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 <linux/fsverity.h>
  17 #include <keys/system_keyring.h>
  18 #include <uapi/linux/fsverity.h>
  19
  20 #include "ima.h"
  21
  22 #ifdef CONFIG_IMA_APPRAISE_BOOTPARAM
  23 static char *ima_appraise_cmdline_default __initdata;
  24 core_param(ima_appraise, ima_appraise_cmdline_default, charp, 0);
  25
  26 void __init ima_appraise_parse_cmdline(void)
  27 {
  28         const char *str = ima_appraise_cmdline_default;
  29         bool sb_state = arch_ima_get_secureboot();
  30         int appraisal_state = ima_appraise;
  31
  32         if (!str)
  33                 return;
  34
  35         if (strncmp(str, "off", 3) == 0)
  36                 appraisal_state = 0;
  37         else if (strncmp(str, "log", 3) == 0)
  38                 appraisal_state = IMA_APPRAISE_LOG;
  39         else if (strncmp(str, "fix", 3) == 0)
  40                 appraisal_state = IMA_APPRAISE_FIX;
  41         else if (strncmp(str, "enforce", 7) == 0)
  42                 appraisal_state = IMA_APPRAISE_ENFORCE;
  43         else
  44                 pr_err("invalid \"%s\" appraise option", str);
  45
  46         /* If appraisal state was changed, but secure boot is enabled,
  47          * keep its default */
  48         if (sb_state) {
  49                 if (!(appraisal_state & IMA_APPRAISE_ENFORCE))
  50                         pr_info("Secure boot enabled: ignoring ima_appraise=%s option",
  51                                 str);
  52         } else {
  53                 ima_appraise = appraisal_state;
  54         }
  55 }
  56 #endif
  57
  58 /*
  59  * is_ima_appraise_enabled - return appraise status
  60  *
  61  * Only return enabled, if not in ima_appraise="fix" or "log" modes.
  62  */
  63 bool is_ima_appraise_enabled(void)
  64 {
  65         return ima_appraise & IMA_APPRAISE_ENFORCE;
  66 }
  67
  68 /*
  69  * ima_must_appraise - set appraise flag
  70  *
  71  * Return 1 to appraise or hash
  72  */
  73 int ima_must_appraise(struct user_namespace *mnt_userns, struct inode *inode,
  74                       int mask, enum ima_hooks func)
  75 {
  76         u32 secid;
  77
  78         if (!ima_appraise)
  79                 return 0;
  80
  81         security_current_getsecid_subj(&secid);
  82         return ima_match_policy(mnt_userns, inode, current_cred(), secid,
  83                                 func, mask, IMA_APPRAISE | IMA_HASH, NULL,
  84                                 NULL, NULL, NULL);
  85 }
  86
  87 static int ima_fix_xattr(struct dentry *dentry,
  88                          struct integrity_iint_cache *iint)
  89 {
  90         int rc, offset;
  91         u8 algo = iint->ima_hash->algo;
  92
  93         if (algo <= HASH_ALGO_SHA1) {
  94                 offset = 1;
  95                 iint->ima_hash->xattr.sha1.type = IMA_XATTR_DIGEST;
  96         } else {
  97                 offset = 0;
  98                 iint->ima_hash->xattr.ng.type = IMA_XATTR_DIGEST_NG;
  99                 iint->ima_hash->xattr.ng.algo = algo;
 100         }
 101         rc = __vfs_setxattr_noperm(&init_user_ns, dentry, XATTR_NAME_IMA,
 102                                    &iint->ima_hash->xattr.data[offset],
 103                                    (sizeof(iint->ima_hash->xattr) - offset) +
 104                                    iint->ima_hash->length, 0);
 105         return rc;
 106 }
 107
 108 /* Return specific func appraised cached result */
 109 enum integrity_status ima_get_cache_status(struct integrity_iint_cache *iint,
 110                                            enum ima_hooks func)
 111 {
 112         switch (func) {
 113         case MMAP_CHECK:
 114                 return iint->ima_mmap_status;
 115         case BPRM_CHECK:
 116                 return iint->ima_bprm_status;
 117         case CREDS_CHECK:
 118                 return iint->ima_creds_status;
 119         case FILE_CHECK:
 120         case POST_SETATTR:
 121                 return iint->ima_file_status;
 122         case MODULE_CHECK ... MAX_CHECK - 1:
 123         default:
