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/module.h>
   9 #include <linux/init.h>
  10 #include <linux/file.h>
  11 #include <linux/fs.h>
  12 #include <linux/xattr.h>
  13 #include <linux/magic.h>
  14 #include <linux/ima.h>
  15 #include <linux/evm.h>
  16 #include <keys/system_keyring.h>
  17
  18 #include "ima.h"
  19
  20 #ifdef CONFIG_IMA_APPRAISE_BOOTPARAM
  21 static char *ima_appraise_cmdline_default __initdata;
  22 core_param(ima_appraise, ima_appraise_cmdline_default, charp, 0);
  23
  24 void __init ima_appraise_parse_cmdline(void)
  25 {
  26         const char *str = ima_appraise_cmdline_default;
  27         bool sb_state = arch_ima_get_secureboot();
  28         int appraisal_state = ima_appraise;
  29
  30         if (!str)
  31                 return;
  32
  33         if (strncmp(str, "off", 3) == 0)
  34                 appraisal_state = 0;
  35         else if (strncmp(str, "log", 3) == 0)
  36                 appraisal_state = IMA_APPRAISE_LOG;
  37         else if (strncmp(str, "fix", 3) == 0)
  38                 appraisal_state = IMA_APPRAISE_FIX;
  39         else if (strncmp(str, "enforce", 7) == 0)
  40                 appraisal_state = IMA_APPRAISE_ENFORCE;
  41         else
  42                 pr_err("invalid \"%s\" appraise option", str);
  43
  44         /* If appraisal state was changed, but secure boot is enabled,
  45          * keep its default */
  46         if (sb_state) {
  47                 if (!(appraisal_state & IMA_APPRAISE_ENFORCE))
  48                         pr_info("Secure boot enabled: ignoring ima_appraise=%s option",
  49                                 str);
  50         } else {
  51                 ima_appraise = appraisal_state;
  52         }
  53 }
  54 #endif
  55
  56 /*
  57  * is_ima_appraise_enabled - return appraise status
  58  *
  59  * Only return enabled, if not in ima_appraise="fix" or "log" modes.
  60  */
  61 bool is_ima_appraise_enabled(void)
  62 {
  63         return ima_appraise & IMA_APPRAISE_ENFORCE;
  64 }
  65
  66 /*
  67  * ima_must_appraise - set appraise flag
  68  *
  69  * Return 1 to appraise or hash
  70  */
  71 int ima_must_appraise(struct inode *inode, int mask, enum ima_hooks func)
  72 {
  73         u32 secid;
  74
  75         if (!ima_appraise)
  76                 return 0;
  77
  78         security_task_getsecid(current, &secid);
  79         return ima_match_policy(inode, current_cred(), secid, func, mask,
  80                                 IMA_APPRAISE | IMA_HASH, NULL, NULL, NULL);
  81 }
  82
  83 static int ima_fix_xattr(struct dentry *dentry,
  84                          struct integrity_iint_cache *iint)
  85 {
  86         int rc, offset;
  87         u8 algo = iint->ima_hash->algo;
  88
  89         if (algo <= HASH_ALGO_SHA1) {
  90                 offset = 1;
  91                 iint->ima_hash->xattr.sha1.type = IMA_XATTR_DIGEST;
  92         } else {
  93                 offset = 0;
  94                 iint->ima_hash->xattr.ng.type = IMA_XATTR_DIGEST_NG;
  95                 iint->ima_hash->xattr.ng.algo = algo;
  96         }
  97         rc = __vfs_setxattr_noperm(dentry, XATTR_NAME_IMA,
  98                                    &iint->ima_hash->xattr.data[offset],
  99                                    (sizeof(iint->ima_hash->xattr) - offset) +
 100                                    iint->ima_hash->length, 0);
 101         return rc;
 102 }
 103
 104 /* Return specific func appraised cached result */
 105 enum integrity_status ima_get_cache_status(struct integrity_iint_cache *iint,
 106                                            enum ima_hooks func)
 107 {
 108         switch (func) {
 109         case MMAP_CHECK:
 110                 return iint->ima_mmap_status;
 111         case BPRM_CHECK:
 112                 return iint->ima_bprm_status;
 113         case CREDS_CHECK:
 114                 return iint->ima_creds_status;
 115         case FILE_CHECK:
 116         case POST_SETATTR:
 117                 return iint->ima_file_status;
 118         case MODULE_CHECK ... MAX_CHECK - 1:
