1 // SPDX-License-Identifier: GPL-2.0-only 2 /* 3 * Copyright (C) 2005-2010 IBM Corporation 4 * 5 * Authors: 6 * Mimi Zohar <zohar@us.ibm.com> 7 * Kylene Hall <kjhall@us.ibm.com> 8 * 9 * File: evm_crypto.c 10 * Using root's kernel master key (kmk), calculate the HMAC 11 */ 12 13 #define pr_fmt(fmt) "EVM: "fmt 14 15 #include <linux/export.h> 16 #include <linux/crypto.h> 17 #include <linux/xattr.h> 18 #include <linux/evm.h> 19 #include <keys/encrypted-type.h> 20 #include <crypto/hash.h> 21 #include <crypto/hash_info.h> 22 #include "evm.h" 23 24 #define EVMKEY "evm-key" 25 #define MAX_KEY_SIZE 128 26 static unsigned char evmkey[MAX_KEY_SIZE]; 27 static const int evmkey_len = MAX_KEY_SIZE; 28 29 static struct crypto_shash *hmac_tfm; 30 static struct crypto_shash *evm_tfm[HASH_ALGO__LAST]; 31 32 static DEFINE_MUTEX(mutex); 33 34 #define EVM_SET_KEY_BUSY 0 35 36 static unsigned long evm_set_key_flags; 37 38 static const char evm_hmac[] = "hmac(sha1)"; 39 40 /** 41 * evm_set_key() - set EVM HMAC key from the kernel 42 * @key: pointer to a buffer with the key data 43 * @keylen: length of the key data 44 * 45 * This function allows setting the EVM HMAC key from the kernel 46 * without using the "encrypted" key subsystem keys. It can be used 47 * by the crypto HW kernel module which has its own way of managing 48 * keys. 49 * 50 * key length should be between 32 and 128 bytes long 51 */ 52 int evm_set_key(void *key, size_t keylen) 53 { 54 int rc; 55 56 rc = -EBUSY; 57 if (test_and_set_bit(EVM_SET_KEY_BUSY, &evm_set_key_flags)) 58 goto busy; 59 rc = -EINVAL; 60 if (keylen > MAX_KEY_SIZE) 61 goto inval; 62 memcpy(evmkey, key, keylen); 63 evm_initialized |= EVM_INIT_HMAC; 64 pr_info("key initialized\n"); 65 return 0; 66 inval: 67 clear_bit(EVM_SET_KEY_BUSY, &evm_set_key_flags); 68 busy: 69 pr_err("key initialization failed\n"); 70 return rc; 71 } 72 EXPORT_SYMBOL_GPL(evm_set_key); 73 74 static struct shash_desc *init_desc(char type, uint8_t hash_algo) 75 { 76 long rc; 77 const char *algo; 78 struct crypto_shash **tfm, *tmp_tfm; 79 struct shash_desc *desc; 80 81 if (type == EVM_XATTR_HMAC) { 82 if (!(evm_initialized & EVM_INIT_HMAC)) { 83 pr_err_once("HMAC key is not set\n"); 84 return ERR_PTR(-ENOKEY); 85 } 86 tfm = &hmac_tfm; 87 algo = evm_hmac; 88 } else { 89 if (hash_algo >= HASH_ALGO__LAST) 90 return ERR_PTR(-EINVAL); 91 92 tfm = &evm_tfm[hash_algo]; 93 algo = hash_algo_name[hash_algo]; 94 } 95 96 if (*tfm) 97 goto alloc; 98 mutex_lock(&mutex); 99 if (*tfm) 100 goto unlock; 101 102 tmp_tfm = crypto_alloc_shash(algo, 0, CRYPTO_NOLOAD); 103 if (IS_ERR(tmp_tfm)) { 104 pr_err("Can not allocate %s (reason: %ld)\n", algo, 105 PTR_ERR(tmp_tfm)); 106 mutex_unlock(&mutex); 107 return ERR_CAST(tmp_tfm); 108 } 109 if (type == EVM_XATTR_HMAC) { 110 rc = crypto_shash_setkey(tmp_tfm, evmkey, evmkey_len); 111 if (rc) { 112 crypto_free_shash(tmp_tfm); 113 mutex_unlock(&mutex); 114 return ERR_PTR(rc); 115 } 116 } 117 *tfm = tmp_tfm; 118 unlock: 119 mutex_unlock(&mutex); 120 alloc: 121 desc = kmalloc(sizeof(*desc) + crypto_shash_descsize(*tfm), 122 GFP_KERNEL); 123 if (!desc) 124 return ERR_PTR(-ENOMEM); 125 126 desc->tfm = *tfm; 127 128 rc = crypto_shash_init(desc); 129 if (rc) { 130 kfree(desc); 131 return ERR_PTR(rc); 132 } 133 return desc; 134 } 135 136 /* Protect against 'cutting & pasting' security.evm xattr, include inode 137 * specific info. 138 * 139 * (Additional directory/file metadata needs to be added for more complete 140 * protection.) 