 124                 return iint->ima_read_status;
 125         }
 126 }
 127
 128 static void ima_set_cache_status(struct integrity_iint_cache *iint,
 129                                  enum ima_hooks func,
 130                                  enum integrity_status status)
 131 {
 132         switch (func) {
 133         case MMAP_CHECK:
 134                 iint->ima_mmap_status = status;
 135                 break;
 136         case BPRM_CHECK:
 137                 iint->ima_bprm_status = status;
 138                 break;
 139         case CREDS_CHECK:
 140                 iint->ima_creds_status = status;
 141                 break;
 142         case FILE_CHECK:
 143         case POST_SETATTR:
 144                 iint->ima_file_status = status;
 145                 break;
 146         case MODULE_CHECK ... MAX_CHECK - 1:
 147         default:
 148                 iint->ima_read_status = status;
 149                 break;
 150         }
 151 }
 152
 153 static void ima_cache_flags(struct integrity_iint_cache *iint,
 154                              enum ima_hooks func)
 155 {
 156         switch (func) {
 157         case MMAP_CHECK:
 158                 iint->flags |= (IMA_MMAP_APPRAISED | IMA_APPRAISED);
 159                 break;
 160         case BPRM_CHECK:
 161                 iint->flags |= (IMA_BPRM_APPRAISED | IMA_APPRAISED);
 162                 break;
 163         case CREDS_CHECK:
 164                 iint->flags |= (IMA_CREDS_APPRAISED | IMA_APPRAISED);
 165                 break;
 166         case FILE_CHECK:
 167         case POST_SETATTR:
 168                 iint->flags |= (IMA_FILE_APPRAISED | IMA_APPRAISED);
 169                 break;
 170         case MODULE_CHECK ... MAX_CHECK - 1:
 171         default:
 172                 iint->flags |= (IMA_READ_APPRAISED | IMA_APPRAISED);
 173                 break;
 174         }
 175 }
 176
 177 enum hash_algo ima_get_hash_algo(const struct evm_ima_xattr_data *xattr_value,
 178                                  int xattr_len)
 179 {
 180         struct signature_v2_hdr *sig;
 181         enum hash_algo ret;
 182
 183         if (!xattr_value || xattr_len < 2)
 184                 /* return default hash algo */
 185                 return ima_hash_algo;
 186
 187         switch (xattr_value->type) {
 188         case IMA_VERITY_DIGSIG:
 189                 sig = (typeof(sig))xattr_value;
 190                 if (sig->version != 3 || xattr_len <= sizeof(*sig) ||
 191                     sig->hash_algo >= HASH_ALGO__LAST)
 192                         return ima_hash_algo;
 193                 return sig->hash_algo;
 194         case EVM_IMA_XATTR_DIGSIG:
 195                 sig = (typeof(sig))xattr_value;
 196                 if (sig->version != 2 || xattr_len <= sizeof(*sig)
 197                     || sig->hash_algo >= HASH_ALGO__LAST)
 198                         return ima_hash_algo;
 199                 return sig->hash_algo;
 200         case IMA_XATTR_DIGEST_NG:
 201                 /* first byte contains algorithm id */
 202                 ret = xattr_value->data[0];
 203                 if (ret < HASH_ALGO__LAST)
 204                         return ret;
 205                 break;
 206         case IMA_XATTR_DIGEST:
 207                 /* this is for backward compatibility */
 208                 if (xattr_len == 21) {
 209                         unsigned int zero = 0;
 210                         if (!memcmp(&xattr_value->data[16], &zero, 4))
 211                                 return HASH_ALGO_MD5;
 212                         else
 213                                 return HASH_ALGO_SHA1;
 214                 } else if (xattr_len == 17)
 215                         return HASH_ALGO_MD5;
 216                 break;
 217         }
 218
 219         /* return default hash algo */
 220         return ima_hash_algo;
 221 }
 222
 223 int ima_read_xattr(struct dentry *dentry,
 224                    struct evm_ima_xattr_data **xattr_value)
 225 {
 226         ssize_t ret;
 227
 228         ret = vfs_getxattr_alloc(&init_user_ns, dentry, XATTR_NAME_IMA,