 119         default:
 120                 return iint->ima_read_status;
 121         }
 122 }
 123
 124 static void ima_set_cache_status(struct integrity_iint_cache *iint,
 125                                  enum ima_hooks func,
 126                                  enum integrity_status status)
 127 {
 128         switch (func) {
 129         case MMAP_CHECK:
 130                 iint->ima_mmap_status = status;
 131                 break;
 132         case BPRM_CHECK:
 133                 iint->ima_bprm_status = status;
 134                 break;
 135         case CREDS_CHECK:
 136                 iint->ima_creds_status = status;
 137                 break;
 138         case FILE_CHECK:
 139         case POST_SETATTR:
 140                 iint->ima_file_status = status;
 141                 break;
 142         case MODULE_CHECK ... MAX_CHECK - 1:
 143         default:
 144                 iint->ima_read_status = status;
 145                 break;
 146         }
 147 }
 148
 149 static void ima_cache_flags(struct integrity_iint_cache *iint,
 150                              enum ima_hooks func)
 151 {
 152         switch (func) {
 153         case MMAP_CHECK:
 154                 iint->flags |= (IMA_MMAP_APPRAISED | IMA_APPRAISED);
 155                 break;
 156         case BPRM_CHECK:
 157                 iint->flags |= (IMA_BPRM_APPRAISED | IMA_APPRAISED);
 158                 break;
 159         case CREDS_CHECK:
 160                 iint->flags |= (IMA_CREDS_APPRAISED | IMA_APPRAISED);
 161                 break;
 162         case FILE_CHECK:
 163         case POST_SETATTR:
 164                 iint->flags |= (IMA_FILE_APPRAISED | IMA_APPRAISED);
 165                 break;
 166         case MODULE_CHECK ... MAX_CHECK - 1:
 167         default:
 168                 iint->flags |= (IMA_READ_APPRAISED | IMA_APPRAISED);
 169                 break;
 170         }
 171 }
 172
 173 enum hash_algo ima_get_hash_algo(struct evm_ima_xattr_data *xattr_value,
 174                                  int xattr_len)
 175 {
 176         struct signature_v2_hdr *sig;
 177         enum hash_algo ret;
 178
 179         if (!xattr_value || xattr_len < 2)
 180                 /* return default hash algo */
 181                 return ima_hash_algo;
 182
 183         switch (xattr_value->type) {
 184         case EVM_IMA_XATTR_DIGSIG:
 185                 sig = (typeof(sig))xattr_value;
 186                 if (sig->version != 2 || xattr_len <= sizeof(*sig))
 187                         return ima_hash_algo;
 188                 return sig->hash_algo;
 189                 break;
 190         case IMA_XATTR_DIGEST_NG:
 191                 /* first byte contains algorithm id */
 192                 ret = xattr_value->data[0];
 193                 if (ret < HASH_ALGO__LAST)
 194                         return ret;
 195                 break;
 196         case IMA_XATTR_DIGEST:
 197                 /* this is for backward compatibility */
 198                 if (xattr_len == 21) {
 199                         unsigned int zero = 0;
 200                         if (!memcmp(&xattr_value->data[16], &zero, 4))
 201                                 return HASH_ALGO_MD5;
 202                         else
 203                                 return HASH_ALGO_SHA1;
 204                 } else if (xattr_len == 17)
 205                         return HASH_ALGO_MD5;
 206                 break;
 207         }
 208
 209         /* return default hash algo */
 210         return ima_hash_algo;
 211 }
 212
 213 int ima_read_xattr(struct dentry *dentry,
 214                    struct evm_ima_xattr_data **xattr_value)
 215 {
 216         ssize_t ret;
 217
 218         ret = vfs_getxattr_alloc(dentry, XATTR_NAME_IMA, (char **)xattr_value,
 219                                  0, GFP_NOFS);
 220         if (ret == -EOPNOTSUPP)
 221                 ret = 0;
 222         return ret;
 223 }
 224
 225 /*
 226  * xattr_verify - verify xattr digest or signature
 227  *
 228  * Verify whether the hash or signature matches the file contents.
