fs/ubifs/auth.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * This file is part of UBIFS.
   4  *
   5  * Copyright (C) 2018 Pengutronix, Sascha Hauer <s.hauer@pengutronix.de>
   6  */
   7
   8 /*
   9  * This file implements various helper functions for UBIFS authentication support
  10  */
  11
  12 #include <linux/crypto.h>
  13 #include <crypto/hash.h>
  14 #include <crypto/sha.h>
  15 #include <crypto/algapi.h>
  16 #include <keys/user-type.h>
  17
  18 #include "ubifs.h"
  19
  20 /**
  21  * ubifs_node_calc_hash - calculate the hash of a UBIFS node
  22  * @c: UBIFS file-system description object
  23  * @node: the node to calculate a hash for
  24  * @hash: the returned hash
  25  *
  26  * Returns 0 for success or a negative error code otherwise.
  27  */
  28 int __ubifs_node_calc_hash(const struct ubifs_info *c, const void *node,
  29                             u8 *hash)
  30 {
  31         const struct ubifs_ch *ch = node;
  32         SHASH_DESC_ON_STACK(shash, c->hash_tfm);
  33         int err;
  34
  35         shash->tfm = c->hash_tfm;
  36
  37         err = crypto_shash_digest(shash, node, le32_to_cpu(ch->len), hash);
  38         if (err < 0)
  39                 return err;
  40         return 0;
  41 }
  42
  43 /**
  44  * ubifs_hash_calc_hmac - calculate a HMAC from a hash
  45  * @c: UBIFS file-system description object
  46  * @hash: the node to calculate a HMAC for
  47  * @hmac: the returned HMAC
  48  *
  49  * Returns 0 for success or a negative error code otherwise.
  50  */
  51 static int ubifs_hash_calc_hmac(const struct ubifs_info *c, const u8 *hash,
  52                                  u8 *hmac)
  53 {
  54         SHASH_DESC_ON_STACK(shash, c->hmac_tfm);
  55         int err;
  56
  57         shash->tfm = c->hmac_tfm;
  58
  59         err = crypto_shash_digest(shash, hash, c->hash_len, hmac);
  60         if (err < 0)
  61                 return err;
  62         return 0;
  63 }
  64
  65 /**
  66  * ubifs_prepare_auth_node - Prepare an authentication node
  67  * @c: UBIFS file-system description object
  68  * @node: the node to calculate a hash for
  69  * @hash: input hash of previous nodes
  70  *
  71  * This function prepares an authentication node for writing onto flash.
  72  * It creates a HMAC from the given input hash and writes it to the node.
  73  *
  74  * Returns 0 for success or a negative error code otherwise.
  75  */
  76 int ubifs_prepare_auth_node(struct ubifs_info *c, void *node,
  77                              struct shash_desc *inhash)
  78 {
  79         SHASH_DESC_ON_STACK(hash_desc, c->hash_tfm);
  80         struct ubifs_auth_node *auth = node;
  81         u8 *hash;
  82         int err;
  83
  84         hash = kmalloc(crypto_shash_descsize(c->hash_tfm), GFP_NOFS);
  85         if (!hash)
  86                 return -ENOMEM;
  87
  88         hash_desc->tfm = c->hash_tfm;
  89         ubifs_shash_copy_state(c, inhash, hash_desc);
  90
  91         err = crypto_shash_final(hash_desc, hash);
  92         if (err)
  93                 goto out;
  94
  95         err = ubifs_hash_calc_hmac(c, hash, auth->hmac);
  96         if (err)
  97                 goto out;
  98
  99         auth->ch.node_type = UBIFS_AUTH_NODE;
 100         ubifs_prepare_node(c, auth, ubifs_auth_node_sz(c), 0);
 101
 102         err = 0;
 103 out:
 104         kfree(hash);
 105
 106         return err;
 107 }
 108
 109 static struct shash_desc *ubifs_get_desc(const struct ubifs_info *c,
 110                                          struct crypto_shash *tfm)
 111 {
 112         struct shash_desc *desc;
 113         int err;
 114
 115         if (!ubifs_authenticated(c))
 116                 return NULL;
 117
 118         desc = kmalloc(sizeof(*desc) + crypto_shash_descsize(tfm), GFP_KERNEL);
 119         if (!desc)
 120                 return ERR_PTR(-ENOMEM);
 121
 122         desc->tfm = tfm;
 123
 124         err = crypto_shash_init(desc);
 125         if (err) {
 126                 kfree(desc);
 127                 return ERR_PTR(err);
 128         }
 129
 130         return desc;
 131 }
 132
 133 /**
 134  * __ubifs_hash_get_desc - get a descriptor suitable for hashing a node
 135  * @c: UBIFS file-system description object
 136  *
 137  * This function returns a descriptor suitable for hashing a node. Free after use
 138  * with kfree.
