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 static 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 void fscrypt_enqueue_decrypt_work(struct work_struct *work)
  55 {
  56         queue_work(fscrypt_read_workqueue, work);
  57 }
  58 EXPORT_SYMBOL(fscrypt_enqueue_decrypt_work);
  59
  60 /**
  61  * fscrypt_release_ctx() - Releases an encryption context
  62  * @ctx: The encryption context to release.
  63  *
  64  * If the encryption context was allocated from the pre-allocated pool, returns
  65  * it to that pool. Else, frees it.
  66  *
  67  * If there's a bounce page in the context, this frees that.
  68  */
  69 void fscrypt_release_ctx(struct fscrypt_ctx *ctx)
  70 {
  71         unsigned long flags;
  72
  73         if (ctx->flags & FS_CTX_HAS_BOUNCE_BUFFER_FL && ctx->w.bounce_page) {
  74                 mempool_free(ctx->w.bounce_page, fscrypt_bounce_page_pool);
  75                 ctx->w.bounce_page = NULL;
  76         }
  77         ctx->w.control_page = NULL;
  78         if (ctx->flags & FS_CTX_REQUIRES_FREE_ENCRYPT_FL) {
  79                 kmem_cache_free(fscrypt_ctx_cachep, ctx);
  80         } else {
  81                 spin_lock_irqsave(&fscrypt_ctx_lock, flags);
  82                 list_add(&ctx->free_list, &fscrypt_free_ctxs);
  83                 spin_unlock_irqrestore(&fscrypt_ctx_lock, flags);
  84         }
  85 }
  86 EXPORT_SYMBOL(fscrypt_release_ctx);
  87
  88 /**
  89  * fscrypt_get_ctx() - Gets an encryption context
  90  * @gfp_flags:   The gfp flag for memory allocation
  91  *
  92  * Allocates and initializes an encryption context.
  93  *
  94  * Return: A new encryption context on success; an ERR_PTR() otherwise.
  95  */
  96 struct fscrypt_ctx *fscrypt_get_ctx(gfp_t gfp_flags)
  97 {
  98         struct fscrypt_ctx *ctx;
  99         unsigned long flags;
 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 void fscrypt_generate_iv(union fscrypt_iv *iv, u64 lblk_num,
 131                          const struct fscrypt_info *ci)
 132 {
 133         memset(iv, 0, ci->ci_mode->ivsize);
 134         iv->lblk_num = cpu_to_le64(lblk_num);
 135
 136         if (ci->ci_flags & FS_POLICY_FLAG_DIRECT_KEY)
 137                 memcpy(iv->nonce, ci->ci_nonce, FS_KEY_DERIVATION_NONCE_SIZE);
 138
 139         if (ci->ci_essiv_tfm != NULL)
 140                 crypto_cipher_encrypt_one(ci->ci_essiv_tfm, iv->raw, iv->raw);
 141 }
 142
 143 int fscrypt_do_page_crypto(const struct inode *inode, fscrypt_direction_t rw,
 144                            u64 lblk_num, struct page *src_page,
 145                            struct page *dest_page, unsigned int len,
 146                            unsigned int offs, gfp_t gfp_flags)
 147 {
 148         union fscrypt_iv iv;
 149         struct skcipher_request *req = NULL;
 150         DECLARE_CRYPTO_WAIT(wait);
 151         struct scatterlist dst, src;
 152         struct fscrypt_info *ci = inode->i_crypt_info;
 153         struct crypto_skcipher *tfm = ci->ci_ctfm;
 154         int res = 0;
 155
 156         BUG_ON(len == 0);
 157
 158         fscrypt_generate_iv(&iv, lblk_num, ci);
 159
 160         req = skcipher_request_alloc(tfm, gfp_flags);
 161         if (!req)
 162                 return -ENOMEM;
 163
 164         skcipher_request_set_callback(
 165                 req, CRYPTO_TFM_REQ_MAY_BACKLOG | CRYPTO_TFM_REQ_MAY_SLEEP,
 166                 crypto_req_done, &wait);
 167
 168         sg_init_table(&dst, 1);
 169         sg_set_page(&dst, dest_page, len, offs);
 170         sg_init_table(&src, 1);
 171         sg_set_page(&src, src_page, len, offs);
 172         skcipher_request_set_crypt(req, &src, &dst, len, &iv);
 173         if (rw == FS_DECRYPT)
 174                 res = crypto_wait_req(crypto_skcipher_decrypt(req), &wait);
 175         else
 176                 res = crypto_wait_req(crypto_skcipher_encrypt(req), &wait);
 177         skcipher_request_free(req);
 178         if (res) {
 179                 fscrypt_err(inode->i_sb,
 180                             "%scryption failed for inode %lu, block %llu: %d",
 181                             (rw == FS_DECRYPT ? "de" : "en"),
 182                             inode->i_ino, lblk_num, res);
 183                 return res;
 184         }
 185         return 0;
 186 }
 187
 188 struct page *fscrypt_alloc_bounce_page(struct fscrypt_ctx *ctx,
 189                                        gfp_t gfp_flags)
 190 {
 191         ctx->w.bounce_page = mempool_alloc(fscrypt_bounce_page_pool, gfp_flags);
 192         if (ctx->w.bounce_page == NULL)
 193                 return ERR_PTR(-ENOMEM);
 194         ctx->flags |= FS_CTX_HAS_BOUNCE_BUFFER_FL;
 195         return ctx->w.bounce_page;
 196 }
 197
 198 /**
 199  * fscypt_encrypt_page() - Encrypts a page
 200  * @inode:     The inode for which the encryption should take place
 201  * @page:      The page to encrypt. Must be locked for bounce-page
 202  *             encryption.
