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         shash->flags = CRYPTO_TFM_REQ_MAY_SLEEP;
  37
  38         err = crypto_shash_digest(shash, node, le32_to_cpu(ch->len), hash);
  39         if (err < 0)
  40                 return err;
  41         return 0;
  42 }
  43
  44 /**
  45  * ubifs_hash_calc_hmac - calculate a HMAC from a hash
  46  * @c: UBIFS file-system description object
  47  * @hash: the node to calculate a HMAC for
  48  * @hmac: the returned HMAC
  49  *
  50  * Returns 0 for success or a negative error code otherwise.
  51  */
  52 static int ubifs_hash_calc_hmac(const struct ubifs_info *c, const u8 *hash,
  53                                  u8 *hmac)
  54 {
  55         SHASH_DESC_ON_STACK(shash, c->hmac_tfm);
  56         int err;
  57
  58         shash->tfm = c->hmac_tfm;
  59         shash->flags = CRYPTO_TFM_REQ_MAY_SLEEP;
  60
  61         err = crypto_shash_digest(shash, hash, c->hash_len, hmac);
  62         if (err < 0)
  63                 return err;
  64         return 0;
  65 }
  66
  67 /**
  68  * ubifs_prepare_auth_node - Prepare an authentication node
  69  * @c: UBIFS file-system description object
  70  * @node: the node to calculate a hash for
  71  * @hash: input hash of previous nodes
  72  *
  73  * This function prepares an authentication node for writing onto flash.
  74  * It creates a HMAC from the given input hash and writes it to the node.
  75  *
  76  * Returns 0 for success or a negative error code otherwise.
  77  */
  78 int ubifs_prepare_auth_node(struct ubifs_info *c, void *node,
  79                              struct shash_desc *inhash)
  80 {
  81         SHASH_DESC_ON_STACK(hash_desc, c->hash_tfm);
  82         struct ubifs_auth_node *auth = node;
  83         u8 *hash;
  84         int err;
  85
  86         hash = kmalloc(crypto_shash_descsize(c->hash_tfm), GFP_NOFS);
  87         if (!hash)
  88                 return -ENOMEM;
  89
  90         hash_desc->tfm = c->hash_tfm;
  91         hash_desc->flags = CRYPTO_TFM_REQ_MAY_SLEEP;
  92         ubifs_shash_copy_state(c, inhash, hash_desc);
  93
  94         err = crypto_shash_final(hash_desc, hash);
  95         if (err)
  96                 goto out;
  97
  98         err = ubifs_hash_calc_hmac(c, hash, auth->hmac);
  99         if (err)
 100                 goto out;
 101
 102         auth->ch.node_type = UBIFS_AUTH_NODE;
 103         ubifs_prepare_node(c, auth, ubifs_auth_node_sz(c), 0);
 104
 105         err = 0;
 106 out:
 107         kfree(hash);
 108
 109         return err;
 110 }
 111
 112 static struct shash_desc *ubifs_get_desc(const struct ubifs_info *c,
 113                                          struct crypto_shash *tfm)
 114 {
 115         struct shash_desc *desc;
 116         int err;
 117
 118         if (!ubifs_authenticated(c))
 119                 return NULL;
 120
 121         desc = kmalloc(sizeof(*desc) + crypto_shash_descsize(tfm), GFP_KERNEL);
 122         if (!desc)
 123                 return ERR_PTR(-ENOMEM);
 124
 125         desc->tfm = tfm;
 126         desc->flags = CRYPTO_TFM_REQ_MAY_SLEEP;
 127
 128         err = crypto_shash_init(desc);
 129         if (err) {
 130                 kfree(desc);
 131                 return ERR_PTR(err);
 132         }
 133
 134         return desc;
 135 }
 136
 137 /**
 138  * __ubifs_hash_get_desc - get a descriptor suitable for hashing a node
 139  * @c: UBIFS file-system description object
 140  *
 141  * This function returns a descriptor suitable for hashing a node. Free after use
 142  * with kfree.
 143  */
 144 struct shash_desc *__ubifs_hash_get_desc(const struct ubifs_info *c)
 145 {
 146         return ubifs_get_desc(c, c->hash_tfm);
 147 }
 148
 149 /**
 150  * __ubifs_shash_final - finalize shash
 151  * @c: UBIFS file-system description object
 152  * @desc: the descriptor
 153  * @out: the output hash
 154  *
 155  * Simple wrapper around crypto_shash_final(), safe to be called with
 156  * disabled authentication.