 229                                  (char **)xattr_value, 0, GFP_NOFS);
 230         if (ret == -EOPNOTSUPP)
 231                 ret = 0;
 232         return ret;
 233 }
 234
 235 /*
 236  * calc_file_id_hash - calculate the hash of the ima_file_id struct data
 237  * @type: xattr type [enum evm_ima_xattr_type]
 238  * @algo: hash algorithm [enum hash_algo]
 239  * @digest: pointer to the digest to be hashed
 240  * @hash: (out) pointer to the hash
 241  *
 242  * IMA signature version 3 disambiguates the data that is signed by
 243  * indirectly signing the hash of the ima_file_id structure data.
 244  *
 245  * Signing the ima_file_id struct is currently only supported for
 246  * IMA_VERITY_DIGSIG type xattrs.
 247  *
 248  * Return 0 on success, error code otherwise.
 249  */
 250 static int calc_file_id_hash(enum evm_ima_xattr_type type,
 251                              enum hash_algo algo, const u8 *digest,
 252                              struct ima_digest_data *hash)
 253 {
 254         struct ima_file_id file_id = {
 255                 .hash_type = IMA_VERITY_DIGSIG, .hash_algorithm = algo};
 256         unsigned int unused = HASH_MAX_DIGESTSIZE - hash_digest_size[algo];
 257
 258         if (type != IMA_VERITY_DIGSIG)
 259                 return -EINVAL;
 260
 261         memcpy(file_id.hash, digest, hash_digest_size[algo]);
 262
 263         hash->algo = algo;
 264         hash->length = hash_digest_size[algo];
 265
 266         return ima_calc_buffer_hash(&file_id, sizeof(file_id) - unused, hash);
 267 }
 268
 269 /*
 270  * xattr_verify - verify xattr digest or signature
 271  *
 272  * Verify whether the hash or signature matches the file contents.
 273  *
 274  * Return 0 on success, error code otherwise.
 275  */
 276 static int xattr_verify(enum ima_hooks func, struct integrity_iint_cache *iint,
 277                         struct evm_ima_xattr_data *xattr_value, int xattr_len,
 278                         enum integrity_status *status, const char **cause)
 279 {
 280         struct ima_max_digest_data hash;
 281         struct signature_v2_hdr *sig;
 282         int rc = -EINVAL, hash_start = 0;
 283         int mask;
 284
 285         switch (xattr_value->type) {
 286         case IMA_XATTR_DIGEST_NG:
 287                 /* first byte contains algorithm id */
 288                 hash_start = 1;
 289                 fallthrough;
 290         case IMA_XATTR_DIGEST:
 291                 if (*status != INTEGRITY_PASS_IMMUTABLE) {
 292                         if (iint->flags & IMA_DIGSIG_REQUIRED) {
 293                                 if (iint->flags & IMA_VERITY_REQUIRED)
 294                                         *cause = "verity-signature-required";
 295                                 else
 296                                         *cause = "IMA-signature-required";
 297                                 *status = INTEGRITY_FAIL;
 298                                 break;
 299                         }
 300                         clear_bit(IMA_DIGSIG, &iint->atomic_flags);
 301                 } else {
 302                         set_bit(IMA_DIGSIG, &iint->atomic_flags);
 303                 }
 304                 if (xattr_len - sizeof(xattr_value->type) - hash_start >=
 305                                 iint->ima_hash->length)
 306                         /*
 307                          * xattr length may be longer. md5 hash in previous
 308                          * version occupied 20 bytes in xattr, instead of 16
 309                          */
 310                         rc = memcmp(&xattr_value->data[hash_start],
 311                                     iint->ima_hash->digest,
 312                                     iint->ima_hash->length);
 313                 else
 314                         rc = -EINVAL;
 315                 if (rc) {
 316                         *cause = "invalid-hash";
 317                         *status = INTEGRITY_FAIL;
 318                         break;
 319                 }
 320                 *status = INTEGRITY_PASS;
 321                 break;
