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 <crypto/skcipher.h>
  31 #include "fscrypt_private.h"
  32
  33 static unsigned int num_prealloc_crypto_pages = 32;
  34 static unsigned int num_prealloc_crypto_ctxs = 128;
  35
  36 module_param(num_prealloc_crypto_pages, uint, 0444);
  37 MODULE_PARM_DESC(num_prealloc_crypto_pages,
  38                 "Number of crypto pages to preallocate");
  39 module_param(num_prealloc_crypto_ctxs, uint, 0444);
  40 MODULE_PARM_DESC(num_prealloc_crypto_ctxs,
  41                 "Number of crypto contexts to preallocate");
  42
  43 static mempool_t *fscrypt_bounce_page_pool = NULL;
  44
  45 static LIST_HEAD(fscrypt_free_ctxs);
  46 static DEFINE_SPINLOCK(fscrypt_ctx_lock);
  47
  48 struct workqueue_struct *fscrypt_read_workqueue;
  49 static DEFINE_MUTEX(fscrypt_init_mutex);
  50
  51 static struct kmem_cache *fscrypt_ctx_cachep;
  52 struct kmem_cache *fscrypt_info_cachep;
  53
  54 /**
  55  * fscrypt_release_ctx() - Releases an encryption context
  56  * @ctx: The encryption context to release.
  57  *
  58  * If the encryption context was allocated from the pre-allocated pool, returns
  59  * it to that pool. Else, frees it.
  60  *
  61  * If there's a bounce page in the context, this frees that.
  62  */
  63 void fscrypt_release_ctx(struct fscrypt_ctx *ctx)
  64 {
  65         unsigned long flags;
  66
  67         if (ctx->flags & FS_CTX_HAS_BOUNCE_BUFFER_FL && ctx->w.bounce_page) {
  68                 mempool_free(ctx->w.bounce_page, fscrypt_bounce_page_pool);
  69                 ctx->w.bounce_page = NULL;
  70         }
  71         ctx->w.control_page = NULL;
  72         if (ctx->flags & FS_CTX_REQUIRES_FREE_ENCRYPT_FL) {
  73                 kmem_cache_free(fscrypt_ctx_cachep, ctx);
  74         } else {
  75                 spin_lock_irqsave(&fscrypt_ctx_lock, flags);
  76                 list_add(&ctx->free_list, &fscrypt_free_ctxs);
  77                 spin_unlock_irqrestore(&fscrypt_ctx_lock, flags);
  78         }
  79 }
  80 EXPORT_SYMBOL(fscrypt_release_ctx);
  81
  82 /**
  83  * fscrypt_get_ctx() - Gets an encryption context
  84  * @inode:       The inode for which we are doing the crypto
  85  * @gfp_flags:   The gfp flag for memory allocation
  86  *
  87  * Allocates and initializes an encryption context.
  88  *
  89  * Return: An allocated and initialized encryption context on success; error
  90  * value or NULL otherwise.
  91  */
  92 struct fscrypt_ctx *fscrypt_get_ctx(const struct inode *inode, gfp_t gfp_flags)
  93 {
  94         struct fscrypt_ctx *ctx = NULL;
  95         struct fscrypt_info *ci = inode->i_crypt_info;
  96         unsigned long flags;
  97
  98         if (ci == NULL)
  99                 return ERR_PTR(-ENOKEY);
 100
 101         /*
 102          * We first try getting the ctx from a free list because in
 103          * the common case the ctx will have an allocated and
 104          * initialized crypto tfm, so it's probably a worthwhile
 105          * optimization. For the bounce page, we first try getting it
 106          * from the kernel allocator because that's just about as fast
 107          * as getting it from a list and because a cache of free pages
 108          * should generally be a "last resort" option for a filesystem
 109          * to be able to do its job.