 139  */
 140 struct shash_desc *__ubifs_hash_get_desc(const struct ubifs_info *c)
 141 {
 142         return ubifs_get_desc(c, c->hash_tfm);
 143 }
 144
 145 /**
 146  * __ubifs_shash_final - finalize shash
 147  * @c: UBIFS file-system description object
 148  * @desc: the descriptor
 149  * @out: the output hash
 150  *
 151  * Simple wrapper around crypto_shash_final(), safe to be called with
 152  * disabled authentication.
 153  */
 154 int __ubifs_shash_final(const struct ubifs_info *c, struct shash_desc *desc,
 155                         u8 *out)
 156 {
 157         if (ubifs_authenticated(c))
 158                 return crypto_shash_final(desc, out);
 159
 160         return 0;
 161 }
 162
 163 /**
 164  * ubifs_bad_hash - Report hash mismatches
 165  * @c: UBIFS file-system description object
 166  * @node: the node
 167  * @hash: the expected hash
 168  * @lnum: the LEB @node was read from
 169  * @offs: offset in LEB @node was read from
 170  *
 171  * This function reports a hash mismatch when a node has a different hash than
 172  * expected.
 173  */
 174 void ubifs_bad_hash(const struct ubifs_info *c, const void *node, const u8 *hash,
 175                     int lnum, int offs)
 176 {
 177         int len = min(c->hash_len, 20);
 178         int cropped = len != c->hash_len;
 179         const char *cont = cropped ? "..." : "";
 180
 181         u8 calc[UBIFS_HASH_ARR_SZ];
 182
 183         __ubifs_node_calc_hash(c, node, calc);
 184
 185         ubifs_err(c, "hash mismatch on node at LEB %d:%d", lnum, offs);
 186         ubifs_err(c, "hash expected:   %*ph%s", len, hash, cont);
 187         ubifs_err(c, "hash calculated: %*ph%s", len, calc, cont);
 188 }
 189
 190 /**
 191  * __ubifs_node_check_hash - check the hash of a node against given hash
 192  * @c: UBIFS file-system description object
 193  * @node: the node
 194  * @expected: the expected hash
 195  *
 196  * This function calculates a hash over a node and compares it to the given hash.
 197  * Returns 0 if both hashes are equal or authentication is disabled, otherwise a
 198  * negative error code is returned.
 199  */
 200 int __ubifs_node_check_hash(const struct ubifs_info *c, const void *node,
 201                             const u8 *expected)
 202 {
 203         u8 calc[UBIFS_HASH_ARR_SZ];
 204         int err;
 205
 206         err = __ubifs_node_calc_hash(c, node, calc);
 207         if (err)
 208                 return err;
 209
 210         if (ubifs_check_hash(c, expected, calc))
 211                 return -EPERM;
 212
 213         return 0;
 214 }
 215
 216 /**
 217  * ubifs_init_authentication - initialize UBIFS authentication support
 218  * @c: UBIFS file-system description object
 219  *
 220  * This function returns 0 for success or a negative error code otherwise.