 322         case EVM_IMA_XATTR_DIGSIG:
 323                 set_bit(IMA_DIGSIG, &iint->atomic_flags);
 324
 325                 mask = IMA_DIGSIG_REQUIRED | IMA_VERITY_REQUIRED;
 326                 if ((iint->flags & mask) == mask) {
 327                         *cause = "verity-signature-required";
 328                         *status = INTEGRITY_FAIL;
 329                         break;
 330                 }
 331
 332                 sig = (typeof(sig))xattr_value;
 333                 if (sig->version >= 3) {
 334                         *cause = "invalid-signature-version";
 335                         *status = INTEGRITY_FAIL;
 336                         break;
 337                 }
 338                 rc = integrity_digsig_verify(INTEGRITY_KEYRING_IMA,
 339                                              (const char *)xattr_value,
 340                                              xattr_len,
 341                                              iint->ima_hash->digest,
 342                                              iint->ima_hash->length);
 343                 if (rc == -EOPNOTSUPP) {
 344                         *status = INTEGRITY_UNKNOWN;
 345                         break;
 346                 }
 347                 if (IS_ENABLED(CONFIG_INTEGRITY_PLATFORM_KEYRING) && rc &&
 348                     func == KEXEC_KERNEL_CHECK)
 349                         rc = integrity_digsig_verify(INTEGRITY_KEYRING_PLATFORM,
 350                                                      (const char *)xattr_value,
 351                                                      xattr_len,
 352                                                      iint->ima_hash->digest,
 353                                                      iint->ima_hash->length);
 354                 if (rc) {
 355                         *cause = "invalid-signature";
 356                         *status = INTEGRITY_FAIL;
 357                 } else {
 358                         *status = INTEGRITY_PASS;
 359                 }
 360                 break;
 361         case IMA_VERITY_DIGSIG:
 362                 set_bit(IMA_DIGSIG, &iint->atomic_flags);
 363
 364                 if (iint->flags & IMA_DIGSIG_REQUIRED) {
 365                         if (!(iint->flags & IMA_VERITY_REQUIRED)) {
 366                                 *cause = "IMA-signature-required";
 367                                 *status = INTEGRITY_FAIL;
 368                                 break;
 369                         }
 370                 }
 371
 372                 sig = (typeof(sig))xattr_value;
 373                 if (sig->version != 3) {
 374                         *cause = "invalid-signature-version";
 375                         *status = INTEGRITY_FAIL;
 376                         break;
 377                 }
 378
 379                 rc = calc_file_id_hash(IMA_VERITY_DIGSIG, iint->ima_hash->algo,
 380                                        iint->ima_hash->digest, &hash.hdr);
 381                 if (rc) {
 382                         *cause = "sigv3-hashing-error";
 383                         *status = INTEGRITY_FAIL;
 384                         break;
 385                 }
 386
 387                 rc = integrity_digsig_verify(INTEGRITY_KEYRING_IMA,
 388                                              (const char *)xattr_value,
 389                                              xattr_len, hash.digest,
 390                                              hash.hdr.length);
 391                 if (rc) {
 392                         *cause = "invalid-verity-signature";
 393                         *status = INTEGRITY_FAIL;
 394                 } else {
 395                         *status = INTEGRITY_PASS;
 396                 }
 397
 398                 break;
 399         default:
 400                 *status = INTEGRITY_UNKNOWN;
 401                 *cause = "unknown-ima-data";
 402                 break;
 403         }
 404
 405         return rc;
 406 }
 407
 408 /*
 409  * modsig_verify - verify modsig signature
 410  *
 411  * Verify whether the signature matches the file contents.