 110          */
 111         spin_lock_irqsave(&fscrypt_ctx_lock, flags);
 112         ctx = list_first_entry_or_null(&fscrypt_free_ctxs,
 113                                         struct fscrypt_ctx, free_list);
 114         if (ctx)
 115                 list_del(&ctx->free_list);
 116         spin_unlock_irqrestore(&fscrypt_ctx_lock, flags);
 117         if (!ctx) {
 118                 ctx = kmem_cache_zalloc(fscrypt_ctx_cachep, gfp_flags);
 119                 if (!ctx)
 120                         return ERR_PTR(-ENOMEM);
 121                 ctx->flags |= FS_CTX_REQUIRES_FREE_ENCRYPT_FL;
 122         } else {
 123                 ctx->flags &= ~FS_CTX_REQUIRES_FREE_ENCRYPT_FL;
 124         }
 125         ctx->flags &= ~FS_CTX_HAS_BOUNCE_BUFFER_FL;
 126         return ctx;
 127 }
 128 EXPORT_SYMBOL(fscrypt_get_ctx);
 129
 130 int fscrypt_do_page_crypto(const struct inode *inode, fscrypt_direction_t rw,
 131                            u64 lblk_num, struct page *src_page,
 132                            struct page *dest_page, unsigned int len,
 133                            unsigned int offs, gfp_t gfp_flags)
 134 {
 135         struct {
 136                 __le64 index;
 137                 u8 padding[FS_IV_SIZE - sizeof(__le64)];
 138         } iv;
 139         struct skcipher_request *req = NULL;
 140         DECLARE_CRYPTO_WAIT(wait);
 141         struct scatterlist dst, src;
 142         struct fscrypt_info *ci = inode->i_crypt_info;
 143         struct crypto_skcipher *tfm = ci->ci_ctfm;
 144         int res = 0;
 145
 146         BUG_ON(len == 0);
 147
 148         BUILD_BUG_ON(sizeof(iv) != FS_IV_SIZE);
 149         BUILD_BUG_ON(AES_BLOCK_SIZE != FS_IV_SIZE);
 150         iv.index = cpu_to_le64(lblk_num);
 151         memset(iv.padding, 0, sizeof(iv.padding));
 152
 153         if (ci->ci_essiv_tfm != NULL) {
 154                 crypto_cipher_encrypt_one(ci->ci_essiv_tfm, (u8 *)&iv,
 155                                           (u8 *)&iv);
 156         }
 157
 158         req = skcipher_request_alloc(tfm, gfp_flags);
 159         if (!req) {
 160                 printk_ratelimited(KERN_ERR
 161                                 "%s: crypto_request_alloc() failed\n",
 162                                 __func__);
 163                 return -ENOMEM;
 164         }
 165
 166         skcipher_request_set_callback(
 167                 req, CRYPTO_TFM_REQ_MAY_BACKLOG | CRYPTO_TFM_REQ_MAY_SLEEP,
 168                 crypto_req_done, &wait);
 169
 170         sg_init_table(&dst, 1);
 171         sg_set_page(&dst, dest_page, len, offs);
 172         sg_init_table(&src, 1);
 173         sg_set_page(&src, src_page, len, offs);
 174         skcipher_request_set_crypt(req, &src, &dst, len, &iv);
 175         if (rw == FS_DECRYPT)
 176                 res = crypto_wait_req(crypto_skcipher_decrypt(req), &wait);
 177         else
 178                 res = crypto_wait_req(crypto_skcipher_encrypt(req), &wait);
 179         skcipher_request_free(req);
 180         if (res) {
 181                 printk_ratelimited(KERN_ERR
 182                         "%s: crypto_skcipher_encrypt() returned %d\n",
 183                         __func__, res);
 184                 return res;
 185         }
 186         return 0;
 187 }
 188
 189 struct page *fscrypt_alloc_bounce_page(struct fscrypt_ctx *ctx,
 190                                        gfp_t gfp_flags)
 191 {
 192         ctx->w.bounce_page = mempool_alloc(fscrypt_bounce_page_pool, gfp_flags);
 193         if (ctx->w.bounce_page == NULL)
 194                 return ERR_PTR(-ENOMEM);
 195         ctx->flags |= FS_CTX_HAS_BOUNCE_BUFFER_FL;
 196         return ctx->w.bounce_page;
 197 }
 198
 199 /**
 200  * fscypt_encrypt_page() - Encrypts a page
 201  * @inode:     The inode for which the encryption should take place
 202  * @page:      The page to encrypt. Must be locked for bounce-page
 203  *             encryption.
