auth.c 12.2 KB
Newer Older
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
// SPDX-License-Identifier: GPL-2.0
/*
 * This file is part of UBIFS.
 *
 * Copyright (C) 2018 Pengutronix, Sascha Hauer <s.hauer@pengutronix.de>
 */

/*
 * This file implements various helper functions for UBIFS authentication support
 */

#include <linux/crypto.h>
#include <crypto/hash.h>
#include <crypto/sha.h>
#include <crypto/algapi.h>
#include <keys/user-type.h>

#include "ubifs.h"

/**
 * ubifs_node_calc_hash - calculate the hash of a UBIFS node
 * @c: UBIFS file-system description object
 * @node: the node to calculate a hash for
 * @hash: the returned hash
 *
 * Returns 0 for success or a negative error code otherwise.
 */
int __ubifs_node_calc_hash(const struct ubifs_info *c, const void *node,
			    u8 *hash)
{
	const struct ubifs_ch *ch = node;
	SHASH_DESC_ON_STACK(shash, c->hash_tfm);
	int err;

	shash->tfm = c->hash_tfm;
	shash->flags = CRYPTO_TFM_REQ_MAY_SLEEP;

	err = crypto_shash_digest(shash, node, le32_to_cpu(ch->len), hash);
	if (err < 0)
		return err;
	return 0;
}

/**
 * ubifs_hash_calc_hmac - calculate a HMAC from a hash
 * @c: UBIFS file-system description object
 * @hash: the node to calculate a HMAC for
 * @hmac: the returned HMAC
 *
 * Returns 0 for success or a negative error code otherwise.
 */
static int ubifs_hash_calc_hmac(const struct ubifs_info *c, const u8 *hash,
				 u8 *hmac)
{
	SHASH_DESC_ON_STACK(shash, c->hmac_tfm);
	int err;

	shash->tfm = c->hmac_tfm;
	shash->flags = CRYPTO_TFM_REQ_MAY_SLEEP;

	err = crypto_shash_digest(shash, hash, c->hash_len, hmac);
	if (err < 0)
		return err;
	return 0;
}

/**
 * ubifs_prepare_auth_node - Prepare an authentication node
 * @c: UBIFS file-system description object
 * @node: the node to calculate a hash for
 * @hash: input hash of previous nodes
 *
 * This function prepares an authentication node for writing onto flash.
 * It creates a HMAC from the given input hash and writes it to the node.
 *
 * Returns 0 for success or a negative error code otherwise.
 */
int ubifs_prepare_auth_node(struct ubifs_info *c, void *node,
			     struct shash_desc *inhash)
{
	SHASH_DESC_ON_STACK(hash_desc, c->hash_tfm);
	struct ubifs_auth_node *auth = node;
	u8 *hash;
	int err;

	hash = kmalloc(crypto_shash_descsize(c->hash_tfm), GFP_NOFS);
	if (!hash)
		return -ENOMEM;

	hash_desc->tfm = c->hash_tfm;
	hash_desc->flags = CRYPTO_TFM_REQ_MAY_SLEEP;
	ubifs_shash_copy_state(c, inhash, hash_desc);

	err = crypto_shash_final(hash_desc, hash);
	if (err)
		goto out;

	err = ubifs_hash_calc_hmac(c, hash, auth->hmac);
	if (err)
		goto out;

	auth->ch.node_type = UBIFS_AUTH_NODE;
	ubifs_prepare_node(c, auth, ubifs_auth_node_sz(c), 0);

	err = 0;
out:
	kfree(hash);

	return err;
}

static struct shash_desc *ubifs_get_desc(const struct ubifs_info *c,
					 struct crypto_shash *tfm)
{
	struct shash_desc *desc;
	int err;

	if (!ubifs_authenticated(c))
		return NULL;

	desc = kmalloc(sizeof(*desc) + crypto_shash_descsize(tfm), GFP_KERNEL);
	if (!desc)
		return ERR_PTR(-ENOMEM);

	desc->tfm = tfm;
	desc->flags = CRYPTO_TFM_REQ_MAY_SLEEP;

	err = crypto_shash_init(desc);
	if (err) {
		kfree(desc);
		return ERR_PTR(err);
	}

	return desc;
}

/**
 * __ubifs_hash_get_desc - get a descriptor suitable for hashing a node
 * @c: UBIFS file-system description object
 *
 * This function returns a descriptor suitable for hashing a node. Free after use
 * with kfree.
 */
struct shash_desc *__ubifs_hash_get_desc(const struct ubifs_info *c)
{
	return ubifs_get_desc(c, c->hash_tfm);
}

