fs/ext4/crypto.c

   1 /*
   2  * linux/fs/ext4/crypto.c
   3  *
   4  * Copyright (C) 2015, Google, Inc.
   5  *
   6  * This contains encryption functions for ext4
   7  *
   8  * Written by Michael Halcrow, 2014.
   9  *
  10  * Filename encryption additions
  11  *      Uday Savagaonkar, 2014
  12  * Encryption policy handling additions
  13  *      Ildar Muslukhov, 2014
  14  *
  15  * This has not yet undergone a rigorous security audit.
  16  *
  17  * The usage of AES-XTS should conform to recommendations in NIST
  18  * Special Publication 800-38E and IEEE P1619/D16.
  19  */
  20
  21 #include <crypto/hash.h>
  22 #include <crypto/sha.h>
  23 #include <keys/user-type.h>
  24 #include <keys/encrypted-type.h>
  25 #include <linux/crypto.h>
  26 #include <linux/ecryptfs.h>
  27 #include <linux/gfp.h>
  28 #include <linux/kernel.h>
  29 #include <linux/key.h>
  30 #include <linux/list.h>
  31 #include <linux/mempool.h>
  32 #include <linux/module.h>
  33 #include <linux/mutex.h>
  34 #include <linux/random.h>
  35 #include <linux/scatterlist.h>
  36 #include <linux/spinlock_types.h>
  37
  38 #include "ext4_extents.h"
  39 #include "xattr.h"
  40
  41 /* Encryption added and removed here! (L: */
  42
  43 static unsigned int num_prealloc_crypto_pages = 32;
  44 static unsigned int num_prealloc_crypto_ctxs = 128;
  45
  46 module_param(num_prealloc_crypto_pages, uint, 0444);
  47 MODULE_PARM_DESC(num_prealloc_crypto_pages,
  48                  "Number of crypto pages to preallocate");
  49 module_param(num_prealloc_crypto_ctxs, uint, 0444);
  50 MODULE_PARM_DESC(num_prealloc_crypto_ctxs,
  51                  "Number of crypto contexts to preallocate");
  52
  53 static mempool_t *ext4_bounce_page_pool;
  54
  55 static LIST_HEAD(ext4_free_crypto_ctxs);
  56 static DEFINE_SPINLOCK(ext4_crypto_ctx_lock);
  57
  58 static struct kmem_cache *ext4_crypto_ctx_cachep;
  59 struct kmem_cache *ext4_crypt_info_cachep;
  60
  61 /**
  62  * ext4_release_crypto_ctx() - Releases an encryption context
  63  * @ctx: The encryption context to release.
  64  *
  65  * If the encryption context was allocated from the pre-allocated pool, returns
  66  * it to that pool. Else, frees it.
  67  *
  68  * If there's a bounce page in the context, this frees that.
  69  */
  70 void ext4_release_crypto_ctx(struct ext4_crypto_ctx *ctx)
  71 {
  72         unsigned long flags;
  73
  74         if (ctx->flags & EXT4_WRITE_PATH_FL && ctx->w.bounce_page)
  75                 mempool_free(ctx->w.bounce_page, ext4_bounce_page_pool);
  76         ctx->w.bounce_page = NULL;
  77         ctx->w.control_page = NULL;
  78         if (ctx->flags & EXT4_CTX_REQUIRES_FREE_ENCRYPT_FL) {
  79                 kmem_cache_free(ext4_crypto_ctx_cachep, ctx);
  80         } else {
  81                 spin_lock_irqsave(&ext4_crypto_ctx_lock, flags);
  82                 list_add(&ctx->free_list, &ext4_free_crypto_ctxs);
  83                 spin_unlock_irqrestore(&ext4_crypto_ctx_lock, flags);
  84         }
  85 }
  86
  87 /**
  88  * ext4_get_crypto_ctx() - Gets an encryption context
  89  * @inode:       The inode for which we are doing the crypto
  90  *
  91  * Allocates and initializes an encryption context.