 204  * @len:       Length of data to encrypt in @page and encrypted
 205  *             data in returned page.
 206  * @offs:      Offset of data within @page and returned
 207  *             page holding encrypted data.
 208  * @lblk_num:  Logical block number. This must be unique for multiple
 209  *             calls with same inode, except when overwriting
 210  *             previously written data.
 211  * @gfp_flags: The gfp flag for memory allocation
 212  *
 213  * Encrypts @page using the ctx encryption context. Performs encryption
 214  * either in-place or into a newly allocated bounce page.
 215  * Called on the page write path.
 216  *
 217  * Bounce page allocation is the default.
 218  * In this case, the contents of @page are encrypted and stored in an
 219  * allocated bounce page. @page has to be locked and the caller must call
 220  * fscrypt_restore_control_page() on the returned ciphertext page to
 221  * release the bounce buffer and the encryption context.
 222  *
 223  * In-place encryption is used by setting the FS_CFLG_OWN_PAGES flag in
 224  * fscrypt_operations. Here, the input-page is returned with its content
 225  * encrypted.
 226  *
 227  * Return: A page with the encrypted content on success. Else, an
 228  * error value or NULL.
 229  */
 230 struct page *fscrypt_encrypt_page(const struct inode *inode,
 231                                 struct page *page,
 232                                 unsigned int len,
 233                                 unsigned int offs,
 234                                 u64 lblk_num, gfp_t gfp_flags)
 235
 236 {
 237         struct fscrypt_ctx *ctx;
 238         struct page *ciphertext_page = page;
 239         int err;
 240
 241         BUG_ON(len % FS_CRYPTO_BLOCK_SIZE != 0);
 242
 243         if (inode->i_sb->s_cop->flags & FS_CFLG_OWN_PAGES) {
 244                 /* with inplace-encryption we just encrypt the page */
 245                 err = fscrypt_do_page_crypto(inode, FS_ENCRYPT, lblk_num, page,
 246                                              ciphertext_page, len, offs,
 247                                              gfp_flags);
 248                 if (err)
 249                         return ERR_PTR(err);
 250
 251                 return ciphertext_page;
 252         }
 253
 254         BUG_ON(!PageLocked(page));
 255
 256         ctx = fscrypt_get_ctx(inode, gfp_flags);
 257         if (IS_ERR(ctx))
 258                 return (struct page *)ctx;
 259
 260         /* The encryption operation will require a bounce page. */
 261         ciphertext_page = fscrypt_alloc_bounce_page(ctx, gfp_flags);
 262         if (IS_ERR(ciphertext_page))
 263                 goto errout;
 264
 265         ctx->w.control_page = page;
 266         err = fscrypt_do_page_crypto(inode, FS_ENCRYPT, lblk_num,
 267                                      page, ciphertext_page, len, offs,
 268                                      gfp_flags);
 269         if (err) {
 270                 ciphertext_page = ERR_PTR(err);
 271                 goto errout;
 272         }
 273         SetPagePrivate(ciphertext_page);
 274         set_page_private(ciphertext_page, (unsigned long)ctx);
 275         lock_page(ciphertext_page);
 276         return ciphertext_page;
 277
 278 errout:
 279         fscrypt_release_ctx(ctx);
 280         return ciphertext_page;
 281 }
 282 EXPORT_SYMBOL(fscrypt_encrypt_page);
 283
 284 /**
 285  * fscrypt_decrypt_page() - Decrypts a page in-place
 286  * @inode:     The corresponding inode for the page to decrypt.
