security/integrity/evm/evm_main.c

   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 <linux/magic.h>
  26
  27 #include <crypto/hash.h>
  28 #include <crypto/hash_info.h>
  29 #include <crypto/algapi.h>
  30 #include "evm.h"
  31
  32 int evm_initialized;
  33
  34 static const char * const integrity_status_msg[] = {
  35         "pass", "pass_immutable", "fail", "no_label", "no_xattrs", "unknown"
  36 };
  37 int evm_hmac_attrs;
  38
  39 static struct xattr_list evm_config_default_xattrnames[] = {
  40 #ifdef CONFIG_SECURITY_SELINUX
  41         {.name = XATTR_NAME_SELINUX},
  42 #endif
  43 #ifdef CONFIG_SECURITY_SMACK
  44         {.name = XATTR_NAME_SMACK},
  45 #ifdef CONFIG_EVM_EXTRA_SMACK_XATTRS
  46         {.name = XATTR_NAME_SMACKEXEC},
  47         {.name = XATTR_NAME_SMACKTRANSMUTE},
  48         {.name = XATTR_NAME_SMACKMMAP},
  49 #endif
  50 #endif
  51 #ifdef CONFIG_SECURITY_APPARMOR
  52         {.name = XATTR_NAME_APPARMOR},
  53 #endif
  54 #ifdef CONFIG_IMA_APPRAISE
  55         {.name = XATTR_NAME_IMA},
  56 #endif
  57         {.name = XATTR_NAME_CAPS},
  58 };
  59
  60 LIST_HEAD(evm_config_xattrnames);
  61
  62 static int evm_fixmode;
  63 static int __init evm_set_fixmode(char *str)
  64 {
  65         if (strncmp(str, "fix", 3) == 0)
  66                 evm_fixmode = 1;
  67         return 0;
  68 }
  69 __setup("evm=", evm_set_fixmode);
  70
  71 static void __init evm_init_config(void)
  72 {
  73         int i, xattrs;
  74
  75         xattrs = ARRAY_SIZE(evm_config_default_xattrnames);
  76
  77         pr_info("Initialising EVM extended attributes:\n");
  78         for (i = 0; i < xattrs; i++) {
  79                 pr_info("%s\n", evm_config_default_xattrnames[i].name);
  80                 list_add_tail(&evm_config_default_xattrnames[i].list,
  81                               &evm_config_xattrnames);
  82         }
  83
  84 #ifdef CONFIG_EVM_ATTR_FSUUID
  85         evm_hmac_attrs |= EVM_ATTR_FSUUID;
  86 #endif
  87         pr_info("HMAC attrs: 0x%x\n", evm_hmac_attrs);
  88 }
  89
  90 static bool evm_key_loaded(void)
  91 {
  92         return (bool)(evm_initialized & EVM_KEY_MASK);
  93 }
  94
  95 static int evm_find_protected_xattrs(struct dentry *dentry)
  96 {
  97         struct inode *inode = d_backing_inode(dentry);
  98         struct xattr_list *xattr;
  99         int error;
 100         int count = 0;
 101
 102         if (!(inode->i_opflags & IOP_XATTR))
 103                 return -EOPNOTSUPP;
 104
 105         list_for_each_entry_rcu(xattr, &evm_config_xattrnames, list) {
 106                 error = __vfs_getxattr(dentry, inode, xattr->name, NULL, 0);
 107                 if (error < 0) {
 108                         if (error == -ENODATA)
 109                                 continue;
 110                         return error;
 111                 }
 112                 count++;
 113         }
 114
 115         return count;
 116 }
 117
 118 /*
 119  * evm_verify_hmac - calculate and compare the HMAC with the EVM xattr
 120  *
 121  * Compute the HMAC on the dentry's protected set of extended attributes
 122  * and compare it against the stored security.evm xattr.