 221  */
 222 int ubifs_init_authentication(struct ubifs_info *c)
 223 {
 224         struct key *keyring_key;
 225         const struct user_key_payload *ukp;
 226         int err;
 227         char hmac_name[CRYPTO_MAX_ALG_NAME];
 228
 229         if (!c->auth_hash_name) {
 230                 ubifs_err(c, "authentication hash name needed with authentication");
 231                 return -EINVAL;
 232         }
 233
 234         c->auth_hash_algo = match_string(hash_algo_name, HASH_ALGO__LAST,
 235                                          c->auth_hash_name);
 236         if ((int)c->auth_hash_algo < 0) {
 237                 ubifs_err(c, "Unknown hash algo %s specified",
 238                           c->auth_hash_name);
 239                 return -EINVAL;
 240         }
 241
 242         snprintf(hmac_name, CRYPTO_MAX_ALG_NAME, "hmac(%s)",
 243                  c->auth_hash_name);
 244
 245         keyring_key = request_key(&key_type_logon, c->auth_key_name, NULL);
 246
 247         if (IS_ERR(keyring_key)) {
 248                 ubifs_err(c, "Failed to request key: %ld",
 249                           PTR_ERR(keyring_key));
 250                 return PTR_ERR(keyring_key);
 251         }
 252
 253         down_read(&keyring_key->sem);
 254
 255         if (keyring_key->type != &key_type_logon) {
 256                 ubifs_err(c, "key type must be logon");
 257                 err = -ENOKEY;
 258                 goto out;
 259         }
 260
 261         ukp = user_key_payload_locked(keyring_key);
 262         if (!ukp) {
 263                 /* key was revoked before we acquired its semaphore */
 264                 err = -EKEYREVOKED;
 265                 goto out;
 266         }
 267
 268         c->hash_tfm = crypto_alloc_shash(c->auth_hash_name, 0, 0);
 269         if (IS_ERR(c->hash_tfm)) {
 270                 err = PTR_ERR(c->hash_tfm);
 271                 ubifs_err(c, "Can not allocate %s: %d",
 272                           c->auth_hash_name, err);
 273                 goto out;
 274         }
 275
 276         c->hash_len = crypto_shash_digestsize(c->hash_tfm);
 277         if (c->hash_len > UBIFS_HASH_ARR_SZ) {
 278                 ubifs_err(c, "hash %s is bigger than maximum allowed hash size (%d > %d)",
 279                           c->auth_hash_name, c->hash_len, UBIFS_HASH_ARR_SZ);
 280                 err = -EINVAL;
 281                 goto out_free_hash;
 282         }
 283
 284         c->hmac_tfm = crypto_alloc_shash(hmac_name, 0, 0);
 285         if (IS_ERR(c->hmac_tfm)) {
 286                 err = PTR_ERR(c->hmac_tfm);
 287                 ubifs_err(c, "Can not allocate %s: %d", hmac_name, err);
 288                 goto out_free_hash;
 289         }
 290
 291         c->hmac_desc_len = crypto_shash_digestsize(c->hmac_tfm);
 292         if (c->hmac_desc_len > UBIFS_HMAC_ARR_SZ) {
 293                 ubifs_err(c, "hmac %s is bigger than maximum allowed hmac size (%d > %d)",
 294                           hmac_name, c->hmac_desc_len, UBIFS_HMAC_ARR_SZ);
 295                 err = -EINVAL;
 296                 goto out_free_hash;
 297         }
 298
 299         err = crypto_shash_setkey(c->hmac_tfm, ukp->data, ukp->datalen);
 300         if (err)
 301                 goto out_free_hmac;
 302
 303         c->authenticated = true;
 304
 305         c->log_hash = ubifs_hash_get_desc(c);
 306         if (IS_ERR(c->log_hash))
 307                 goto out_free_hmac;
 308
 309         err = 0;
 310
 311 out_free_hmac:
 312         if (err)
 313                 crypto_free_shash(c->hmac_tfm);
 314 out_free_hash:
 315         if (err)
 316                 crypto_free_shash(c->hash_tfm);
 317 out:
 318         up_read(&keyring_key->sem);
 319         key_put(keyring_key);
 320
 321         return err;
 322 }
 323
 324 /**
 325  * __ubifs_exit_authentication - release resource
 326  * @c: UBIFS file-system description object
 327  *
 328  * This function releases the authentication related resources.
 329  */
 330 void __ubifs_exit_authentication(struct ubifs_info *c)
 331 {
 332         if (!ubifs_authenticated(c))
 333                 return;
 334
 335         crypto_free_shash(c->hmac_tfm);
 336         crypto_free_shash(c->hash_tfm);
 337         kfree(c->log_hash);
 338 }
 339
 340 /**
 341  * ubifs_node_calc_hmac - calculate the HMAC of a UBIFS node
 342  * @c: UBIFS file-system description object
 343  * @node: the node to insert a HMAC into.
 344  * @len: the length of the node
 345  * @ofs_hmac: the offset in the node where the HMAC is inserted
 346  * @hmac: returned HMAC
 347  *
 348  * This function calculates a HMAC of a UBIFS node. The HMAC is expected to be
 349  * embedded into the node, so this area is not covered by the HMAC. Also not
 350  * covered is the UBIFS_NODE_MAGIC and the CRC of the node.
