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/skcipher.h>
  22 #include <keys/user-type.h>
  23 #include <keys/encrypted-type.h>
  24 #include <linux/ecryptfs.h>
  25 #include <linux/gfp.h>
  26 #include <linux/kernel.h>
  27 #include <linux/key.h>
  28 #include <linux/list.h>
  29 #include <linux/mempool.h>
  30 #include <linux/module.h>
  31 #include <linux/mutex.h>
  32 #include <linux/random.h>
  33 #include <linux/scatterlist.h>
  34 #include <linux/spinlock_types.h>
  35
  36 #include "ext4_extents.h"
  37 #include "xattr.h"
  38
  39 /* Encryption added and removed here! (L: */
  40
  41 static unsigned int num_prealloc_crypto_pages = 32;
  42 static unsigned int num_prealloc_crypto_ctxs = 128;
  43
  44 module_param(num_prealloc_crypto_pages, uint, 0444);
  45 MODULE_PARM_DESC(num_prealloc_crypto_pages,
  46                  "Number of crypto pages to preallocate");
  47 module_param(num_prealloc_crypto_ctxs, uint, 0444);
  48 MODULE_PARM_DESC(num_prealloc_crypto_ctxs,
  49                  "Number of crypto contexts to preallocate");
  50
  51 static mempool_t *ext4_bounce_page_pool;
  52
  53 static LIST_HEAD(ext4_free_crypto_ctxs);
  54 static DEFINE_SPINLOCK(ext4_crypto_ctx_lock);
  55
  56 static struct kmem_cache *ext4_crypto_ctx_cachep;
  57 struct kmem_cache *ext4_crypt_info_cachep;
  58
  59 /**
  60  * ext4_release_crypto_ctx() - Releases an encryption context
  61  * @ctx: The encryption context to release.
  62  *
  63  * If the encryption context was allocated from the pre-allocated pool, returns
  64  * it to that pool. Else, frees it.
  65  *
  66  * If there's a bounce page in the context, this frees that.
  67  */
  68 void ext4_release_crypto_ctx(struct ext4_crypto_ctx *ctx)
  69 {
  70         unsigned long flags;
  71
  72         if (ctx->flags & EXT4_WRITE_PATH_FL && ctx->w.bounce_page)
  73                 mempool_free(ctx->w.bounce_page, ext4_bounce_page_pool);
  74         ctx->w.bounce_page = NULL;
  75         ctx->w.control_page = NULL;
  76         if (ctx->flags & EXT4_CTX_REQUIRES_FREE_ENCRYPT_FL) {
  77                 kmem_cache_free(ext4_crypto_ctx_cachep, ctx);
  78         } else {
  79                 spin_lock_irqsave(&ext4_crypto_ctx_lock, flags);
  80                 list_add(&ctx->free_list, &ext4_free_crypto_ctxs);
  81                 spin_unlock_irqrestore(&ext4_crypto_ctx_lock, flags);
  82         }
  83 }
  84
  85 /**
  86  * ext4_get_crypto_ctx() - Gets an encryption context
  87  * @inode:       The inode for which we are doing the crypto
  88  *
  89  * Allocates and initializes an encryption context.
  90  *
  91  * Return: An allocated and initialized encryption context on success; error
  92  * value or NULL otherwise.
  93  */
  94 struct ext4_crypto_ctx *ext4_get_crypto_ctx(struct inode *inode,
  95                                             gfp_t gfp_flags)
  96 {
  97         struct ext4_crypto_ctx *ctx = NULL;
  98         int res = 0;
  99         unsigned long flags;
 100         struct ext4_crypt_info *ci = EXT4_I(inode)->i_crypt_info;
 101
 102         if (ci == NULL)
 103                 return ERR_PTR(-ENOKEY);
 104
 105         /*
 106          * We first try getting the ctx from a free list because in
 107          * the common case the ctx will have an allocated and
 108          * initialized crypto tfm, so it's probably a worthwhile
 109          * optimization. For the bounce page, we first try getting it
 110          * from the kernel allocator because that's just about as fast
 111          * as getting it from a list and because a cache of free pages
 112          * should generally be a "last resort" option for a filesystem
 113          * to be able to do its job.
