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