 123  *
 124  * For performance:
 125  * - use the previoulsy retrieved xattr value and length to calculate the
 126  *   HMAC.)
 127  * - cache the verification result in the iint, when available.
 128  *
 129  * Returns integrity status
 130  */
 131 static enum integrity_status evm_verify_hmac(struct dentry *dentry,
 132                                              const char *xattr_name,
 133                                              char *xattr_value,
 134                                              size_t xattr_value_len,
 135                                              struct integrity_iint_cache *iint)
 136 {
 137         struct evm_ima_xattr_data *xattr_data = NULL;
 138         struct signature_v2_hdr *hdr;
 139         enum integrity_status evm_status = INTEGRITY_PASS;
 140         struct evm_digest digest;
 141         struct inode *inode;
 142         int rc, xattr_len;
 143
 144         if (iint && (iint->evm_status == INTEGRITY_PASS ||
 145                      iint->evm_status == INTEGRITY_PASS_IMMUTABLE))
 146                 return iint->evm_status;
 147
 148         /* if status is not PASS, try to check again - against -ENOMEM */
 149
 150         /* first need to know the sig type */
 151         rc = vfs_getxattr_alloc(dentry, XATTR_NAME_EVM, (char **)&xattr_data, 0,
 152                                 GFP_NOFS);
 153         if (rc <= 0) {
 154                 evm_status = INTEGRITY_FAIL;
 155                 if (rc == -ENODATA) {
 156                         rc = evm_find_protected_xattrs(dentry);
 157                         if (rc > 0)
 158                                 evm_status = INTEGRITY_NOLABEL;
 159                         else if (rc == 0)
 160                                 evm_status = INTEGRITY_NOXATTRS; /* new file */
 161                 } else if (rc == -EOPNOTSUPP) {
 162                         evm_status = INTEGRITY_UNKNOWN;
 163                 }
 164                 goto out;
 165         }
 166
 167         xattr_len = rc;
 168
 169         /* check value type */
 170         switch (xattr_data->type) {
 171         case EVM_XATTR_HMAC:
 172                 if (xattr_len != sizeof(struct evm_ima_xattr_data)) {
 173                         evm_status = INTEGRITY_FAIL;
 174                         goto out;
 175                 }
 176
 177                 digest.hdr.algo = HASH_ALGO_SHA1;
 178                 rc = evm_calc_hmac(dentry, xattr_name, xattr_value,
 179                                    xattr_value_len, &digest);
 180                 if (rc)
 181                         break;
 182                 rc = crypto_memneq(xattr_data->digest, digest.digest,
 183                                    SHA1_DIGEST_SIZE);
 184                 if (rc)
 185                         rc = -EINVAL;
 186                 break;
 187         case EVM_IMA_XATTR_DIGSIG:
 188         case EVM_XATTR_PORTABLE_DIGSIG:
 189                 hdr = (struct signature_v2_hdr *)xattr_data;
 190                 digest.hdr.algo = hdr->hash_algo;
 191                 rc = evm_calc_hash(dentry, xattr_name, xattr_value,
 192                                    xattr_value_len, xattr_data->type, &digest);
 193                 if (rc)
 194                         break;
 195                 rc = integrity_digsig_verify(INTEGRITY_KEYRING_EVM,
 196                                         (const char *)xattr_data, xattr_len,
 197                                         digest.digest, digest.hdr.length);
 198                 if (!rc) {
 199                         inode = d_backing_inode(dentry);
 200
 201                         if (xattr_data->type == EVM_XATTR_PORTABLE_DIGSIG) {
 202                                 if (iint)
 203                                         iint->flags |= EVM_IMMUTABLE_DIGSIG;
 204                                 evm_status = INTEGRITY_PASS_IMMUTABLE;
 205                         } else if (!IS_RDONLY(inode) &&
 206                                    !(inode->i_sb->s_readonly_remount) &&
 207                                    !IS_IMMUTABLE(inode)) {
 208                                 evm_update_evmxattr(dentry, xattr_name,
 209                                                     xattr_value,
 210                                                     xattr_value_len);
 211                         }
 212                 }
 213                 break;
 214         default:
 215                 rc = -EINVAL;
 216                 break;
 217         }
 218
 219         if (rc)
 220                 evm_status = (rc == -ENODATA) ?
