1 /* 2 * Copyright (C) 2005-2010 IBM Corporation 3 * 4 * Author: 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_main.c 13 * implements evm_inode_setxattr, evm_inode_post_setxattr, 14 * evm_inode_removexattr, and evm_verifyxattr 15 */ 16 17 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt 18 19 #include <linux/module.h> 20 #include <linux/crypto.h> 21 #include <linux/audit.h> 22 #include <linux/xattr.h> 23 #include <linux/integrity.h> 24 #include <linux/evm.h> 25 #include <crypto/hash.h> 26 #include <crypto/algapi.h> 27 #include "evm.h" 28 29 int evm_initialized; 30 31 static char *integrity_status_msg[] = { 32 "pass", "fail", "no_label", "no_xattrs", "unknown" 33 }; 34 char *evm_hmac = "hmac(sha1)"; 35 char *evm_hash = "sha1"; 36 int evm_hmac_attrs; 37 38 char *evm_config_xattrnames[] = { 39 #ifdef CONFIG_SECURITY_SELINUX 40 XATTR_NAME_SELINUX, 41 #endif 42 #ifdef CONFIG_SECURITY_SMACK 43 XATTR_NAME_SMACK, 44 #ifdef CONFIG_EVM_EXTRA_SMACK_XATTRS 45 XATTR_NAME_SMACKEXEC, 46 XATTR_NAME_SMACKTRANSMUTE, 47 XATTR_NAME_SMACKMMAP, 48 #endif 49 #endif 50 #ifdef CONFIG_IMA_APPRAISE 51 XATTR_NAME_IMA, 52 #endif 53 XATTR_NAME_CAPS, 54 NULL 55 }; 56 57 static int evm_fixmode; 58 static int __init evm_set_fixmode(char *str) 59 { 60 if (strncmp(str, "fix", 3) == 0) 61 evm_fixmode = 1; 62 return 0; 63 } 64 __setup("evm=", evm_set_fixmode); 65 66 static void __init evm_init_config(void) 67 { 68 #ifdef CONFIG_EVM_ATTR_FSUUID 69 evm_hmac_attrs |= EVM_ATTR_FSUUID; 70 #endif 71 pr_info("HMAC attrs: 0x%x\n", evm_hmac_attrs); 72 } 73 74 static int evm_find_protected_xattrs(struct dentry *dentry) 75 { 76 struct inode *inode = d_backing_inode(dentry); 77 char **xattr; 78 int error; 79 int count = 0; 80 81 if (!inode->i_op->getxattr) 82 return -EOPNOTSUPP; 83 84 for (xattr = evm_config_xattrnames; *xattr != NULL; xattr++) { 85 error = inode->i_op->getxattr(dentry, inode, *xattr, NULL, 0); 86 if (error < 0) { 87 if (error == -ENODATA) 88 continue; 89 return error; 90 } 91 count++; 92 } 93 94 return count; 95 } 96 97 /* 98 * evm_verify_hmac - calculate and compare the HMAC with the EVM xattr 99 * 100 * Compute the HMAC on the dentry's protected set of extended attributes 101 * and compare it against the stored security.evm xattr. 102 * 103 * For performance: 104 * - use the previoulsy retrieved xattr value and length to calculate the 105 * HMAC.) 106 * - cache the verification result in the iint, when available. 107 * 108 * Returns integrity status 109 */ 110 static enum integrity_status evm_verify_hmac(struct dentry *dentry, 111 const char *xattr_name, 112 char *xattr_value, 113 size_t xattr_value_len, 114 struct integrity_iint_cache *iint) 115 { 116 struct evm_ima_xattr_data *xattr_data = NULL; 117 struct evm_ima_xattr_data calc; 118 enum integrity_status evm_status = INTEGRITY_PASS; 119 int rc, xattr_len; 120 121 if (iint && iint->evm_status == INTEGRITY_PASS) 122 return iint->evm_status; 123 124 /* if status is not PASS, try to check again - against -ENOMEM */ 125 126 /* first need to know the sig type */ 127 rc = vfs_getxattr_alloc(dentry, XATTR_NAME_EVM, (char **)&xattr_data, 0, 