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