 221                                 INTEGRITY_NOXATTRS : INTEGRITY_FAIL;
 222 out:
 223         if (iint)
 224                 iint->evm_status = evm_status;
 225         kfree(xattr_data);
 226         return evm_status;
 227 }
 228
 229 static int evm_protected_xattr(const char *req_xattr_name)
 230 {
 231         int namelen;
 232         int found = 0;
 233         struct xattr_list *xattr;
 234
 235         namelen = strlen(req_xattr_name);
 236         list_for_each_entry_rcu(xattr, &evm_config_xattrnames, list) {
 237                 if ((strlen(xattr->name) == namelen)
 238                     && (strncmp(req_xattr_name, xattr->name, namelen) == 0)) {
 239                         found = 1;
 240                         break;
 241                 }
 242                 if (strncmp(req_xattr_name,
 243                             xattr->name + XATTR_SECURITY_PREFIX_LEN,
 244                             strlen(req_xattr_name)) == 0) {
 245                         found = 1;
 246                         break;
 247                 }
 248         }
 249
 250         return found;
 251 }
 252
 253 /**
 254  * evm_verifyxattr - verify the integrity of the requested xattr
 255  * @dentry: object of the verify xattr
 256  * @xattr_name: requested xattr
 257  * @xattr_value: requested xattr value
 258  * @xattr_value_len: requested xattr value length
 259  *
 260  * Calculate the HMAC for the given dentry and verify it against the stored
 261  * security.evm xattr. For performance, use the xattr value and length
 262  * previously retrieved to calculate the HMAC.
 263  *
 264  * Returns the xattr integrity status.
 265  *
 266  * This function requires the caller to lock the inode's i_mutex before it
 267  * is executed.
 268  */
 269 enum integrity_status evm_verifyxattr(struct dentry *dentry,
 270                                       const char *xattr_name,
 271                                       void *xattr_value, size_t xattr_value_len,
 272                                       struct integrity_iint_cache *iint)
 273 {
 274         if (!evm_key_loaded() || !evm_protected_xattr(xattr_name))
 275                 return INTEGRITY_UNKNOWN;
 276
 277         if (!iint) {
 278                 iint = integrity_iint_find(d_backing_inode(dentry));
 279                 if (!iint)
 280                         return INTEGRITY_UNKNOWN;
 281         }
 282         return evm_verify_hmac(dentry, xattr_name, xattr_value,
 283                                  xattr_value_len, iint);
 284 }
 285 EXPORT_SYMBOL_GPL(evm_verifyxattr);
 286
 287 /*
 288  * evm_verify_current_integrity - verify the dentry's metadata integrity
 289  * @dentry: pointer to the affected dentry
 290  *
 291  * Verify and return the dentry's metadata integrity. The exceptions are
 292  * before EVM is initialized or in 'fix' mode.
 293  */
 294 static enum integrity_status evm_verify_current_integrity(struct dentry *dentry)
 295 {
 296         struct inode *inode = d_backing_inode(dentry);
 297
 298         if (!evm_key_loaded() || !S_ISREG(inode->i_mode) || evm_fixmode)
 299                 return 0;
 300         return evm_verify_hmac(dentry, NULL, NULL, 0, NULL);
 301 }
 302
 303 /*
 304  * evm_protect_xattr - protect the EVM extended attribute
 305  *
 306  * Prevent security.evm from being modified or removed without the
 307  * necessary permissions or when the existing value is invalid.
