security/integrity/ima/ima_appraise.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  * Copyright (C) 2011 IBM Corporation
   4  *
   5  * Author:
   6  * Mimi Zohar <zohar@us.ibm.com>
   7  */
   8 #include <linux/init.h>
   9 #include <linux/file.h>
  10 #include <linux/fs.h>
  11 #include <linux/xattr.h>
  12 #include <linux/magic.h>
  13 #include <linux/ima.h>
  14 #include <linux/evm.h>
  15 #include <keys/system_keyring.h>
  16
  17 #include "ima.h"
  18
  19 static int __init default_appraise_setup(char *str)
  20 {
  21 #ifdef CONFIG_IMA_APPRAISE_BOOTPARAM
  22         bool sb_state = arch_ima_get_secureboot();
  23         int appraisal_state = ima_appraise;
  24
  25         if (strncmp(str, "off", 3) == 0)
  26                 appraisal_state = 0;
  27         else if (strncmp(str, "log", 3) == 0)
  28                 appraisal_state = IMA_APPRAISE_LOG;
  29         else if (strncmp(str, "fix", 3) == 0)
  30                 appraisal_state = IMA_APPRAISE_FIX;
  31         else if (strncmp(str, "enforce", 7) == 0)
  32                 appraisal_state = IMA_APPRAISE_ENFORCE;
  33         else
  34                 pr_err("invalid \"%s\" appraise option", str);
  35
  36         /* If appraisal state was changed, but secure boot is enabled,
  37          * keep its default */
  38         if (sb_state) {
  39                 if (!(appraisal_state & IMA_APPRAISE_ENFORCE))
  40                         pr_info("Secure boot enabled: ignoring ima_appraise=%s option",
  41                                 str);
  42         } else {
  43                 ima_appraise = appraisal_state;
  44         }
  45 #endif
  46         return 1;
  47 }
  48
  49 __setup("ima_appraise=", default_appraise_setup);
  50
  51 /*
  52  * is_ima_appraise_enabled - return appraise status
  53  *
  54  * Only return enabled, if not in ima_appraise="fix" or "log" modes.
  55  */
  56 bool is_ima_appraise_enabled(void)
  57 {
  58         return ima_appraise & IMA_APPRAISE_ENFORCE;
  59 }
  60
  61 /*
  62  * ima_must_appraise - set appraise flag
  63  *
  64  * Return 1 to appraise or hash
  65  */
  66 int ima_must_appraise(struct inode *inode, int mask, enum ima_hooks func)
  67 {
  68         u32 secid;
  69
  70         if (!ima_appraise)
  71                 return 0;
  72
  73         security_task_getsecid(current, &secid);
  74         return ima_match_policy(inode, current_cred(), secid, func, mask,
  75                                 IMA_APPRAISE | IMA_HASH, NULL, NULL, NULL);
  76 }
  77
  78 static int ima_fix_xattr(struct dentry *dentry,
  79                          struct integrity_iint_cache *iint)
  80 {
  81         int rc, offset;
  82         u8 algo = iint->ima_hash->algo;
  83
  84         if (algo <= HASH_ALGO_SHA1) {
  85                 offset = 1;
  86                 iint->ima_hash->xattr.sha1.type = IMA_XATTR_DIGEST;
  87         } else {
  88                 offset = 0;
  89                 iint->ima_hash->xattr.ng.type = IMA_XATTR_DIGEST_NG;
  90                 iint->ima_hash->xattr.ng.algo = algo;
  91         }
  92         rc = __vfs_setxattr_noperm(dentry, XATTR_NAME_IMA,
  93                                    &iint->ima_hash->xattr.data[offset],
  94                                    (sizeof(iint->ima_hash->xattr) - offset) +
  95                                    iint->ima_hash->length, 0);
  96         return rc;
  97 }
  98
  99 /* Return specific func appraised cached result */
 100 enum integrity_status ima_get_cache_status(struct integrity_iint_cache *iint,
 101                                            enum ima_hooks func)
 102 {
 103         switch (func) {
 104         case MMAP_CHECK:
 105                 return iint->ima_mmap_status;
 106         case BPRM_CHECK:
 107                 return iint->ima_bprm_status;
 108         case CREDS_CHECK:
 109                 return iint->ima_creds_status;
 110         case FILE_CHECK:
 111         case POST_SETATTR:
 112                 return iint->ima_file_status;
 113         case MODULE_CHECK ... MAX_CHECK - 1:
