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; 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(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 /* 204 * Calculate the HMAC value across the set of protected security xattrs. 205 * 206 * Instead of retrieving the requested xattr, for performance, calculate 207 * the hmac using the requested xattr value. Don't alloc/free memory for 208 * each xattr, but attempt to re-use the previously allocated memory. 209 */ 210 static int evm_calc_hmac_or_hash(struct dentry *dentry, 211 const char *req_xattr_name, 212 const char *req_xattr_value, 213 size_t req_xattr_value_len, 214 uint8_t type, struct evm_digest *data) 215 { 216 struct inode *inode = d_backing_inode(dentry); 217 struct xattr_list *xattr; 218 struct shash_desc *desc; 219 size_t xattr_size = 0; 220 char *xattr_value = NULL; 221 int error; 222 int size, user_space_size; 223 bool ima_present = false; 224 225 if (!(inode->i_opflags & IOP_XATTR) || 226 inode->i_sb->s_user_ns != &init_user_ns) 227 return -EOPNOTSUPP; 228 229 desc = init_desc(type, data->hdr.algo); 230 if (IS_ERR(desc)) 231 return PTR_ERR(desc); 232 233 data->hdr.length = crypto_shash_digestsize(desc->tfm); 234 235 error = -ENODATA; 236 list_for_each_entry_lockless(xattr, &evm_config_xattrnames, list) { 237 bool is_ima = false; 238 239 if (strcmp(xattr->name, XATTR_NAME_IMA) == 0) 240 is_ima = true; 241 242 /* 243 * Skip non-enabled xattrs for locally calculated 244 * signatures/HMACs. 245 */ 246 if (type != EVM_XATTR_PORTABLE_DIGSIG && !xattr->enabled) 247 continue; 248 249 if ((req_xattr_name && req_xattr_value) 250 && !strcmp(xattr->name, req_xattr_name)) { 251 error = 0; 252 crypto_shash_update(desc, (const u8 *)req_xattr_value, 253 req_xattr_value_len); 254 if (is_ima) 255 ima_present = true; 256 257 if (req_xattr_value_len < 64) 258 pr_debug("%s: (%zu) [%*phN]\n", req_xattr_name, 259 req_xattr_value_len, 260 (int)req_xattr_value_len, 261 req_xattr_value); 262 else 263 dump_security_xattr(req_xattr_name, 264 req_xattr_value, 265 req_xattr_value_len); 266 continue; 267 } 268 size = vfs_getxattr_alloc(&init_user_ns, dentry, xattr->name, 269 &xattr_value, xattr_size, GFP_NOFS); 270 if (size == -ENOMEM) { 271 error = -ENOMEM; 272 goto out; 273 } 274 if (size < 0) 275 continue; 276 277 user_space_size = vfs_getxattr(&init_user_ns, dentry, 278 xattr->name, NULL, 0); 279 if (user_space_size != size) 280 pr_debug("file %s: xattr %s size mismatch (kernel: %d, user: %d)\n", 281 dentry->d_name.name, xattr->name, size, 282 user_space_size); 283 error = 0; 284 xattr_size = size; 285 crypto_shash_update(desc, (const u8 *)xattr_value, xattr_size); 286 if (is_ima) 287 ima_present = true; 288 289 if (xattr_size < 64) 290 pr_debug("%s: (%zu) [%*phN]", xattr->name, xattr_size, 291 (int)xattr_size, xattr_value); 292 else 293 dump_security_xattr(xattr->name, xattr_value, 294 xattr_size); 295 } 296 hmac_add_misc(desc, inode, type, data->digest); 297 298 /* Portable EVM signatures must include an IMA hash */ 299 if (type == EVM_XATTR_PORTABLE_DIGSIG && !ima_present) 300 error = -EPERM; 301 out: 302 kfree(xattr_value); 303 kfree(desc); 304 return error; 305 } 306 307 int evm_calc_hmac(struct dentry *dentry, const char *req_xattr_name, 308 const char *req_xattr_value, size_t