 308  *
 309  * The posix xattr acls are 'system' prefixed, which normally would not
 310  * affect security.evm.  An interesting side affect of writing posix xattr
 311  * acls is their modifying of the i_mode, which is included in security.evm.
 312  * For posix xattr acls only, permit security.evm, even if it currently
 313  * doesn't exist, to be updated unless the EVM signature is immutable.
 314  */
 315 static int evm_protect_xattr(struct dentry *dentry, const char *xattr_name,
 316                              const void *xattr_value, size_t xattr_value_len)
 317 {
 318         enum integrity_status evm_status;
 319
 320         if (strcmp(xattr_name, XATTR_NAME_EVM) == 0) {
 321                 if (!capable(CAP_SYS_ADMIN))
 322                         return -EPERM;
 323         } else if (!evm_protected_xattr(xattr_name)) {
 324                 if (!posix_xattr_acl(xattr_name))
 325                         return 0;
 326                 evm_status = evm_verify_current_integrity(dentry);
 327                 if ((evm_status == INTEGRITY_PASS) ||
 328                     (evm_status == INTEGRITY_NOXATTRS))
 329                         return 0;
 330                 goto out;
 331         }
 332
 333         evm_status = evm_verify_current_integrity(dentry);
 334         if (evm_status == INTEGRITY_NOXATTRS) {
 335                 struct integrity_iint_cache *iint;
 336
 337                 iint = integrity_iint_find(d_backing_inode(dentry));
 338                 if (iint && (iint->flags & IMA_NEW_FILE))
 339                         return 0;
 340
 341                 /* exception for pseudo filesystems */
 342                 if (dentry->d_sb->s_magic == TMPFS_MAGIC
 343                     || dentry->d_sb->s_magic == SYSFS_MAGIC)
 344                         return 0;
 345
 346                 integrity_audit_msg(AUDIT_INTEGRITY_METADATA,
 347                                     dentry->d_inode, dentry->d_name.name,
 348                                     "update_metadata",
 349                                     integrity_status_msg[evm_status],
 350                                     -EPERM, 0);
 351         }
 352 out:
 353         if (evm_status != INTEGRITY_PASS)
 354                 integrity_audit_msg(AUDIT_INTEGRITY_METADATA, d_backing_inode(dentry),
 355                                     dentry->d_name.name, "appraise_metadata",
 356                                     integrity_status_msg[evm_status],
 357                                     -EPERM, 0);
 358         return evm_status == INTEGRITY_PASS ? 0 : -EPERM;
 359 }
 360
 361 /**
 362  * evm_inode_setxattr - protect the EVM extended attribute
 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  * Before allowing the 'security.evm' protected xattr to be updated,
 369  * verify the existing value is valid.  As only the kernel should have
 370  * access to the EVM encrypted key needed to calculate the HMAC, prevent
 371  * userspace from writing HMAC value.  Writing 'security.evm' requires
 372  * requires CAP_SYS_ADMIN privileges.
 373  */
 374 int evm_inode_setxattr(struct dentry *dentry, const char *xattr_name,
 375                        const void *xattr_value, size_t xattr_value_len)
 376 {
 377         const struct evm_ima_xattr_data *xattr_data = xattr_value;
 378
 379         /* Policy permits modification of the protected xattrs even though
 380          * there's no HMAC key loaded
 381          */
 382         if (evm_initialized & EVM_ALLOW_METADATA_WRITES)
 383                 return 0;
 384
 385         if (strcmp(xattr_name, XATTR_NAME_EVM) == 0) {
 386                 if (!xattr_value_len)
 387                         return -EINVAL;
 388                 if (xattr_data->type != EVM_IMA_XATTR_DIGSIG &&
 389                     xattr_data->type != EVM_XATTR_PORTABLE_DIGSIG)
 390                         return -EPERM;
 391         }
 392         return evm_protect_xattr(dentry, xattr_name, xattr_value,
 393                                  xattr_value_len);
 394 }
 395
 396 /**
 397  * evm_inode_removexattr - protect the EVM extended attribute
 398  * @dentry: pointer to the affected dentry
 399  * @xattr_name: pointer to the affected extended attribute name
 400  *
 401  * Removing 'security.evm' requires CAP_SYS_ADMIN privileges and that
 402  * the current value is valid.