/**
 * __ubifs_shash_final - finalize shash
 * @c: UBIFS file-system description object
 * @desc: the descriptor
 * @out: the output hash
 *
 * Simple wrapper around crypto_shash_final(), safe to be called with
 * disabled authentication.
 */
int __ubifs_shash_final(const struct ubifs_info *c, struct shash_desc *desc,
			u8 *out)
{
	if (ubifs_authenticated(c))
		return crypto_shash_final(desc, out);

	return 0;
}

/**
 * ubifs_bad_hash - Report hash mismatches
 * @c: UBIFS file-system description object
 * @node: the node
 * @hash: the expected hash
 * @lnum: the LEB @node was read from
 * @offs: offset in LEB @node was read from
 *
 * This function reports a hash mismatch when a node has a different hash than
 * expected.
 */
void ubifs_bad_hash(const struct ubifs_info *c, const void *node, const u8 *hash,
		    int lnum, int offs)
{
	int len = min(c->hash_len, 20);
	int cropped = len != c->hash_len;
	const char *cont = cropped ? "..." : "";

	u8 calc[UBIFS_HASH_ARR_SZ];

	__ubifs_node_calc_hash(c, node, calc);

	ubifs_err(c, "hash mismatch on node at LEB %d:%d", lnum, offs);
	ubifs_err(c, "hash expected:   %*ph%s", len, hash, cont);
	ubifs_err(c, "hash calculated: %*ph%s", len, calc, cont);
}

/**
 * __ubifs_node_check_hash - check the hash of a node against given hash
 * @c: UBIFS file-system description object
 * @node: the node
 * @expected: the expected hash
 *
 * This function calculates a hash over a node and compares it to the given hash.
 * Returns 0 if both hashes are equal or authentication is disabled, otherwise a
 * negative error code is returned.
 */
int __ubifs_node_check_hash(const struct ubifs_info *c, const void *node,
			    const u8 *expected)
{
	u8 calc[UBIFS_HASH_ARR_SZ];
	int err;

	err = __ubifs_node_calc_hash(c, node, calc);
	if (err)
		return err;

	if (ubifs_check_hash(c, expected, calc))
		return -EPERM;

	return 0;
}

/**
 * ubifs_init_authentication - initialize UBIFS authentication support
 * @c: UBIFS file-system description object
 *
 * This function returns 0 for success or a negative error code otherwise.
 */
int ubifs_init_authentication(struct ubifs_info *c)
{
	struct key *keyring_key;
	const struct user_key_payload *ukp;
	int err;
	char hmac_name[CRYPTO_MAX_ALG_NAME];

	if (!c->auth_hash_name) {
		ubifs_err(c, "authentication hash name needed with authentication");
		return -EINVAL;
	}

	c->auth_hash_algo = match_string(hash_algo_name, HASH_ALGO__LAST,
					 c->auth_hash_name);
	if ((int)c->auth_hash_algo < 0) {
		ubifs_err(c, "Unknown hash algo %s specified",
			  c->auth_hash_name);
		return -EINVAL;
	}

	snprintf(hmac_name, CRYPTO_MAX_ALG_NAME, "hmac(%s)",
		 c->auth_hash_name);

	keyring_key = request_key(&key_type_logon, c->auth_key_name, NULL);

	if (IS_ERR(keyring_key)) {
		ubifs_err(c, "Failed to request key: %ld",
			  PTR_ERR(keyring_key));
		return PTR_ERR(keyring_key);
	}

	down_read(&keyring_key->sem);

	if (keyring_key->type != &key_type_logon) {
		ubifs_err(c, "key type must be logon");
		err = -ENOKEY;
		goto out;
	}

	ukp = user_key_payload_locked(keyring_key);
	if (!ukp) {
		/* key was revoked before we acquired its semaphore */
		err = -EKEYREVOKED;
		goto out;
	}