  92  *
  93  * Return: An allocated and initialized encryption context on success; error
  94  * value or NULL otherwise.
  95  */
  96 struct ext4_crypto_ctx *ext4_get_crypto_ctx(struct inode *inode)
  97 {
  98         struct ext4_crypto_ctx *ctx = NULL;
  99         int res = 0;
 100         unsigned long flags;
 101         struct ext4_crypt_info *ci = EXT4_I(inode)->i_crypt_info;
 102
 103         if (ci == NULL)
 104                 return ERR_PTR(-ENOKEY);
 105
 106         /*
 107          * We first try getting the ctx from a free list because in
 108          * the common case the ctx will have an allocated and
 109          * initialized crypto tfm, so it's probably a worthwhile
 110          * optimization. For the bounce page, we first try getting it
 111          * from the kernel allocator because that's just about as fast
 112          * as getting it from a list and because a cache of free pages
 113          * should generally be a "last resort" option for a filesystem
 114          * to be able to do its job.
 115          */
 116         spin_lock_irqsave(&ext4_crypto_ctx_lock, flags);
 117         ctx = list_first_entry_or_null(&ext4_free_crypto_ctxs,
 118                                        struct ext4_crypto_ctx, free_list);
 119         if (ctx)
 120                 list_del(&ctx->free_list);
 121         spin_unlock_irqrestore(&ext4_crypto_ctx_lock, flags);
 122         if (!ctx) {
 123                 ctx = kmem_cache_zalloc(ext4_crypto_ctx_cachep, GFP_NOFS);
 124                 if (!ctx) {
 125                         res = -ENOMEM;
 126                         goto out;
 127                 }
 128                 ctx->flags |= EXT4_CTX_REQUIRES_FREE_ENCRYPT_FL;
 129         } else {
 130                 ctx->flags &= ~EXT4_CTX_REQUIRES_FREE_ENCRYPT_FL;
 131         }
 132         ctx->flags &= ~EXT4_WRITE_PATH_FL;
 133
 134 out:
 135         if (res) {
 136                 if (!IS_ERR_OR_NULL(ctx))
 137                         ext4_release_crypto_ctx(ctx);
 138                 ctx = ERR_PTR(res);
 139         }
 140         return ctx;
 141 }
 142
 143 struct workqueue_struct *ext4_read_workqueue;
 144 static DEFINE_MUTEX(crypto_init);
 145
 146 /**
 147  * ext4_exit_crypto() - Shutdown the ext4 encryption system
 148  */
 149 void ext4_exit_crypto(void)
 150 {
 151         struct ext4_crypto_ctx *pos, *n;
 152
 153         list_for_each_entry_safe(pos, n, &ext4_free_crypto_ctxs, free_list)
 154                 kmem_cache_free(ext4_crypto_ctx_cachep, pos);
 155         INIT_LIST_HEAD(&ext4_free_crypto_ctxs);
 156         if (ext4_bounce_page_pool)
 157                 mempool_destroy(ext4_bounce_page_pool);
 158         ext4_bounce_page_pool = NULL;
 159         if (ext4_read_workqueue)
 160                 destroy_workqueue(ext4_read_workqueue);
 161         ext4_read_workqueue = NULL;
 162         if (ext4_crypto_ctx_cachep)
 163                 kmem_cache_destroy(ext4_crypto_ctx_cachep);
 164         ext4_crypto_ctx_cachep = NULL;
 165         if (ext4_crypt_info_cachep)
 166                 kmem_cache_destroy(ext4_crypt_info_cachep);
 167         ext4_crypt_info_cachep = NULL;
 168 }
 169
 170 /**
 171  * ext4_init_crypto() - Set up for ext4 encryption.
 172  *
 173  * We only call this when we start accessing encrypted files, since it
 174  * results in memory getting allocated that wouldn't otherwise be used.
 175  *
 176  * Return: Zero on success, non-zero otherwise.