 403  */
 404 int evm_inode_removexattr(struct dentry *dentry, const char *xattr_name)
 405 {
 406         /* Policy permits modification of the protected xattrs even though
 407          * there's no HMAC key loaded
 408          */
 409         if (evm_initialized & EVM_ALLOW_METADATA_WRITES)
 410                 return 0;
 411
 412         return evm_protect_xattr(dentry, xattr_name, NULL, 0);
 413 }
 414
 415 static void evm_reset_status(struct inode *inode)
 416 {
 417         struct integrity_iint_cache *iint;
 418
 419         iint = integrity_iint_find(inode);
 420         if (iint)
 421                 iint->evm_status = INTEGRITY_UNKNOWN;
 422 }
 423
 424 /**
 425  * evm_inode_post_setxattr - update 'security.evm' to reflect the changes
 426  * @dentry: pointer to the affected dentry
 427  * @xattr_name: pointer to the affected extended attribute name
 428  * @xattr_value: pointer to the new extended attribute value
 429  * @xattr_value_len: pointer to the new extended attribute value length
 430  *
 431  * Update the HMAC stored in 'security.evm' to reflect the change.
 432  *
 433  * No need to take the i_mutex lock here, as this function is called from
 434  * __vfs_setxattr_noperm().  The caller of which has taken the inode's
 435  * i_mutex lock.
 436  */
 437 void evm_inode_post_setxattr(struct dentry *dentry, const char *xattr_name,
 438                              const void *xattr_value, size_t xattr_value_len)
 439 {
 440         if (!evm_key_loaded() || (!evm_protected_xattr(xattr_name)
 441                                   && !posix_xattr_acl(xattr_name)))
 442                 return;
 443
 444         evm_reset_status(dentry->d_inode);
 445
 446         evm_update_evmxattr(dentry, xattr_name, xattr_value, xattr_value_len);
 447 }
 448
 449 /**
 450  * evm_inode_post_removexattr - update 'security.evm' after removing the xattr
 451  * @dentry: pointer to the affected dentry
 452  * @xattr_name: pointer to the affected extended attribute name
 453  *
 454  * Update the HMAC stored in 'security.evm' to reflect removal of the xattr.
 455  *
 456  * No need to take the i_mutex lock here, as this function is called from
 457  * vfs_removexattr() which takes the i_mutex.
 458  */
 459 void evm_inode_post_removexattr(struct dentry *dentry, const char *xattr_name)
 460 {
 461         if (!evm_key_loaded() || !evm_protected_xattr(xattr_name))
 462                 return;
 463
 464         evm_reset_status(dentry->d_inode);
 465
 466         evm_update_evmxattr(dentry, xattr_name, NULL, 0);
 467 }
 468
 469 /**
 470  * evm_inode_setattr - prevent updating an invalid EVM extended attribute
 471  * @dentry: pointer to the affected dentry
 472  *
 473  * Permit update of file attributes when files have a valid EVM signature,
 474  * except in the case of them having an immutable portable signature.
