root/security/integrity/evm/evm_main.c

DEFINITIONS

1. evm_set_fixmode
2. evm_init_config
3. evm_key_loaded
4. evm_find_protected_xattrs
5. evm_verify_hmac
6. evm_protected_xattr
7. evm_verifyxattr
8. evm_verify_current_integrity
9. evm_protect_xattr
10. evm_inode_setxattr
11. evm_inode_removexattr
12. evm_reset_status
13. evm_inode_post_setxattr
14. evm_inode_post_removexattr
15. evm_inode_setattr
16. evm_inode_post_setattr
17. evm_inode_init_security
18. evm_load_x509
19. init_evm

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  * Copyright (C) 2005-2010 IBM Corporation
   4  *
   5  * Author:
   6  * Mimi Zohar <zohar@us.ibm.com>
   7  * Kylene Hall <kjhall@us.ibm.com>
   8  *
   9  * File: evm_main.c
  10  *      implements evm_inode_setxattr, evm_inode_post_setxattr,
  11  *      evm_inode_removexattr, and evm_verifyxattr
  12  */
  13 
  14 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  15 
  16 #include <linux/init.h>
  17 #include <linux/crypto.h>
  18 #include <linux/audit.h>
  19 #include <linux/xattr.h>
  20 #include <linux/integrity.h>
  21 #include <linux/evm.h>
  22 #include <linux/magic.h>
  23 
  24 #include <crypto/hash.h>
  25 #include <crypto/hash_info.h>
  26 #include <crypto/algapi.h>
  27 #include "evm.h"
  28 
  29 int evm_initialized;
  30 
  31 static const char * const integrity_status_msg[] = {
  32         "pass", "pass_immutable", "fail", "no_label", "no_xattrs", "unknown"
  33 };
  34 int evm_hmac_attrs;
  35 
  36 static struct xattr_list evm_config_default_xattrnames[] = {
  37 #ifdef CONFIG_SECURITY_SELINUX
  38         {.name = XATTR_NAME_SELINUX},
  39 #endif
  40 #ifdef CONFIG_SECURITY_SMACK
  41         {.name = XATTR_NAME_SMACK},
  42 #ifdef CONFIG_EVM_EXTRA_SMACK_XATTRS
  43         {.name = XATTR_NAME_SMACKEXEC},
  44         {.name = XATTR_NAME_SMACKTRANSMUTE},
  45         {.name = XATTR_NAME_SMACKMMAP},
  46 #endif
  47 #endif
  48 #ifdef CONFIG_SECURITY_APPARMOR
  49         {.name = XATTR_NAME_APPARMOR},
  50 #endif
  51 #ifdef CONFIG_IMA_APPRAISE
  52         {.name = XATTR_NAME_IMA},
  53 #endif
  54         {.name = XATTR_NAME_CAPS},
  55 };
  56 
  57 LIST_HEAD(evm_config_xattrnames);
  58 
  59 static int evm_fixmode;
  60 static int __init evm_set_fixmode(char *str)
  61 {
  62         if (strncmp(str, "fix", 3) == 0)
  63                 evm_fixmode = 1;
  64         return 0;
  65 }
  66 __setup("evm=", evm_set_fixmode);
  67 
  68 static void __init evm_init_config(void)
  69 {
  70         int i, xattrs;
  71 
  72         xattrs = ARRAY_SIZE(evm_config_default_xattrnames);
  73 
  74         pr_info("Initialising EVM extended attributes:\n");
  75         for (i = 0; i < xattrs; i++) {
  76                 pr_info("%s\n", evm_config_default_xattrnames[i].name);
  77                 list_add_tail(&evm_config_default_xattrnames[i].list,
  78                               &evm_config_xattrnames);
  79         }
  80 
  81 #ifdef CONFIG_EVM_ATTR_FSUUID
  82         evm_hmac_attrs |= EVM_ATTR_FSUUID;
  83 #endif
  84         pr_info("HMAC attrs: 0x%x\n", evm_hmac_attrs);
  85 }
  86 
  87 static bool evm_key_loaded(void)
  88 {
  89         return (bool)(evm_initialized & EVM_KEY_MASK);
  90 }
  91 
  92 static int evm_find_protected_xattrs(struct dentry *dentry)
  93 {
  94         struct inode *inode = d_backing_inode(dentry);
  95         struct xattr_list *xattr;
  96         int error;
  97         int count = 0;
  98 
  99         if (!(inode->i_opflags & IOP_XATTR))
 100                 return -EOPNOTSUPP;
 101 
 102         list_for_each_entry_lockless(xattr, &evm_config_xattrnames, list) {
 103                 error = __vfs_getxattr(dentry, inode, xattr->name, NULL, 0);
 104                 if (error < 0) {
 105                         if (error == -ENODATA)
 106                                 continue;
 107                         return error;
 108                 }
 109                 count++;
 110         }
 111 
 112         return count;
 113 }
 114 
 115 /*
 116  * evm_verify_hmac - calculate and compare the HMAC with the EVM xattr
 117  *
 118  * Compute the HMAC on the dentry's protected set of extended attributes
 119  * and compare it against the stored security.evm xattr.