 177  */
 178 int ext4_init_crypto(void)
 179 {
 180         int i, res = -ENOMEM;
 181
 182         mutex_lock(&crypto_init);
 183         if (ext4_read_workqueue)
 184                 goto already_initialized;
 185         ext4_read_workqueue = alloc_workqueue("ext4_crypto", WQ_HIGHPRI, 0);
 186         if (!ext4_read_workqueue)
 187                 goto fail;
 188
 189         ext4_crypto_ctx_cachep = KMEM_CACHE(ext4_crypto_ctx,
 190                                             SLAB_RECLAIM_ACCOUNT);
 191         if (!ext4_crypto_ctx_cachep)
 192                 goto fail;
 193
 194         ext4_crypt_info_cachep = KMEM_CACHE(ext4_crypt_info,
 195                                             SLAB_RECLAIM_ACCOUNT);
 196         if (!ext4_crypt_info_cachep)
 197                 goto fail;
 198
 199         for (i = 0; i < num_prealloc_crypto_ctxs; i++) {
 200                 struct ext4_crypto_ctx *ctx;
 201
 202                 ctx = kmem_cache_zalloc(ext4_crypto_ctx_cachep, GFP_NOFS);
 203                 if (!ctx) {
 204                         res = -ENOMEM;
 205                         goto fail;
 206                 }
 207                 list_add(&ctx->free_list, &ext4_free_crypto_ctxs);
 208         }
 209
 210         ext4_bounce_page_pool =
 211                 mempool_create_page_pool(num_prealloc_crypto_pages, 0);
 212         if (!ext4_bounce_page_pool) {
 213                 res = -ENOMEM;
 214                 goto fail;
 215         }
 216 already_initialized:
 217         mutex_unlock(&crypto_init);
 218         return 0;
 219 fail:
 220         ext4_exit_crypto();
 221         mutex_unlock(&crypto_init);
 222         return res;
 223 }
 224
 225 void ext4_restore_control_page(struct page *data_page)
 226 {
 227         struct ext4_crypto_ctx *ctx =
 228                 (struct ext4_crypto_ctx *)page_private(data_page);
 229
 230         set_page_private(data_page, (unsigned long)NULL);
 231         ClearPagePrivate(data_page);
 232         unlock_page(data_page);
 233         ext4_release_crypto_ctx(ctx);
 234 }
 235
 236 /**
 237  * ext4_crypt_complete() - The completion callback for page encryption
 238  * @req: The asynchronous encryption request context
 239  * @res: The result of the encryption operation
 240  */
 241 static void ext4_crypt_complete(struct crypto_async_request *req, int res)
 242 {
 243         struct ext4_completion_result *ecr = req->data;
 244
 245         if (res == -EINPROGRESS)
 246                 return;
 247         ecr->res = res;
 248         complete(&ecr->completion);
 249 }
 250
 251 typedef enum {
 252         EXT4_DECRYPT = 0,
 253         EXT4_ENCRYPT,
 254 } ext4_direction_t;
 255
 256 static int ext4_page_crypto(struct inode *inode,
 257                             ext4_direction_t rw,
 258                             pgoff_t index,
 259                             struct page *src_page,
 260                             struct page *dest_page)
 261
 262 {
 263         u8 xts_tweak[EXT4_XTS_TWEAK_SIZE];
 264         struct ablkcipher_request *req = NULL;
 265         DECLARE_EXT4_COMPLETION_RESULT(ecr);
 266         struct scatterlist dst, src;
 267         struct ext4_crypt_info *ci = EXT4_I(inode)->i_crypt_info;
 268         struct crypto_ablkcipher *tfm = ci->ci_ctfm;
 269         int res = 0;
 270
 271         req = ablkcipher_request_alloc(tfm, GFP_NOFS);
 272         if (!req) {
 273                 printk_ratelimited(KERN_ERR
 274                                    "%s: crypto_request_alloc() failed\n",
 275                                    __func__);
 276                 return -ENOMEM;
 277         }
 278         ablkcipher_request_set_callback(