141 */ 142 static void hmac_add_misc(struct shash_desc *desc, struct inode *inode, 143 char type, char *digest) 144 { 145 struct h_misc { 146 unsigned long ino; 147 __u32 generation; 148 uid_t uid; 149 gid_t gid; 150 umode_t mode; 151 } hmac_misc; 152 153 memset(&hmac_misc, 0, sizeof(hmac_misc)); 154 /* Don't include the inode or generation number in portable 155 * signatures 156 */ 157 if (type != EVM_XATTR_PORTABLE_DIGSIG) { 158 hmac_misc.ino = inode->i_ino; 159 hmac_misc.generation = inode->i_generation; 160 } 161 /* The hmac uid and gid must be encoded in the initial user 162 * namespace (not the filesystems user namespace) as encoding 163 * them in the filesystems user namespace allows an attack 164 * where first they are written in an unprivileged fuse mount 165 * of a filesystem and then the system is tricked to mount the 166 * filesystem for real on next boot and trust it because 167 * everything is signed. 168 */ 169 hmac_misc.uid = from_kuid(&init_user_ns, inode->i_uid); 170 hmac_misc.gid = from_kgid(&init_user_ns, inode->i_gid); 171 hmac_misc.mode = inode->i_mode; 172 crypto_shash_update(desc, (const u8 *)&hmac_misc, sizeof(hmac_misc)); 173 if ((evm_hmac_attrs & EVM_ATTR_FSUUID) && 174 type != EVM_XATTR_PORTABLE_DIGSIG) 175 crypto_shash_update(desc, (u8 *)&inode->i_sb->s_uuid, UUID_SIZE); 176 crypto_shash_final(desc, digest); 177 178 pr_debug("hmac_misc: (%zu) [%*phN]\n", sizeof(struct h_misc), 179 (int)sizeof(struct h_misc), &hmac_misc); 180 } 181 182 /* 183 * Dump large security xattr values as a continuous ascii hexademical string. 184 * (pr_debug is limited to 64 bytes.) 185 */ 186 static void dump_security_xattr_l(const char *prefix, const void *src, 187 size_t count) 188 { 189 #if defined(DEBUG) || defined(CONFIG_DYNAMIC_DEBUG) 190 char *asciihex, *p; 191 192 p = asciihex = kmalloc(count * 2 + 1, GFP_KERNEL); 193 if (!asciihex) 194 return; 195 196 p = bin2hex(p, src, count); 197 *p = 0; 198 pr_debug("%s: (%zu) %.*s\n", prefix, count, (int)count * 2, asciihex); 199 kfree(asciihex); 200 #endif 201 } 202 203 static void dump_security_xattr(const char *name, const char *value, 204 size_t value_len) 205 { 206 if (value_len < 64) 207 pr_debug("%s: (%zu) [%*phN]\n", name, value_len, 208 (int)value_len, value); 209 else 210 dump_security_xattr_l(name, value, value_len); 211 } 212 213 /* 214 * Calculate the HMAC value across the set of protected security xattrs. 215 * 216 * Instead of retrieving the requested xattr, for performance, calculate 217 * the hmac using the requested xattr value. Don't alloc/free memory for 218 * each xattr, but attempt to re-use the previously allocated memory. 