 229  *
 230  * Return 0 on success, error code otherwise.
 231  */
 232 static int xattr_verify(enum ima_hooks func, struct integrity_iint_cache *iint,
 233                         struct evm_ima_xattr_data *xattr_value, int xattr_len,
 234                         enum integrity_status *status, const char **cause)
 235 {
 236         int rc = -EINVAL, hash_start = 0;
 237
 238         switch (xattr_value->type) {
 239         case IMA_XATTR_DIGEST_NG:
 240                 /* first byte contains algorithm id */
 241                 hash_start = 1;
 242                 fallthrough;
 243         case IMA_XATTR_DIGEST:
 244                 if (iint->flags & IMA_DIGSIG_REQUIRED) {
 245                         *cause = "IMA-signature-required";
 246                         *status = INTEGRITY_FAIL;
 247                         break;
 248                 }
 249                 clear_bit(IMA_DIGSIG, &iint->atomic_flags);
 250                 if (xattr_len - sizeof(xattr_value->type) - hash_start >=
 251                                 iint->ima_hash->length)
 252                         /*
 253                          * xattr length may be longer. md5 hash in previous
 254                          * version occupied 20 bytes in xattr, instead of 16
 255                          */
 256                         rc = memcmp(&xattr_value->data[hash_start],
 257                                     iint->ima_hash->digest,
 258                                     iint->ima_hash->length);
 259                 else
 260                         rc = -EINVAL;
 261                 if (rc) {
 262                         *cause = "invalid-hash";
 263                         *status = INTEGRITY_FAIL;
 264                         break;
 265                 }
 266                 *status = INTEGRITY_PASS;
 267                 break;
 268         case EVM_IMA_XATTR_DIGSIG:
 269                 set_bit(IMA_DIGSIG, &iint->atomic_flags);
 270                 rc = integrity_digsig_verify(INTEGRITY_KEYRING_IMA,
 271                                              (const char *)xattr_value,
 272                                              xattr_len,
 273                                              iint->ima_hash->digest,
 274                                              iint->ima_hash->length);
 275                 if (rc == -EOPNOTSUPP) {
 276                         *status = INTEGRITY_UNKNOWN;
 277                         break;
 278                 }
 279                 if (IS_ENABLED(CONFIG_INTEGRITY_PLATFORM_KEYRING) && rc &&
 280                     func == KEXEC_KERNEL_CHECK)
 281                         rc = integrity_digsig_verify(INTEGRITY_KEYRING_PLATFORM,
 282                                                      (const char *)xattr_value,
 283                                                      xattr_len,
 284                                                      iint->ima_hash->digest,
 285                                                      iint->ima_hash->length);
 286                 if (rc) {
 287                         *cause = "invalid-signature";
 288                         *status = INTEGRITY_FAIL;
 289                 } else {
 290                         *status = INTEGRITY_PASS;
 291                 }
 292                 break;
 293         default:
 294                 *status = INTEGRITY_UNKNOWN;
 295                 *cause = "unknown-ima-data";
 296                 break;
 297         }
 298
 299         return rc;
 300 }
 301
 302 /*
 303  * modsig_verify - verify modsig signature
 304  *
 305  * Verify whether the signature matches the file contents.
 306  *
 307  * Return 0 on success, error code otherwise.
