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 * @size: 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 = NULL; 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 crypto_free_shash(tmp_tfm); 125 return ERR_PTR(-ENOMEM); 126 } 127 128 desc->tfm = *tfm; 129 130 rc = crypto_shash_init(desc); 131 if (rc) { 132 crypto_free_shash(tmp_tfm); 133 kfree(desc); 134 return ERR_PTR(rc); 135 } 136 return desc; 137 } 138 139 /* Protect against 'cutting & pasting' security.evm xattr, include inode 140 * specific info. 141 * 142 * (Additional directory/file metadata needs to be added for more complete 143 * protection.) 144 */ 145 static void hmac_add_misc(struct shash_desc *desc, struct inode *inode, 146 char type, char *digest) 147 { 148 struct h_misc { 149 unsigned long ino; 150 __u32 generation; 151 uid_t uid; 152 gid_t gid; 153 umode_t mode; 154 } hmac_misc; 155 156 memset(&hmac_misc, 0, sizeof(hmac_misc)); 157 /* Don't include the inode or generation number in portable 158 * signatures 159 */ 160 if (type != EVM_XATTR_PORTABLE_DIGSIG) { 161 hmac_misc.ino = inode->i_ino; 162 hmac_misc.generation = inode->i_generation; 163 } 164 /* The hmac uid and gid must be encoded in the initial user 165 * namespace (not the filesystems user namespace) as encoding 166 * them in the filesystems user namespace allows an attack 167 * where first they are written in an unprivileged fuse mount 168 * of a filesystem and then the system is tricked to mount the 169 * filesystem for real on next boot and trust it because 170 * everything is signed. 171 */ 172 hmac_misc.uid = from_kuid(&init_user_ns, inode->i_uid); 173 hmac_misc.gid = from_kgid(&init_user_ns, inode->i_gid); 174 hmac_misc.mode = inode->i_mode; 175 crypto_shash_update(desc, (const u8 *)&hmac_misc, sizeof(hmac_misc)); 176 if ((evm_hmac_attrs & EVM_ATTR_FSUUID) && 177 type != EVM_XATTR_PORTABLE_DIGSIG) 178 crypto_shash_update(desc, (u8 *)&inode->i_sb->s_uuid, UUID_SIZE); 179 crypto_shash_final(desc, digest); 180 181 pr_debug("hmac_misc: (%zu) [%*phN]\n", sizeof(struct h_misc), 182 (int)sizeof(struct h_misc), &hmac_misc); 183 } 184 185 /* 186 * Dump large security xattr values as a continuous ascii hexademical string. 187 * (pr_debug is limited to 64 bytes.) 188 */ 189 static void dump_security_xattr(const char *prefix, const void *src, 190 size_t count) 191 { 192 #if defined(DEBUG) || defined(CONFIG_DYNAMIC_DEBUG) 193 char *asciihex, *p; 194 195 p = asciihex = kmalloc(count * 2 + 1, GFP_KERNEL); 196 if (!asciihex) 197 return; 198 199 p = bin2hex(p, src, count); 200 *p = 0; 201 pr_debug("%s: (%zu) %.*s\n", prefix, count, (int)count * 2, asciihex); 202 kfree(asciihex); 203 #endif 204 } 205 206 /* 207 * Calculate the HMAC value across the set of protected security xattrs. 208 * 209 * Instead of retrieving the requested xattr, for performance, calculate 210 * the hmac using the requested xattr value. Don't alloc/free memory for 211 * each xattr, but attempt to re-use the previously allocated memory. 