 203  * @len:       Length of data to encrypt in @page and encrypted
 204  *             data in returned page.
 205  * @offs:      Offset of data within @page and returned
 206  *             page holding encrypted data.
 207  * @lblk_num:  Logical block number. This must be unique for multiple
 208  *             calls with same inode, except when overwriting
 209  *             previously written data.
 210  * @gfp_flags: The gfp flag for memory allocation
 211  *
 212  * Encrypts @page using the ctx encryption context. Performs encryption
 213  * either in-place or into a newly allocated bounce page.
 214  * Called on the page write path.
 215  *
 216  * Bounce page allocation is the default.
 217  * In this case, the contents of @page are encrypted and stored in an
 218  * allocated bounce page. @page has to be locked and the caller must call
 219  * fscrypt_restore_control_page() on the returned ciphertext page to
 220  * release the bounce buffer and the encryption context.
 221  *
 222  * In-place encryption is used by setting the FS_CFLG_OWN_PAGES flag in
 223  * fscrypt_operations. Here, the input-page is returned with its content
 224  * encrypted.
 225  *
 226  * Return: A page with the encrypted content on success. Else, an
 227  * error value or NULL.
 228  */
 229 struct page *fscrypt_encrypt_page(const struct inode *inode,
 230                                 struct page *page,
 231                                 unsigned int len,
 232                                 unsigned int offs,
 233                                 u64 lblk_num, gfp_t gfp_flags)
 234
 235 {
 236         struct fscrypt_ctx *ctx;
 237         struct page *ciphertext_page = page;
 238         int err;
 239
 240         BUG_ON(len % FS_CRYPTO_BLOCK_SIZE != 0);
 241
 242         if (inode->i_sb->s_cop->flags & FS_CFLG_OWN_PAGES) {
 243                 /* with inplace-encryption we just encrypt the page */
 244                 err = fscrypt_do_page_crypto(inode, FS_ENCRYPT, lblk_num, page,
 245                                              ciphertext_page, len, offs,
 246                                              gfp_flags);
 247                 if (err)
 248                         return ERR_PTR(err);
 249
 250                 return ciphertext_page;
 251         }
 252
 253         BUG_ON(!PageLocked(page));
 254
 255         ctx = fscrypt_get_ctx(gfp_flags);
 256         if (IS_ERR(ctx))
 257                 return ERR_CAST(ctx);
 258
 259         /* The encryption operation will require a bounce page. */
 260         ciphertext_page = fscrypt_alloc_bounce_page(ctx, gfp_flags);
 261         if (IS_ERR(ciphertext_page))
 262                 goto errout;
 263
 264         ctx->w.control_page = page;
 265         err = fscrypt_do_page_crypto(inode, FS_ENCRYPT, lblk_num,
 266                                      page, ciphertext_page, len, offs,
 267                                      gfp_flags);
 268         if (err) {
 269                 ciphertext_page = ERR_PTR(err);
 270                 goto errout;
 271         }
 272         SetPagePrivate(ciphertext_page);
 273         set_page_private(ciphertext_page, (unsigned long)ctx);
 274         lock_page(ciphertext_page);
 275         return ciphertext_page;
 276
 277 errout:
 278         fscrypt_release_ctx(ctx);
 279         return ciphertext_page;
 280 }
 281 EXPORT_SYMBOL(fscrypt_encrypt_page);
 282
 283 /**
 284  * fscrypt_decrypt_page() - Decrypts a page in-place
 285  * @inode:     The corresponding inode for the page to decrypt.
