security/integrity/evm/evm_main.c

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