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