128 GFP_NOFS); 129 if (rc <= 0) { 130 evm_status = INTEGRITY_FAIL; 131 if (rc == -ENODATA) { 132 rc = evm_find_protected_xattrs(dentry); 133 if (rc > 0) 134 evm_status = INTEGRITY_NOLABEL; 135 else if (rc == 0) 136 evm_status = INTEGRITY_NOXATTRS; /* new file */ 137 } else if (rc == -EOPNOTSUPP) { 138 evm_status = INTEGRITY_UNKNOWN; 139 } 140 goto out; 141 } 142 143 xattr_len = rc; 144 145 /* check value type */ 146 switch (xattr_data->type) { 147 case EVM_XATTR_HMAC: 148 rc = evm_calc_hmac(dentry, xattr_name, xattr_value, 149 xattr_value_len, calc.digest); 150 if (rc) 151 break; 152 rc = crypto_memneq(xattr_data->digest, calc.digest, 153 sizeof(calc.digest)); 154 if (rc) 155 rc = -EINVAL; 156 break; 157 case EVM_IMA_XATTR_DIGSIG: 158 rc = evm_calc_hash(dentry, xattr_name, xattr_value, 159 xattr_value_len, calc.digest); 160 if (rc) 161 break; 162 rc = integrity_digsig_verify(INTEGRITY_KEYRING_EVM, 163 (const char *)xattr_data, xattr_len, 164 calc.digest, sizeof(calc.digest)); 165 if (!rc) { 166 /* Replace RSA with HMAC if not mounted readonly and 167 * not immutable 168 */ 169 if (!IS_RDONLY(d_backing_inode(dentry)) && 170 !IS_IMMUTABLE(d_backing_inode(dentry))) 171 evm_update_evmxattr(dentry, xattr_name, 172 xattr_value, 173 xattr_value_len); 174 } 175 break; 176 default: 177 rc = -EINVAL; 178 break; 179 } 180 181 if (rc) 182 evm_status = (rc == -ENODATA) ? 183 INTEGRITY_NOXATTRS : INTEGRITY_FAIL; 184 out: 185 if (iint) 186 iint->evm_status = evm_status; 187 kfree(xattr_data); 188 return evm_status; 189 } 190 191 static int evm_protected_xattr(const char *req_xattr_name) 192 { 193 char **xattrname; 194 int namelen; 195 int found = 0; 196 197 namelen = strlen(req_xattr_name); 198 for (xattrname = evm_config_xattrnames; *xattrname != NULL; xattrname++) { 199 if ((strlen(*xattrname) == namelen) 200 && (strncmp(req_xattr_name, *xattrname, namelen) == 0)) { 201 found = 1; 202 break; 203 } 204 if (strncmp(req_xattr_name, 205 *xattrname + XATTR_SECURITY_PREFIX_LEN, 206 strlen(req_xattr_name)) == 0) { 207 found = 1; 208 break; 209 } 210 } 211 return found; 212 } 213 214 /** 215 * evm_verifyxattr - verify the integrity of the requested xattr 216 * @dentry: object of the verify xattr 217 * @xattr_name: requested xattr 218 * @xattr_value: requested xattr value 219 * @xattr_value_len: requested xattr value length 220 * 221 * Calculate the HMAC for the given dentry and verify it against the stored 222 * security.evm xattr. For performance, use the xattr value and length 223 * previously retrieved to calculate the HMAC. 224 * 225 * Returns the xattr integrity status. 226 * 227 * This function requires the caller to lock the inode's i_mutex before it 228 * is executed. 