 412  *
 413  * Return 0 on success, error code otherwise.
 414  */
 415 static int modsig_verify(enum ima_hooks func, const struct modsig *modsig,
 416                          enum integrity_status *status, const char **cause)
 417 {
 418         int rc;
 419
 420         rc = integrity_modsig_verify(INTEGRITY_KEYRING_IMA, modsig);
 421         if (IS_ENABLED(CONFIG_INTEGRITY_PLATFORM_KEYRING) && rc &&
 422             func == KEXEC_KERNEL_CHECK)
 423                 rc = integrity_modsig_verify(INTEGRITY_KEYRING_PLATFORM,
 424                                              modsig);
 425         if (rc) {
 426                 *cause = "invalid-signature";
 427                 *status = INTEGRITY_FAIL;
 428         } else {
 429                 *status = INTEGRITY_PASS;
 430         }
 431
 432         return rc;
 433 }
 434
 435 /*
 436  * ima_check_blacklist - determine if the binary is blacklisted.
 437  *
 438  * Add the hash of the blacklisted binary to the measurement list, based
 439  * on policy.
 440  *
 441  * Returns -EPERM if the hash is blacklisted.
 442  */
 443 int ima_check_blacklist(struct integrity_iint_cache *iint,
 444                         const struct modsig *modsig, int pcr)
 445 {
 446         enum hash_algo hash_algo;
 447         const u8 *digest = NULL;
 448         u32 digestsize = 0;
 449         int rc = 0;
 450
 451         if (!(iint->flags & IMA_CHECK_BLACKLIST))
 452                 return 0;
 453
 454         if (iint->flags & IMA_MODSIG_ALLOWED && modsig) {
 455                 ima_get_modsig_digest(modsig, &hash_algo, &digest, &digestsize);
 456
 457                 rc = is_binary_blacklisted(digest, digestsize);
 458                 if ((rc == -EPERM) && (iint->flags & IMA_MEASURE))
 459                         process_buffer_measurement(&init_user_ns, NULL, digest, digestsize,
 460                                                    "blacklisted-hash", NONE,
 461                                                    pcr, NULL, false, NULL, 0);
 462         }
 463
 464         return rc;
 465 }
 466
 467 /*
 468  * ima_appraise_measurement - appraise file measurement
 469  *
 470  * Call evm_verifyxattr() to verify the integrity of 'security.ima'.
 471  * Assuming success, compare the xattr hash with the collected measurement.
 472  *
 473  * Return 0 on success, error code otherwise
 474  */
 475 int ima_appraise_measurement(enum ima_hooks func,
 476                              struct integrity_iint_cache *iint,
 477                              struct file *file, const unsigned char *filename,
 478                              struct evm_ima_xattr_data *xattr_value,
 479                              int xattr_len, const struct modsig *modsig)
 480 {
 481         static const char op[] = "appraise_data";
 482         const char *cause = "unknown";
 483         struct dentry *dentry = file_dentry(file);
 484         struct inode *inode = d_backing_inode(dentry);
 485         enum integrity_status status = INTEGRITY_UNKNOWN;
 486         int rc = xattr_len;
 487         bool try_modsig = iint->flags & IMA_MODSIG_ALLOWED && modsig;
 488
 489         /* If not appraising a modsig, we need an xattr. */
 490         if (!(inode->i_opflags & IOP_XATTR) && !try_modsig)
 491                 return INTEGRITY_UNKNOWN;
 492
 493         /* If reading the xattr failed and there's no modsig, error out. */
 494         if (rc <= 0 && !try_modsig) {
 495                 if (rc && rc != -ENODATA)
 496                         goto out;
 497
 498                 if (iint->flags & IMA_DIGSIG_REQUIRED) {
 499                         if (iint->flags & IMA_VERITY_REQUIRED)
 500                                 cause = "verity-signature-required";
