Loading...
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 604 605 606 607 608 609 610 611 612 | // SPDX-License-Identifier: GPL-2.0
/*
* key management facility for FS encryption support.
*
* Copyright (C) 2015, Google, Inc.
*
* This contains encryption key functions.
*
* Written by Michael Halcrow, Ildar Muslukhov, and Uday Savagaonkar, 2015.
*/
#include <keys/user-type.h>
#include <linux/hashtable.h>
#include <linux/scatterlist.h>
#include <linux/ratelimit.h>
#include <crypto/aes.h>
#include <crypto/algapi.h>
#include <crypto/sha.h>
#include <crypto/skcipher.h>
#include "fscrypt_private.h"
static struct crypto_shash *essiv_hash_tfm;
/* Table of keys referenced by FS_POLICY_FLAG_DIRECT_KEY policies */
static DEFINE_HASHTABLE(fscrypt_master_keys, 6); /* 6 bits = 64 buckets */
static DEFINE_SPINLOCK(fscrypt_master_keys_lock);
/*
* Key derivation function. This generates the derived key by encrypting the
* master key with AES-128-ECB using the inode's nonce as the AES key.
*
* The master key must be at least as long as the derived key. If the master
* key is longer, then only the first 'derived_keysize' bytes are used.
*/
static int derive_key_aes(const u8 *master_key,
const struct fscrypt_context *ctx,
u8 *derived_key, unsigned int derived_keysize)
{
int res = 0;
struct skcipher_request *req = NULL;
DECLARE_CRYPTO_WAIT(wait);
struct scatterlist src_sg, dst_sg;
struct crypto_skcipher *tfm = crypto_alloc_skcipher("ecb(aes)", 0, 0);
if (IS_ERR(tfm)) {
res = PTR_ERR(tfm);
tfm = NULL;
goto out;
}
crypto_skcipher_set_flags(tfm, CRYPTO_TFM_REQ_FORBID_WEAK_KEYS);
req = skcipher_request_alloc(tfm, GFP_NOFS);
if (!req) {
res = -ENOMEM;
goto out;
}
skcipher_request_set_callback(req,
CRYPTO_TFM_REQ_MAY_BACKLOG | CRYPTO_TFM_REQ_MAY_SLEEP,
crypto_req_done, &wait);
res = crypto_skcipher_setkey(tfm, ctx->nonce, sizeof(ctx->nonce));
if (res < 0)
goto out;
sg_init_one(&src_sg, master_key, derived_keysize);
sg_init_one(&dst_sg, derived_key, derived_keysize);
skcipher_request_set_crypt(req, &src_sg, &dst_sg, derived_keysize,
NULL);
res = crypto_wait_req(crypto_skcipher_encrypt(req), &wait);
out:
skcipher_request_free(req);
crypto_free_skcipher(tfm);
return res;
}
/*
* Search the current task's subscribed keyrings for a "logon" key with
* description prefix:descriptor, and if found acquire a read lock on it and
* return a pointer to its validated payload in *payload_ret.
*/
static struct key *
find_and_lock_process_key(const char *prefix,
const u8 descriptor[FS_KEY_DESCRIPTOR_SIZE],
unsigned int min_keysize,
const struct fscrypt_key **payload_ret)
{
char *description;
struct key *key;
const struct user_key_payload *ukp;
const struct fscrypt_key *payload;
description = kasprintf(GFP_NOFS, "%s%*phN", prefix,
FS_KEY_DESCRIPTOR_SIZE, descriptor);
if (!description)
return ERR_PTR(-ENOMEM);
key = request_key(&key_type_logon, description, NULL);
kfree(description);
if (IS_ERR(key))
return key;
down_read(&key->sem);
ukp = user_key_payload_locked(key);
if (!ukp) /* was the key revoked before we acquired its semaphore? */
goto invalid;
payload = (const struct fscrypt_key *)ukp->data;
if (ukp->datalen != sizeof(struct fscrypt_key) ||
payload->size < 1 || payload->size > FS_MAX_KEY_SIZE) {
fscrypt_warn(NULL,
"key with description '%s' has invalid payload",
key->description);
goto invalid;
}
if (payload->size < min_keysize) {
fscrypt_warn(NULL,
"key with description '%s' is too short (got %u bytes, need %u+ bytes)",
key->description, payload->size, min_keysize);
goto invalid;
}
*payload_ret = payload;
return key;