 120  *
 121  * For performance:
 122  * - use the previoulsy retrieved xattr value and length to calculate the
 123  *   HMAC.)
 124  * - cache the verification result in the iint, when available.
 125  *
 126  * Returns integrity status
 127  */
 128 static enum integrity_status evm_verify_hmac(struct dentry *dentry,
 129                                              const char *xattr_name,
 130                                              char *xattr_value,
 131                                              size_t xattr_value_len,
 132                                              struct integrity_iint_cache *iint)
 133 {
 134         struct evm_ima_xattr_data *xattr_data = NULL;
 135         struct signature_v2_hdr *hdr;
 136         enum integrity_status evm_status = INTEGRITY_PASS;
 137         struct evm_digest digest;
 138         struct inode *inode;
 139         int rc, xattr_len;
 140 
 141         if (iint && (iint->evm_status == INTEGRITY_PASS ||
 142                      iint->evm_status == INTEGRITY_PASS_IMMUTABLE))
 143                 return iint->evm_status;
 144 
 145         /* if status is not PASS, try to check again - against -ENOMEM */
 146 
 147         /* first need to know the sig type */
 148         rc = vfs_getxattr_alloc(dentry, XATTR_NAME_EVM, (char **)&xattr_data, 0,
 149                                 GFP_NOFS);
 150         if (rc <= 0) {
 151                 evm_status = INTEGRITY_FAIL;
 152                 if (rc == -ENODATA) {
 153                         rc = evm_find_protected_xattrs(dentry);
 154                         if (rc > 0)
 155                                 evm_status = INTEGRITY_NOLABEL;
 156                         else if (rc == 0)
 157                                 evm_status = INTEGRITY_NOXATTRS; /* new file */
 158                 } else if (rc == -EOPNOTSUPP) {
 159                         evm_status = INTEGRITY_UNKNOWN;
 160                 }
 161                 goto out;
 162         }
 163 
 164         xattr_len = rc;
 165 
 166         /* check value type */
 167         switch (xattr_data->type) {
 168         case EVM_XATTR_HMAC:
 169                 if (xattr_len != sizeof(struct evm_xattr)) {
 170                         evm_status = INTEGRITY_FAIL;
 171                         goto out;
 172                 }
 173 
 174                 digest.hdr.algo = HASH_ALGO_SHA1;
 175                 rc = evm_calc_hmac(dentry, xattr_name, xattr_value,
 176                                    xattr_value_len, &digest);
 177                 if (rc)
 178                         break;
 179                 rc = crypto_memneq(xattr_data->data, digest.digest,
 180                                    SHA1_DIGEST_SIZE);
 181                 if (rc)
 182                         rc = -EINVAL;
 183                 break;
 184         case EVM_IMA_XATTR_DIGSIG:
 185         case EVM_XATTR_PORTABLE_DIGSIG:
 186                 hdr = (struct signature_v2_hdr *)xattr_data;
 187                 digest.hdr.algo = hdr->hash_algo;
 188                 rc = evm_calc_hash(dentry, xattr_name, xattr_value,
 189                                    xattr_value_len, xattr_data->type, &digest);
 190                 if (rc)
 191                         break;
 192                 rc = integrity_digsig_verify(INTEGRITY_KEYRING_EVM,
 193                                         (const char *)xattr_data, xattr_len,
 194                                         digest.digest, digest.hdr.length);
 195                 if (!rc) {
 196                         inode = d_backing_inode(dentry);
 197 
 198                         if (xattr_data->type == EVM_XATTR_PORTABLE_DIGSIG) {
 199                                 if (iint)
