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_opflags & IOP_XATTR)) 82 return -EOPNOTSUPP; 83 84 for (xattr = evm_config_xattrnames; *xattr != NULL; xattr++) { 85 error = __vfs_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 if (xattr_len != sizeof(struct evm_ima_xattr_data)) { 149 evm_status = INTEGRITY_FAIL; 150 goto out; 151 } 152 rc = evm_calc_hmac(dentry, xattr_name, xattr_value, 153 xattr_value_len, calc.digest); 154 if (rc) 155 break; 156 rc = crypto_memneq(xattr_data->digest, calc.digest, 157 sizeof(calc.digest)); 158 if (rc) 159 rc = -EINVAL; 160 break; 161 case EVM_IMA_XATTR_DIGSIG: 162 rc = evm_calc_hash(dentry, xattr_name, xattr_value, 163 xattr_value_len, calc.digest); 164 if (rc) 165 break; 166 rc = integrity_digsig_verify(INTEGRITY_KEYRING_EVM, 167 (const char *)xattr_data, xattr_len, 168 calc.digest, sizeof(calc.digest)); 169 if (!rc) { 170 /* Replace RSA with HMAC if not mounted readonly and 171 * not immutable 172 */ 173 if (!IS_RDONLY(d_backing_inode(dentry)) && 174 !IS_IMMUTABLE(d_backing_inode(dentry))) 175 evm_update_evmxattr(dentry, xattr_name, 176 xattr_value, 177 xattr_value_len); 178 } 179 break; 180 default: 181 rc = -EINVAL; 182 break; 183 } 184 185 if (rc) 186 evm_status = (rc == -ENODATA) ? 187 INTEGRITY_NOXATTRS : INTEGRITY_FAIL; 188 out: 189 if (iint) 190 iint->evm_status = evm_status; 191 kfree(xattr_data); 192 return evm_status; 193 } 194 195 static int evm_protected_xattr(const char *req_xattr_name) 196 { 197 char **xattrname; 198 int namelen; 199 int found = 0; 200 201 namelen = strlen(req_xattr_name); 202 for (xattrname = evm_config_xattrnames; *xattrname != NULL; xattrname++) { 203 if ((strlen(*xattrname) == namelen) 204 && (strncmp(req_xattr_name, *xattrname, namelen) == 0)) { 205 found = 1; 206 break; 207 } 208 if (strncmp(req_xattr_name, 209 *xattrname + XATTR_SECURITY_PREFIX_LEN, 210 strlen(req_xattr_name)) == 0) { 211 found = 1; 212 break; 213 } 214 } 215 return found; 216 } 217 218 /** 219 * evm_verifyxattr - verify the integrity of the requested xattr 220 * @dentry: object of the verify xattr 221 * @xattr_name: requested xattr 222 * @xattr_value: requested xattr value 223 * @xattr_value_len: requested xattr value length 224 * 225 * Calculate the HMAC for the given dentry and verify it against the stored 226 * security.evm xattr. For performance, use the xattr value and length 227 * previously retrieved to calculate the HMAC. 228 * 229 * Returns the xattr integrity status. 230 * 231 * This function requires the caller to lock the inode's i_mutex before it 232 * is executed. 233 */ 234 enum integrity_status evm_verifyxattr(struct dentry *dentry, 235 const char *xattr_name, 236 void *xattr_value, size_t xattr_value_len, 237 struct integrity_iint_cache *iint) 238 { 239 if (!evm_initialized || !evm_protected_xattr(xattr_name)) 240 return INTEGRITY_UNKNOWN; 241 242 if (!iint) { 243 iint = integrity_iint_find(d_backing_inode(dentry)); 244 if (!iint) 245 return INTEGRITY_UNKNOWN; 246 } 247 return evm_verify_hmac(dentry, xattr_name, xattr_value, 248 xattr_value_len, iint); 249 } 250 EXPORT_SYMBOL_GPL(evm_verifyxattr); 251 252 /* 253 * evm_verify_current_integrity - verify the dentry's metadata integrity 254 * @dentry: pointer to the affected dentry 255 * 256 * Verify and return the dentry's metadata integrity. The exceptions are 257 * before EVM is initialized or in 'fix' mode. 258 */ 259 static enum integrity_status evm_verify_current_integrity(struct dentry *dentry) 260 { 261 struct inode *inode = d_backing_inode(dentry); 262 263 if (!evm_initialized || !S_ISREG(inode->i_mode) || evm_fixmode) 264 return 0; 265 return evm_verify_hmac(dentry, NULL, NULL, 0, NULL); 266 } 267 268 /* 269 * evm_protect_xattr - protect the EVM extended attribute 270 * 271 * Prevent security.evm from being modified or removed without the 272 * necessary permissions or when the existing value is invalid. 273 * 274 * The posix xattr acls are 'system' prefixed, which normally would not 275 * affect security.evm. An interesting side affect of writing posix xattr 276 * acls is their modifying of the i_mode, which is included in security.evm. 277 * For posix xattr acls only, permit security.evm, even if it currently 278 * doesn't exist, to be updated. 