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