 200                                         iint->flags |= EVM_IMMUTABLE_DIGSIG;
 201                                 evm_status = INTEGRITY_PASS_IMMUTABLE;
 202                         } else if (!IS_RDONLY(inode) &&
 203                                    !(inode->i_sb->s_readonly_remount) &&
 204                                    !IS_IMMUTABLE(inode)) {
 205                                 evm_update_evmxattr(dentry, xattr_name,
 206                                                     xattr_value,
 207                                                     xattr_value_len);
 208                         }
 209                 }
 210                 break;
 211         default:
 212                 rc = -EINVAL;
 213                 break;
 214         }
 215 
 216         if (rc)
 217                 evm_status = (rc == -ENODATA) ?
 218                                 INTEGRITY_NOXATTRS : INTEGRITY_FAIL;
 219 out:
 220         if (iint)
 221                 iint->evm_status = evm_status;
 222         kfree(xattr_data);
 223         return evm_status;
 224 }
 225 
 226 static int evm_protected_xattr(const char *req_xattr_name)
 227 {
 228         int namelen;
 229         int found = 0;
 230         struct xattr_list *xattr;
 231 
 232         namelen = strlen(req_xattr_name);
 233         list_for_each_entry_lockless(xattr, &evm_config_xattrnames, list) {
 234                 if ((strlen(xattr->name) == namelen)
 235                     && (strncmp(req_xattr_name, xattr->name, namelen) == 0)) {
 236                         found = 1;
 237                         break;
 238                 }
 239                 if (strncmp(req_xattr_name,
 240                             xattr->name + XATTR_SECURITY_PREFIX_LEN,
 241                             strlen(req_xattr_name)) == 0) {
 242                         found = 1;
 243                         break;
 244                 }
 245         }
 246 
 247         return found;
 248 }
 249 
 250 /**
 251  * evm_verifyxattr - verify the integrity of the requested xattr
 252  * @dentry: object of the verify xattr
 253  * @xattr_name: requested xattr
 254  * @xattr_value: requested xattr value
 255  * @xattr_value_len: requested xattr value length
 256  *
 257  * Calculate the HMAC for the given dentry and verify it against the stored
 258  * security.evm xattr. For performance, use the xattr value and length
 259  * previously retrieved to calculate the HMAC.
 260  *
 261  * Returns the xattr integrity status.
 262  *
 263  * This function requires the caller to lock the inode's i_mutex before it
 264  * is executed.
 265  */
 266 enum integrity_status evm_verifyxattr(struct dentry *dentry,
 267                                       const char *xattr_name,
 268                                       void *xattr_value, size_t xattr_value_len,
 269                                       struct integrity_iint_cache *iint)
 270 {
 271         if (!evm_key_loaded() || !evm_protected_xattr(xattr_name))
 272                 return INTEGRITY_UNKNOWN;
 273 
 274         if (!iint) {
 275                 iint = integrity_iint_find(d_backing_inode(dentry));
 276                 if (!iint)
 277                         return INTEGRITY_UNKNOWN;
 278         }
 279         return evm_verify_hmac(dentry, xattr_name, xattr_value,
 280                                  xattr_value_len, iint);
 281 }
 282 EXPORT_SYMBOL_GPL(evm_verifyxattr);
 283 
 284 /*
 285  * evm_verify_current_integrity - verify the dentry's metadata integrity
 286  * @dentry: pointer to the affected dentry
 287  *
 288  * Verify and return the dentry's metadata integrity. The exceptions are
 289  * before EVM is initialized or in 'fix' mode.