279 */ 280 static int evm_protect_xattr(struct dentry *dentry, const char *xattr_name, 281 const void *xattr_value, size_t xattr_value_len) 282 { 283 enum integrity_status evm_status; 284 285 if (strcmp(xattr_name, XATTR_NAME_EVM) == 0) { 286 if (!capable(CAP_SYS_ADMIN)) 287 return -EPERM; 288 } else if (!evm_protected_xattr(xattr_name)) { 289 if (!posix_xattr_acl(xattr_name)) 290 return 0; 291 evm_status = evm_verify_current_integrity(dentry); 292 if ((evm_status == INTEGRITY_PASS) || 293 (evm_status == INTEGRITY_NOXATTRS)) 294 return 0; 295 goto out; 296 } 297 evm_status = evm_verify_current_integrity(dentry); 298 if (evm_status == INTEGRITY_NOXATTRS) { 299 struct integrity_iint_cache *iint; 300 301 iint = integrity_iint_find(d_backing_inode(dentry)); 302 if (iint && (iint->flags & IMA_NEW_FILE)) 303 return 0; 304 305 /* exception for pseudo filesystems */ 306 if (dentry->d_sb->s_magic == TMPFS_MAGIC 307 || dentry->d_sb->s_magic == SYSFS_MAGIC) 308 return 0; 309 310 integrity_audit_msg(AUDIT_INTEGRITY_METADATA, 311 dentry->d_inode, dentry->d_name.name, 312 "update_metadata", 313 integrity_status_msg[evm_status], 314 -EPERM, 0); 315 } 316 out: 317 if (evm_status != INTEGRITY_PASS) 318 integrity_audit_msg(AUDIT_INTEGRITY_METADATA, d_backing_inode(dentry), 319 dentry->d_name.name, "appraise_metadata", 320 integrity_status_msg[evm_status], 321 -EPERM, 0); 322 return evm_status == INTEGRITY_PASS ? 0 : -EPERM; 323 } 324 325 /** 326 * evm_inode_setxattr - protect the EVM extended attribute 327 * @dentry: pointer to the affected dentry 328 * @xattr_name: pointer to the affected extended attribute name 329 * @xattr_value: pointer to the new extended attribute value 330 * @xattr_value_len: pointer to the new extended attribute value length 331 * 332 * Before allowing the 'security.evm' protected xattr to be updated, 333 * verify the existing value is valid. As only the kernel should have 334 * access to the EVM encrypted key needed to calculate the HMAC, prevent 335 * userspace from writing HMAC value. Writing 'security.evm' requires 336 * requires CAP_SYS_ADMIN privileges. 337 */ 338 int evm_inode_setxattr(struct dentry *dentry, const char *xattr_name, 339 const void *xattr_value, size_t xattr_value_len) 340 { 341 const struct evm_ima_xattr_data *xattr_data = xattr_value; 342 343 if (strcmp(xattr_name, XATTR_NAME_EVM) == 0) { 344 if (!xattr_value_len) 345 return -EINVAL; 346 if (xattr_data->type != EVM_IMA_XATTR_DIGSIG) 347 return -EPERM; 348 } 349 return evm_protect_xattr(dentry, xattr_name, xattr_value, 350 xattr_value_len); 351 } 352 353 /** 354 * evm_inode_removexattr - protect the EVM extended attribute 355 * @dentry: pointer to the affected dentry 356 * @xattr_name: pointer to the affected extended attribute name 357 * 358 * Removing 'security.evm' requires CAP_SYS_ADMIN privileges and that 359 * the current value is valid. 360 */ 361 int evm_inode_removexattr(struct dentry *dentry, const char *xattr_name) 362 { 363 return evm_protect_xattr(dentry, xattr_name, NULL, 0); 364 } 365 366 static void evm_reset_status(struct inode *inode) 367 { 368 struct integrity_iint_cache *iint; 369 370 iint = integrity_iint_find(inode); 371 if (iint) 372 iint->evm_status = INTEGRITY_UNKNOWN; 373 } 374 375 /** 376 * evm_inode_post_setxattr - update 'security.evm' to reflect the changes 377 * @dentry: pointer to the affected dentry 378 * @xattr_name: pointer to the affected extended attribute name 379 * @xattr_value: pointer to the new extended attribute value 380 * @xattr_value_len: pointer to the new extended attribute value length 381 * 382 * Update the HMAC stored in 'security.evm' to reflect the change. 