 279                 req, CRYPTO_TFM_REQ_MAY_BACKLOG | CRYPTO_TFM_REQ_MAY_SLEEP,
 280                 ext4_crypt_complete, &ecr);
 281
 282         BUILD_BUG_ON(EXT4_XTS_TWEAK_SIZE < sizeof(index));
 283         memcpy(xts_tweak, &index, sizeof(index));
 284         memset(&xts_tweak[sizeof(index)], 0,
 285                EXT4_XTS_TWEAK_SIZE - sizeof(index));
 286
 287         sg_init_table(&dst, 1);
 288         sg_set_page(&dst, dest_page, PAGE_CACHE_SIZE, 0);
 289         sg_init_table(&src, 1);
 290         sg_set_page(&src, src_page, PAGE_CACHE_SIZE, 0);
 291         ablkcipher_request_set_crypt(req, &src, &dst, PAGE_CACHE_SIZE,
 292                                      xts_tweak);
 293         if (rw == EXT4_DECRYPT)
 294                 res = crypto_ablkcipher_decrypt(req);
 295         else
 296                 res = crypto_ablkcipher_encrypt(req);
 297         if (res == -EINPROGRESS || res == -EBUSY) {
 298                 wait_for_completion(&ecr.completion);
 299                 res = ecr.res;
 300         }
 301         ablkcipher_request_free(req);
 302         if (res) {
 303                 printk_ratelimited(
 304                         KERN_ERR
 305                         "%s: crypto_ablkcipher_encrypt() returned %d\n",
 306                         __func__, res);
 307                 return res;
 308         }
 309         return 0;
 310 }
 311
 312 static struct page *alloc_bounce_page(struct ext4_crypto_ctx *ctx)
 313 {
 314         ctx->w.bounce_page = mempool_alloc(ext4_bounce_page_pool, GFP_NOWAIT);
 315         if (ctx->w.bounce_page == NULL)
 316                 return ERR_PTR(-ENOMEM);
 317         ctx->flags |= EXT4_WRITE_PATH_FL;
 318         return ctx->w.bounce_page;
 319 }
 320
 321 /**
 322  * ext4_encrypt() - Encrypts a page
 323  * @inode:          The inode for which the encryption should take place
 324  * @plaintext_page: The page to encrypt. Must be locked.
 325  *
 326  * Allocates a ciphertext page and encrypts plaintext_page into it using the ctx
 327  * encryption context.
 328  *
 329  * Called on the page write path.  The caller must call
 330  * ext4_restore_control_page() on the returned ciphertext page to
 331  * release the bounce buffer and the encryption context.
 332  *
 333  * Return: An allocated page with the encrypted content on success. Else, an
 334  * error value or NULL.
 335  */
 336 struct page *ext4_encrypt(struct inode *inode,
 337                           struct page *plaintext_page)
 338 {
 339         struct ext4_crypto_ctx *ctx;
 340         struct page *ciphertext_page = NULL;
 341         int err;
 342
 343         BUG_ON(!PageLocked(plaintext_page));
 344
 345         ctx = ext4_get_crypto_ctx(inode);
 346         if (IS_ERR(ctx))
 347                 return (struct page *) ctx;
 348
 349         /* The encryption operation will require a bounce page. */
 350         ciphertext_page = alloc_bounce_page(ctx);
 351         if (IS_ERR(ciphertext_page))
 352                 goto errout;
 353         ctx->w.control_page = plaintext_page;
 354         err = ext4_page_crypto(inode, EXT4_ENCRYPT, plaintext_page->index,
 355                                plaintext_page, ciphertext_page);
 356         if (err) {
 357                 ciphertext_page = ERR_PTR(err);
 358         errout:
 359                 ext4_release_crypto_ctx(ctx);
 360                 return ciphertext_page;
 361         }
 362         SetPagePrivate(ciphertext_page);
 363         set_page_private(ciphertext_page, (unsigned long)ctx);
 364         lock_page(ciphertext_page);
 365         return ciphertext_page;
 366 }
 367
 368 /**
 369  * ext4_decrypt() - Decrypts a page in-place
 370  * @ctx:  The encryption context.