 114          */
 115         spin_lock_irqsave(&ext4_crypto_ctx_lock, flags);
 116         ctx = list_first_entry_or_null(&ext4_free_crypto_ctxs,
 117                                        struct ext4_crypto_ctx, free_list);
 118         if (ctx)
 119                 list_del(&ctx->free_list);
 120         spin_unlock_irqrestore(&ext4_crypto_ctx_lock, flags);
 121         if (!ctx) {
 122                 ctx = kmem_cache_zalloc(ext4_crypto_ctx_cachep, gfp_flags);
 123                 if (!ctx) {
 124                         res = -ENOMEM;
 125                         goto out;
 126                 }
 127                 ctx->flags |= EXT4_CTX_REQUIRES_FREE_ENCRYPT_FL;
 128         } else {
 129                 ctx->flags &= ~EXT4_CTX_REQUIRES_FREE_ENCRYPT_FL;
 130         }
 131         ctx->flags &= ~EXT4_WRITE_PATH_FL;
 132
 133 out:
 134         if (res) {
 135                 if (!IS_ERR_OR_NULL(ctx))
 136                         ext4_release_crypto_ctx(ctx);
 137                 ctx = ERR_PTR(res);
 138         }
 139         return ctx;
 140 }
 141
 142 struct workqueue_struct *ext4_read_workqueue;
 143 static DEFINE_MUTEX(crypto_init);
 144
 145 /**
 146  * ext4_exit_crypto() - Shutdown the ext4 encryption system
 147  */
 148 void ext4_exit_crypto(void)
 149 {
 150         struct ext4_crypto_ctx *pos, *n;
 151
 152         list_for_each_entry_safe(pos, n, &ext4_free_crypto_ctxs, free_list)
 153                 kmem_cache_free(ext4_crypto_ctx_cachep, pos);
 154         INIT_LIST_HEAD(&ext4_free_crypto_ctxs);
 155         if (ext4_bounce_page_pool)
 156                 mempool_destroy(ext4_bounce_page_pool);
 157         ext4_bounce_page_pool = NULL;
 158         if (ext4_read_workqueue)
 159                 destroy_workqueue(ext4_read_workqueue);
 160         ext4_read_workqueue = NULL;
 161         if (ext4_crypto_ctx_cachep)
 162                 kmem_cache_destroy(ext4_crypto_ctx_cachep);
 163         ext4_crypto_ctx_cachep = NULL;
 164         if (ext4_crypt_info_cachep)
 165                 kmem_cache_destroy(ext4_crypt_info_cachep);
 166         ext4_crypt_info_cachep = NULL;
 167 }
 168
 169 /**
 170  * ext4_init_crypto() - Set up for ext4 encryption.
 171  *
 172  * We only call this when we start accessing encrypted files, since it
 173  * results in memory getting allocated that wouldn't otherwise be used.
 174  *
 175  * Return: Zero on success, non-zero otherwise.