229 */ 230 enum integrity_status evm_verifyxattr(struct dentry *dentry, 231 const char *xattr_name, 232 void *xattr_value, size_t xattr_value_len, 233 struct integrity_iint_cache *iint) 234 { 235 if (!evm_initialized || !evm_protected_xattr(xattr_name)) 236 return INTEGRITY_UNKNOWN; 237 238 if (!iint) { 239 iint = integrity_iint_find(d_backing_inode(dentry)); 240 if (!iint) 241 return INTEGRITY_UNKNOWN; 242 } 243 return evm_verify_hmac(dentry, xattr_name, xattr_value, 244 xattr_value_len, iint); 245 } 246 EXPORT_SYMBOL_GPL(evm_verifyxattr); 247 248 /* 249 * evm_verify_current_integrity - verify the dentry's metadata integrity 250 * @dentry: pointer to the affected dentry 251 * 252 * Verify and return the dentry's metadata integrity. The exceptions are 253 * before EVM is initialized or in 'fix' mode. 254 */ 255 static enum integrity_status evm_verify_current_integrity(struct dentry *dentry) 256 { 257 struct inode *inode = d_backing_inode(dentry); 258 259 if (!evm_initialized || !S_ISREG(inode->i_mode) || evm_fixmode) 260 return 0; 261 return evm_verify_hmac(dentry, NULL, NULL, 0, NULL); 262 } 263 264 /* 265 * evm_protect_xattr - protect the EVM extended attribute 266 * 267 * Prevent security.evm from being modified or removed without the 268 * necessary permissions or when the existing value is invalid. 269 * 270 * The posix xattr acls are 'system' prefixed, which normally would not 271 * affect security.evm. An interesting side affect of writing posix xattr 272 * acls is their modifying of the i_mode, which is included in security.evm. 273 * For posix xattr acls only, permit security.evm, even if it currently 274 * doesn't exist, to be updated. 275 */ 276 static int evm_protect_xattr(struct dentry *dentry, const char *xattr_name, 277 const void *xattr_value, size_t xattr_value_len) 278 { 279 enum integrity_status evm_status; 280 281 if (strcmp(xattr_name, XATTR_NAME_EVM) == 0) { 282 if (!capable(CAP_SYS_ADMIN)) 283 return -EPERM; 284 } else if (!evm_protected_xattr(xattr_name)) { 285 if (!posix_xattr_acl(xattr_name)) 286 return 0; 287 evm_status = evm_verify_current_integrity(dentry); 288 if ((evm_status == INTEGRITY_PASS) || 289 (evm_status == INTEGRITY_NOXATTRS)) 290 return 0; 291 goto out; 292 } 293 evm_status = evm_verify_current_integrity(dentry); 294 if (evm_status == INTEGRITY_NOXATTRS) { 295 struct integrity_iint_cache *iint; 296 297 iint = integrity_iint_find(d_backing_inode(dentry)); 298 if (iint && (iint->flags & IMA_NEW_FILE)) 299 return 0; 300 301 /* exception for pseudo filesystems */ 302 if (dentry->d_sb->s_magic == TMPFS_MAGIC 303 || dentry->d_sb->s_magic == SYSFS_MAGIC) 304 return 0; 305 306 integrity_audit_msg(AUDIT_INTEGRITY_METADATA, 307 dentry->d_inode, dentry->d_name.name, 308 "update_metadata", 309 integrity_status_msg[evm_status], 310 -EPERM, 0); 311 } 312 out: 313 if (evm_status != INTEGRITY_PASS) 314 integrity_audit_msg(AUDIT_INTEGRITY_METADATA, d_backing_inode(dentry), 315 dentry->d_name.name, "appraise_metadata", 316 integrity_status_msg[evm_status], 317 -EPERM, 0); 318 return evm_status == INTEGRITY_PASS ? 0 : -EPERM; 319 } 320 321 /** 322 * evm_inode_setxattr - protect the EVM extended attribute 323 * @dentry: pointer to the affected dentry 324 * @xattr_name: pointer to the affected extended attribute name 325 * @xattr_value: pointer to the new extended attribute value 326 * @xattr_value_len: pointer to the new extended attribute value length 327 * 328 * Before allowing the 'security.evm' protected xattr to be updated, 329 * verify the existing value is valid. As only the kernel should have 330 * access to the EVM encrypted key needed to calculate the HMAC, prevent 331 * userspace from writing HMAC value. Writing 'security.evm' requires 332 * requires CAP_SYS_ADMIN privileges. 