 157  */
 158 int __ubifs_shash_final(const struct ubifs_info *c, struct shash_desc *desc,
 159                         u8 *out)
 160 {
 161         if (ubifs_authenticated(c))
 162                 return crypto_shash_final(desc, out);
 163
 164         return 0;
 165 }
 166
 167 /**
 168  * ubifs_bad_hash - Report hash mismatches
 169  * @c: UBIFS file-system description object
 170  * @node: the node
 171  * @hash: the expected hash
 172  * @lnum: the LEB @node was read from
 173  * @offs: offset in LEB @node was read from
 174  *
 175  * This function reports a hash mismatch when a node has a different hash than
 176  * expected.
 177  */
 178 void ubifs_bad_hash(const struct ubifs_info *c, const void *node, const u8 *hash,
 179                     int lnum, int offs)
 180 {
 181         int len = min(c->hash_len, 20);
 182         int cropped = len != c->hash_len;
 183         const char *cont = cropped ? "..." : "";
 184
 185         u8 calc[UBIFS_HASH_ARR_SZ];
 186
 187         __ubifs_node_calc_hash(c, node, calc);
 188
 189         ubifs_err(c, "hash mismatch on node at LEB %d:%d", lnum, offs);
 190         ubifs_err(c, "hash expected:   %*ph%s", len, hash, cont);
 191         ubifs_err(c, "hash calculated: %*ph%s", len, calc, cont);
 192 }
 193
 194 /**
 195  * __ubifs_node_check_hash - check the hash of a node against given hash
 196  * @c: UBIFS file-system description object
 197  * @node: the node
 198  * @expected: the expected hash
 199  *
 200  * This function calculates a hash over a node and compares it to the given hash.
 201  * Returns 0 if both hashes are equal or authentication is disabled, otherwise a
 202  * negative error code is returned.
 203  */
 204 int __ubifs_node_check_hash(const struct ubifs_info *c, const void *node,
 205                             const u8 *expected)
 206 {
 207         u8 calc[UBIFS_HASH_ARR_SZ];
 208         int err;
 209
 210         err = __ubifs_node_calc_hash(c, node, calc);
 211         if (err)
 212                 return err;
 213
 214         if (ubifs_check_hash(c, expected, calc))
 215                 return -EPERM;
 216
 217         return 0;
 218 }
 219
 220 /**
 221  * ubifs_init_authentication - initialize UBIFS authentication support
 222  * @c: UBIFS file-system description object
 223  *
 224  * This function returns 0 for success or a negative error code otherwise.
 225  */
 226 int ubifs_init_authentication(struct ubifs_info *c)
 227 {
 228         struct key *keyring_key;
 229         const struct user_key_payload *ukp;
 230         int err;
 231         char hmac_name[CRYPTO_MAX_ALG_NAME];
 232
 233         if (!c->auth_hash_name) {
 234                 ubifs_err(c, "authentication hash name needed with authentication");
 235                 return -EINVAL;
 236         }
 237
 238         c->auth_hash_algo = match_string(hash_algo_name, HASH_ALGO__LAST,
 239                                          c->auth_hash_name);
 240         if ((int)c->auth_hash_algo < 0) {
 241                 ubifs_err(c, "Unknown hash algo %s specified",
 242                           c->auth_hash_name);
 243                 return -EINVAL;
 244         }
 245
 246         snprintf(hmac_name, CRYPTO_MAX_ALG_NAME, "hmac(%s)",
 247                  c->auth_hash_name);
 248
 249         keyring_key = request_key(&key_type_logon, c->auth_key_name, NULL);
 250
 251         if (IS_ERR(keyring_key)) {
 252                 ubifs_err(c, "Failed to request key: %ld",
 253                           PTR_ERR(keyring_key));
 254                 return PTR_ERR(keyring_key);
 255         }
 256
 257         down_read(&keyring_key->sem);
 258
 259         if (keyring_key->type != &key_type_logon) {
 260                 ubifs_err(c, "key type must be logon");
 261                 err = -ENOKEY;
 262                 goto out;
 263         }
 264
 265         ukp = user_key_payload_locked(keyring_key);
 266         if (!ukp) {
 267                 /* key was revoked before we acquired its semaphore */
 268                 err = -EKEYREVOKED;
 269                 goto out;
 270         }
 271
 272         c->hash_tfm = crypto_alloc_shash(c->auth_hash_name, 0,
 273                                          CRYPTO_ALG_ASYNC);
 274         if (IS_ERR(c->hash_tfm)) {
 275                 err = PTR_ERR(c->hash_tfm);