212 */ 213 static int evm_calc_hmac_or_hash(struct dentry *dentry, 214 const char *req_xattr_name, 215 const char *req_xattr_value, 216 size_t req_xattr_value_len, 217 uint8_t type, struct evm_digest *data) 218 { 219 struct inode *inode = d_backing_inode(dentry); 220 struct xattr_list *xattr; 221 struct shash_desc *desc; 222 size_t xattr_size = 0; 223 char *xattr_value = NULL; 224 int error; 225 int size, user_space_size; 226 bool ima_present = false; 227 228 if (!(inode->i_opflags & IOP_XATTR) || 229 inode->i_sb->s_user_ns != &init_user_ns) 230 return -EOPNOTSUPP; 231 232 desc = init_desc(type, data->hdr.algo); 233 if (IS_ERR(desc)) 234 return PTR_ERR(desc); 235 236 data->hdr.length = crypto_shash_digestsize(desc->tfm); 237 238 error = -ENODATA; 239 list_for_each_entry_lockless(xattr, &evm_config_xattrnames, list) { 240 bool is_ima = false; 241 242 if (strcmp(xattr->name, XATTR_NAME_IMA) == 0) 243 is_ima = true; 244 245 /* 246 * Skip non-enabled xattrs for locally calculated 247 * signatures/HMACs. 248 */ 249 if (type != EVM_XATTR_PORTABLE_DIGSIG && !xattr->enabled) 250 continue; 251 252 if ((req_xattr_name && req_xattr_value) 253 && !strcmp(xattr->name, req_xattr_name)) { 254 error = 0; 255 crypto_shash_update(desc, (const u8 *)req_xattr_value, 256 req_xattr_value_len); 257 if (is_ima) 258 ima_present = true; 259 260 if (req_xattr_value_len < 64) 261 pr_debug("%s: (%zu) [%*phN]\n", req_xattr_name, 262 req_xattr_value_len, 263 (int)req_xattr_value_len, 264 req_xattr_value); 265 else 266 dump_security_xattr(req_xattr_name, 267 req_xattr_value, 268 req_xattr_value_len); 269 continue; 270 } 271 size = vfs_getxattr_alloc(&init_user_ns, dentry, xattr->name, 272 &xattr_value, xattr_size, GFP_NOFS); 273 if (size == -ENOMEM) { 274 error = -ENOMEM; 275 goto out; 276 } 277 if (size < 0) 278 continue; 279 280 user_space_size = vfs_getxattr(&init_user_ns, dentry, 281 xattr->name, NULL, 0); 282 if (user_space_size != size) 283 pr_debug("file %s: xattr %s size mismatch (kernel: %d, user: %d)\n", 284 dentry->d_name.name, xattr->name, size, 285 user_space_size); 286 error = 0; 287 xattr_size = size; 288 crypto_shash_update(desc, (const u8 *)xattr_value, xattr_size); 289 if (is_ima) 290 ima_present = true; 291 292 if (xattr_size < 64) 293 pr_debug("%s: (%zu) [%*phN]", xattr->name, xattr_size, 294 (int)xattr_size, xattr_value); 295 else 296 dump_security_xattr(xattr->name, xattr_value, 297 xattr_size); 298 } 299 hmac_add_misc(desc, inode, type, data->digest); 300 301 /* Portable EVM signatures must include an IMA hash */ 302 if (type == EVM_XATTR_PORTABLE_DIGSIG && !ima_present) 303 error = -EPERM; 304 out: 305 kfree(xattr_value); 306 kfree(desc); 307 return error; 308 } 309 310 int evm_calc_hmac(struct dentry *dentry, const char *req_xattr_name, 311 const char *req_xattr_value, size_t req_xattr_value_len, 312 struct evm_digest *data) 313 { 314 return evm_calc_hmac_or_hash(dentry, req_xattr_name, req_xattr_value, 315 req_xattr_value_len, EVM_XATTR_HMAC, data); 316 } 317 318 int evm_calc_hash(struct dentry *dentry, const char *req_xattr_name, 319 const char *req_xattr_value, size_t req_xattr_value_len, 320 char type, struct evm_digest *data) 321 { 322 return evm_calc_hmac_or_hash(dentry, req_xattr_name, req_xattr_value, 323 req_xattr_value_len, type, data); 324 } 325 326 static int evm_is_immutable(struct dentry *dentry, struct inode *inode) 327 { 328 const struct evm_ima_xattr_data *xattr_data = NULL; 329 struct integrity_iint_cache *iint; 330 int rc = 0; 331 332 iint = integrity_iint_find(inode); 333 if (iint && (iint->flags & EVM_IMMUTABLE_DIGSIG)) 334 return 1; 335 336 /* Do this the hard way */ 337 rc = vfs_getxattr_alloc(&init_user_ns, dentry, XATTR_NAME_EVM, 338 (char **)&xattr_data, 0, GFP_NOFS); 339 if (rc <= 0) { 340 if (rc == -ENODATA) 341 return 0; 342 return rc; 343 } 344 if (xattr_data->type == EVM_XATTR_PORTABLE_DIGSIG) 345 rc = 1; 346 else 347 rc = 0; 348 349 kfree(xattr_data); 350 return rc; 351 } 352 353 354 /* 355 * Calculate the hmac and update security.evm xattr 356 * 357 * Expects to be called with i_mutex locked. 358 */ 359 int evm_update_evmxattr(struct dentry *dentry, const char *xattr_name, 360 const char *xattr_value, size_t xattr_value_len) 361 { 362 struct inode *inode = d_backing_inode(dentry); 363 struct evm_digest data; 364 int rc = 0; 365 366 /* 367 * Don't permit any transformation of the EVM xattr if the signature 368 * is of an immutable type 369 */ 370 rc = evm_is_immutable(dentry, inode); 371 if (rc < 0) 372 return rc; 373 if (rc) 374 return -EPERM; 375 376 data.hdr.algo = HASH_ALGO_SHA1; 377 rc = evm_calc_hmac(dentry, xattr_name, xattr_value, 378 xattr_value_len, &data); 379 if (rc == 0) { 380 data.hdr.xattr.sha1.type = EVM_XATTR_HMAC; 381 rc = __vfs_setxattr_noperm(&init_user_ns, dentry, 382 XATTR_NAME_EVM, 383 &data.hdr.xattr.data[1], 384 SHA1_DIGEST_SIZE + 1, 0); 385 } else if (rc == -ENODATA && (inode->i_opflags & IOP_XATTR)) { 386 rc = __vfs_removexattr(&init_user_ns, dentry, XATTR_NAME_EVM); 387 } 388 return rc; 389 } 390 391 int evm_init_hmac(struct inode *inode, const struct xattr *lsm_xattr, 392 char *hmac_val) 393 { 394 struct shash_desc *desc; 395 396 desc = init_desc(EVM_XATTR_HMAC, HASH_ALGO_SHA1); 397 if (IS_ERR(desc)) { 398 pr_info("init_desc failed\n"); 399 return PTR_ERR(desc); 400 } 401 402 crypto_shash_update(desc, lsm_xattr->value, lsm_xattr->value_len); 403 hmac_add_misc(desc, inode, EVM_XATTR_HMAC, hmac_val); 404 kfree(desc); 405 return 0; 406 } 407 408 /* 409 * Get the key from the TPM for the SHA1-HMAC 410 */ 411 int evm_init_key(void) 412 { 413 struct key *evm_key; 414 struct encrypted_key_payload *ekp; 415 int rc; 416 417 evm_key = request_key(&key_type_encrypted, EVMKEY, NULL); 418 if (IS_ERR(evm_key)) 419 return -ENOENT; 420 421 down_read(&evm_key->sem); 422 ekp = evm_key->payload.data[0]; 423 424 rc = evm_set_key(ekp->decrypted_data, ekp->decrypted_datalen); 425 426 /* burn the original key contents */ 427 memset(ekp->decrypted_data, 0, ekp->decrypted_datalen); 428 up_read(&evm_key->sem); 429 key_put(evm_key); 430 return rc; 431 } 432