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