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; 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 == NULL) { 95 mutex_lock(&mutex); 96 if (*tfm) 97 goto out; 98 *tfm = crypto_alloc_shash(algo, 0, CRYPTO_NOLOAD); 99 if (IS_ERR(*tfm)) { 100 rc = PTR_ERR(*tfm); 101 pr_err("Can not allocate %s (reason: %ld)\n", algo, rc); 102 *tfm = NULL; 103 mutex_unlock(&mutex); 104 return ERR_PTR(rc); 105 } 106 if (type == EVM_XATTR_HMAC) { 107 rc = crypto_shash_setkey(*tfm, evmkey, evmkey_len); 108 if (rc) { 109 crypto_free_shash(*tfm); 110 *tfm = NULL; 111 mutex_unlock(&mutex); 112 return ERR_PTR(rc); 113 } 114 } 115 out: 116 mutex_unlock(&mutex); 117 } 118 119 desc = kmalloc(sizeof(*desc) + crypto_shash_descsize(*tfm), 120 GFP_KERNEL); 121 if (!desc) 122 return ERR_PTR(-ENOMEM); 123 124 desc->tfm = *tfm; 125 126 rc = crypto_shash_init(desc); 127 if (rc) { 128 kfree(desc); 129 return ERR_PTR(rc); 130 } 131 return desc; 132 } 133 134 /* Protect against 'cutting & pasting' security.evm xattr, include inode 135 * specific info. 136 * 137 * (Additional directory/file metadata needs to be added for more complete 138 * protection.) 139 */ 140 static void hmac_add_misc(struct shash_desc *desc, struct inode *inode, 141 char type, char *digest) 142 { 143 struct h_misc { 144 unsigned long ino; 145 __u32 generation; 146 uid_t uid; 147 gid_t gid; 148 umode_t mode; 149 } hmac_misc; 150 151 memset(&hmac_misc, 0, sizeof(hmac_misc)); 152 /* Don't include the inode or generation number in portable 153 * signatures 154 */ 155 if (type != EVM_XATTR_PORTABLE_DIGSIG) { 156 hmac_misc.ino = inode->i_ino; 157 hmac_misc.generation = inode->i_generation; 158 } 159 /* The hmac uid and gid must be encoded in the initial user 160 * namespace (not the filesystems user namespace) as encoding 161 * them in the filesystems user namespace allows an attack 162 * where first they are written in an unprivileged fuse mount 163 * of a filesystem and then the system is tricked to mount the 164 * filesystem for real on next boot and trust it because 165 * everything is signed. 166 */ 167 hmac_misc.uid = from_kuid(&init_user_ns, inode->i_uid); 168 hmac_misc.gid = from_kgid(&init_user_ns, inode->i_gid); 169 hmac_misc.mode = inode->i_mode; 170 crypto_shash_update(desc, (const u8 *)&hmac_misc, sizeof(hmac_misc)); 171 if ((evm_hmac_attrs & EVM_ATTR_FSUUID) && 172 type != EVM_XATTR_PORTABLE_DIGSIG) 173 crypto_shash_update(desc, (u8 *)&inode->i_sb->s_uuid, UUID_SIZE); 174 crypto_shash_final(desc, digest); 175 } 176 177 /* 178 * Calculate the HMAC value across the set of protected security xattrs. 179 * 180 * Instead of retrieving the requested xattr, for performance, calculate 181 * the hmac using the requested xattr value. Don't alloc/free memory for 182 * each xattr, but attempt to re-use the previously allocated memory. 183 */ 184 static int evm_calc_hmac_or_hash(struct dentry *dentry, 185 const char *req_xattr_name, 186 const char *req_xattr_value, 187 size_t req_xattr_value_len, 188 uint8_t type, struct evm_digest *data) 189 { 190 struct inode *inode = d_backing_inode(dentry); 191 struct xattr_list *xattr; 192 struct shash_desc *desc; 193 size_t xattr_size = 0; 194 char *xattr_value = NULL; 195 int error; 196 int size; 197 bool ima_present = false; 198 199 if (!(inode->i_opflags & IOP_XATTR) || 200 inode->i_sb->s_user_ns != &init_user_ns) 201 return -EOPNOTSUPP; 202 203 desc = init_desc(type, data->hdr.algo); 204 if (IS_ERR(desc)) 205 return PTR_ERR(desc); 206 207 data->hdr.length = crypto_shash_digestsize(desc->tfm); 208 209 error = -ENODATA; 210 list_for_each_entry_rcu(xattr, &evm_config_xattrnames, list) { 211 bool is_ima = false; 212 213 if (strcmp(xattr->name, XATTR_NAME_IMA) == 0) 214 is_ima = true; 215 216 if ((req_xattr_name && req_xattr_value) 217 && !strcmp(xattr->name, req_xattr_name)) { 218 error = 0; 219 crypto_shash_update(desc, (const u8 *)req_xattr_value, 220 req_xattr_value_len); 221 if (is_ima) 222 ima_present = true; 223 continue; 