 287  * @page:      The page to decrypt. Must be locked in case
 288  *             it is a writeback page (FS_CFLG_OWN_PAGES unset).
 289  * @len:       Number of bytes in @page to be decrypted.
 290  * @offs:      Start of data in @page.
 291  * @lblk_num:  Logical block number.
 292  *
 293  * Decrypts page in-place using the ctx encryption context.
 294  *
 295  * Called from the read completion callback.
 296  *
 297  * Return: Zero on success, non-zero otherwise.
 298  */
 299 int fscrypt_decrypt_page(const struct inode *inode, struct page *page,
 300                         unsigned int len, unsigned int offs, u64 lblk_num)
 301 {
 302         if (!(inode->i_sb->s_cop->flags & FS_CFLG_OWN_PAGES))
 303                 BUG_ON(!PageLocked(page));
 304
 305         return fscrypt_do_page_crypto(inode, FS_DECRYPT, lblk_num, page, page,
 306                                       len, offs, GFP_NOFS);
 307 }
 308 EXPORT_SYMBOL(fscrypt_decrypt_page);
 309
 310 /*
 311  * Validate dentries for encrypted directories to make sure we aren't
 312  * potentially caching stale data after a key has been added or
 313  * removed.
 314  */
 315 static int fscrypt_d_revalidate(struct dentry *dentry, unsigned int flags)
 316 {
 317         struct dentry *dir;
 318         int dir_has_key, cached_with_key;
 319
 320         if (flags & LOOKUP_RCU)
 321                 return -ECHILD;
 322
 323         dir = dget_parent(dentry);
 324         if (!IS_ENCRYPTED(d_inode(dir))) {
 325                 dput(dir);
 326                 return 0;
 327         }
 328
 329         /* this should eventually be an flag in d_flags */
 330         spin_lock(&dentry->d_lock);
 331         cached_with_key = dentry->d_flags & DCACHE_ENCRYPTED_WITH_KEY;
 332         spin_unlock(&dentry->d_lock);
 333         dir_has_key = (d_inode(dir)->i_crypt_info != NULL);
 334         dput(dir);
 335
 336         /*
 337          * If the dentry was cached without the key, and it is a
 338          * negative dentry, it might be a valid name.  We can't check
 339          * if the key has since been made available due to locking
 340          * reasons, so we fail the validation so ext4_lookup() can do
 341          * this check.
 342          *
 343          * We also fail the validation if the dentry was created with
 344          * the key present, but we no longer have the key, or vice versa.
 345          */
 346         if ((!cached_with_key && d_is_negative(dentry)) ||
 347                         (!cached_with_key && dir_has_key) ||
 348                         (cached_with_key && !dir_has_key))
 349                 return 0;
 350         return 1;
 351 }
 352
 353 const struct dentry_operations fscrypt_d_ops = {
 354         .d_revalidate = fscrypt_d_revalidate,
 355 };
 356 EXPORT_SYMBOL(fscrypt_d_ops);
 357
 358 void fscrypt_restore_control_page(struct page *page)
 359 {
 360         struct fscrypt_ctx *ctx;
 361
 362         ctx = (struct fscrypt_ctx *)page_private(page);
 363         set_page_private(page, (unsigned long)NULL);
 364         ClearPagePrivate(page);
 365         unlock_page(page);
 366         fscrypt_release_ctx(ctx);
 367 }
 368 EXPORT_SYMBOL(fscrypt_restore_control_page);
 369
 370 static void fscrypt_destroy(void)
 371 {
 372         struct fscrypt_ctx *pos, *n;
 373
 374         list_for_each_entry_safe(pos, n, &fscrypt_free_ctxs, free_list)
 375                 kmem_cache_free(fscrypt_ctx_cachep, pos);
 376         INIT_LIST_HEAD(&fscrypt_free_ctxs);
 377         mempool_destroy(fscrypt_bounce_page_pool);
 378         fscrypt_bounce_page_pool = NULL;
 379 }
 380
 381 /**
 382  * fscrypt_initialize() - allocate major buffers for fs encryption.