 371  * @page: The page to decrypt. Must be locked.
 372  *
 373  * Decrypts page in-place using the ctx encryption context.
 374  *
 375  * Called from the read completion callback.
 376  *
 377  * Return: Zero on success, non-zero otherwise.
 378  */
 379 int ext4_decrypt(struct page *page)
 380 {
 381         BUG_ON(!PageLocked(page));
 382
 383         return ext4_page_crypto(page->mapping->host,
 384                                 EXT4_DECRYPT, page->index, page, page);
 385 }
 386
 387 int ext4_encrypted_zeroout(struct inode *inode, struct ext4_extent *ex)
 388 {
 389         struct ext4_crypto_ctx  *ctx;
 390         struct page             *ciphertext_page = NULL;
 391         struct bio              *bio;
 392         ext4_lblk_t             lblk = le32_to_cpu(ex->ee_block);
 393         ext4_fsblk_t            pblk = ext4_ext_pblock(ex);
 394         unsigned int            len = ext4_ext_get_actual_len(ex);
 395         int                     ret, err = 0;
 396
 397 #if 0
 398         ext4_msg(inode->i_sb, KERN_CRIT,
 399                  "ext4_encrypted_zeroout ino %lu lblk %u len %u",
 400                  (unsigned long) inode->i_ino, lblk, len);
 401 #endif
 402
 403         BUG_ON(inode->i_sb->s_blocksize != PAGE_CACHE_SIZE);
 404
 405         ctx = ext4_get_crypto_ctx(inode);
 406         if (IS_ERR(ctx))
 407                 return PTR_ERR(ctx);
 408
 409         ciphertext_page = alloc_bounce_page(ctx);
 410         if (IS_ERR(ciphertext_page)) {
 411                 err = PTR_ERR(ciphertext_page);
 412                 goto errout;
 413         }
 414
 415         while (len--) {
 416                 err = ext4_page_crypto(inode, EXT4_ENCRYPT, lblk,
 417                                        ZERO_PAGE(0), ciphertext_page);
 418                 if (err)
 419                         goto errout;
 420
 421                 bio = bio_alloc(GFP_KERNEL, 1);
 422                 if (!bio) {
 423                         err = -ENOMEM;
 424                         goto errout;
 425                 }
 426                 bio->bi_bdev = inode->i_sb->s_bdev;
 427                 bio->bi_iter.bi_sector =
 428                         pblk << (inode->i_sb->s_blocksize_bits - 9);
 429                 ret = bio_add_page(bio, ciphertext_page,
 430                                    inode->i_sb->s_blocksize, 0);
 431                 if (ret != inode->i_sb->s_blocksize) {
 432                         /* should never happen! */
 433                         ext4_msg(inode->i_sb, KERN_ERR,
 434                                  "bio_add_page failed: %d", ret);
 435                         WARN_ON(1);
 436                         bio_put(bio);
 437                         err = -EIO;
 438                         goto errout;
 439                 }
 440                 err = submit_bio_wait(WRITE, bio);
 441                 if ((err == 0) && bio->bi_error)
 442                         err = -EIO;
 443                 bio_put(bio);
 444                 if (err)
 445                         goto errout;
 446                 lblk++; pblk++;
 447         }
 448         err = 0;
 449 errout:
 450         ext4_release_crypto_ctx(ctx);
 451         return err;
 452 }
 453
 454 bool ext4_valid_contents_enc_mode(uint32_t mode)
 455 {
 456         return (mode == EXT4_ENCRYPTION_MODE_AES_256_XTS);
 457 }
 458
 459 /**
 460  * ext4_validate_encryption_key_size() - Validate the encryption key size
 461  * @mode: The key mode.
 462  * @size: The key size to validate.
 463  *
 464  * Return: The validated key size for @mode. Zero if invalid.
 465  */
 466 uint32_t ext4_validate_encryption_key_size(uint32_t mode, uint32_t size)
 467 {
 468         if (size == ext4_encryption_key_size(mode))
 469                 return size;
 470         return 0;
 471 }