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 "evm.h" 25 26 #define EVMKEY "evm-key" 27 #define MAX_KEY_SIZE 128 28 static unsigned char evmkey[MAX_KEY_SIZE]; 29 static int evmkey_len = MAX_KEY_SIZE; 30 31 struct crypto_shash *hmac_tfm; 32 struct crypto_shash *hash_tfm; 33 34 static DEFINE_MUTEX(mutex); 35 36 #define EVM_SET_KEY_BUSY 0 37 38 static unsigned long evm_set_key_flags; 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) 75 { 76 long rc; 77 char *algo; 78 struct crypto_shash **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 tfm = &hash_tfm; 90 algo = evm_hash; 91 } 92 93 if (*tfm == NULL) { 94 mutex_lock(&mutex); 95 if (*tfm) 96 goto out; 97 *tfm = crypto_alloc_shash(algo, 0, CRYPTO_ALG_ASYNC); 98 if (IS_ERR(*tfm)) { 99 rc = PTR_ERR(*tfm); 100 pr_err("Can not allocate %s (reason: %ld)\n", algo, rc); 101 *tfm = NULL; 102 mutex_unlock(&mutex); 103 return ERR_PTR(rc); 104 } 105 if (type == EVM_XATTR_HMAC) { 106 rc = crypto_shash_setkey(*tfm, evmkey, evmkey_len); 107 if (rc) { 108 crypto_free_shash(*tfm); 109 *tfm = NULL; 110 mutex_unlock(&mutex); 111 return ERR_PTR(rc); 112 } 113 } 114 out: 115 mutex_unlock(&mutex); 116 } 117 118 desc = kmalloc(sizeof(*desc) + crypto_shash_descsize(*tfm), 119 GFP_KERNEL); 120 if (!desc) 121 return ERR_PTR(-ENOMEM); 122 123 desc->tfm = *tfm; 124 desc->flags = CRYPTO_TFM_REQ_MAY_SLEEP; 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, &inode->i_sb->s_uuid.b[0], 174 sizeof(inode->i_sb->s_uuid)); 175 crypto_shash_final(desc, digest); 176 } 177 178 /* 179 * Calculate the HMAC value across the set of protected security xattrs. 180 * 181 * Instead of retrieving the requested xattr, for performance, calculate 182 * the hmac using the requested xattr value. Don't alloc/free memory for 183 * each xattr, but attempt to re-use the previously allocated memory. 184 */ 185 static int evm_calc_hmac_or_hash(struct dentry *dentry, 186 const char *req_xattr_name, 187 const char *req_xattr_value, 188 size_t req_xattr_value_len, 189 char type, char *digest) 190 { 191 struct inode *inode = d_backing_inode(dentry); 192 struct shash_desc *desc; 193 char **xattrname; 194 size_t xattr_size = 0; 195 char *xattr_value = NULL; 196 int error; 197 int size; 198 bool ima_present = false; 199 200 if (!(inode->i_opflags & IOP_XATTR)) 201 return -EOPNOTSUPP; 202 203 desc = init_desc(type); 204 if (IS_ERR(desc)) 205 return PTR_ERR(desc); 206 207 error = -ENODATA; 208 for (xattrname = evm_config_xattrnames; *xattrname != NULL; xattrname++) { 209 bool is_ima = false; 210 211 if (strcmp(*xattrname, XATTR_NAME_IMA) == 0) 212 is_ima = true; 213 214 if ((req_xattr_name && req_xattr_value) 215 && !strcmp(*xattrname, req_xattr_name)) { 216 error = 0; 217 crypto_shash_update(desc, (const u8 *)req_xattr_value, 218 req_xattr_value_len); 219 if (is_ima) 220 ima_present = true; 221 continue; 222 } 223 size = vfs_getxattr_alloc(dentry, *xattrname, 224 &xattr_value, xattr_size, GFP_NOFS); 225 if (size == -ENOMEM) { 226 error = -ENOMEM; 227 goto out; 228 } 229 if (size < 0) 230 continue; 231 232 error = 0; 233 xattr_size = size; 234 crypto_shash_update(desc, (const u8 *)xattr_value, xattr_size); 235 if (is_ima) 236 ima_present = true; 237 } 238 hmac_add_misc(desc, inode, type, digest); 239 240 /* Portable EVM signatures must include an IMA hash */ 241 if (type == EVM_XATTR_PORTABLE_DIGSIG && !ima_present) 