383 * 384 * No need to take the i_mutex lock here, as this function is called from 385 * __vfs_setxattr_noperm(). The caller of which has taken the inode's 386 * i_mutex lock. 387 */ 388 void evm_inode_post_setxattr(struct dentry *dentry, const char *xattr_name, 389 const void *xattr_value, size_t xattr_value_len) 390 { 391 if (!evm_initialized || (!evm_protected_xattr(xattr_name) 392 && !posix_xattr_acl(xattr_name))) 393 return; 394 395 evm_reset_status(dentry->d_inode); 396 397 evm_update_evmxattr(dentry, xattr_name, xattr_value, xattr_value_len); 398 } 399 400 /** 401 * evm_inode_post_removexattr - update 'security.evm' after removing the xattr 402 * @dentry: pointer to the affected dentry 403 * @xattr_name: pointer to the affected extended attribute name 404 * 405 * Update the HMAC stored in 'security.evm' to reflect removal of the xattr. 406 * 407 * No need to take the i_mutex lock here, as this function is called from 408 * vfs_removexattr() which takes the i_mutex. 409 */ 410 void evm_inode_post_removexattr(struct dentry *dentry, const char *xattr_name) 411 { 412 if (!evm_initialized || !evm_protected_xattr(xattr_name)) 413 return; 414 415 evm_reset_status(dentry->d_inode); 416 417 evm_update_evmxattr(dentry, xattr_name, NULL, 0); 418 } 419 420 /** 421 * evm_inode_setattr - prevent updating an invalid EVM extended attribute 422 * @dentry: pointer to the affected dentry 423 */ 424 int evm_inode_setattr(struct dentry *dentry, struct iattr *attr) 425 { 426 unsigned int ia_valid = attr->ia_valid; 427 enum integrity_status evm_status; 428 429 if (!(ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID))) 430 return 0; 431 evm_status = evm_verify_current_integrity(dentry); 432 if ((evm_status == INTEGRITY_PASS) || 433 (evm_status == INTEGRITY_NOXATTRS)) 434 return 0; 435 integrity_audit_msg(AUDIT_INTEGRITY_METADATA, d_backing_inode(dentry), 436 dentry->d_name.name, "appraise_metadata", 437 integrity_status_msg[evm_status], -EPERM, 0); 438 return -EPERM; 439 } 440 441 /** 442 * evm_inode_post_setattr - update 'security.evm' after modifying metadata 443 * @dentry: pointer to the affected dentry 444 * @ia_valid: for the UID and GID status 445 * 446 * For now, update the HMAC stored in 'security.evm' to reflect UID/GID 447 * changes. 448 * 449 * This function is called from notify_change(), which expects the caller 450 * to lock the inode's i_mutex. 451 */ 452 void evm_inode_post_setattr(struct dentry *dentry, int ia_valid) 453 { 454 if (!evm_initialized) 455 return; 456 457 if (ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID)) 458 evm_update_evmxattr(dentry, NULL, NULL, 0); 459 } 460 461 /* 462 * evm_inode_init_security - initializes security.evm 463 */ 464 int evm_inode_init_security(struct inode *inode, 465 const struct xattr *lsm_xattr, 466 struct xattr *evm_xattr) 467 { 468 struct evm_ima_xattr_data *xattr_data; 469 int rc; 470 471 if (!evm_initialized || !evm_protected_xattr(lsm_xattr->name)) 472 return 0; 473 474 xattr_data = kzalloc(sizeof(*xattr_data), GFP_NOFS); 475 if (!xattr_data) 476 return -ENOMEM; 477 478 xattr_data->type = EVM_XATTR_HMAC; 479 rc = evm_init_hmac(inode, lsm_xattr, xattr_data->digest); 480 if (rc < 0) 481 goto out; 482 483 evm_xattr->value = xattr_data; 484 evm_xattr->value_len = sizeof(*xattr_data); 485 evm_xattr->name = XATTR_EVM_SUFFIX; 486 return 0; 487 out: 488 kfree(xattr_data); 489 return rc; 490 } 491 EXPORT_SYMBOL_GPL(evm_inode_init_security); 492 493 #ifdef CONFIG_EVM_LOAD_X509 494 void __init evm_load_x509(void) 495 { 496 int rc; 497 498 rc = integrity_load_x509(INTEGRITY_KEYRING_EVM, CONFIG_EVM_X509_PATH); 499 if (!rc) 500 evm_initialized |= EVM_INIT_X509; 501 } 502 #endif 503 504 static int __init init_evm(void) 505 { 506 int error; 507 508 evm_init_config(); 509 510 error = integrity_init_keyring(INTEGRITY_KEYRING_EVM); 511 if (error) 512 return error; 513 514 error = evm_init_secfs(); 515 if (error < 0) { 516 pr_info("Error registering secfs\n"); 517 return error; 518 } 519 520 return 0; 521 } 522 523 /* 524 * evm_display_config - list the EVM protected security extended attributes 525 */ 526 static int __init evm_display_config(void) 527 { 528 char **xattrname; 529 530 for (xattrname = evm_config_xattrnames; *xattrname != NULL; xattrname++) 531 pr_info("%s\n", *xattrname); 532 return 0; 533 } 534 535 pure_initcall(evm_display_config); 536 late_initcall(init_evm); 537 538 MODULE_DESCRIPTION("Extended Verification Module"); 539 MODULE_LICENSE("GPL"); 540