 290  */
 291 static enum integrity_status evm_verify_current_integrity(struct dentry *dentry)
 292 {
 293         struct inode *inode = d_backing_inode(dentry);
 294 
 295         if (!evm_key_loaded() || !S_ISREG(inode->i_mode) || evm_fixmode)
 296                 return 0;
 297         return evm_verify_hmac(dentry, NULL, NULL, 0, NULL);
 298 }
 299 
 300 /*
 301  * evm_protect_xattr - protect the EVM extended attribute
 302  *
 303  * Prevent security.evm from being modified or removed without the
 304  * necessary permissions or when the existing value is invalid.
 305  *
 306  * The posix xattr acls are 'system' prefixed, which normally would not
 307  * affect security.evm.  An interesting side affect of writing posix xattr
 308  * acls is their modifying of the i_mode, which is included in security.evm.
 309  * For posix xattr acls only, permit security.evm, even if it currently
 310  * doesn't exist, to be updated unless the EVM signature is immutable.
 311  */
 312 static int evm_protect_xattr(struct dentry *dentry, const char *xattr_name,
 313                              const void *xattr_value, size_t xattr_value_len)
 314 {
 315         enum integrity_status evm_status;
 316 
 317         if (strcmp(xattr_name, XATTR_NAME_EVM) == 0) {
 318                 if (!capable(CAP_SYS_ADMIN))
 319                         return -EPERM;
 320         } else if (!evm_protected_xattr(xattr_name)) {
 321                 if (!posix_xattr_acl(xattr_name))
 322                         return 0;
 323                 evm_status = evm_verify_current_integrity(dentry);
 324                 if ((evm_status == INTEGRITY_PASS) ||
 325                     (evm_status == INTEGRITY_NOXATTRS))
 326                         return 0;
 327                 goto out;
 328         }
 329 
 330         evm_status = evm_verify_current_integrity(dentry);
 331         if (evm_status == INTEGRITY_NOXATTRS) {
 332                 struct integrity_iint_cache *iint;
 333 
 334                 iint = integrity_iint_find(d_backing_inode(dentry));
 335                 if (iint && (iint->flags & IMA_NEW_FILE))
 336                         return 0;
 337 
 338                 /* exception for pseudo filesystems */
 339                 if (dentry->d_sb->s_magic == TMPFS_MAGIC
 340                     || dentry->d_sb->s_magic == SYSFS_MAGIC)
 341                         return 0;
 342 
 343                 integrity_audit_msg(AUDIT_INTEGRITY_METADATA,
 344                                     dentry->d_inode, dentry->d_name.name,
 345                                     "update_metadata",
 346                                     integrity_status_msg[evm_status],
 347                                     -EPERM, 0);
 348         }
 349 out:
 350         if (evm_status != INTEGRITY_PASS)
 351                 integrity_audit_msg(AUDIT_INTEGRITY_METADATA, d_backing_inode(dentry),
 352                                     dentry->d_name.name, "appraise_metadata",
 353                                     integrity_status_msg[evm_status],
 354                                     -EPERM, 0);
 355         return evm_status == INTEGRITY_PASS ? 0 : -EPERM;
 356 }
 357 
 358 /**
 359  * evm_inode_setxattr - protect the EVM extended attribute
 360  * @dentry: pointer to the affected dentry
 361  * @xattr_name: pointer to the affected extended attribute name
 362  * @xattr_value: pointer to the new extended attribute value
 363  * @xattr_value_len: pointer to the new extended attribute value length
 364  *
 365  * Before allowing the 'security.evm' protected xattr to be updated,
 366  * verify the existing value is valid.  As only the kernel should have
 367  * access to the EVM encrypted key needed to calculate the HMAC, prevent
 368  * userspace from writing HMAC value.  Writing 'security.evm' requires
 369  * requires CAP_SYS_ADMIN privileges.