219 */ 220 static int evm_calc_hmac_or_hash(struct dentry *dentry, 221 const char *req_xattr_name, 222 const char *req_xattr_value, 223 size_t req_xattr_value_len, 224 uint8_t type, struct evm_digest *data, 225 struct evm_iint_cache *iint) 226 { 227 struct inode *inode = d_inode(d_real(dentry, D_REAL_METADATA)); 228 struct xattr_list *xattr; 229 struct shash_desc *desc; 230 size_t xattr_size = 0; 231 char *xattr_value = NULL; 232 int error; 233 int size, user_space_size; 234 bool ima_present = false; 235 u64 i_version = 0; 236 237 if (!(inode->i_opflags & IOP_XATTR) || 238 inode->i_sb->s_user_ns != &init_user_ns) 239 return -EOPNOTSUPP; 240 241 desc = init_desc(type, data->hdr.algo); 242 if (IS_ERR(desc)) 243 return PTR_ERR(desc); 244 245 data->hdr.length = crypto_shash_digestsize(desc->tfm); 246 247 error = -ENODATA; 248 list_for_each_entry_lockless(xattr, &evm_config_xattrnames, list) { 249 bool is_ima = false; 250 251 if (strcmp(xattr->name, XATTR_NAME_IMA) == 0) 252 is_ima = true; 253 254 /* 255 * Skip non-enabled xattrs for locally calculated 256 * signatures/HMACs. 257 */ 258 if (type != EVM_XATTR_PORTABLE_DIGSIG && !xattr->enabled) 259 continue; 260 261 if ((req_xattr_name && req_xattr_value) 262 && !strcmp(xattr->name, req_xattr_name)) { 263 error = 0; 264 crypto_shash_update(desc, (const u8 *)req_xattr_value, 265 req_xattr_value_len); 266 if (is_ima) 267 ima_present = true; 268 269 dump_security_xattr(req_xattr_name, 270 req_xattr_value, 271 req_xattr_value_len); 272 continue; 273 } 274 size = vfs_getxattr_alloc(&nop_mnt_idmap, dentry, xattr->name, 275 &xattr_value, xattr_size, GFP_NOFS); 276 if (size == -ENOMEM) { 277 error = -ENOMEM; 278 goto out; 279 } 280 if (size < 0) 281 continue; 282 283 user_space_size = vfs_getxattr(&nop_mnt_idmap, dentry, 284 xattr->name, NULL, 0); 285 if (user_space_size != size) 286 pr_debug("file %s: xattr %s size mismatch (kernel: %d, user: %d)\n", 287 dentry->d_name.name, xattr->name, size, 288 user_space_size); 289 error = 0; 290 xattr_size = size; 291 crypto_shash_update(desc, (const u8 *)xattr_value, xattr_size); 292 if (is_ima) 293 ima_present = true; 294 295 dump_security_xattr(xattr->name, xattr_value, xattr_size); 296 } 297 hmac_add_misc(desc, inode, type, data->digest); 298 299 if (inode != d_backing_inode(dentry) && iint) { 300 if (IS_I_VERSION(inode)) 301 i_version = inode_query_iversion(inode); 302 integrity_inode_attrs_store(&iint->metadata_inode, i_version, 303 inode); 304 } 305 306 /* Portable EVM signatures must include an IMA hash */ 307 if (type == EVM_XATTR_PORTABLE_DIGSIG && !ima_present) 308 error = -EPERM; 309 out: 310 kfree(xattr_value); 311 kfree(desc); 312 return error; 313 } 314 315 int evm_calc_hmac(struct dentry *dentry, const char *req_xattr_name, 316 const char *req_xattr_value, size_t req_xattr_value_len, 317 struct evm_digest *data, struct evm_iint_cache *iint) 318 { 319 return evm_calc_hmac_or_hash(dentry, req_xattr_name, req_xattr_value, 320 req_xattr_value_len, EVM_XATTR_HMAC, data, 321 iint); 322 } 323 324 int evm_calc_hash(struct dentry *dentry, const char *req_xattr_name, 325 const char *req_xattr_value, size_t req_xattr_value_len, 326 char type, struct evm_digest *data, struct evm_iint_cache *iint) 