invalid:
up_read(&key->sem);
key_put(key);
return ERR_PTR(-ENOKEY);
}
static struct fscrypt_mode available_modes[] = {
[FS_ENCRYPTION_MODE_AES_256_XTS] = {
.friendly_name = "AES-256-XTS",
.cipher_str = "xts(aes)",
.keysize = 64,
.ivsize = 16,
},
[FS_ENCRYPTION_MODE_AES_256_CTS] = {
.friendly_name = "AES-256-CTS-CBC",
.cipher_str = "cts(cbc(aes))",
.keysize = 32,
.ivsize = 16,
},
[FS_ENCRYPTION_MODE_AES_128_CBC] = {
.friendly_name = "AES-128-CBC",
.cipher_str = "cbc(aes)",
.keysize = 16,
.ivsize = 16,
.needs_essiv = true,
},
[FS_ENCRYPTION_MODE_AES_128_CTS] = {
.friendly_name = "AES-128-CTS-CBC",
.cipher_str = "cts(cbc(aes))",
.keysize = 16,
.ivsize = 16,
},
[FS_ENCRYPTION_MODE_ADIANTUM] = {
.friendly_name = "Adiantum",
.cipher_str = "adiantum(xchacha12,aes)",
.keysize = 32,
.ivsize = 32,
},
};
static struct fscrypt_mode *
select_encryption_mode(const struct fscrypt_info *ci, const struct inode *inode)
{
if (!fscrypt_valid_enc_modes(ci->ci_data_mode, ci->ci_filename_mode)) {
fscrypt_warn(inode->i_sb,
"inode %lu uses unsupported encryption modes (contents mode %d, filenames mode %d)",
inode->i_ino, ci->ci_data_mode,
ci->ci_filename_mode);
return ERR_PTR(-EINVAL);
}
if (S_ISREG(inode->i_mode))
return &available_modes[ci->ci_data_mode];
if (S_ISDIR(inode->i_mode) || S_ISLNK(inode->i_mode))
return &available_modes[ci->ci_filename_mode];
WARN_ONCE(1, "fscrypt: filesystem tried to load encryption info for inode %lu, which is not encryptable (file type %d)\n",
inode->i_ino, (inode->i_mode & S_IFMT));
return ERR_PTR(-EINVAL);
}
/* Find the master key, then derive the inode's actual encryption key */
static int find_and_derive_key(const struct inode *inode,
const struct fscrypt_context *ctx,
u8 *derived_key, const struct fscrypt_mode *mode)
{
struct key *key;
const struct fscrypt_key *payload;
int err;
key = find_and_lock_process_key(FS_KEY_DESC_PREFIX,
ctx->master_key_descriptor,
mode->keysize, &payload);
if (key == ERR_PTR(-ENOKEY) && inode->i_sb->s_cop->key_prefix) {
key = find_and_lock_process_key(inode->i_sb->s_cop->key_prefix,
ctx->master_key_descriptor,
mode->keysize, &payload);
}
if (IS_ERR(key))
return PTR_ERR(key);
if (ctx->flags & FS_POLICY_FLAG_DIRECT_KEY) {
if (mode->ivsize < offsetofend(union fscrypt_iv, nonce)) {
fscrypt_warn(inode->i_sb,
"direct key mode not allowed with %s",
mode->friendly_name);
err = -EINVAL;
} else if (ctx->contents_encryption_mode !=
ctx->filenames_encryption_mode) {
fscrypt_warn(inode->i_sb,
"direct key mode not allowed with different contents and filenames modes");
err = -EINVAL;
} else {
memcpy(derived_key, payload->raw, mode->keysize);
err = 0;
}
} else {
err = derive_key_aes(payload->raw, ctx, derived_key,
mode->keysize);
}
up_read(&key->sem);
key_put(key);
return err;
}
/* Allocate and key a symmetric cipher object for the given encryption mode */
static struct crypto_skcipher *
allocate_skcipher_for_mode(struct fscrypt_mode *mode, const u8 *raw_key,
const struct inode *inode)
{
struct crypto_skcipher *tfm;
int err;
tfm = crypto_alloc_skcipher(mode->cipher_str, 0, 0);
if (IS_ERR(tfm)) {
fscrypt_warn(inode->i_sb,
"error allocating '%s' transform for inode %lu: %ld",
mode->cipher_str, inode->i_ino, PTR_ERR(tfm));
return tfm;
}
if (unlikely(!mode->logged_impl_name)) {
/*
* fscrypt performance can vary greatly depending on which
* crypto algorithm implementation is used. Help people debug
* performance problems by logging the ->cra_driver_name the
* first time a mode is used. Note that multiple threads can
* race here, but it doesn't really matter.