242 return -EPERM; 243 out: 244 kfree(xattr_value); 245 kfree(desc); 246 return error; 247 } 248 249 int evm_calc_hmac(struct dentry *dentry, const char *req_xattr_name, 250 const char *req_xattr_value, size_t req_xattr_value_len, 251 char *digest) 252 { 253 return evm_calc_hmac_or_hash(dentry, req_xattr_name, req_xattr_value, 254 req_xattr_value_len, EVM_XATTR_HMAC, digest); 255 } 256 257 int evm_calc_hash(struct dentry *dentry, const char *req_xattr_name, 258 const char *req_xattr_value, size_t req_xattr_value_len, 259 char type, char *digest) 260 { 261 return evm_calc_hmac_or_hash(dentry, req_xattr_name, req_xattr_value, 262 req_xattr_value_len, type, digest); 263 } 264 265 static int evm_is_immutable(struct dentry *dentry, struct inode *inode) 266 { 267 const struct evm_ima_xattr_data *xattr_data = NULL; 268 struct integrity_iint_cache *iint; 269 int rc = 0; 270 271 iint = integrity_iint_find(inode); 272 if (iint && (iint->flags & EVM_IMMUTABLE_DIGSIG)) 273 return 1; 274 275 /* Do this the hard way */ 276 rc = vfs_getxattr_alloc(dentry, XATTR_NAME_EVM, (char **)&xattr_data, 0, 277 GFP_NOFS); 278 if (rc <= 0) { 279 if (rc == -ENODATA) 280 return 0; 281 return rc; 282 } 283 if (xattr_data->type == EVM_XATTR_PORTABLE_DIGSIG) 284 rc = 1; 285 else 286 rc = 0; 287 288 kfree(xattr_data); 289 return rc; 290 } 291 292 293 /* 294 * Calculate the hmac and update security.evm xattr 295 * 296 * Expects to be called with i_mutex locked. 297 */ 298 int evm_update_evmxattr(struct dentry *dentry, const char *xattr_name, 299 const char *xattr_value, size_t xattr_value_len) 300 { 301 struct inode *inode = d_backing_inode(dentry); 302 struct evm_ima_xattr_data xattr_data; 303 int rc = 0; 304 305 /* 306 * Don't permit any transformation of the EVM xattr if the signature 307 * is of an immutable type 308 */ 309 rc = evm_is_immutable(dentry, inode); 310 if (rc < 0) 311 return rc; 312 if (rc) 313 return -EPERM; 314 315 rc = evm_calc_hmac(dentry, xattr_name, xattr_value, 316 xattr_value_len, xattr_data.digest); 317 if (rc == 0) { 318 xattr_data.type = EVM_XATTR_HMAC; 319 rc = __vfs_setxattr_noperm(dentry, XATTR_NAME_EVM, 320 &xattr_data, 321 sizeof(xattr_data), 0); 322 } else if (rc == -ENODATA && (inode->i_opflags & IOP_XATTR)) { 323 rc = __vfs_removexattr(dentry, XATTR_NAME_EVM); 324 } 325 return rc; 326 } 327 328 int evm_init_hmac(struct inode *inode, const struct xattr *lsm_xattr, 329 char *hmac_val) 330 { 331 struct shash_desc *desc; 332 333 desc = init_desc(EVM_XATTR_HMAC); 334 if (IS_ERR(desc)) { 335 pr_info("init_desc failed\n"); 336 return PTR_ERR(desc); 337 } 338 339 crypto_shash_update(desc, lsm_xattr->value, lsm_xattr->value_len); 340 hmac_add_misc(desc, inode, EVM_XATTR_HMAC, hmac_val); 341 kfree(desc); 342 return 0; 343 } 344 345 /* 346 * Get the key from the TPM for the SHA1-HMAC 347 */ 348 int evm_init_key(void) 349 { 350 struct key *evm_key; 351 struct encrypted_key_payload *ekp; 352 int rc; 353 354 evm_key = request_key(&key_type_encrypted, EVMKEY, NULL); 355 if (IS_ERR(evm_key)) 356 return -ENOENT; 357 358 down_read(&evm_key->sem); 359 ekp = evm_key->payload.data[0]; 360 361 rc = evm_set_key(ekp->decrypted_data, ekp->decrypted_datalen); 362 363 /* burn the original key contents */ 364 memset(ekp->decrypted_data, 0, ekp->decrypted_datalen); 365 up_read(&evm_key->sem); 366 key_put(evm_key); 367 return rc; 368 } 369