 501                         else
 502                                 cause = "IMA-signature-required";
 503                 } else {
 504                         cause = "missing-hash";
 505                 }
 506
 507                 status = INTEGRITY_NOLABEL;
 508                 if (file->f_mode & FMODE_CREATED)
 509                         iint->flags |= IMA_NEW_FILE;
 510                 if ((iint->flags & IMA_NEW_FILE) &&
 511                     (!(iint->flags & IMA_DIGSIG_REQUIRED) ||
 512                      (inode->i_size == 0)))
 513                         status = INTEGRITY_PASS;
 514                 goto out;
 515         }
 516
 517         status = evm_verifyxattr(dentry, XATTR_NAME_IMA, xattr_value, rc, iint);
 518         switch (status) {
 519         case INTEGRITY_PASS:
 520         case INTEGRITY_PASS_IMMUTABLE:
 521         case INTEGRITY_UNKNOWN:
 522                 break;
 523         case INTEGRITY_NOXATTRS:        /* No EVM protected xattrs. */
 524                 /* It's fine not to have xattrs when using a modsig. */
 525                 if (try_modsig)
 526                         break;
 527                 fallthrough;
 528         case INTEGRITY_NOLABEL:         /* No security.evm xattr. */
 529                 cause = "missing-HMAC";
 530                 goto out;
 531         case INTEGRITY_FAIL_IMMUTABLE:
 532                 set_bit(IMA_DIGSIG, &iint->atomic_flags);
 533                 cause = "invalid-fail-immutable";
 534                 goto out;
 535         case INTEGRITY_FAIL:            /* Invalid HMAC/signature. */
 536                 cause = "invalid-HMAC";
 537                 goto out;
 538         default:
 539                 WARN_ONCE(true, "Unexpected integrity status %d\n", status);
 540         }
 541
 542         if (xattr_value)
 543                 rc = xattr_verify(func, iint, xattr_value, xattr_len, &status,
 544                                   &cause);
 545
 546         /*
 547          * If we have a modsig and either no imasig or the imasig's key isn't
 548          * known, then try verifying the modsig.
 549          */
 550         if (try_modsig &&
 551             (!xattr_value || xattr_value->type == IMA_XATTR_DIGEST_NG ||
 552              rc == -ENOKEY))
 553                 rc = modsig_verify(func, modsig, &status, &cause);
 554
 555 out:
 556         /*
 557          * File signatures on some filesystems can not be properly verified.
 558          * When such filesystems are mounted by an untrusted mounter or on a
 559          * system not willing to accept such a risk, fail the file signature
 560          * verification.
 561          */
 562         if ((inode->i_sb->s_iflags & SB_I_IMA_UNVERIFIABLE_SIGNATURE) &&
 563             ((inode->i_sb->s_iflags & SB_I_UNTRUSTED_MOUNTER) ||
 564              (iint->flags & IMA_FAIL_UNVERIFIABLE_SIGS))) {
 565                 status = INTEGRITY_FAIL;
 566                 cause = "unverifiable-signature";
 567                 integrity_audit_msg(AUDIT_INTEGRITY_DATA, inode, filename,
 568                                     op, cause, rc, 0);
 569         } else if (status != INTEGRITY_PASS) {
 570                 /* Fix mode, but don't replace file signatures. */
 571                 if ((ima_appraise & IMA_APPRAISE_FIX) && !try_modsig &&
 572                     (!xattr_value ||
 573                      xattr_value->type != EVM_IMA_XATTR_DIGSIG)) {
 574                         if (!ima_fix_xattr(dentry, iint))
 575                                 status = INTEGRITY_PASS;
 576                 }
 577
 578                 /*
 579                  * Permit new files with file/EVM portable signatures, but
 580                  * without data.