*/
mode->logged_impl_name = true;
pr_info("fscrypt: %s using implementation \"%s\"\n",
mode->friendly_name,
crypto_skcipher_alg(tfm)->base.cra_driver_name);
}
crypto_skcipher_set_flags(tfm, CRYPTO_TFM_REQ_FORBID_WEAK_KEYS);
err = crypto_skcipher_setkey(tfm, raw_key, mode->keysize);
if (err)
goto err_free_tfm;
return tfm;
err_free_tfm:
crypto_free_skcipher(tfm);
return ERR_PTR(err);
}
/* Master key referenced by FS_POLICY_FLAG_DIRECT_KEY policy */
struct fscrypt_master_key {
struct hlist_node mk_node;
refcount_t mk_refcount;
const struct fscrypt_mode *mk_mode;
struct crypto_skcipher *mk_ctfm;
u8 mk_descriptor[FS_KEY_DESCRIPTOR_SIZE];
u8 mk_raw[FS_MAX_KEY_SIZE];
};
static void free_master_key(struct fscrypt_master_key *mk)
{
if (mk) {
crypto_free_skcipher(mk->mk_ctfm);
kzfree(mk);
}
}
static void put_master_key(struct fscrypt_master_key *mk)
{
if (!refcount_dec_and_lock(&mk->mk_refcount, &fscrypt_master_keys_lock))
return;
hash_del(&mk->mk_node);
spin_unlock(&fscrypt_master_keys_lock);
free_master_key(mk);
}
/*
* Find/insert the given master key into the fscrypt_master_keys table. If
* found, it is returned with elevated refcount, and 'to_insert' is freed if
* non-NULL. If not found, 'to_insert' is inserted and returned if it's
* non-NULL; otherwise NULL is returned.
*/
static struct fscrypt_master_key *
find_or_insert_master_key(struct fscrypt_master_key *to_insert,
const u8 *raw_key, const struct fscrypt_mode *mode,
const struct fscrypt_info *ci)
{
unsigned long hash_key;
struct fscrypt_master_key *mk;
/*
* Careful: to avoid potentially leaking secret key bytes via timing
* information, we must key the hash table by descriptor rather than by
* raw key, and use crypto_memneq() when comparing raw keys.
*/
BUILD_BUG_ON(sizeof(hash_key) > FS_KEY_DESCRIPTOR_SIZE);
memcpy(&hash_key, ci->ci_master_key_descriptor, sizeof(hash_key));
spin_lock(&fscrypt_master_keys_lock);
hash_for_each_possible(fscrypt_master_keys, mk, mk_node, hash_key) {
if (memcmp(ci->ci_master_key_descriptor, mk->mk_descriptor,
FS_KEY_DESCRIPTOR_SIZE) != 0)
continue;
if (mode != mk->mk_mode)
continue;
if (crypto_memneq(raw_key, mk->mk_raw, mode->keysize))
continue;
/* using existing tfm with same (descriptor, mode, raw_key) */
refcount_inc(&mk->mk_refcount);
spin_unlock(&fscrypt_master_keys_lock);
free_master_key(to_insert);
return mk;
}
if (to_insert)
hash_add(fscrypt_master_keys, &to_insert->mk_node, hash_key);
spin_unlock(&fscrypt_master_keys_lock);
return to_insert;
}
/* Prepare to encrypt directly using the master key in the given mode */
static struct fscrypt_master_key *
fscrypt_get_master_key(const struct fscrypt_info *ci, struct fscrypt_mode *mode,
const u8 *raw_key, const struct inode *inode)
{
struct fscrypt_master_key *mk;
int err;
/* Is there already a tfm for this key? */
mk = find_or_insert_master_key(NULL, raw_key, mode, ci);
if (mk)
return mk;
/* Nope, allocate one. */
mk = kzalloc(sizeof(*mk), GFP_NOFS);
if (!mk)
return ERR_PTR(-ENOMEM);
refcount_set(&mk->mk_refcount, 1);
mk->mk_mode = mode;