 114         default:
 115                 return iint->ima_read_status;
 116         }
 117 }
 118
 119 static void ima_set_cache_status(struct integrity_iint_cache *iint,
 120                                  enum ima_hooks func,
 121                                  enum integrity_status status)
 122 {
 123         switch (func) {
 124         case MMAP_CHECK:
 125                 iint->ima_mmap_status = status;
 126                 break;
 127         case BPRM_CHECK:
 128                 iint->ima_bprm_status = status;
 129                 break;
 130         case CREDS_CHECK:
 131                 iint->ima_creds_status = status;
 132                 break;
 133         case FILE_CHECK:
 134         case POST_SETATTR:
 135                 iint->ima_file_status = status;
 136                 break;
 137         case MODULE_CHECK ... MAX_CHECK - 1:
 138         default:
 139                 iint->ima_read_status = status;
 140                 break;
 141         }
 142 }
 143
 144 static void ima_cache_flags(struct integrity_iint_cache *iint,
 145                              enum ima_hooks func)
 146 {
 147         switch (func) {
 148         case MMAP_CHECK:
 149                 iint->flags |= (IMA_MMAP_APPRAISED | IMA_APPRAISED);
 150                 break;
 151         case BPRM_CHECK:
 152                 iint->flags |= (IMA_BPRM_APPRAISED | IMA_APPRAISED);
 153                 break;
 154         case CREDS_CHECK:
 155                 iint->flags |= (IMA_CREDS_APPRAISED | IMA_APPRAISED);
 156                 break;
 157         case FILE_CHECK:
 158         case POST_SETATTR:
 159                 iint->flags |= (IMA_FILE_APPRAISED | IMA_APPRAISED);
 160                 break;
 161         case MODULE_CHECK ... MAX_CHECK - 1:
 162         default:
 163                 iint->flags |= (IMA_READ_APPRAISED | IMA_APPRAISED);
 164                 break;
 165         }
 166 }
 167
 168 enum hash_algo ima_get_hash_algo(struct evm_ima_xattr_data *xattr_value,
 169                                  int xattr_len)
 170 {
 171         struct signature_v2_hdr *sig;
 172         enum hash_algo ret;
 173
 174         if (!xattr_value || xattr_len < 2)
 175                 /* return default hash algo */
 176                 return ima_hash_algo;
 177
 178         switch (xattr_value->type) {
 179         case EVM_IMA_XATTR_DIGSIG:
 180                 sig = (typeof(sig))xattr_value;
 181                 if (sig->version != 2 || xattr_len <= sizeof(*sig))
 182                         return ima_hash_algo;
 183                 return sig->hash_algo;
 184                 break;
 185         case IMA_XATTR_DIGEST_NG:
 186                 /* first byte contains algorithm id */
 187                 ret = xattr_value->data[0];
 188                 if (ret < HASH_ALGO__LAST)
 189                         return ret;
 190                 break;
 191         case IMA_XATTR_DIGEST:
 192                 /* this is for backward compatibility */
 193                 if (xattr_len == 21) {
 194                         unsigned int zero = 0;
 195                         if (!memcmp(&xattr_value->data[16], &zero, 4))
 196                                 return HASH_ALGO_MD5;
 197                         else
 198                                 return HASH_ALGO_SHA1;
 199                 } else if (xattr_len == 17)
 200                         return HASH_ALGO_MD5;
 201                 break;
 202         }
 203
 204         /* return default hash algo */
 205         return ima_hash_algo;
 206 }
 207
 208 int ima_read_xattr(struct dentry *dentry,
 209                    struct evm_ima_xattr_data **xattr_value)
 210 {
 211         ssize_t ret;
 212
 213         ret = vfs_getxattr_alloc(dentry, XATTR_NAME_IMA, (char **)xattr_value,
 214                                  0, GFP_NOFS);
 215         if (ret == -EOPNOTSUPP)
 216                 ret = 0;
 217         return ret;
 218 }
 219
 220 /*
 221  * xattr_verify - verify xattr digest or signature
 222  *
 223  * Verify whether the hash or signature matches the file contents.