 581                  */
 582                 if (inode->i_size == 0 && iint->flags & IMA_NEW_FILE &&
 583                     test_bit(IMA_DIGSIG, &iint->atomic_flags)) {
 584                         status = INTEGRITY_PASS;
 585                 }
 586
 587                 integrity_audit_msg(AUDIT_INTEGRITY_DATA, inode, filename,
 588                                     op, cause, rc, 0);
 589         } else {
 590                 ima_cache_flags(iint, func);
 591         }
 592
 593         ima_set_cache_status(iint, func, status);
 594         return status;
 595 }
 596
 597 /*
 598  * ima_update_xattr - update 'security.ima' hash value
 599  */
 600 void ima_update_xattr(struct integrity_iint_cache *iint, struct file *file)
 601 {
 602         struct dentry *dentry = file_dentry(file);
 603         int rc = 0;
 604
 605         /* do not collect and update hash for digital signatures */
 606         if (test_bit(IMA_DIGSIG, &iint->atomic_flags))
 607                 return;
 608
 609         if ((iint->ima_file_status != INTEGRITY_PASS) &&
 610             !(iint->flags & IMA_HASH))
 611                 return;
 612
 613         rc = ima_collect_measurement(iint, file, NULL, 0, ima_hash_algo, NULL);
 614         if (rc < 0)
 615                 return;
 616
 617         inode_lock(file_inode(file));
 618         ima_fix_xattr(dentry, iint);
 619         inode_unlock(file_inode(file));
 620 }
 621
 622 /**
 623  * ima_inode_post_setattr - reflect file metadata changes
 624  * @mnt_userns: user namespace of the mount the inode was found from
 625  * @dentry: pointer to the affected dentry
 626  *
 627  * Changes to a dentry's metadata might result in needing to appraise.
 628  *
 629  * This function is called from notify_change(), which expects the caller
 630  * to lock the inode's i_mutex.
 631  */
 632 void ima_inode_post_setattr(struct user_namespace *mnt_userns,
 633                             struct dentry *dentry)
 634 {
 635         struct inode *inode = d_backing_inode(dentry);
 636         struct integrity_iint_cache *iint;
 637         int action;
 638
 639         if (!(ima_policy_flag & IMA_APPRAISE) || !S_ISREG(inode->i_mode)
 640             || !(inode->i_opflags & IOP_XATTR))
 641                 return;
 642
 643         action = ima_must_appraise(mnt_userns, inode, MAY_ACCESS, POST_SETATTR);
 644         iint = integrity_iint_find(inode);
 645         if (iint) {
 646                 set_bit(IMA_CHANGE_ATTR, &iint->atomic_flags);
 647                 if (!action)
 648                         clear_bit(IMA_UPDATE_XATTR, &iint->atomic_flags);
 649         }
 650 }
 651
 652 /*
 653  * ima_protect_xattr - protect 'security.ima'
 654  *
 655  * Ensure that not just anyone can modify or remove 'security.ima'.
 656  */
 657 static int ima_protect_xattr(struct dentry *dentry, const char *xattr_name,
 658                              const void *xattr_value, size_t xattr_value_len)
 659 {
 660         if (strcmp(xattr_name, XATTR_NAME_IMA) == 0) {
 661                 if (!capable(CAP_SYS_ADMIN))
 662                         return -EPERM;
 663                 return 1;
 664         }
 665         return 0;
 666 }
 667
 668 static void ima_reset_appraise_flags(struct inode *inode, int digsig)
 669 {
 670         struct integrity_iint_cache *iint;
 671
 672         if (!(ima_policy_flag & IMA_APPRAISE) || !S_ISREG(inode->i_mode))
 673                 return;
 674
 675         iint = integrity_iint_find(inode);
 676         if (!iint)
 677                 return;
 678         iint->measured_pcrs = 0;
 679         set_bit(IMA_CHANGE_XATTR, &iint->atomic_flags);
 680         if (digsig)
 681                 set_bit(IMA_DIGSIG, &iint->atomic_flags);
 682         else
 683                 clear_bit(IMA_DIGSIG, &iint->atomic_flags);
 684 }
 685
 686 /**
 687  * validate_hash_algo() - Block setxattr with unsupported hash algorithms
 688  * @dentry: object of the setxattr()
 689  * @xattr_value: userland supplied xattr value
 690  * @xattr_value_len: length of xattr_value
 691  *
 692  * The xattr value is mapped to its hash algorithm, and this algorithm
 693  * must be built in the kernel for the setxattr to be allowed.