 308  */
 309 static int modsig_verify(enum ima_hooks func, const struct modsig *modsig,
 310                          enum integrity_status *status, const char **cause)
 311 {
 312         int rc;
 313
 314         rc = integrity_modsig_verify(INTEGRITY_KEYRING_IMA, modsig);
 315         if (IS_ENABLED(CONFIG_INTEGRITY_PLATFORM_KEYRING) && rc &&
 316             func == KEXEC_KERNEL_CHECK)
 317                 rc = integrity_modsig_verify(INTEGRITY_KEYRING_PLATFORM,
 318                                              modsig);
 319         if (rc) {
 320                 *cause = "invalid-signature";
 321                 *status = INTEGRITY_FAIL;
 322         } else {
 323                 *status = INTEGRITY_PASS;
 324         }
 325
 326         return rc;
 327 }
 328
 329 /*
 330  * ima_check_blacklist - determine if the binary is blacklisted.
 331  *
 332  * Add the hash of the blacklisted binary to the measurement list, based
 333  * on policy.
 334  *
 335  * Returns -EPERM if the hash is blacklisted.
 336  */
 337 int ima_check_blacklist(struct integrity_iint_cache *iint,
 338                         const struct modsig *modsig, int pcr)
 339 {
 340         enum hash_algo hash_algo;
 341         const u8 *digest = NULL;
 342         u32 digestsize = 0;
 343         int rc = 0;
 344
 345         if (!(iint->flags & IMA_CHECK_BLACKLIST))
 346                 return 0;
 347
 348         if (iint->flags & IMA_MODSIG_ALLOWED && modsig) {
 349                 ima_get_modsig_digest(modsig, &hash_algo, &digest, &digestsize);
 350
 351                 rc = is_binary_blacklisted(digest, digestsize);
 352                 if ((rc == -EPERM) && (iint->flags & IMA_MEASURE))
 353                         process_buffer_measurement(NULL, digest, digestsize,
 354                                                    "blacklisted-hash", NONE,
 355                                                    pcr, NULL);
 356         }
 357
 358         return rc;
 359 }
 360
 361 /*
 362  * ima_appraise_measurement - appraise file measurement
 363  *
 364  * Call evm_verifyxattr() to verify the integrity of 'security.ima'.
 365  * Assuming success, compare the xattr hash with the collected measurement.
 366  *
 367  * Return 0 on success, error code otherwise
 368  */
 369 int ima_appraise_measurement(enum ima_hooks func,
 370                              struct integrity_iint_cache *iint,
 371                              struct file *file, const unsigned char *filename,
 372                              struct evm_ima_xattr_data *xattr_value,
 373                              int xattr_len, const struct modsig *modsig)
 374 {
 375         static const char op[] = "appraise_data";
 376         const char *cause = "unknown";
 377         struct dentry *dentry = file_dentry(file);
 378         struct inode *inode = d_backing_inode(dentry);
 379         enum integrity_status status = INTEGRITY_UNKNOWN;
 380         int rc = xattr_len;
 381         bool try_modsig = iint->flags & IMA_MODSIG_ALLOWED && modsig;
 382
 383         /* If not appraising a modsig, we need an xattr. */
 384         if (!(inode->i_opflags & IOP_XATTR) && !try_modsig)
 385                 return INTEGRITY_UNKNOWN;
 386
 387         /* If reading the xattr failed and there's no modsig, error out. */
 388         if (rc <= 0 && !try_modsig) {
 389                 if (rc && rc != -ENODATA)
 390                         goto out;
 391
 392                 cause = iint->flags & IMA_DIGSIG_REQUIRED ?