 224  *
 225  * Return 0 on success, error code otherwise.
 226  */
 227 static int xattr_verify(enum ima_hooks func, struct integrity_iint_cache *iint,
 228                         struct evm_ima_xattr_data *xattr_value, int xattr_len,
 229                         enum integrity_status *status, const char **cause)
 230 {
 231         int rc = -EINVAL, hash_start = 0;
 232
 233         switch (xattr_value->type) {
 234         case IMA_XATTR_DIGEST_NG:
 235                 /* first byte contains algorithm id */
 236                 hash_start = 1;
 237                 fallthrough;
 238         case IMA_XATTR_DIGEST:
 239                 if (iint->flags & IMA_DIGSIG_REQUIRED) {
 240                         *cause = "IMA-signature-required";
 241                         *status = INTEGRITY_FAIL;
 242                         break;
 243                 }
 244                 clear_bit(IMA_DIGSIG, &iint->atomic_flags);
 245                 if (xattr_len - sizeof(xattr_value->type) - hash_start >=
 246                                 iint->ima_hash->length)
 247                         /*
 248                          * xattr length may be longer. md5 hash in previous
 249                          * version occupied 20 bytes in xattr, instead of 16
 250                          */
 251                         rc = memcmp(&xattr_value->data[hash_start],
 252                                     iint->ima_hash->digest,
 253                                     iint->ima_hash->length);
 254                 else
 255                         rc = -EINVAL;
 256                 if (rc) {
 257                         *cause = "invalid-hash";
 258                         *status = INTEGRITY_FAIL;
 259                         break;
 260                 }
 261                 *status = INTEGRITY_PASS;
 262                 break;
 263         case EVM_IMA_XATTR_DIGSIG:
 264                 set_bit(IMA_DIGSIG, &iint->atomic_flags);
 265                 rc = integrity_digsig_verify(INTEGRITY_KEYRING_IMA,
 266                                              (const char *)xattr_value,
 267                                              xattr_len,
 268                                              iint->ima_hash->digest,
 269                                              iint->ima_hash->length);
 270                 if (rc == -EOPNOTSUPP) {
 271                         *status = INTEGRITY_UNKNOWN;
 272                         break;
 273                 }
 274                 if (IS_ENABLED(CONFIG_INTEGRITY_PLATFORM_KEYRING) && rc &&
 275                     func == KEXEC_KERNEL_CHECK)
 276                         rc = integrity_digsig_verify(INTEGRITY_KEYRING_PLATFORM,
 277                                                      (const char *)xattr_value,
 278                                                      xattr_len,
 279                                                      iint->ima_hash->digest,
 280                                                      iint->ima_hash->length);
 281                 if (rc) {
 282                         *cause = "invalid-signature";
 283                         *status = INTEGRITY_FAIL;
 284                 } else {
 285                         *status = INTEGRITY_PASS;
 286                 }
 287                 break;
 288         default:
 289                 *status = INTEGRITY_UNKNOWN;
 290                 *cause = "unknown-ima-data";
 291                 break;
 292         }
 293
 294         return rc;
 295 }
 296
 297 /*
 298  * modsig_verify - verify modsig signature
 299  *
 300  * Verify whether the signature matches the file contents.
 301  *
 302  * Return 0 on success, error code otherwise.