272
	c->hash_tfm = crypto_alloc_shash(c->auth_hash_name, 0, 0);
273 274 275 276 277 278 279 280 281 282 283 284 285 286 287
	if (IS_ERR(c->hash_tfm)) {
		err = PTR_ERR(c->hash_tfm);
		ubifs_err(c, "Can not allocate %s: %d",
			  c->auth_hash_name, err);
		goto out;
	}

	c->hash_len = crypto_shash_digestsize(c->hash_tfm);
	if (c->hash_len > UBIFS_HASH_ARR_SZ) {
		ubifs_err(c, "hash %s is bigger than maximum allowed hash size (%d > %d)",
			  c->auth_hash_name, c->hash_len, UBIFS_HASH_ARR_SZ);
		err = -EINVAL;
		goto out_free_hash;
	}

288
	c->hmac_tfm = crypto_alloc_shash(hmac_name, 0, 0);
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
	if (IS_ERR(c->hmac_tfm)) {
		err = PTR_ERR(c->hmac_tfm);
		ubifs_err(c, "Can not allocate %s: %d", hmac_name, err);
		goto out_free_hash;
	}

	c->hmac_desc_len = crypto_shash_digestsize(c->hmac_tfm);
	if (c->hmac_desc_len > UBIFS_HMAC_ARR_SZ) {
		ubifs_err(c, "hmac %s is bigger than maximum allowed hmac size (%d > %d)",
			  hmac_name, c->hmac_desc_len, UBIFS_HMAC_ARR_SZ);
		err = -EINVAL;
		goto out_free_hash;
	}

	err = crypto_shash_setkey(c->hmac_tfm, ukp->data, ukp->datalen);
	if (err)
		goto out_free_hmac;

	c->authenticated = true;

	c->log_hash = ubifs_hash_get_desc(c);
	if (IS_ERR(c->log_hash))
		goto out_free_hmac;

	err = 0;

out_free_hmac:
	if (err)
		crypto_free_shash(c->hmac_tfm);
out_free_hash:
	if (err)
		crypto_free_shash(c->hash_tfm);
out:
	up_read(&keyring_key->sem);
	key_put(keyring_key);

	return err;
}

/**
 * __ubifs_exit_authentication - release resource
 * @c: UBIFS file-system description object
 *
 * This function releases the authentication related resources.
 */
void __ubifs_exit_authentication(struct ubifs_info *c)
{
	if (!ubifs_authenticated(c))
		return;

	crypto_free_shash(c->hmac_tfm);
	crypto_free_shash(c->hash_tfm);
	kfree(c->log_hash);
}

/**
 * ubifs_node_calc_hmac - calculate the HMAC of a UBIFS node
 * @c: UBIFS file-system description object
 * @node: the node to insert a HMAC into.
 * @len: the length of the node
 * @ofs_hmac: the offset in the node where the HMAC is inserted
 * @hmac: returned HMAC
 *
 * This function calculates a HMAC of a UBIFS node. The HMAC is expected to be
 * embedded into the node, so this area is not covered by the HMAC. Also not
 * covered is the UBIFS_NODE_MAGIC and the CRC of the node.
 */
static int ubifs_node_calc_hmac(const struct ubifs_info *c, const void *node,
				int len, int ofs_hmac, void *hmac)
{
	SHASH_DESC_ON_STACK(shash, c->hmac_tfm);
	int hmac_len = c->hmac_desc_len;
	int err;

	ubifs_assert(c, ofs_hmac > 8);
	ubifs_assert(c, ofs_hmac + hmac_len < len);

	shash->tfm = c->hmac_tfm;
	shash->flags = CRYPTO_TFM_REQ_MAY_SLEEP;

	err = crypto_shash_init(shash);
	if (err)
		return err;