 286  * @page:      The page to decrypt. Must be locked in case
 287  *             it is a writeback page (FS_CFLG_OWN_PAGES unset).
 288  * @len:       Number of bytes in @page to be decrypted.
 289  * @offs:      Start of data in @page.
 290  * @lblk_num:  Logical block number.
 291  *
 292  * Decrypts page in-place using the ctx encryption context.
 293  *
 294  * Called from the read completion callback.
 295  *
 296  * Return: Zero on success, non-zero otherwise.
 297  */
 298 int fscrypt_decrypt_page(const struct inode *inode, struct page *page,
 299                         unsigned int len, unsigned int offs, u64 lblk_num)
 300 {
 301         if (!(inode->i_sb->s_cop->flags & FS_CFLG_OWN_PAGES))
 302                 BUG_ON(!PageLocked(page));
 303
 304         return fscrypt_do_page_crypto(inode, FS_DECRYPT, lblk_num, page, page,
 305                                       len, offs, GFP_NOFS);
 306 }
 307 EXPORT_SYMBOL(fscrypt_decrypt_page);
 308
 309 /*
 310  * Validate dentries in encrypted directories to make sure we aren't potentially
 311  * caching stale dentries after a key has been added.
 312  */
 313 static int fscrypt_d_revalidate(struct dentry *dentry, unsigned int flags)
 314 {
 315         struct dentry *dir;
 316         int err;
 317         int valid;
 318
 319         /*
 320          * Plaintext names are always valid, since fscrypt doesn't support
 321          * reverting to ciphertext names without evicting the directory's inode
 322          * -- which implies eviction of the dentries in the directory.
 323          */
 324         if (!(dentry->d_flags & DCACHE_ENCRYPTED_NAME))
 325                 return 1;
 326
 327         /*
 328          * Ciphertext name; valid if the directory's key is still unavailable.
 329          *
 330          * Although fscrypt forbids rename() on ciphertext names, we still must
 331          * use dget_parent() here rather than use ->d_parent directly.  That's
 332          * because a corrupted fs image may contain directory hard links, which
 333          * the VFS handles by moving the directory's dentry tree in the dcache
 334          * each time ->lookup() finds the directory and it already has a dentry
 335          * elsewhere.  Thus ->d_parent can be changing, and we must safely grab
 336          * a reference to some ->d_parent to prevent it from being freed.
 337          */
 338
 339         if (flags & LOOKUP_RCU)
 340                 return -ECHILD;
 341
 342         dir = dget_parent(dentry);
 343         err = fscrypt_get_encryption_info(d_inode(dir));
 344         valid = !fscrypt_has_encryption_key(d_inode(dir));
 345         dput(dir);
 346
 347         if (err < 0)
 348                 return err;
 349
 350         return valid;
 351 }
 352
 353 const struct dentry_operations fscrypt_d_ops = {
 354         .d_revalidate = fscrypt_d_revalidate,
 355 };
 356
 357 void fscrypt_restore_control_page(struct page *page)
 358 {
 359         struct fscrypt_ctx *ctx;
 360
 361         ctx = (struct fscrypt_ctx *)page_private(page);
 362         set_page_private(page, (unsigned long)NULL);
 363         ClearPagePrivate(page);
 364         unlock_page(page);
 365         fscrypt_release_ctx(ctx);
 366 }
 367 EXPORT_SYMBOL(fscrypt_restore_control_page);
 368
 369 static void fscrypt_destroy(void)
 370 {
 371         struct fscrypt_ctx *pos, *n;
 372
 373         list_for_each_entry_safe(pos, n, &fscrypt_free_ctxs, free_list)
 374                 kmem_cache_free(fscrypt_ctx_cachep, pos);
 375         INIT_LIST_HEAD(&fscrypt_free_ctxs);
 376         mempool_destroy(fscrypt_bounce_page_pool);
 377         fscrypt_bounce_page_pool = NULL;
 378 }
 379
 380 /**
 381  * fscrypt_initialize() - allocate major buffers for fs encryption.
 382  * @cop_flags:  fscrypt operations flags
 383  *
 384  * We only call this when we start accessing encrypted files, since it
 385  * results in memory getting allocated that wouldn't otherwise be used.