 303  */
 304 static int modsig_verify(enum ima_hooks func, const struct modsig *modsig,
 305                          enum integrity_status *status, const char **cause)
 306 {
 307         int rc;
 308
 309         rc = integrity_modsig_verify(INTEGRITY_KEYRING_IMA, modsig);
 310         if (IS_ENABLED(CONFIG_INTEGRITY_PLATFORM_KEYRING) && rc &&
 311             func == KEXEC_KERNEL_CHECK)
 312                 rc = integrity_modsig_verify(INTEGRITY_KEYRING_PLATFORM,
 313                                              modsig);
 314         if (rc) {
 315                 *cause = "invalid-signature";
 316                 *status = INTEGRITY_FAIL;
 317         } else {
 318                 *status = INTEGRITY_PASS;
 319         }
 320
 321         return rc;
 322 }
 323
 324 /*
 325  * ima_check_blacklist - determine if the binary is blacklisted.
 326  *
 327  * Add the hash of the blacklisted binary to the measurement list, based
 328  * on policy.
 329  *
 330  * Returns -EPERM if the hash is blacklisted.
 331  */
 332 int ima_check_blacklist(struct integrity_iint_cache *iint,
 333                         const struct modsig *modsig, int pcr)
 334 {
 335         enum hash_algo hash_algo;
 336         const u8 *digest = NULL;
 337         u32 digestsize = 0;
 338         int rc = 0;
 339
 340         if (!(iint->flags & IMA_CHECK_BLACKLIST))
 341                 return 0;
 342
 343         if (iint->flags & IMA_MODSIG_ALLOWED && modsig) {
 344                 ima_get_modsig_digest(modsig, &hash_algo, &digest, &digestsize);
 345
 346                 rc = is_binary_blacklisted(digest, digestsize);
 347                 if ((rc == -EPERM) && (iint->flags & IMA_MEASURE))
 348                         process_buffer_measurement(NULL, digest, digestsize,
 349                                                    "blacklisted-hash", NONE,
 350                                                    pcr, NULL);
 351         }
 352
 353         return rc;
 354 }
 355
 356 /*
 357  * ima_appraise_measurement - appraise file measurement
 358  *
 359  * Call evm_verifyxattr() to verify the integrity of 'security.ima'.
 360  * Assuming success, compare the xattr hash with the collected measurement.
 361  *
 362  * Return 0 on success, error code otherwise
 363  */
 364 int ima_appraise_measurement(enum ima_hooks func,
 365                              struct integrity_iint_cache *iint,
 366                              struct file *file, const unsigned char *filename,
 367                              struct evm_ima_xattr_data *xattr_value,
 368                              int xattr_len, const struct modsig *modsig)
 369 {
 370         static const char op[] = "appraise_data";
 371         const char *cause = "unknown";
 372         struct dentry *dentry = file_dentry(file);
 373         struct inode *inode = d_backing_inode(dentry);
 374         enum integrity_status status = INTEGRITY_UNKNOWN;
 375         int rc = xattr_len;
 376         bool try_modsig = iint->flags & IMA_MODSIG_ALLOWED && modsig;
 377
 378         /* If not appraising a modsig, we need an xattr. */
 379         if (!(inode->i_opflags & IOP_XATTR) && !try_modsig)
 380                 return INTEGRITY_UNKNOWN;
 381
 382         /* If reading the xattr failed and there's no modsig, error out. */
 383         if (rc <= 0 && !try_modsig) {
 384                 if (rc && rc != -ENODATA)
 385                         goto out;
 386
 387                 cause = iint->flags & IMA_DIGSIG_REQUIRED ?
