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