 276                 ubifs_err(c, "Can not allocate %s: %d",
 277                           c->auth_hash_name, err);
 278                 goto out;
 279         }
 280
 281         c->hash_len = crypto_shash_digestsize(c->hash_tfm);
 282         if (c->hash_len > UBIFS_HASH_ARR_SZ) {
 283                 ubifs_err(c, "hash %s is bigger than maximum allowed hash size (%d > %d)",
 284                           c->auth_hash_name, c->hash_len, UBIFS_HASH_ARR_SZ);
 285                 err = -EINVAL;
 286                 goto out_free_hash;
 287         }
 288
 289         c->hmac_tfm = crypto_alloc_shash(hmac_name, 0, CRYPTO_ALG_ASYNC);
 290         if (IS_ERR(c->hmac_tfm)) {
 291                 err = PTR_ERR(c->hmac_tfm);
 292                 ubifs_err(c, "Can not allocate %s: %d", hmac_name, err);
 293                 goto out_free_hash;
 294         }
 295
 296         c->hmac_desc_len = crypto_shash_digestsize(c->hmac_tfm);
 297         if (c->hmac_desc_len > UBIFS_HMAC_ARR_SZ) {
 298                 ubifs_err(c, "hmac %s is bigger than maximum allowed hmac size (%d > %d)",
 299                           hmac_name, c->hmac_desc_len, UBIFS_HMAC_ARR_SZ);
 300                 err = -EINVAL;
 301                 goto out_free_hash;
 302         }
 303
 304         err = crypto_shash_setkey(c->hmac_tfm, ukp->data, ukp->datalen);
 305         if (err)
 306                 goto out_free_hmac;
 307
 308         c->authenticated = true;
 309
 310         c->log_hash = ubifs_hash_get_desc(c);
 311         if (IS_ERR(c->log_hash))
 312                 goto out_free_hmac;
 313
 314         err = 0;
 315
 316 out_free_hmac:
 317         if (err)
 318                 crypto_free_shash(c->hmac_tfm);
 319 out_free_hash:
 320         if (err)
 321                 crypto_free_shash(c->hash_tfm);
 322 out:
 323         up_read(&keyring_key->sem);
 324         key_put(keyring_key);
 325
 326         return err;
 327 }
 328
 329 /**
 330  * __ubifs_exit_authentication - release resource
 331  * @c: UBIFS file-system description object
 332  *
 333  * This function releases the authentication related resources.
 334  */
 335 void __ubifs_exit_authentication(struct ubifs_info *c)
 336 {
 337         if (!ubifs_authenticated(c))
 338                 return;
 339
 340         crypto_free_shash(c->hmac_tfm);
 341         crypto_free_shash(c->hash_tfm);
 342         kfree(c->log_hash);
 343 }
 344
 345 /**
 346  * ubifs_node_calc_hmac - calculate the HMAC of a UBIFS node
 347  * @c: UBIFS file-system description object
 348  * @node: the node to insert a HMAC into.
 349  * @len: the length of the node
 350  * @ofs_hmac: the offset in the node where the HMAC is inserted
 351  * @hmac: returned HMAC
 352  *
 353  * This function calculates a HMAC of a UBIFS node. The HMAC is expected to be
 354  * embedded into the node, so this area is not covered by the HMAC. Also not
 355  * covered is the UBIFS_NODE_MAGIC and the CRC of the node.
 356  */
 357 static int ubifs_node_calc_hmac(const struct ubifs_info *c, const void *node,
 358                                 int len, int ofs_hmac, void *hmac)
 359 {
 360         SHASH_DESC_ON_STACK(shash, c->hmac_tfm);
 361         int hmac_len = c->hmac_desc_len;
 362         int err;
 363
 364         ubifs_assert(c, ofs_hmac > 8);
 365         ubifs_assert(c, ofs_hmac + hmac_len < len);
 366
 367         shash->tfm = c->hmac_tfm;
 368         shash->flags = CRYPTO_TFM_REQ_MAY_SLEEP;
 369
 370         err = crypto_shash_init(shash);
 371         if (err)
 372                 return err;
 373
 374         /* behind common node header CRC up to HMAC begin */
 375         err = crypto_shash_update(shash, node + 8, ofs_hmac - 8);
 376         if (err < 0)
 377                 return err;
 378
 379         /* behind HMAC, if any */
 380         if (len - ofs_hmac - hmac_len > 0) {
 381                 err = crypto_shash_update(shash, node + ofs_hmac + hmac_len,
 382                             len - ofs_hmac - hmac_len);
 383                 if (err < 0)
 384                         return err;
 385         }
 386
 387         return crypto_shash_final(shash, hmac);
 388 }
 389
 390 /**
 391  * __ubifs_node_insert_hmac - insert a HMAC into a UBIFS node
 392  * @c: UBIFS file-system description object
 393  * @node: the node to insert a HMAC into.