 370  */
 371 int evm_inode_setxattr(struct dentry *dentry, const char *xattr_name,
 372                        const void *xattr_value, size_t xattr_value_len)
 373 {
 374         const struct evm_ima_xattr_data *xattr_data = xattr_value;
 375 
 376         /* Policy permits modification of the protected xattrs even though
 377          * there's no HMAC key loaded
 378          */
 379         if (evm_initialized & EVM_ALLOW_METADATA_WRITES)
 380                 return 0;
 381 
 382         if (strcmp(xattr_name, XATTR_NAME_EVM) == 0) {
 383                 if (!xattr_value_len)
 384                         return -EINVAL;
 385                 if (xattr_data->type != EVM_IMA_XATTR_DIGSIG &&
 386                     xattr_data->type != EVM_XATTR_PORTABLE_DIGSIG)
 387                         return -EPERM;
 388         }
 389         return evm_protect_xattr(dentry, xattr_name, xattr_value,
 390                                  xattr_value_len);
 391 }
 392 
 393 /**
 394  * evm_inode_removexattr - protect the EVM extended attribute
 395  * @dentry: pointer to the affected dentry
 396  * @xattr_name: pointer to the affected extended attribute name
 397  *
 398  * Removing 'security.evm' requires CAP_SYS_ADMIN privileges and that
 399  * the current value is valid.
 400  */
 401 int evm_inode_removexattr(struct dentry *dentry, const char *xattr_name)
 402 {
 403         /* Policy permits modification of the protected xattrs even though
 404          * there's no HMAC key loaded
 405          */
 406         if (evm_initialized & EVM_ALLOW_METADATA_WRITES)
 407                 return 0;
 408 
 409         return evm_protect_xattr(dentry, xattr_name, NULL, 0);
 410 }
 411 
 412 static void evm_reset_status(struct inode *inode)
 413 {
 414         struct integrity_iint_cache *iint;
 415 
 416         iint = integrity_iint_find(inode);
 417         if (iint)
 418                 iint->evm_status = INTEGRITY_UNKNOWN;
 419 }
 420 
 421 /**
 422  * evm_inode_post_setxattr - update 'security.evm' to reflect the changes
 423  * @dentry: pointer to the affected dentry
 424  * @xattr_name: pointer to the affected extended attribute name
 425  * @xattr_value: pointer to the new extended attribute value
 426  * @xattr_value_len: pointer to the new extended attribute value length
 427  *
 428  * Update the HMAC stored in 'security.evm' to reflect the change.
 429  *
 430  * No need to take the i_mutex lock here, as this function is called from
 431  * __vfs_setxattr_noperm().  The caller of which has taken the inode's
 432  * i_mutex lock.
 433  */
 434 void evm_inode_post_setxattr(struct dentry *dentry, const char *xattr_name,
 435                              const void *xattr_value, size_t xattr_value_len)
 436 {
 437         if (!evm_key_loaded() || (!evm_protected_xattr(xattr_name)
 438                                   && !posix_xattr_acl(xattr_name)))
 439                 return;
 440 
 441         evm_reset_status(dentry->d_inode);
 442 
 443         evm_update_evmxattr(dentry, xattr_name, xattr_value, xattr_value_len);
 444 }
 445 
 446 /**
 447  * evm_inode_post_removexattr - update 'security.evm' after removing the xattr
 448  * @dentry: pointer to the affected dentry
 449  * @xattr_name: pointer to the affected extended attribute name
 450  *
 451  * Update the HMAC stored in 'security.evm' to reflect removal of the xattr.
 452  *
 453  * No need to take the i_mutex lock here, as this function is called from
 454  * vfs_removexattr() which takes the i_mutex.
 455  */
 456 void evm_inode_post_removexattr(struct dentry *dentry, const char *xattr_name)
 457 {
 458         if (!evm_key_loaded() || !evm_protected_xattr(xattr_name))
 459                 return;
 460 
 461         evm_reset_status(dentry->d_inode);
 462 
 463         evm_update_evmxattr(dentry, xattr_name, NULL, 0);
 464 }
 465 
 466 /**
 467  * evm_inode_setattr - prevent updating an invalid EVM extended attribute
 468  * @dentry: pointer to the affected dentry
 469  *
 470  * Permit update of file attributes when files have a valid EVM signature,
 471  * except in the case of them having an immutable portable signature.
