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/export.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 const 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 const char 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, CRYPTO_NOLOAD); 101 if (IS_ERR(*tfm)) { 102 rc = PTR_ERR(*tfm); 103 pr_err("Can not allocate %s (reason: %ld)\n", algo, rc); 104 *tfm = NULL; 105 mutex_unlock(&mutex); 106 return ERR_PTR(rc); 107 } 108 if (type == EVM_XATTR_HMAC) { 109 rc = crypto_shash_setkey(*tfm, evmkey, evmkey_len); 110 if (rc) { 111 crypto_free_shash(*tfm); 112 *tfm = NULL; 113 mutex_unlock(&mutex); 114 return ERR_PTR(rc); 115 } 116 } 117 out: 118 mutex_unlock(&mutex); 119 } 120 121 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 desc->flags = CRYPTO_TFM_REQ_MAY_SLEEP; 128 129 rc = crypto_shash_init(desc); 130 if (rc) { 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, &inode->i_sb->s_uuid.b[0], 177 sizeof(inode->i_sb->s_uuid)); 178 crypto_shash_final(desc, digest); 179 } 180 181 /* 182 * Calculate the HMAC value across the set of protected security xattrs. 183 * 184 * Instead of retrieving the requested xattr, for performance, calculate 185 * the hmac using the requested xattr value. Don't alloc/free memory for 186 * each xattr, but attempt to re-use the previously allocated memory. 187 */ 188 static int evm_calc_hmac_or_hash(struct dentry *dentry, 189 const char *req_xattr_name, 190 const char *req_xattr_value, 191 size_t req_xattr_value_len, 192 uint8_t type, struct evm_digest *data) 193 { 194 struct inode *inode = d_backing_inode(dentry); 195 struct xattr_list *xattr; 196 struct shash_desc *desc; 197 size_t xattr_size = 0; 198 char *xattr_value = NULL; 199 int error; 200 int size; 201 bool ima_present = false; 202 203 if (!(inode->i_opflags & IOP_XATTR) || 204 inode->i_sb->s_user_ns != &init_user_ns) 205 return -EOPNOTSUPP; 206 207 desc = init_desc(type, data->hdr.algo); 208 if (IS_ERR(desc)) 209 return PTR_ERR(desc); 210 211 data->hdr.length = crypto_shash_digestsize(desc->tfm); 212 213 error = -ENODATA; 214 list_for_each_entry_rcu(xattr, &evm_config_xattrnames, list) { 215 bool is_ima = false; 216 217 if (strcmp(xattr->name, XATTR_NAME_IMA) == 0) 218 is_ima = true; 219 220 if ((req_xattr_name && req_xattr_value) 221 && !strcmp(xattr->name, req_xattr_name)) { 222 error = 0; 223 crypto_shash_update(desc, (const u8 *)req_xattr_value, 224 req_xattr_value_len); 225 if (is_ima) 226 ima_present = true; 227 continue; 228 } 229 size = vfs_getxattr_alloc(dentry, xattr->name, 230 &xattr_value, xattr_size, GFP_NOFS); 231 if (size == -ENOMEM) { 232 error = -ENOMEM; 233 goto out; 234 } 235 if (size < 0) 236 continue; 237 238 error = 0; 239 xattr_size = size; 240 crypto_shash_update(desc, (const u8 *)xattr_value, xattr_size); 241 if (is_ima) 242 ima_present = true; 243 } 244 hmac_add_misc(desc, inode, type, data->digest); 245 246 /* Portable EVM signatures must include an IMA hash */ 247 if (type == EVM_XATTR_PORTABLE_DIGSIG && !ima_present) 248 return -EPERM; 249 out: 250 kfree(xattr_value); 251 kfree(desc); 252 return error; 253 } 254 255 int evm_calc_hmac(struct dentry *dentry, const char *req_xattr_name, 256 const char *req_xattr_value, size_t req_xattr_value_len, 257 struct evm_digest *data) 258 { 259 return evm_calc_hmac_or_hash(dentry, req_xattr_name, req_xattr_value, 260 req_xattr_value_len, EVM_XATTR_HMAC, data); 261 } 262 263 int evm_calc_hash(struct dentry *dentry, const char *req_xattr_name, 264 const char *req_xattr_value, size_t req_xattr_value_len, 265 char type, struct evm_digest *data) 266 { 267 return evm_calc_hmac_or_hash(dentry, req_xattr_name, req_xattr_value, 268 req_xattr_value_len, type, data); 269 } 270 271 static int evm_is_immutable(struct dentry *dentry, struct inode *inode) 272 { 273 const struct evm_ima_xattr_data *xattr_data = NULL; 274 struct integrity_iint_cache *iint; 275 int rc = 0; 276 277 iint = integrity_iint_find(inode); 278 if (iint && (iint->flags & EVM_IMMUTABLE_DIGSIG)) 279 return 1; 280 281 /* Do this the hard way */ 282 rc = vfs_getxattr_alloc(dentry, XATTR_NAME_EVM, (char **)&xattr_data, 0, 283 GFP_NOFS); 284 if (rc <= 0) { 285 if (rc == -ENODATA) 286 return 0; 287 return rc; 288 } 289 if (xattr_data->type == EVM_XATTR_PORTABLE_DIGSIG) 290 rc = 1; 291 else 292 rc = 0; 293 294 kfree(xattr_data); 295 return rc; 296 } 297 298 299 /* 300 * Calculate the hmac and update security.evm xattr 301 * 302 * Expects to be called with i_mutex locked. 303 */ 304 int evm_update_evmxattr(struct dentry *dentry, const char *xattr_name, 305 const char *xattr_value, size_t xattr_value_len) 306 { 307 struct inode *inode = d_backing_inode(dentry); 308 struct evm_digest data; 309 int rc = 0; 310 311 /* 312 * Don't permit any transformation of the EVM xattr if the signature 313 * is of an immutable type 314 */ 315 rc = evm_is_immutable(dentry, inode); 316 if (rc < 0) 317 return rc; 318 if (rc) 319 return -EPERM; 320 321 data.hdr.algo = HASH_ALGO_SHA1; 322 rc = evm_calc_hmac(dentry, xattr_name, xattr_value, 323 xattr_value_len, &data); 324 if (rc == 0) { 325 data.hdr.xattr.sha1.type = EVM_XATTR_HMAC; 326 rc = __vfs_setxattr_noperm(dentry, 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(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