 388                                 "IMA-signature-required" : "missing-hash";
 389                 status = INTEGRITY_NOLABEL;
 390                 if (file->f_mode & FMODE_CREATED)
 391                         iint->flags |= IMA_NEW_FILE;
 392                 if ((iint->flags & IMA_NEW_FILE) &&
 393                     (!(iint->flags & IMA_DIGSIG_REQUIRED) ||
 394                      (inode->i_size == 0)))
 395                         status = INTEGRITY_PASS;
 396                 goto out;
 397         }
 398
 399         status = evm_verifyxattr(dentry, XATTR_NAME_IMA, xattr_value, rc, iint);
 400         switch (status) {
 401         case INTEGRITY_PASS:
 402         case INTEGRITY_PASS_IMMUTABLE:
 403         case INTEGRITY_UNKNOWN:
 404                 break;
 405         case INTEGRITY_NOXATTRS:        /* No EVM protected xattrs. */
 406                 /* It's fine not to have xattrs when using a modsig. */
 407                 if (try_modsig)
 408                         break;
 409                 fallthrough;
 410         case INTEGRITY_NOLABEL:         /* No security.evm xattr. */
 411                 cause = "missing-HMAC";
 412                 goto out;
 413         case INTEGRITY_FAIL:            /* Invalid HMAC/signature. */
 414                 cause = "invalid-HMAC";
 415                 goto out;
 416         default:
 417                 WARN_ONCE(true, "Unexpected integrity status %d\n", status);
 418         }
 419
 420         if (xattr_value)
 421                 rc = xattr_verify(func, iint, xattr_value, xattr_len, &status,
 422                                   &cause);
 423
 424         /*
 425          * If we have a modsig and either no imasig or the imasig's key isn't
 426          * known, then try verifying the modsig.
 427          */
 428         if (try_modsig &&
 429             (!xattr_value || xattr_value->type == IMA_XATTR_DIGEST_NG ||
 430              rc == -ENOKEY))
 431                 rc = modsig_verify(func, modsig, &status, &cause);
 432
 433 out:
 434         /*
 435          * File signatures on some filesystems can not be properly verified.
 436          * When such filesystems are mounted by an untrusted mounter or on a
 437          * system not willing to accept such a risk, fail the file signature
 438          * verification.
 439          */
 440         if ((inode->i_sb->s_iflags & SB_I_IMA_UNVERIFIABLE_SIGNATURE) &&
 441             ((inode->i_sb->s_iflags & SB_I_UNTRUSTED_MOUNTER) ||
 442              (iint->flags & IMA_FAIL_UNVERIFIABLE_SIGS))) {
 443                 status = INTEGRITY_FAIL;
 444                 cause = "unverifiable-signature";
 445                 integrity_audit_msg(AUDIT_INTEGRITY_DATA, inode, filename,
 446                                     op, cause, rc, 0);
 447         } else if (status != INTEGRITY_PASS) {
 448                 /* Fix mode, but don't replace file signatures. */
 449                 if ((ima_appraise & IMA_APPRAISE_FIX) && !try_modsig &&
 450                     (!xattr_value ||
 451                      xattr_value->type != EVM_IMA_XATTR_DIGSIG)) {
 452                         if (!ima_fix_xattr(dentry, iint))
 453                                 status = INTEGRITY_PASS;
 454                 }
 455
 456                 /* Permit new files with file signatures, but without data. */
 457                 if (inode->i_size == 0 && iint->flags & IMA_NEW_FILE &&
 458                     xattr_value && xattr_value->type == EVM_IMA_XATTR_DIGSIG) {
 459                         status = INTEGRITY_PASS;
 460                 }
 461
 462                 integrity_audit_msg(AUDIT_INTEGRITY_DATA, inode, filename,
 463                                     op, cause, rc, 0);
 464         } else {
 465                 ima_cache_flags(iint, func);
 466         }
 467
 468         ima_set_cache_status(iint, func, status);
 469         return status;
 470 }
 471
 472 /*
 473  * ima_update_xattr - update 'security.ima' hash value
 474  */
 475 void ima_update_xattr(struct integrity_iint_cache *iint, struct file *file)
 476 {
 477         struct dentry *dentry = file_dentry(file);
 478         int rc = 0;
 479
 480         /* do not collect and update hash for digital signatures */
 481         if (test_bit(IMA_DIGSIG, &iint->atomic_flags))
 482                 return;
 483
 484         if ((iint->ima_file_status != INTEGRITY_PASS) &&
 485             !(iint->flags & IMA_HASH))
 486                 return;
 487
 488         rc = ima_collect_measurement(iint, file, NULL, 0, ima_hash_algo, NULL);
 489         if (rc < 0)
 490                 return;
 491
 492         inode_lock(file_inode(file));
 493         ima_fix_xattr(dentry, iint);
 494         inode_unlock(file_inode(file));
 495 }
 496
 497 /**
 498  * ima_inode_post_setattr - reflect file metadata changes
 499  * @dentry: pointer to the affected dentry
 500  *
 501  * Changes to a dentry's metadata might result in needing to appraise.