 694  *
 695  * Emit an audit message when the algorithm is invalid.
 696  *
 697  * Return: 0 on success, else an error.
 698  */
 699 static int validate_hash_algo(struct dentry *dentry,
 700                               const struct evm_ima_xattr_data *xattr_value,
 701                               size_t xattr_value_len)
 702 {
 703         char *path = NULL, *pathbuf = NULL;
 704         enum hash_algo xattr_hash_algo;
 705         const char *errmsg = "unavailable-hash-algorithm";
 706         unsigned int allowed_hashes;
 707
 708         xattr_hash_algo = ima_get_hash_algo(xattr_value, xattr_value_len);
 709
 710         allowed_hashes = atomic_read(&ima_setxattr_allowed_hash_algorithms);
 711
 712         if (allowed_hashes) {
 713                 /* success if the algorithm is allowed in the ima policy */
 714                 if (allowed_hashes & (1U << xattr_hash_algo))
 715                         return 0;
 716
 717                 /*
 718                  * We use a different audit message when the hash algorithm
 719                  * is denied by a policy rule, instead of not being built
 720                  * in the kernel image
 721                  */
 722                 errmsg = "denied-hash-algorithm";
 723         } else {
 724                 if (likely(xattr_hash_algo == ima_hash_algo))
 725                         return 0;
 726
 727                 /* allow any xattr using an algorithm built in the kernel */
 728                 if (crypto_has_alg(hash_algo_name[xattr_hash_algo], 0, 0))
 729                         return 0;
 730         }
 731
 732         pathbuf = kmalloc(PATH_MAX, GFP_KERNEL);
 733         if (!pathbuf)
 734                 return -EACCES;
 735
 736         path = dentry_path(dentry, pathbuf, PATH_MAX);
 737
 738         integrity_audit_msg(AUDIT_INTEGRITY_DATA, d_inode(dentry), path,
 739                             "set_data", errmsg, -EACCES, 0);
 740
 741         kfree(pathbuf);
 742
 743         return -EACCES;
 744 }
 745
 746 int ima_inode_setxattr(struct dentry *dentry, const char *xattr_name,
 747                        const void *xattr_value, size_t xattr_value_len)
 748 {
 749         const struct evm_ima_xattr_data *xvalue = xattr_value;
 750         int digsig = 0;
 751         int result;
 752
 753         result = ima_protect_xattr(dentry, xattr_name, xattr_value,
 754                                    xattr_value_len);
 755         if (result == 1) {
 756                 if (!xattr_value_len || (xvalue->type >= IMA_XATTR_LAST))
 757                         return -EINVAL;
 758                 digsig = (xvalue->type == EVM_IMA_XATTR_DIGSIG);
 759         } else if (!strcmp(xattr_name, XATTR_NAME_EVM) && xattr_value_len > 0) {
 760                 digsig = (xvalue->type == EVM_XATTR_PORTABLE_DIGSIG);
 761         }
 762         if (result == 1 || evm_revalidate_status(xattr_name)) {
 763                 result = validate_hash_algo(dentry, xvalue, xattr_value_len);
 764                 if (result)
 765                         return result;
 766
 767                 ima_reset_appraise_flags(d_backing_inode(dentry), digsig);
 768         }
 769         return result;
 770 }
 771
 772 int ima_inode_removexattr(struct dentry *dentry, const char *xattr_name)
 773 {
 774         int result;
 775
 776         result = ima_protect_xattr(dentry, xattr_name, NULL, 0);
 777         if (result == 1 || evm_revalidate_status(xattr_name)) {
 778                 ima_reset_appraise_flags(d_backing_inode(dentry), 0);
 779                 if (result == 1)
 780                         result = 0;
 781         }
 782         return result;
 783 }