypt_restore_control_page);
 388
 389 static void fscrypt_destroy(void)
 390 {
 391         struct fscrypt_ctx *pos, *n;
 392
 393         list_for_each_entry_safe(pos, n, &fscrypt_free_ctxs, free_list)
 394                 kmem_cache_free(fscrypt_ctx_cachep, pos);
 395         INIT_LIST_HEAD(&fscrypt_free_ctxs);
 396         mempool_destroy(fscrypt_bounce_page_pool);
 397         fscrypt_bounce_page_pool = NULL;
 398 }
 399
 400 /**
 401  * fscrypt_initialize() - allocate major buffers for fs encryption.
 402  * @cop_flags:  fscrypt operations flags
 403  *
 404  * We only call this when we start accessing encrypted files, since it
 405  * results in memory getting allocated that wouldn't otherwise be used.
 406  *
 407  * Return: Zero on success, non-zero otherwise.
 408  */
 409 int fscrypt_initialize(unsigned int cop_flags)
 410 {
 411         int i, res = -ENOMEM;
 412
 413         /*
 414          * No need to allocate a bounce page pool if there already is one or
 415          * this FS won't use it.
 416          */
 417         if (cop_flags & FS_CFLG_OWN_PAGES || fscrypt_bounce_page_pool)
 418                 return 0;
 419
 420         mutex_lock(&fscrypt_init_mutex);
 421         if (fscrypt_bounce_page_pool)
 422                 goto already_initialized;
 423
 424         for (i = 0; i < num_prealloc_crypto_ctxs; i++) {
 425                 struct fscrypt_ctx *ctx;
 426
 427                 ctx = kmem_cache_zalloc(fscrypt_ctx_cachep, GFP_NOFS);
 428                 if (!ctx)
 429                         goto fail;
 430                 list_add(&ctx->free_list, &fscrypt_free_ctxs);
 431         }
 432
 433         fscrypt_bounce_page_pool =
 434                 mempool_create_page_pool(num_prealloc_crypto_pages, 0);
 435         if (!fscrypt_bounce_page_pool)
 436                 goto fail;
 437
 438 already_initialized:
 439         mutex_unlock(&fscrypt_init_mutex);
 440         return 0;
 441 fail:
 442         fscrypt_destroy();
 443         mutex_unlock(&fscrypt_init_mutex);
 444         return res;
 445 }
 446
 447 /**
 448  * fscrypt_init() - Set up for fs encryption.
 449  */
 450 static int __init fscrypt_init(void)
 451 {
 452         fscrypt_read_workqueue = alloc_workqueue("fscrypt_read_queue",
 453                                                         WQ_HIGHPRI, 0);
 454         if (!fscrypt_read_workqueue)
 455                 goto fail;
 456
 457         fscrypt_ctx_cachep = KMEM_CACHE(fscrypt_ctx, SLAB_RECLAIM_ACCOUNT);
 458         if (!fscrypt_ctx_cachep)
 459                 goto fail_free_queue;
 460
 461         fscrypt_info_cachep = KMEM_CACHE(fscrypt_info, SLAB_RECLAIM_ACCOUNT);
 462         if (!fscrypt_info_cachep)
 463                 goto fail_free_ctx;
 464
 465         return 0;
 466
 467 fail_free_ctx:
 468         kmem_cache_destroy(fscrypt_ctx_cachep);
 469 fail_free_queue:
 470         destroy_workqueue(fscrypt_read_workqueue);
 471 fail:
 472         return -ENOMEM;
 473 }
 474 module_init(fscrypt_init)
 475
 476 /**
 477  * fscrypt_exit() - Shutdown the fs encryption system
 478  */
 479 static void __exit fscrypt_exit(void)
 480 {
 481         fscrypt_destroy();
 482
 483         if (fscrypt_read_workqueue)
 484                 destroy_workqueue(fscrypt_read_workqueue);
 485         kmem_cache_destroy(fscrypt_ctx_cachep);
 486         kmem_cache_destroy(fscrypt_info_cachep);
 487
 488         fscrypt_essiv_cleanup();
 489 }
 490 module_exit(fscrypt_exit);
 491
 492 MODULE_LICENSE("GPL");