 176  */
 177 int ext4_init_crypto(void)
 178 {
 179         int i, res = -ENOMEM;
 180
 181         mutex_lock(&crypto_init);
 182         if (ext4_read_workqueue)
 183                 goto already_initialized;
 184         ext4_read_workqueue = alloc_workqueue("ext4_crypto", WQ_HIGHPRI, 0);
 185         if (!ext4_read_workqueue)
 186                 goto fail;
 187
 188         ext4_crypto_ctx_cachep = KMEM_CACHE(ext4_crypto_ctx,
 189                                             SLAB_RECLAIM_ACCOUNT);
 190         if (!ext4_crypto_ctx_cachep)
 191                 goto fail;
 192
 193         ext4_crypt_info_cachep = KMEM_CACHE(ext4_crypt_info,
 194                                             SLAB_RECLAIM_ACCOUNT);
 195         if (!ext4_crypt_info_cachep)
 196                 goto fail;
 197
 198         for (i = 0; i < num_prealloc_crypto_ctxs; i++) {
 199                 struct ext4_crypto_ctx *ctx;
 200
 201                 ctx = kmem_cache_zalloc(ext4_crypto_ctx_cachep, GFP_NOFS);
 202                 if (!ctx) {
 203                         res = -ENOMEM;
 204                         goto fail;
 205                 }
 206                 list_add(&ctx->free_list, &ext4_free_crypto_ctxs);
 207         }
 208
 209         ext4_bounce_page_pool =
 210                 mempool_create_page_pool(num_prealloc_crypto_pages, 0);
 211         if (!ext4_bounce_page_pool) {
 212                 res = -ENOMEM;
 213                 goto fail;
 214         }
 215 already_initialized:
 216         mutex_unlock(&crypto_init);
 217         return 0;
 218 fail:
 219         ext4_exit_crypto();
 220         mutex_unlock(&crypto_init);
 221         return res;
 222 }
 223
 224 void ext4_restore_control_page(struct page *data_page)
 225 {
 226         struct ext4_crypto_ctx *ctx =
 227                 (struct ext4_crypto_ctx *)page_private(data_page);
 228
 229         set_page_private(data_page, (unsigned long)NULL);
 230         ClearPagePrivate(data_page);
 231         unlock_page(data_page);
 232         ext4_release_crypto_ctx(ctx);
 233 }
 234
 235 /**
 236  * ext4_crypt_complete() - The completion callback for page encryption
 237  * @req: The asynchronous encryption request context
 238  * @res: The result of the encryption operation
 239  */
 240 static void ext4_crypt_complete(struct crypto_async_request *req, int res)
 241 {
 242         struct ext4_completion_result *ecr = req->data;
 243
 244         if (res == -EINPROGRESS)
 245                 return;
 246         ecr->res = res;
 247         complete(&ecr->completion);
 248 }
 249
 250 typedef enum {
 251         EXT4_DECRYPT = 0,
 252         EXT4_ENCRYPT,
 253 } ext4_direction_t;
 254
 255 static int ext4_page_crypto(struct inode *inode,
 256                             ext4_direction_t rw,
 257                             pgoff_t index,
 258                             struct page *src_page,
 259                             struct page *dest_page,
 260                             gfp_t gfp_flags)
 261
 262 {
 263         u8 xts_tweak[EXT4_XTS_TWEAK_SIZE];
 264         struct skcipher_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_skcipher *tfm = ci->ci_ctfm;
 269         int res = 0;
 270
 271         req = skcipher_request_alloc(tfm, gfp_flags);
 272         if (!req) {
 273                 printk_ratelimited(KERN_ERR
 274                                    "%s: crypto_request_alloc() failed\n",
 275                                    __func__);
 276                 return -ENOMEM;
 277         }
 278         skcipher_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_SIZE, 0);
 289         sg_init_table(&src, 1);
 290         sg_set_page(&src, src_page, PAGE_SIZE, 0);
 291         skcipher_request_set_crypt(req, &src, &dst, PAGE_SIZE,
 292                                    xts_tweak);
 293         if (rw == EXT4_DECRYPT)
 294                 res = crypto_skcipher_decrypt(req);
 295         else
 296                 res = crypto_skcipher_encrypt(req);
 297         if (res == -EINPROGRESS || res == -EBUSY) {
 298                 wait_for_completion(&ecr.completion);
 299                 res = ecr.res;
 300         }
 301         skcipher_request_free(req);
 302         if (res) {
 303                 printk_ratelimited(
 304                         KERN_ERR
 305                         "%s: crypto_skcipher_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                                       gfp_t gfp_flags)
 314 {
 315         ctx->w.bounce_page = mempool_alloc(ext4_bounce_page_pool, gfp_flags);
 316         if (ctx->w.bounce_page == NULL)
 317                 return ERR_PTR(-ENOMEM);
 318         ctx->flags |= EXT4_WRITE_PATH_FL;
 319         return ctx->w.bounce_page;
 320 }
 321
 322 /**
 323  * ext4_encrypt() - Encrypts a page
 324  * @inode:          The inode for which the encryption should take place
 325  * @plaintext_page: The page to encrypt. Must be locked.