 351  */
 352 static int ubifs_node_calc_hmac(const struct ubifs_info *c, const void *node,
 353                                 int len, int ofs_hmac, void *hmac)
 354 {
 355         SHASH_DESC_ON_STACK(shash, c->hmac_tfm);
 356         int hmac_len = c->hmac_desc_len;
 357         int err;
 358
 359         ubifs_assert(c, ofs_hmac > 8);
 360         ubifs_assert(c, ofs_hmac + hmac_len < len);
 361
 362         shash->tfm = c->hmac_tfm;
 363
 364         err = crypto_shash_init(shash);
 365         if (err)
 366                 return err;
 367
 368         /* behind common node header CRC up to HMAC begin */
 369         err = crypto_shash_update(shash, node + 8, ofs_hmac - 8);
 370         if (err < 0)
 371                 return err;
 372
 373         /* behind HMAC, if any */
 374         if (len - ofs_hmac - hmac_len > 0) {
 375                 err = crypto_shash_update(shash, node + ofs_hmac + hmac_len,
 376                             len - ofs_hmac - hmac_len);
 377                 if (err < 0)
 378                         return err;
 379         }
 380
 381         return crypto_shash_final(shash, hmac);
 382 }
 383
 384 /**
 385  * __ubifs_node_insert_hmac - insert a HMAC into a UBIFS node
 386  * @c: UBIFS file-system description object
 387  * @node: the node to insert a HMAC into.
 388  * @len: the length of the node
 389  * @ofs_hmac: the offset in the node where the HMAC is inserted
 390  *
 391  * This function inserts a HMAC at offset @ofs_hmac into the node given in
 392  * @node.
 393  *
 394  * This function returns 0 for success or a negative error code otherwise.
 395  */
 396 int __ubifs_node_insert_hmac(const struct ubifs_info *c, void *node, int len,
 397                             int ofs_hmac)
 398 {
 399         return ubifs_node_calc_hmac(c, node, len, ofs_hmac, node + ofs_hmac);
 400 }
 401
 402 /**
 403  * __ubifs_node_verify_hmac - verify the HMAC of UBIFS node
 404  * @c: UBIFS file-system description object
 405  * @node: the node to insert a HMAC into.
 406  * @len: the length of the node
 407  * @ofs_hmac: the offset in the node where the HMAC is inserted
 408  *
 409  * This function verifies the HMAC at offset @ofs_hmac of the node given in
 410  * @node. Returns 0 if successful or a negative error code otherwise.
 411  */
 412 int __ubifs_node_verify_hmac(const struct ubifs_info *c, const void *node,
 413                              int len, int ofs_hmac)
 414 {
 415         int hmac_len = c->hmac_desc_len;
 416         u8 *hmac;
 417         int err;
 418
 419         hmac = kmalloc(hmac_len, GFP_NOFS);
 420         if (!hmac)
 421                 return -ENOMEM;
 422
 423         err = ubifs_node_calc_hmac(c, node, len, ofs_hmac, hmac);
 424         if (err)
 425                 return err;
 426
 427         err = crypto_memneq(hmac, node + ofs_hmac, hmac_len);
 428
 429         kfree(hmac);
 430
 431         if (!err)
 432                 return 0;
 433
 434         return -EPERM;
 435 }
 436
 437 int __ubifs_shash_copy_state(const struct ubifs_info *c, struct shash_desc *src,
 438                              struct shash_desc *target)
 439 {
 440         u8 *state;
 441         int err;
 442
 443         state = kmalloc(crypto_shash_descsize(src->tfm), GFP_NOFS);
 444         if (!state)
 445                 return -ENOMEM;
 446
 447         err = crypto_shash_export(src, state);
 448         if (err)
 449                 goto out;
 450
 451         err = crypto_shash_import(target, state);
 452
 453 out:
 454         kfree(state);
 455
 456         return err;
 457 }
 458
 459 /**
 460  * ubifs_hmac_wkm - Create a HMAC of the well known message
 461  * @c: UBIFS file-system description object
 462  * @hmac: The HMAC of the well known message
 463  *
 464  * This function creates a HMAC of a well known message. This is used
 465  * to check if the provided key is suitable to authenticate a UBIFS
 466  * image. This is only a convenience to the user to provide a better
 467  * error message when the wrong key is provided.
 468  *
 469  * This function returns 0 for success or a negative error code otherwise.
 470  */
 471 int ubifs_hmac_wkm(struct ubifs_info *c, u8 *hmac)
 472 {
 473         SHASH_DESC_ON_STACK(shash, c->hmac_tfm);
 474         int err;
 475         const char well_known_message[] = "UBIFS";
 476
 477         if (!ubifs_authenticated(c))
 478                 return 0;
 479
 480         shash->tfm = c->hmac_tfm;
 481
 482         err = crypto_shash_init(shash);
 483         if (err)
 484                 return err;
 485
 486         err = crypto_shash_update(shash, well_known_message,
 487                                   sizeof(well_known_message) - 1);
 488         if (err < 0)
 489                 return err;
 490
 491         err = crypto_shash_final(shash, hmac);
 492         if (err)
 493                 return err;
 494         return 0;
 495 }