 393                                 "IMA-signature-required" : "missing-hash";
 394                 status = INTEGRITY_NOLABEL;
 395                 if (file->f_mode & FMODE_CREATED)
 396                         iint->flags |= IMA_NEW_FILE;
 397                 if ((iint->flags & IMA_NEW_FILE) &&
 398                     (!(iint->flags & IMA_DIGSIG_REQUIRED) ||
 399                      (inode->i_size == 0)))
 400                         status = INTEGRITY_PASS;
 401                 goto out;
 402         }
 403
 404         status = evm_verifyxattr(dentry, XATTR_NAME_IMA, xattr_value, rc, iint);
 405         switch (status) {
 406         case INTEGRITY_PASS:
 407         case INTEGRITY_PASS_IMMUTABLE:
 408         case INTEGRITY_UNKNOWN:
 409                 break;
 410         case INTEGRITY_NOXATTRS:        /* No EVM protected xattrs. */
 411                 /* It's fine not to have xattrs when using a modsig. */
 412                 if (try_modsig)
 413                         break;
 414                 fallthrough;
 415         case INTEGRITY_NOLABEL:         /* No security.evm xattr. */
 416                 cause = "missing-HMAC";
 417                 goto out;
 418         case INTEGRITY_FAIL:            /* Invalid HMAC/signature. */
 419                 cause = "invalid-HMAC";
 420                 goto out;
 421         default:
 422                 WARN_ONCE(true, "Unexpected integrity status %d\n", status);
 423         }
 424
 425         if (xattr_value)
 426                 rc = xattr_verify(func, iint, xattr_value, xattr_len, &status,
 427                                   &cause);
 428
 429         /*
 430          * If we have a modsig and either no imasig or the imasig's key isn't
 431          * known, then try verifying the modsig.
 432          */
 433         if (try_modsig &&
 434             (!xattr_value || xattr_value->type == IMA_XATTR_DIGEST_NG ||
 435              rc == -ENOKEY))
 436                 rc = modsig_verify(func, modsig, &status, &cause);
 437
 438 out:
 439         /*
 440          * File signatures on some filesystems can not be properly verified.
 441          * When such filesystems are mounted by an untrusted mounter or on a
 442          * system not willing to accept such a risk, fail the file signature
 443          * verification.
 444          */
 445         if ((inode->i_sb->s_iflags & SB_I_IMA_UNVERIFIABLE_SIGNATURE) &&
 446             ((inode->i_sb->s_iflags & SB_I_UNTRUSTED_MOUNTER) ||
 447              (iint->flags & IMA_FAIL_UNVERIFIABLE_SIGS))) {
 448                 status = INTEGRITY_FAIL;
 449                 cause = "unverifiable-signature";
 450                 integrity_audit_msg(AUDIT_INTEGRITY_DATA, inode, filename,
 451                                     op, cause, rc, 0);
 452         } else if (status != INTEGRITY_PASS) {
 453                 /* Fix mode, but don't replace file signatures. */
 454                 if ((ima_appraise & IMA_APPRAISE_FIX) && !try_modsig &&
 455                     (!xattr_value ||
 456                      xattr_value->type != EVM_IMA_XATTR_DIGSIG)) {
 457                         if (!ima_fix_xattr(dentry, iint))
 458                                 status = INTEGRITY_PASS;
 459                 }
 460
 461                 /* Permit new files with file signatures, but without data. */
 462                 if (inode->i_size == 0 && iint->flags & IMA_NEW_FILE &&
 463                     xattr_value && xattr_value->type == EVM_IMA_XATTR_DIGSIG) {
 464                         status = INTEGRITY_PASS;
 465                 }
 466
 467                 integrity_audit_msg(AUDIT_INTEGRITY_DATA, inode, filename,
 468                                     op, cause, rc, 0);
 469         } else {
 470                 ima_cache_flags(iint, func);
 471         }
 472
 473         ima_set_cache_status(iint, func, status);
 474         return status;
 475 }
 476
 477 /*
 478  * ima_update_xattr - update 'security.ima' hash value
 479  */
 480 void ima_update_xattr(struct integrity_iint_cache *iint, struct file *file)
 481 {
 482         struct dentry *dentry = file_dentry(file);
 483         int rc = 0;
 484
 485         /* do not collect and update hash for digital signatures */
 486         if (test_bit(IMA_DIGSIG, &iint->atomic_flags))
 487                 return;
 488
 489         if ((iint->ima_file_status != INTEGRITY_PASS) &&
 490             !(iint->flags & IMA_HASH))
 491                 return;
 492
 493         rc = ima_collect_measurement(iint, file, NULL, 0, ima_hash_algo, NULL);
 494         if (rc < 0)
 495                 return;
 496
 497         inode_lock(file_inode(file));
 498         ima_fix_xattr(dentry, iint);
 499         inode_unlock(file_inode(file));
 500 }
 501
 502 /**
 503  * ima_inode_post_setattr - reflect file metadata changes
 504  * @dentry: pointer to the affected dentry
 505  *
 506  * Changes to a dentry's metadata might result in needing to appraise.