327 { 328 return evm_calc_hmac_or_hash(dentry, req_xattr_name, req_xattr_value, 329 req_xattr_value_len, type, data, iint); 330 } 331 332 static int evm_is_immutable(struct dentry *dentry, struct inode *inode) 333 { 334 const struct evm_ima_xattr_data *xattr_data = NULL; 335 struct evm_iint_cache *iint; 336 int rc = 0; 337 338 iint = evm_iint_inode(inode); 339 if (iint && (iint->flags & EVM_IMMUTABLE_DIGSIG)) 340 return 1; 341 342 /* Do this the hard way */ 343 rc = vfs_getxattr_alloc(&nop_mnt_idmap, dentry, XATTR_NAME_EVM, 344 (char **)&xattr_data, 0, GFP_NOFS); 345 if (rc <= 0) { 346 if (rc == -ENODATA) 347 rc = 0; 348 goto out; 349 } 350 if (xattr_data->type == EVM_XATTR_PORTABLE_DIGSIG) 351 rc = 1; 352 else 353 rc = 0; 354 355 out: 356 kfree(xattr_data); 357 return rc; 358 } 359 360 361 /* 362 * Calculate the hmac and update security.evm xattr 363 * 364 * Expects to be called with i_mutex locked. 365 */ 366 int evm_update_evmxattr(struct dentry *dentry, const char *xattr_name, 367 const char *xattr_value, size_t xattr_value_len) 368 { 369 struct inode *inode = d_backing_inode(dentry); 370 struct evm_iint_cache *iint = evm_iint_inode(inode); 371 struct evm_digest data; 372 int rc = 0; 373 374 /* 375 * Don't permit any transformation of the EVM xattr if the signature 376 * is of an immutable type 377 */ 378 rc = evm_is_immutable(dentry, inode); 379 if (rc < 0) 380 return rc; 381 if (rc) 382 return -EPERM; 383 384 data.hdr.algo = HASH_ALGO_SHA1; 385 rc = evm_calc_hmac(dentry, xattr_name, xattr_value, 386 xattr_value_len, &data, iint); 387 if (rc == 0) { 388 data.hdr.xattr.sha1.type = EVM_XATTR_HMAC; 389 rc = __vfs_setxattr_noperm(&nop_mnt_idmap, dentry, 390 XATTR_NAME_EVM, 391 &data.hdr.xattr.data[1], 392 SHA1_DIGEST_SIZE + 1, 0); 393 } else if (rc == -ENODATA && (inode->i_opflags & IOP_XATTR)) { 394 rc = __vfs_removexattr(&nop_mnt_idmap, dentry, XATTR_NAME_EVM); 395 } 396 return rc; 397 } 398 399 int evm_init_hmac(struct inode *inode, const struct xattr *xattrs, 400 char *hmac_val) 401 { 402 struct shash_desc *desc; 403 const struct xattr *xattr; 404 405 desc = init_desc(EVM_XATTR_HMAC, HASH_ALGO_SHA1); 406 if (IS_ERR(desc)) { 407 pr_info("init_desc failed\n"); 408 return PTR_ERR(desc); 409 } 410 411 for (xattr = xattrs; xattr->name; xattr++) { 412 if (!evm_protected_xattr(xattr->name)) 413 continue; 414 415 crypto_shash_update(desc, xattr->value, xattr->value_len); 416 } 417 418 hmac_add_misc(desc, inode, EVM_XATTR_HMAC, hmac_val); 419 kfree(desc); 420 return 0; 421 } 422 423 /* 424 * Get the key from the TPM for the SHA1-HMAC 425 */ 426 int evm_init_key(void) 427 { 428 struct key *evm_key; 429 struct encrypted_key_payload *ekp; 430 int rc; 431 432 evm_key = request_key(&key_type_encrypted, EVMKEY, NULL); 433 if (IS_ERR(evm_key)) 434 return -ENOENT; 435 436 down_read(&evm_key->sem); 437 ekp = evm_key->payload.data[0]; 438 439 rc = evm_set_key(ekp->decrypted_data, ekp->decrypted_datalen); 440 441 /* burn the original key contents */ 442 memset(ekp->decrypted_data, 0, ekp->decrypted_datalen); 443 up_read(&evm_key->sem); 444 key_put(evm_key); 445 return rc; 446 } 447