 326  *
 327  * Allocates a ciphertext page and encrypts plaintext_page into it using the ctx
 328  * encryption context.
 329  *
 330  * Called on the page write path.  The caller must call
 331  * ext4_restore_control_page() on the returned ciphertext page to
 332  * release the bounce buffer and the encryption context.
 333  *
 334  * Return: An allocated page with the encrypted content on success. Else, an
 335  * error value or NULL.
 336  */
 337 struct page *ext4_encrypt(struct inode *inode,
 338                           struct page *plaintext_page,
 339                           gfp_t gfp_flags)
 340 {
 341         struct ext4_crypto_ctx *ctx;
 342         struct page *ciphertext_page = NULL;
 343         int err;
 344
 345         BUG_ON(!PageLocked(plaintext_page));
 346
 347         ctx = ext4_get_crypto_ctx(inode, gfp_flags);
 348         if (IS_ERR(ctx))
 349                 return (struct page *) ctx;
 350
 351         /* The encryption operation will require a bounce page. */
 352         ciphertext_page = alloc_bounce_page(ctx, gfp_flags);
 353         if (IS_ERR(ciphertext_page))
 354                 goto errout;
 355         ctx->w.control_page = plaintext_page;
 356         err = ext4_page_crypto(inode, EXT4_ENCRYPT, plaintext_page->index,
 357                                plaintext_page, ciphertext_page, gfp_flags);
 358         if (err) {
 359                 ciphertext_page = ERR_PTR(err);
 360         errout:
 361                 ext4_release_crypto_ctx(ctx);
 362                 return ciphertext_page;
 363         }
 364         SetPagePrivate(ciphertext_page);
 365         set_page_private(ciphertext_page, (unsigned long)ctx);
 366         lock_page(ciphertext_page);
 367         return ciphertext_page;
 368 }
 369
 370 /**
 371  * ext4_decrypt() - Decrypts a page in-place
 372  * @ctx:  The encryption context.
 373  * @page: The page to decrypt. Must be locked.
 374  *
 375  * Decrypts page in-place using the ctx encryption context.
 376  *
 377  * Called from the read completion callback.
 378  *
 379  * Return: Zero on success, non-zero otherwise.
 380  */
 381 int ext4_decrypt(struct page *page)
 382 {
 383         BUG_ON(!PageLocked(page));
 384
 385         return ext4_page_crypto(page->mapping->host, EXT4_DECRYPT,
 386                                 page->index, page, page, GFP_NOFS);
 387 }
 388
 389 int ext4_encrypted_zeroout(struct inode *inode, ext4_lblk_t lblk,
 390                            ext4_fsblk_t pblk, ext4_lblk_t len)
 391 {
 392         struct ext4_crypto_ctx  *ctx;
 393         struct page             *ciphertext_page = NULL;
 394         struct bio              *bio;
 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_SIZE);
 404
 405         ctx = ext4_get_crypto_ctx(inode, GFP_NOFS);
 406         if (IS_ERR(ctx))
 407                 return PTR_ERR(ctx);
 408
 409         ciphertext_page = alloc_bounce_page(ctx, GFP_NOWAIT);
 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                                        GFP_NOFS);
 419                 if (err)
 420                         goto errout;
 421
 422                 bio = bio_alloc(GFP_NOWAIT, 1);
 423                 if (!bio) {
 424                         err = -ENOMEM;
 425                         goto errout;
 426                 }
 427                 bio->bi_bdev = inode->i_sb->s_bdev;
 428                 bio->bi_iter.bi_sector =
 429                         pblk << (inode->i_sb->s_blocksize_bits - 9);
 430                 ret = bio_add_page(bio, ciphertext_page,
 431                                    inode->i_sb->s_blocksize, 0);
 432                 if (ret != inode->i_sb->s_blocksize) {
 433                         /* should never happen! */
 434                         ext4_msg(inode->i_sb, KERN_ERR,
 435                                  "bio_add_page failed: %d", ret);
 436                         WARN_ON(1);
 437                         bio_put(bio);
 438                         err = -EIO;
 439                         goto errout;
 440                 }
 441                 err = submit_bio_wait(WRITE, bio);
 442                 if ((err == 0) && bio->bi_error)
 443                         err = -EIO;
 444                 bio_put(bio);
 445                 if (err)
 446                         goto errout;
 447                 lblk++; pblk++;
 448         }
 449         err = 0;
 450 errout:
 451         ext4_release_crypto_ctx(ctx);
 452         return err;
 453 }
 454
 455 bool ext4_valid_contents_enc_mode(uint32_t mode)
 456 {
 457         return (mode == EXT4_ENCRYPTION_MODE_AES_256_XTS);
 458 }
 459
 460 /**
 461  * ext4_validate_encryption_key_size() - Validate the encryption key size
 462  * @mode: The key mode.