req_xattr_value_len, 309 struct evm_digest *data) 310 { 311 return evm_calc_hmac_or_hash(dentry, req_xattr_name, req_xattr_value, 312 req_xattr_value_len, EVM_XATTR_HMAC, data); 313 } 314 315 int evm_calc_hash(struct dentry *dentry, const char *req_xattr_name, 316 const char *req_xattr_value, size_t req_xattr_value_len, 317 char type, struct evm_digest *data) 318 { 319 return evm_calc_hmac_or_hash(dentry, req_xattr_name, req_xattr_value, 320 req_xattr_value_len, type, data); 321 } 322 323 static int evm_is_immutable(struct dentry *dentry, struct inode *inode) 324 { 325 const struct evm_ima_xattr_data *xattr_data = NULL; 326 struct integrity_iint_cache *iint; 327 int rc = 0; 328 329 iint = integrity_iint_find(inode); 330 if (iint && (iint->flags & EVM_IMMUTABLE_DIGSIG)) 331 return 1; 332 333 /* Do this the hard way */ 334 rc = vfs_getxattr_alloc(&init_user_ns, dentry, XATTR_NAME_EVM, 335 (char **)&xattr_data, 0, GFP_NOFS); 336 if (rc <= 0) { 337 if (rc == -ENODATA) 338 return 0; 339 return rc; 340 } 341 if (xattr_data->type == EVM_XATTR_PORTABLE_DIGSIG) 342 rc = 1; 343 else 344 rc = 0; 345 346 kfree(xattr_data); 347 return rc; 348 } 349 350 351 /* 352 * Calculate the hmac and update security.evm xattr 353 * 354 * Expects to be called with i_mutex locked. 355 */ 356 int evm_update_evmxattr(struct dentry *dentry, const char *xattr_name, 357 const char *xattr_value, size_t xattr_value_len) 358 { 359 struct inode *inode = d_backing_inode(dentry); 360 struct evm_digest data; 361 int rc = 0; 362 363 /* 364 * Don't permit any transformation of the EVM xattr if the signature 365 * is of an immutable type 366 */ 367 rc = evm_is_immutable(dentry, inode); 368 if (rc < 0) 369 return rc; 370 if (rc) 371 return -EPERM; 372 373 data.hdr.algo = HASH_ALGO_SHA1; 374 rc = evm_calc_hmac(dentry, xattr_name, xattr_value, 375 xattr_value_len, &data); 376 if (rc == 0) { 377 data.hdr.xattr.sha1.type = EVM_XATTR_HMAC; 378 rc = __vfs_setxattr_noperm(&init_user_ns, dentry, 379 XATTR_NAME_EVM, 380 &data.hdr.xattr.data[1], 381 SHA1_DIGEST_SIZE + 1, 0); 382 } else if (rc == -ENODATA && (inode->i_opflags & IOP_XATTR)) { 383 rc = __vfs_removexattr(&init_user_ns, dentry, XATTR_NAME_EVM); 384 } 385 return rc; 386 } 387 388 int evm_init_hmac(struct inode *inode, const struct xattr *lsm_xattr, 389 char *hmac_val) 390 { 391 struct shash_desc *desc; 392 393 desc = init_desc(EVM_XATTR_HMAC, HASH_ALGO_SHA1); 394 if (IS_ERR(desc)) { 395 pr_info("init_desc failed\n"); 396 return PTR_ERR(desc); 397 } 398 399 crypto_shash_update(desc, lsm_xattr->value, lsm_xattr->value_len); 400 hmac_add_misc(desc, inode, EVM_XATTR_HMAC, hmac_val); 401 kfree(desc); 402 return 0; 403 } 404 405 /* 406 * Get the key from the TPM for the SHA1-HMAC 407 */ 408 int evm_init_key(void) 409 { 410 struct key *evm_key; 411 struct encrypted_key_payload *ekp; 412 int rc; 413 414 evm_key = request_key(&key_type_encrypted, EVMKEY, NULL); 415 if (IS_ERR(evm_key)) 416 return -ENOENT; 417 418 down_read(&evm_key->sem); 419 ekp = evm_key->payload.data[0]; 420 421 rc = evm_set_key(ekp->decrypted_data, ekp->decrypted_datalen); 422 423 /* burn the original key contents */ 424 memset(ekp->decrypted_data, 0, ekp->decrypted_datalen); 425 up_read(&evm_key->sem); 426 key_put(evm_key); 427 return rc; 428 } 429