333 */ 334 int evm_inode_setxattr(struct dentry *dentry, const char *xattr_name, 335 const void *xattr_value, size_t xattr_value_len) 336 { 337 const struct evm_ima_xattr_data *xattr_data = xattr_value; 338 339 if (strcmp(xattr_name, XATTR_NAME_EVM) == 0) { 340 if (!xattr_value_len) 341 return -EINVAL; 342 if (xattr_data->type != EVM_IMA_XATTR_DIGSIG) 343 return -EPERM; 344 } 345 return evm_protect_xattr(dentry, xattr_name, xattr_value, 346 xattr_value_len); 347 } 348 349 /** 350 * evm_inode_removexattr - protect the EVM extended attribute 351 * @dentry: pointer to the affected dentry 352 * @xattr_name: pointer to the affected extended attribute name 353 * 354 * Removing 'security.evm' requires CAP_SYS_ADMIN privileges and that 355 * the current value is valid. 356 */ 357 int evm_inode_removexattr(struct dentry *dentry, const char *xattr_name) 358 { 359 return evm_protect_xattr(dentry, xattr_name, NULL, 0); 360 } 361 362 static void evm_reset_status(struct inode *inode) 363 { 364 struct integrity_iint_cache *iint; 365 366 iint = integrity_iint_find(inode); 367 if (iint) 368 iint->evm_status = INTEGRITY_UNKNOWN; 369 } 370 371 /** 372 * evm_inode_post_setxattr - update 'security.evm' to reflect the changes 373 * @dentry: pointer to the affected dentry 374 * @xattr_name: pointer to the affected extended attribute name 375 * @xattr_value: pointer to the new extended attribute value 376 * @xattr_value_len: pointer to the new extended attribute value length 377 * 378 * Update the HMAC stored in 'security.evm' to reflect the change. 379 * 380 * No need to take the i_mutex lock here, as this function is called from 381 * __vfs_setxattr_noperm(). The caller of which has taken the inode's 382 * i_mutex lock. 383 */ 384 void evm_inode_post_setxattr(struct dentry *dentry, const char *xattr_name, 385 const void *xattr_value, size_t xattr_value_len) 386 { 387 if (!evm_initialized || (!evm_protected_xattr(xattr_name) 388 && !posix_xattr_acl(xattr_name))) 389 return; 390 391 evm_reset_status(dentry->d_inode); 392 393 evm_update_evmxattr(dentry, xattr_name, xattr_value, xattr_value_len); 394 } 395 396 /** 397 * evm_inode_post_removexattr - update 'security.evm' after removing the xattr 398 * @dentry: pointer to the affected dentry 399 * @xattr_name: pointer to the affected extended attribute name 400 * 401 * Update the HMAC stored in 'security.evm' to reflect removal of the xattr. 402 * 403 * No need to take the i_mutex lock here, as this function is called from 404 * vfs_removexattr() which takes the i_mutex. 405 */ 406 void evm_inode_post_removexattr(struct dentry *dentry, const char *xattr_name) 407 { 408 if (!evm_initialized || !evm_protected_xattr(xattr_name)) 409 return; 410 411 evm_reset_status(dentry->d_inode); 412 413 evm_update_evmxattr(dentry, xattr_name, NULL, 0); 414 } 415 416 /** 417 * evm_inode_setattr - prevent updating an invalid EVM extended attribute 418 * @dentry: pointer to the affected dentry 419 */ 420 int evm_inode_setattr(struct dentry *dentry, struct iattr *attr) 421 { 422 unsigned int ia_valid = attr->ia_valid; 423 enum integrity_status evm_status; 424 425 if (!(ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID))) 426 return 0; 427 evm_status = evm_verify_current_integrity(dentry); 428 if ((evm_status == INTEGRITY_PASS) || 429 (evm_status == INTEGRITY_NOXATTRS)) 430 return 0; 431 integrity_audit_msg(AUDIT_INTEGRITY_METADATA, d_backing_inode(dentry), 432 dentry->d_name.name, "appraise_metadata", 433 integrity_status_msg[evm_status], -EPERM, 0); 434 return -EPERM; 435 } 436 437 /** 438 * evm_inode_post_setattr - update 'security.evm' after modifying metadata 439 * @dentry: pointer to the affected dentry 440 * @ia_valid: for the UID and GID status 441 * 442 * For now, update the HMAC stored in 'security.evm' to reflect UID/GID 443 * changes. 444 * 445 * This function is called from notify_change(), which expects the caller 446 * to lock the inode's i_mutex. 447 */ 448 void evm_inode_post_setattr(struct dentry *dentry, int ia_valid) 449 { 450 if (!evm_initialized) 451 return; 452 453 if (ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID)) 454 evm_update_evmxattr(dentry, NULL, NULL, 0); 455 } 456 457 /* 458 * evm_inode_init_security - initializes security.evm 459 */ 460 int evm_inode_init_security(struct inode *inode, 461 const struct xattr *lsm_xattr, 462 struct xattr *evm_xattr) 463 { 464 struct evm_ima_xattr_data *xattr_data; 465 int rc; 466 467 if (!evm_initialized || !evm_protected_xattr(lsm_xattr->name)) 468 return 0; 469 470 xattr_data = kzalloc(sizeof(*xattr_data), GFP_NOFS); 471 if (!xattr_data) 472 return -ENOMEM; 473 474 xattr_data->type = EVM_XATTR_HMAC; 475 rc = evm_init_hmac(inode, lsm_xattr, xattr_data->digest); 476 if (rc < 0) 477 goto out; 478 479 evm_xattr->value = xattr_data; 480 evm_xattr->value_len = sizeof(*xattr_data); 481 evm_xattr->name = XATTR_EVM_SUFFIX; 482 return 0; 483 out: 484 kfree(xattr_data); 485 return rc; 486 } 487 EXPORT_SYMBOL_GPL(evm_inode_init_security); 488 489 #ifdef CONFIG_EVM_LOAD_X509 490 void __init evm_load_x509(void) 491 { 492 int rc; 493 494 rc = integrity_load_x509(INTEGRITY_KEYRING_EVM, CONFIG_EVM_X509_PATH); 495 if (!rc) 496 evm_initialized |= EVM_INIT_X509; 497 } 498 #endif 499 500 static int __init init_evm(void) 501 { 502 int error; 503 504 evm_init_config(); 505 506 error = integrity_init_keyring(INTEGRITY_KEYRING_EVM); 507 if (error) 508 return error; 509 510 error = evm_init_secfs(); 511 if (error < 0) { 512 pr_info("Error registering secfs\n"); 513 return error; 514 } 515 516 return 0; 517 } 518 519 /* 520 * evm_display_config - list the EVM protected security extended attributes 521 */ 522 static int __init evm_display_config(void) 523 { 524 char **xattrname; 525 526 for (xattrname = evm_config_xattrnames; *xattrname != NULL; xattrname++) 527 pr_info("%s\n", *xattrname); 528 return 0; 529 } 530 531 pure_initcall(evm_display_config); 532 late_initcall(init_evm); 533 534 MODULE_DESCRIPTION("Extended Verification Module"); 535 MODULE_LICENSE("GPL"); 536