 507  *
 508  * This function is called from notify_change(), which expects the caller
 509  * to lock the inode's i_mutex.
 510  */
 511 void ima_inode_post_setattr(struct dentry *dentry)
 512 {
 513         struct inode *inode = d_backing_inode(dentry);
 514         struct integrity_iint_cache *iint;
 515         int action;
 516
 517         if (!(ima_policy_flag & IMA_APPRAISE) || !S_ISREG(inode->i_mode)
 518             || !(inode->i_opflags & IOP_XATTR))
 519                 return;
 520
 521         action = ima_must_appraise(inode, MAY_ACCESS, POST_SETATTR);
 522         if (!action)
 523                 __vfs_removexattr(dentry, XATTR_NAME_IMA);
 524         iint = integrity_iint_find(inode);
 525         if (iint) {
 526                 set_bit(IMA_CHANGE_ATTR, &iint->atomic_flags);
 527                 if (!action)
 528                         clear_bit(IMA_UPDATE_XATTR, &iint->atomic_flags);
 529         }
 530 }
 531
 532 /*
 533  * ima_protect_xattr - protect 'security.ima'
 534  *
 535  * Ensure that not just anyone can modify or remove 'security.ima'.
 536  */
 537 static int ima_protect_xattr(struct dentry *dentry, const char *xattr_name,
 538                              const void *xattr_value, size_t xattr_value_len)
 539 {
 540         if (strcmp(xattr_name, XATTR_NAME_IMA) == 0) {
 541                 if (!capable(CAP_SYS_ADMIN))
 542                         return -EPERM;
 543                 return 1;
 544         }
 545         return 0;
 546 }
 547
 548 static void ima_reset_appraise_flags(struct inode *inode, int digsig)
 549 {
 550         struct integrity_iint_cache *iint;
 551
 552         if (!(ima_policy_flag & IMA_APPRAISE) || !S_ISREG(inode->i_mode))
 553                 return;
 554
 555         iint = integrity_iint_find(inode);
 556         if (!iint)
 557                 return;
 558         iint->measured_pcrs = 0;
 559         set_bit(IMA_CHANGE_XATTR, &iint->atomic_flags);
 560         if (digsig)
 561                 set_bit(IMA_DIGSIG, &iint->atomic_flags);
 562         else
 563                 clear_bit(IMA_DIGSIG, &iint->atomic_flags);
 564 }
 565
 566 int ima_inode_setxattr(struct dentry *dentry, const char *xattr_name,
 567                        const void *xattr_value, size_t xattr_value_len)
 568 {
 569         const struct evm_ima_xattr_data *xvalue = xattr_value;
 570         int result;
 571
 572         result = ima_protect_xattr(dentry, xattr_name, xattr_value,
 573                                    xattr_value_len);
 574         if (result == 1) {
 575                 if (!xattr_value_len || (xvalue->type >= IMA_XATTR_LAST))
 576                         return -EINVAL;
 577                 ima_reset_appraise_flags(d_backing_inode(dentry),
 578                         xvalue->type == EVM_IMA_XATTR_DIGSIG);
 579                 result = 0;
 580         }
 581         return result;
 582 }
 583
 584 int ima_inode_removexattr(struct dentry *dentry, const char *xattr_name)
 585 {
 586         int result;
 587
 588         result = ima_protect_xattr(dentry, xattr_name, NULL, 0);
 589         if (result == 1) {
 590                 ima_reset_appraise_flags(d_backing_inode(dentry), 0);
 591                 result = 0;
 592         }
 593         return result;
 594 }