mk->mk_ctfm = allocate_skcipher_for_mode(mode, raw_key, inode);
if (IS_ERR(mk->mk_ctfm)) {
err = PTR_ERR(mk->mk_ctfm);
mk->mk_ctfm = NULL;
goto err_free_mk;
}
memcpy(mk->mk_descriptor, ci->ci_master_key_descriptor,
FS_KEY_DESCRIPTOR_SIZE);
memcpy(mk->mk_raw, raw_key, mode->keysize);
return find_or_insert_master_key(mk, raw_key, mode, ci);
err_free_mk:
free_master_key(mk);
return ERR_PTR(err);
}
static int derive_essiv_salt(const u8 *key, int keysize, u8 *salt)
{
struct crypto_shash *tfm = READ_ONCE(essiv_hash_tfm);
/* init hash transform on demand */
if (unlikely(!tfm)) {
struct crypto_shash *prev_tfm;
tfm = crypto_alloc_shash("sha256", 0, 0);
if (IS_ERR(tfm)) {
fscrypt_warn(NULL,
"error allocating SHA-256 transform: %ld",
PTR_ERR(tfm));
return PTR_ERR(tfm);
}
prev_tfm = cmpxchg(&essiv_hash_tfm, NULL, tfm);
if (prev_tfm) {
crypto_free_shash(tfm);
tfm = prev_tfm;
}
}
{
SHASH_DESC_ON_STACK(desc, tfm);
desc->tfm = tfm;
return crypto_shash_digest(desc, key, keysize, salt);
}
}
static int init_essiv_generator(struct fscrypt_info *ci, const u8 *raw_key,
int keysize)
{
int err;
struct crypto_cipher *essiv_tfm;
u8 salt[SHA256_DIGEST_SIZE];
essiv_tfm = crypto_alloc_cipher("aes", 0, 0);
if (IS_ERR(essiv_tfm))
return PTR_ERR(essiv_tfm);
ci->ci_essiv_tfm = essiv_tfm;
err = derive_essiv_salt(raw_key, keysize, salt);
if (err)
goto out;
/*
* Using SHA256 to derive the salt/key will result in AES-256 being
* used for IV generation. File contents encryption will still use the
* configured keysize (AES-128) nevertheless.
*/
err = crypto_cipher_setkey(essiv_tfm, salt, sizeof(salt));
if (err)
goto out;
out:
memzero_explicit(salt, sizeof(salt));
return err;
}
void __exit fscrypt_essiv_cleanup(void)
{
crypto_free_shash(essiv_hash_tfm);
}
/*
* Given the encryption mode and key (normally the derived key, but for
* FS_POLICY_FLAG_DIRECT_KEY mode it's the master key), set up the inode's
* symmetric cipher transform object(s).
*/
static int setup_crypto_transform(struct fscrypt_info *ci,
struct fscrypt_mode *mode,
const u8 *raw_key, const struct inode *inode)
{
struct fscrypt_master_key *mk;
struct crypto_skcipher *ctfm;
int err;
if (ci->ci_flags & FS_POLICY_FLAG_DIRECT_KEY) {
mk = fscrypt_get_master_key(ci, mode, raw_key, inode);
if (IS_ERR(mk))
return PTR_ERR(mk);
ctfm = mk->mk_ctfm;
} else {
mk = NULL;
ctfm = allocate_skcipher_for_mode(mode, raw_key, inode);
if (IS_ERR(ctfm))
return PTR_ERR(ctfm);
}
ci->ci_master_key = mk;
ci->ci_ctfm = ctfm;
if (mode->needs_essiv) {
/* ESSIV implies 16-byte IVs which implies !DIRECT_KEY */
WARN_ON(mode->ivsize != AES_BLOCK_SIZE);
WARN_ON(ci->ci_flags & FS_POLICY_FLAG_DIRECT_KEY);
err = init_essiv_generator(ci, raw_key, mode->keysize);
if (err) {
fscrypt_warn(inode->i_sb,
"error initializing ESSIV generator for inode %lu: %d",
inode->i_ino, err);
return err;
}
}
return 0;
}
static void put_crypt_info(struct fscrypt_info *ci)
{
if (!ci)
return;
if (ci->ci_master_key) {
put_master_key(ci->ci_master_key);
} else {
crypto_free_skcipher(ci->ci_ctfm);