224 } 225 size = vfs_getxattr_alloc(dentry, xattr->name, 226 &xattr_value, xattr_size, GFP_NOFS); 227 if (size == -ENOMEM) { 228 error = -ENOMEM; 229 goto out; 230 } 231 if (size < 0) 232 continue; 233 234 error = 0; 235 xattr_size = size; 236 crypto_shash_update(desc, (const u8 *)xattr_value, xattr_size); 237 if (is_ima) 238 ima_present = true; 239 } 240 hmac_add_misc(desc, inode, type, data->digest); 241 242 /* Portable EVM signatures must include an IMA hash */ 243 if (type == EVM_XATTR_PORTABLE_DIGSIG && !ima_present) 244 return -EPERM; 245 out: 246 kfree(xattr_value); 247 kfree(desc); 248 return error; 249 } 250 251 int evm_calc_hmac(struct dentry *dentry, const char *req_xattr_name, 252 const char *req_xattr_value, size_t req_xattr_value_len, 253 struct evm_digest *data) 254 { 255 return evm_calc_hmac_or_hash(dentry, req_xattr_name, req_xattr_value, 256 req_xattr_value_len, EVM_XATTR_HMAC, data); 257 } 258 259 int evm_calc_hash(struct dentry *dentry, const char *req_xattr_name, 260 const char *req_xattr_value, size_t req_xattr_value_len, 261 char type, struct evm_digest *data) 262 { 263 return evm_calc_hmac_or_hash(dentry, req_xattr_name, req_xattr_value, 264 req_xattr_value_len, type, data); 265 } 266 267 static int evm_is_immutable(struct dentry *dentry, struct inode *inode) 268 { 269 const struct evm_ima_xattr_data *xattr_data = NULL; 270 struct integrity_iint_cache *iint; 271 int rc = 0; 272 273 iint = integrity_iint_find(inode); 274 if (iint && (iint->flags & EVM_IMMUTABLE_DIGSIG)) 275 return 1; 276 277 /* Do this the hard way */ 278 rc = vfs_getxattr_alloc(dentry, XATTR_NAME_EVM, (char **)&xattr_data, 0, 279 GFP_NOFS); 280 if (rc <= 0) { 281 if (rc == -ENODATA) 282 return 0; 283 return rc; 284 } 285 if (xattr_data->type == EVM_XATTR_PORTABLE_DIGSIG) 286 rc = 1; 287 else 288 rc = 0; 289 290 kfree(xattr_data); 291 return rc; 292 } 293 294 295 /* 296 * Calculate the hmac and update security.evm xattr 297 * 298 * Expects to be called with i_mutex locked. 299 */ 300 int evm_update_evmxattr(struct dentry *dentry, const char *xattr_name, 301 const char *xattr_value, size_t xattr_value_len) 302 { 303 struct inode *inode = d_backing_inode(dentry); 304 struct evm_digest data; 305 int rc = 0; 306 307 /* 308 * Don't permit any transformation of the EVM xattr if the signature 309 * is of an immutable type 310 */ 311 rc = evm_is_immutable(dentry, inode); 312 if (rc < 0) 313 return rc; 314 if (rc) 315 return -EPERM; 316 317 data.hdr.algo = HASH_ALGO_SHA1; 318 rc = evm_calc_hmac(dentry, xattr_name, xattr_value, 319 xattr_value_len, &data); 320 if (rc == 0) { 321 data.hdr.xattr.sha1.type = EVM_XATTR_HMAC; 322 rc = __vfs_setxattr_noperm(dentry, XATTR_NAME_EVM, 323 &data.hdr.xattr.data[1], 324 SHA1_DIGEST_SIZE + 1, 0); 325 } else if (rc == -ENODATA && (inode->i_opflags & IOP_XATTR)) { 326 rc = __vfs_removexattr(dentry, XATTR_NAME_EVM); 327 } 328 return rc; 329 } 330 331 int evm_init_hmac(struct inode *inode, const struct xattr *lsm_xattr, 332 char *hmac_val) 333 { 334 struct shash_desc *desc; 335 336 desc = init_desc(EVM_XATTR_HMAC, HASH_ALGO_SHA1); 337 if (IS_ERR(desc)) { 338 pr_info("init_desc failed\n"); 339 return PTR_ERR(desc); 340 } 341 342 crypto_shash_update(desc, lsm_xattr->value, lsm_xattr->value_len); 343 hmac_add_misc(desc, inode, EVM_XATTR_HMAC, hmac_val); 344 kfree(desc); 345 return 0; 346 } 347 348 /* 349 * Get the key from the TPM for the SHA1-HMAC 350 */ 351 int evm_init_key(void) 352 { 353 struct key *evm_key; 354 struct encrypted_key_payload *ekp; 355 int rc; 356 357 evm_key = request_key(&key_type_encrypted, EVMKEY, NULL); 358 if (IS_ERR(evm_key)) 359 return -ENOENT; 360 361 down_read(&evm_key->sem); 362 ekp = evm_key->payload.data[0]; 363 364 rc = evm_set_key(ekp->decrypted_data, ekp->decrypted_datalen); 365 366 /* burn the original key contents */ 367 memset(ekp->decrypted_data, 0, ekp->decrypted_datalen); 368 up_read(&evm_key->sem); 369 key_put(evm_key); 370 return rc; 371 } 372