 463  * @size: The key size to validate.
 464  *
 465  * Return: The validated key size for @mode. Zero if invalid.
 466  */
 467 uint32_t ext4_validate_encryption_key_size(uint32_t mode, uint32_t size)
 468 {
 469         if (size == ext4_encryption_key_size(mode))
 470                 return size;
 471         return 0;
 472 }
 473
 474 /*
 475  * Validate dentries for encrypted directories to make sure we aren't
 476  * potentially caching stale data after a key has been added or
 477  * removed.
 478  */
 479 static int ext4_d_revalidate(struct dentry *dentry, unsigned int flags)
 480 {
 481         struct dentry *dir;
 482         struct ext4_crypt_info *ci;
 483         int dir_has_key, cached_with_key;
 484
 485         dir = dget_parent(dentry);
 486         if (!ext4_encrypted_inode(d_inode(dir))) {
 487                 dput(dir);
 488                 return 0;
 489         }
 490         ci = EXT4_I(d_inode(dir))->i_crypt_info;
 491         if (ci && ci->ci_keyring_key &&
 492             (ci->ci_keyring_key->flags & ((1 << KEY_FLAG_INVALIDATED) |
 493                                           (1 << KEY_FLAG_REVOKED) |
 494                                           (1 << KEY_FLAG_DEAD))))
 495                 ci = NULL;
 496
 497         /* this should eventually be an flag in d_flags */
 498         cached_with_key = dentry->d_fsdata != NULL;
 499         dir_has_key = (ci != NULL);
 500         dput(dir);
 501
 502         /*
 503          * If the dentry was cached without the key, and it is a
 504          * negative dentry, it might be a valid name.  We can't check
 505          * if the key has since been made available due to locking
 506          * reasons, so we fail the validation so ext4_lookup() can do
 507          * this check.
 508          *
 509          * We also fail the validation if the dentry was created with
 510          * the key present, but we no longer have the key, or vice versa.
 511          */
 512         if ((!cached_with_key && d_is_negative(dentry)) ||
 513             (!cached_with_key && dir_has_key) ||
 514             (cached_with_key && !dir_has_key)) {
 515 #if 0                           /* Revalidation debug */
 516                 char buf[80];
 517                 char *cp = simple_dname(dentry, buf, sizeof(buf));
 518
 519                 if (IS_ERR(cp))
 520                         cp = (char *) "???";
 521                 pr_err("revalidate: %s %p %d %d %d\n", cp, dentry->d_fsdata,
 522                        cached_with_key, d_is_negative(dentry),
 523                        dir_has_key);
 524 #endif
 525                 return 0;
 526         }
 527         return 1;
 528 }
 529
 530 const struct dentry_operations ext4_encrypted_d_ops = {
 531         .d_revalidate = ext4_d_revalidate,
 532 };