 383  * @cop_flags:  fscrypt operations flags
 384  *
 385  * We only call this when we start accessing encrypted files, since it
 386  * results in memory getting allocated that wouldn't otherwise be used.
 387  *
 388  * Return: Zero on success, non-zero otherwise.
 389  */
 390 int fscrypt_initialize(unsigned int cop_flags)
 391 {
 392         int i, res = -ENOMEM;
 393
 394         /* No need to allocate a bounce page pool if this FS won't use it. */
 395         if (cop_flags & FS_CFLG_OWN_PAGES)
 396                 return 0;
 397
 398         mutex_lock(&fscrypt_init_mutex);
 399         if (fscrypt_bounce_page_pool)
 400                 goto already_initialized;
 401
 402         for (i = 0; i < num_prealloc_crypto_ctxs; i++) {
 403                 struct fscrypt_ctx *ctx;
 404
 405                 ctx = kmem_cache_zalloc(fscrypt_ctx_cachep, GFP_NOFS);
 406                 if (!ctx)
 407                         goto fail;
 408                 list_add(&ctx->free_list, &fscrypt_free_ctxs);
 409         }
 410
 411         fscrypt_bounce_page_pool =
 412                 mempool_create_page_pool(num_prealloc_crypto_pages, 0);
 413         if (!fscrypt_bounce_page_pool)
 414                 goto fail;
 415
 416 already_initialized:
 417         mutex_unlock(&fscrypt_init_mutex);
 418         return 0;
 419 fail:
 420         fscrypt_destroy();
 421         mutex_unlock(&fscrypt_init_mutex);
 422         return res;
 423 }
 424
 425 /**
 426  * fscrypt_init() - Set up for fs encryption.
 427  */
 428 static int __init fscrypt_init(void)
 429 {
 430         fscrypt_read_workqueue = alloc_workqueue("fscrypt_read_queue",
 431                                                         WQ_HIGHPRI, 0);
 432         if (!fscrypt_read_workqueue)
 433                 goto fail;
 434
 435         fscrypt_ctx_cachep = KMEM_CACHE(fscrypt_ctx, SLAB_RECLAIM_ACCOUNT);
 436         if (!fscrypt_ctx_cachep)
 437                 goto fail_free_queue;
 438
 439         fscrypt_info_cachep = KMEM_CACHE(fscrypt_info, SLAB_RECLAIM_ACCOUNT);
 440         if (!fscrypt_info_cachep)
 441                 goto fail_free_ctx;
 442
 443         return 0;
 444
 445 fail_free_ctx:
 446         kmem_cache_destroy(fscrypt_ctx_cachep);
 447 fail_free_queue:
 448         destroy_workqueue(fscrypt_read_workqueue);
 449 fail:
 450         return -ENOMEM;
 451 }
 452 module_init(fscrypt_init)
 453
 454 /**
 455  * fscrypt_exit() - Shutdown the fs encryption system
 456  */
 457 static void __exit fscrypt_exit(void)
 458 {
 459         fscrypt_destroy();
 460
 461         if (fscrypt_read_workqueue)
 462                 destroy_workqueue(fscrypt_read_workqueue);
 463         kmem_cache_destroy(fscrypt_ctx_cachep);
 464         kmem_cache_destroy(fscrypt_info_cachep);
 465
 466         fscrypt_essiv_cleanup();
 467 }
 468 module_exit(fscrypt_exit);
 469
 470 MODULE_LICENSE("GPL");