 394  * @len: the length of the node
 395  * @ofs_hmac: the offset in the node where the HMAC is inserted
 396  *
 397  * This function inserts a HMAC at offset @ofs_hmac into the node given in
 398  * @node.
 399  *
 400  * This function returns 0 for success or a negative error code otherwise.
 401  */
 402 int __ubifs_node_insert_hmac(const struct ubifs_info *c, void *node, int len,
 403                             int ofs_hmac)
 404 {
 405         return ubifs_node_calc_hmac(c, node, len, ofs_hmac, node + ofs_hmac);
 406 }
 407
 408 /**
 409  * __ubifs_node_verify_hmac - verify the HMAC of UBIFS node
 410  * @c: UBIFS file-system description object
 411  * @node: the node to insert a HMAC into.
 412  * @len: the length of the node
 413  * @ofs_hmac: the offset in the node where the HMAC is inserted
 414  *
 415  * This function verifies the HMAC at offset @ofs_hmac of the node given in
 416  * @node. Returns 0 if successful or a negative error code otherwise.
 417  */
 418 int __ubifs_node_verify_hmac(const struct ubifs_info *c, const void *node,
 419                              int len, int ofs_hmac)
 420 {
 421         int hmac_len = c->hmac_desc_len;
 422         u8 *hmac;
 423         int err;
 424
 425         hmac = kmalloc(hmac_len, GFP_NOFS);
 426         if (!hmac)
 427                 return -ENOMEM;
 428
 429         err = ubifs_node_calc_hmac(c, node, len, ofs_hmac, hmac);
 430         if (err)
 431                 return err;
 432
 433         err = crypto_memneq(hmac, node + ofs_hmac, hmac_len);
 434
 435         kfree(hmac);
 436
 437         if (!err)
 438                 return 0;
 439
 440         return -EPERM;
 441 }
 442
 443 int __ubifs_shash_copy_state(const struct ubifs_info *c, struct shash_desc *src,
 444                              struct shash_desc *target)
 445 {
 446         u8 *state;
 447         int err;
 448
 449         state = kmalloc(crypto_shash_descsize(src->tfm), GFP_NOFS);
 450         if (!state)
 451                 return -ENOMEM;
 452
 453         err = crypto_shash_export(src, state);
 454         if (err)
 455                 goto out;
 456
 457         err = crypto_shash_import(target, state);
 458
 459 out:
 460         kfree(state);
 461
 462         return err;
 463 }
 464
 465 /**
 466  * ubifs_hmac_wkm - Create a HMAC of the well known message
 467  * @c: UBIFS file-system description object
 468  * @hmac: The HMAC of the well known message
 469  *
 470  * This function creates a HMAC of a well known message. This is used
 471  * to check if the provided key is suitable to authenticate a UBIFS
 472  * image. This is only a convenience to the user to provide a better
 473  * error message when the wrong key is provided.
 474  *
 475  * This function returns 0 for success or a negative error code otherwise.
 476  */
 477 int ubifs_hmac_wkm(struct ubifs_info *c, u8 *hmac)
 478 {
 479         SHASH_DESC_ON_STACK(shash, c->hmac_tfm);
 480         int err;
 481         const char well_known_message[] = "UBIFS";
 482
 483         if (!ubifs_authenticated(c))
 484                 return 0;
 485
 486         shash->tfm = c->hmac_tfm;
 487         shash->flags = CRYPTO_TFM_REQ_MAY_SLEEP;
 488
 489         err = crypto_shash_init(shash);
 490         if (err)
 491                 return err;
 492
 493         err = crypto_shash_update(shash, well_known_message,
 494                                   sizeof(well_known_message) - 1);
 495         if (err < 0)
 496                 return err;
 497
 498         err = crypto_shash_final(shash, hmac);
 499         if (err)
 500                 return err;
 501         return 0;
 502 }