crypto_free_cipher(ci->ci_essiv_tfm);
}
kmem_cache_free(fscrypt_info_cachep, ci);
}
int fscrypt_get_encryption_info(struct inode *inode)
{
struct fscrypt_info *crypt_info;
struct fscrypt_context ctx;
struct fscrypt_mode *mode;
u8 *raw_key = NULL;
int res;
if (fscrypt_has_encryption_key(inode))
return 0;
res = fscrypt_initialize(inode->i_sb->s_cop->flags);
if (res)
return res;
res = inode->i_sb->s_cop->get_context(inode, &ctx, sizeof(ctx));
if (res < 0) {
if (!fscrypt_dummy_context_enabled(inode) ||
IS_ENCRYPTED(inode))
return res;
/* Fake up a context for an unencrypted directory */
memset(&ctx, 0, sizeof(ctx));
ctx.format = FS_ENCRYPTION_CONTEXT_FORMAT_V1;
ctx.contents_encryption_mode = FS_ENCRYPTION_MODE_AES_256_XTS;
ctx.filenames_encryption_mode = FS_ENCRYPTION_MODE_AES_256_CTS;
memset(ctx.master_key_descriptor, 0x42, FS_KEY_DESCRIPTOR_SIZE);
} else if (res != sizeof(ctx)) {
return -EINVAL;
}
if (ctx.format != FS_ENCRYPTION_CONTEXT_FORMAT_V1)
return -EINVAL;
if (ctx.flags & ~FS_POLICY_FLAGS_VALID)
return -EINVAL;
crypt_info = kmem_cache_zalloc(fscrypt_info_cachep, GFP_NOFS);
if (!crypt_info)
return -ENOMEM;
crypt_info->ci_flags = ctx.flags;
crypt_info->ci_data_mode = ctx.contents_encryption_mode;
crypt_info->ci_filename_mode = ctx.filenames_encryption_mode;
memcpy(crypt_info->ci_master_key_descriptor, ctx.master_key_descriptor,
FS_KEY_DESCRIPTOR_SIZE);
memcpy(crypt_info->ci_nonce, ctx.nonce, FS_KEY_DERIVATION_NONCE_SIZE);
mode = select_encryption_mode(crypt_info, inode);
if (IS_ERR(mode)) {
res = PTR_ERR(mode);
goto out;
}
WARN_ON(mode->ivsize > FSCRYPT_MAX_IV_SIZE);
crypt_info->ci_mode = mode;
/*
* This cannot be a stack buffer because it may be passed to the
* scatterlist crypto API as part of key derivation.
*/
res = -ENOMEM;
raw_key = kmalloc(mode->keysize, GFP_NOFS);
if (!raw_key)
goto out;
res = find_and_derive_key(inode, &ctx, raw_key, mode);
if (res)
goto out;
res = setup_crypto_transform(crypt_info, mode, raw_key, inode);
if (res)
goto out;
if (cmpxchg_release(&inode->i_crypt_info, NULL, crypt_info) == NULL)
crypt_info = NULL;
out:
if (res == -ENOKEY)
res = 0;
put_crypt_info(crypt_info);
kzfree(raw_key);
return res;
}
EXPORT_SYMBOL(fscrypt_get_encryption_info);
/**
* fscrypt_put_encryption_info - free most of an inode's fscrypt data
*
* Free the inode's fscrypt_info. Filesystems must call this when the inode is
* being evicted. An RCU grace period need not have elapsed yet.
*/
void fscrypt_put_encryption_info(struct inode *inode)
{
put_crypt_info(inode->i_crypt_info);
inode->i_crypt_info = NULL;
}
EXPORT_SYMBOL(fscrypt_put_encryption_info);
/**
* fscrypt_free_inode - free an inode's fscrypt data requiring RCU delay
*
* Free the inode's cached decrypted symlink target, if any. Filesystems must
* call this after an RCU grace period, just before they free the inode.
*/
void fscrypt_free_inode(struct inode *inode)
{
if (IS_ENCRYPTED(inode) && S_ISLNK(inode->i_mode)) {
kfree(inode->i_link);
inode->i_link = NULL;
}
}
EXPORT_SYMBOL(fscrypt_free_inode);
|