 475  */
 476 int evm_inode_setattr(struct dentry *dentry, struct iattr *attr)
 477 {
 478         unsigned int ia_valid = attr->ia_valid;
 479         enum integrity_status evm_status;
 480
 481         /* Policy permits modification of the protected attrs even though
 482          * there's no HMAC key loaded
 483          */
 484         if (evm_initialized & EVM_ALLOW_METADATA_WRITES)
 485                 return 0;
 486
 487         if (!(ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID)))
 488                 return 0;
 489         evm_status = evm_verify_current_integrity(dentry);
 490         if ((evm_status == INTEGRITY_PASS) ||
 491             (evm_status == INTEGRITY_NOXATTRS))
 492                 return 0;
 493         integrity_audit_msg(AUDIT_INTEGRITY_METADATA, d_backing_inode(dentry),
 494                             dentry->d_name.name, "appraise_metadata",
 495                             integrity_status_msg[evm_status], -EPERM, 0);
 496         return -EPERM;
 497 }
 498
 499 /**
 500  * evm_inode_post_setattr - update 'security.evm' after modifying metadata
 501  * @dentry: pointer to the affected dentry
 502  * @ia_valid: for the UID and GID status
 503  *
 504  * For now, update the HMAC stored in 'security.evm' to reflect UID/GID
 505  * changes.
 506  *
 507  * This function is called from notify_change(), which expects the caller
 508  * to lock the inode's i_mutex.
 509  */
 510 void evm_inode_post_setattr(struct dentry *dentry, int ia_valid)
 511 {
 512         if (!evm_key_loaded())
 513                 return;
 514
 515         if (ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID))
 516                 evm_update_evmxattr(dentry, NULL, NULL, 0);
 517 }
 518
 519 /*
 520  * evm_inode_init_security - initializes security.evm
 521  */
 522 int evm_inode_init_security(struct inode *inode,
 523                                  const struct xattr *lsm_xattr,
 524                                  struct xattr *evm_xattr)
 525 {
 526         struct evm_ima_xattr_data *xattr_data;
 527         int rc;
 528
 529         if (!evm_key_loaded() || !evm_protected_xattr(lsm_xattr->name))
 530                 return 0;
 531
 532         xattr_data = kzalloc(sizeof(*xattr_data), GFP_NOFS);
 533         if (!xattr_data)
 534                 return -ENOMEM;
 535
 536         xattr_data->type = EVM_XATTR_HMAC;
 537         rc = evm_init_hmac(inode, lsm_xattr, xattr_data->digest);
 538         if (rc < 0)
 539                 goto out;
 540
 541         evm_xattr->value = xattr_data;
 542         evm_xattr->value_len = sizeof(*xattr_data);
 543         evm_xattr->name = XATTR_EVM_SUFFIX;
 544         return 0;
 545 out:
 546         kfree(xattr_data);
 547         return rc;
 548 }
 549 EXPORT_SYMBOL_GPL(evm_inode_init_security);
 550
 551 #ifdef CONFIG_EVM_LOAD_X509
 552 void __init evm_load_x509(void)
 553 {
 554         int rc;
 555
 556         rc = integrity_load_x509(INTEGRITY_KEYRING_EVM, CONFIG_EVM_X509_PATH);
 557         if (!rc)
 558                 evm_initialized |= EVM_INIT_X509;
 559 }
 560 #endif
 561
 562 static int __init init_evm(void)
 563 {
 564         int error;
 565         struct list_head *pos, *q;
 566         struct xattr_list *xattr;
 567
 568         evm_init_config();
 569
 570         error = integrity_init_keyring(INTEGRITY_KEYRING_EVM);
 571         if (error)
 572                 goto error;
 573
 574         error = evm_init_secfs();
 575         if (error < 0) {
 576                 pr_info("Error registering secfs\n");
 577                 goto error;
 578         }
 579
 580 error:
 581         if (error != 0) {
 582                 if (!list_empty(&evm_config_xattrnames)) {
 583                         list_for_each_safe(pos, q, &evm_config_xattrnames) {
 584                                 xattr = list_entry(pos, struct xattr_list,
 585                                                    list);
 586                                 list_del(pos);
 587                         }
 588                 }
 589         }
 590
 591         return error;
 592 }
 593
 594 late_initcall(init_evm);
 595
 596 MODULE_DESCRIPTION("Extended Verification Module");
 597 MODULE_LICENSE("GPL");