 386  *
 387  * Return: Zero on success, non-zero otherwise.
 388  */
 389 int fscrypt_initialize(unsigned int cop_flags)
 390 {
 391         int i, res = -ENOMEM;
 392
 393         /* No need to allocate a bounce page pool if this FS won't use it. */
 394         if (cop_flags & FS_CFLG_OWN_PAGES)
 395                 return 0;
 396
 397         mutex_lock(&fscrypt_init_mutex);
 398         if (fscrypt_bounce_page_pool)
 399                 goto already_initialized;
 400
 401         for (i = 0; i < num_prealloc_crypto_ctxs; i++) {
 402                 struct fscrypt_ctx *ctx;
 403
 404                 ctx = kmem_cache_zalloc(fscrypt_ctx_cachep, GFP_NOFS);
 405                 if (!ctx)
 406                         goto fail;
 407                 list_add(&ctx->free_list, &fscrypt_free_ctxs);
 408         }
 409
 410         fscrypt_bounce_page_pool =
 411                 mempool_create_page_pool(num_prealloc_crypto_pages, 0);
 412         if (!fscrypt_bounce_page_pool)
 413                 goto fail;
 414
 415 already_initialized:
 416         mutex_unlock(&fscrypt_init_mutex);
 417         return 0;
 418 fail:
 419         fscrypt_destroy();
 420         mutex_unlock(&fscrypt_init_mutex);
 421         return res;
 422 }
 423
 424 void fscrypt_msg(struct super_block *sb, const char *level,
 425                  const char *fmt, ...)
 426 {
 427         static DEFINE_RATELIMIT_STATE(rs, DEFAULT_RATELIMIT_INTERVAL,
 428                                       DEFAULT_RATELIMIT_BURST);
 429         struct va_format vaf;
 430         va_list args;
 431
 432         if (!__ratelimit(&rs))
 433                 return;
 434
 435         va_start(args, fmt);
 436         vaf.fmt = fmt;
 437         vaf.va = &args;
 438         if (sb)
 439                 printk("%sfscrypt (%s): %pV\n", level, sb->s_id, &vaf);
 440         else
 441                 printk("%sfscrypt: %pV\n", level, &vaf);
 442         va_end(args);
 443 }
 444
 445 /**
 446  * fscrypt_init() - Set up for fs encryption.
 447  */
 448 static int __init fscrypt_init(void)
 449 {
 450         /*
 451          * Use an unbound workqueue to allow bios to be decrypted in parallel
 452          * even when they happen to complete on the same CPU.  This sacrifices
 453          * locality, but it's worthwhile since decryption is CPU-intensive.
 454          *
 455          * Also use a high-priority workqueue to prioritize decryption work,
 456          * which blocks reads from completing, over regular application tasks.
 457          */
 458         fscrypt_read_workqueue = alloc_workqueue("fscrypt_read_queue",
 459                                                  WQ_UNBOUND | WQ_HIGHPRI,
 460                                                  num_online_cpus());
 461         if (!fscrypt_read_workqueue)
 462                 goto fail;
 463
 464         fscrypt_ctx_cachep = KMEM_CACHE(fscrypt_ctx, SLAB_RECLAIM_ACCOUNT);
 465         if (!fscrypt_ctx_cachep)
 466                 goto fail_free_queue;
 467
 468         fscrypt_info_cachep = KMEM_CACHE(fscrypt_info, SLAB_RECLAIM_ACCOUNT);
 469         if (!fscrypt_info_cachep)
 470                 goto fail_free_ctx;
 471
 472         return 0;
 473
 474 fail_free_ctx:
 475         kmem_cache_destroy(fscrypt_ctx_cachep);
 476 fail_free_queue:
 477         destroy_workqueue(fscrypt_read_workqueue);
 478 fail:
 479         return -ENOMEM;
 480 }
 481 module_init(fscrypt_init)
 482
 483 /**
 484  * fscrypt_exit() - Shutdown the fs encryption system
 485  */
 486 static void __exit fscrypt_exit(void)
 487 {
 488         fscrypt_destroy();
 489
 490         if (fscrypt_read_workqueue)
 491                 destroy_workqueue(fscrypt_read_workqueue);
 492         kmem_cache_destroy(fscrypt_ctx_cachep);
 493         kmem_cache_destroy(fscrypt_info_cachep);
 494
 495         fscrypt_essiv_cleanup();
 496 }
 497 module_exit(fscrypt_exit);
 498
 499 MODULE_LICENSE("GPL");