 502  *
 503  * This function is called from notify_change(), which expects the caller
 504  * to lock the inode's i_mutex.
 505  */
 506 void ima_inode_post_setattr(struct dentry *dentry)
 507 {
 508         struct inode *inode = d_backing_inode(dentry);
 509         struct integrity_iint_cache *iint;
 510         int action;
 511
 512         if (!(ima_policy_flag & IMA_APPRAISE) || !S_ISREG(inode->i_mode)
 513             || !(inode->i_opflags & IOP_XATTR))
 514                 return;
 515
 516         action = ima_must_appraise(inode, MAY_ACCESS, POST_SETATTR);
 517         if (!action)
 518                 __vfs_removexattr(dentry, XATTR_NAME_IMA);
 519         iint = integrity_iint_find(inode);
 520         if (iint) {
 521                 set_bit(IMA_CHANGE_ATTR, &iint->atomic_flags);
 522                 if (!action)
 523                         clear_bit(IMA_UPDATE_XATTR, &iint->atomic_flags);
 524         }
 525 }
 526
 527 /*
 528  * ima_protect_xattr - protect 'security.ima'
 529  *
 530  * Ensure that not just anyone can modify or remove 'security.ima'.
 531  */
 532 static int ima_protect_xattr(struct dentry *dentry, const char *xattr_name,
 533                              const void *xattr_value, size_t xattr_value_len)
 534 {
 535         if (strcmp(xattr_name, XATTR_NAME_IMA) == 0) {
 536                 if (!capable(CAP_SYS_ADMIN))
 537                         return -EPERM;
 538                 return 1;
 539         }
 540         return 0;
 541 }
 542
 543 static void ima_reset_appraise_flags(struct inode *inode, int digsig)
 544 {
 545         struct integrity_iint_cache *iint;
 546
 547         if (!(ima_policy_flag & IMA_APPRAISE) || !S_ISREG(inode->i_mode))
 548                 return;
 549
 550         iint = integrity_iint_find(inode);
 551         if (!iint)
 552                 return;
 553         iint->measured_pcrs = 0;
 554         set_bit(IMA_CHANGE_XATTR, &iint->atomic_flags);
 555         if (digsig)
 556                 set_bit(IMA_DIGSIG, &iint->atomic_flags);
 557         else
 558                 clear_bit(IMA_DIGSIG, &iint->atomic_flags);
 559 }
 560
 561 int ima_inode_setxattr(struct dentry *dentry, const char *xattr_name,
 562                        const void *xattr_value, size_t xattr_value_len)
 563 {
 564         const struct evm_ima_xattr_data *xvalue = xattr_value;
 565         int result;
 566
 567         result = ima_protect_xattr(dentry, xattr_name, xattr_value,
 568                                    xattr_value_len);
 569         if (result == 1) {
 570                 if (!xattr_value_len || (xvalue->type >= IMA_XATTR_LAST))
 571                         return -EINVAL;
 572                 ima_reset_appraise_flags(d_backing_inode(dentry),
 573                         xvalue->type == EVM_IMA_XATTR_DIGSIG);
 574                 result = 0;
 575         }
 576         return result;
 577 }
 578
 579 int ima_inode_removexattr(struct dentry *dentry, const char *xattr_name)
 580 {
 581         int result;
 582
 583         result = ima_protect_xattr(dentry, xattr_name, NULL, 0);
 584         if (result == 1) {
 585                 ima_reset_appraise_flags(d_backing_inode(dentry), 0);
 586                 result = 0;
 587         }
 588         return result;
 589 }