	/* behind common node header CRC up to HMAC begin */
	err = crypto_shash_update(shash, node + 8, ofs_hmac - 8);
	if (err < 0)
		return err;

	/* behind HMAC, if any */
	if (len - ofs_hmac - hmac_len > 0) {
		err = crypto_shash_update(shash, node + ofs_hmac + hmac_len,
			    len - ofs_hmac - hmac_len);
		if (err < 0)
			return err;
	}

	return crypto_shash_final(shash, hmac);
}

/**
 * __ubifs_node_insert_hmac - insert a HMAC into a UBIFS node
 * @c: UBIFS file-system description object
 * @node: the node to insert a HMAC into.
 * @len: the length of the node
 * @ofs_hmac: the offset in the node where the HMAC is inserted
 *
 * This function inserts a HMAC at offset @ofs_hmac into the node given in
 * @node.
 *
 * This function returns 0 for success or a negative error code otherwise.
 */
int __ubifs_node_insert_hmac(const struct ubifs_info *c, void *node, int len,
			    int ofs_hmac)
{
	return ubifs_node_calc_hmac(c, node, len, ofs_hmac, node + ofs_hmac);
}

/**
 * __ubifs_node_verify_hmac - verify the HMAC of UBIFS node
 * @c: UBIFS file-system description object
 * @node: the node to insert a HMAC into.
 * @len: the length of the node
 * @ofs_hmac: the offset in the node where the HMAC is inserted
 *
 * This function verifies the HMAC at offset @ofs_hmac of the node given in
 * @node. Returns 0 if successful or a negative error code otherwise.
 */
int __ubifs_node_verify_hmac(const struct ubifs_info *c, const void *node,
			     int len, int ofs_hmac)
{
	int hmac_len = c->hmac_desc_len;
	u8 *hmac;
	int err;

	hmac = kmalloc(hmac_len, GFP_NOFS);
	if (!hmac)
		return -ENOMEM;

	err = ubifs_node_calc_hmac(c, node, len, ofs_hmac, hmac);
	if (err)
		return err;

	err = crypto_memneq(hmac, node + ofs_hmac, hmac_len);

	kfree(hmac);

	if (!err)
		return 0;

	return -EPERM;
}

int __ubifs_shash_copy_state(const struct ubifs_info *c, struct shash_desc *src,
			     struct shash_desc *target)
{
	u8 *state;
	int err;

	state = kmalloc(crypto_shash_descsize(src->tfm), GFP_NOFS);
	if (!state)
		return -ENOMEM;

	err = crypto_shash_export(src, state);
	if (err)
		goto out;

	err = crypto_shash_import(target, state);

out:
	kfree(state);

	return err;
}

/**
 * ubifs_hmac_wkm - Create a HMAC of the well known message
 * @c: UBIFS file-system description object
 * @hmac: The HMAC of the well known message
 *
 * This function creates a HMAC of a well known message. This is used
 * to check if the provided key is suitable to authenticate a UBIFS
 * image. This is only a convenience to the user to provide a better
 * error message when the wrong key is provided.
 *
 * This function returns 0 for success or a negative error code otherwise.
 */
int ubifs_hmac_wkm(struct ubifs_info *c, u8 *hmac)
{
	SHASH_DESC_ON_STACK(shash, c->hmac_tfm);
	int err;
	const char well_known_message[] = "UBIFS";

	if (!ubifs_authenticated(c))
		return 0;

	shash->tfm = c->hmac_tfm;
	shash->flags = CRYPTO_TFM_REQ_MAY_SLEEP;

	err = crypto_shash_init(shash);
	if (err)
		return err;

	err = crypto_shash_update(shash, well_known_message,
				  sizeof(well_known_message) - 1);
	if (err < 0)
		return err;

	err = crypto_shash_final(shash, hmac);
	if (err)
		return err;
	return 0;
}