 472  */
 473 int evm_inode_setattr(struct dentry *dentry, struct iattr *attr)
 474 {
 475         unsigned int ia_valid = attr->ia_valid;
 476         enum integrity_status evm_status;
 477 
 478         /* Policy permits modification of the protected attrs even though
 479          * there's no HMAC key loaded
 480          */
 481         if (evm_initialized & EVM_ALLOW_METADATA_WRITES)
 482                 return 0;
 483 
 484         if (!(ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID)))
 485                 return 0;
 486         evm_status = evm_verify_current_integrity(dentry);
 487         if ((evm_status == INTEGRITY_PASS) ||
 488             (evm_status == INTEGRITY_NOXATTRS))
 489                 return 0;
 490         integrity_audit_msg(AUDIT_INTEGRITY_METADATA, d_backing_inode(dentry),
 491                             dentry->d_name.name, "appraise_metadata",
 492                             integrity_status_msg[evm_status], -EPERM, 0);
 493         return -EPERM;
 494 }
 495 
 496 /**
 497  * evm_inode_post_setattr - update 'security.evm' after modifying metadata
 498  * @dentry: pointer to the affected dentry
 499  * @ia_valid: for the UID and GID status
 500  *
 501  * For now, update the HMAC stored in 'security.evm' to reflect UID/GID
 502  * changes.
 503  *
 504  * This function is called from notify_change(), which expects the caller
 505  * to lock the inode's i_mutex.
 506  */
 507 void evm_inode_post_setattr(struct dentry *dentry, int ia_valid)
 508 {
 509         if (!evm_key_loaded())
 510                 return;
 511 
 512         if (ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID))
 513                 evm_update_evmxattr(dentry, NULL, NULL, 0);
 514 }
 515 
 516 /*
 517  * evm_inode_init_security - initializes security.evm
 518  */
 519 int evm_inode_init_security(struct inode *inode,
 520                                  const struct xattr *lsm_xattr,
 521                                  struct xattr *evm_xattr)
 522 {
 523         struct evm_xattr *xattr_data;
 524         int rc;
 525 
 526         if (!evm_key_loaded() || !evm_protected_xattr(lsm_xattr->name))
 527                 return 0;
 528 
 529         xattr_data = kzalloc(sizeof(*xattr_data), GFP_NOFS);
 530         if (!xattr_data)
 531                 return -ENOMEM;
 532 
 533         xattr_data->data.type = EVM_XATTR_HMAC;
 534         rc = evm_init_hmac(inode, lsm_xattr, xattr_data->digest);
 535         if (rc < 0)
 536                 goto out;
 537 
 538         evm_xattr->value = xattr_data;
 539         evm_xattr->value_len = sizeof(*xattr_data);
 540         evm_xattr->name = XATTR_EVM_SUFFIX;
 541         return 0;
 542 out:
 543         kfree(xattr_data);
 544         return rc;
 545 }
 546 EXPORT_SYMBOL_GPL(evm_inode_init_security);
 547 
 548 #ifdef CONFIG_EVM_LOAD_X509
 549 void __init evm_load_x509(void)
 550 {
 551         int rc;
 552 
 553         rc = integrity_load_x509(INTEGRITY_KEYRING_EVM, CONFIG_EVM_X509_PATH);
 554         if (!rc)
 555                 evm_initialized |= EVM_INIT_X509;
 556 }
 557 #endif
 558 
 559 static int __init init_evm(void)
 560 {
 561         int error;
 562         struct list_head *pos, *q;
 563 
 564         evm_init_config();
 565 
 566         error = integrity_init_keyring(INTEGRITY_KEYRING_EVM);
 567         if (error)
 568                 goto error;
 569 
 570         error = evm_init_secfs();
 571         if (error < 0) {
 572                 pr_info("Error registering secfs\n");
 573                 goto error;
 574         }
 575 
 576 error:
 577         if (error != 0) {
 578                 if (!list_empty(&evm_config_xattrnames)) {
 579                         list_for_each_safe(pos, q, &evm_config_xattrnames)
 580                                 list_del(pos);
 581                 }
 582         }
 583 
 584         return error;
 585 }
 586 
 587 late_initcall(init_evm);