LXR linux/security/integrity/ima/ima

   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
  21static char *ima_appraise_cmdline_default __initdata;
  22core_param(ima_appraise, ima_appraise_cmdline_default, charp, 0);
  23
  24void __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 */
  61bool 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 */
  71int ima_must_appraise(struct user_namespace *mnt_userns, struct inode *inode,
  72                      int mask, enum ima_hooks func)
  73{
  74        u32 secid;
  75
  76        if (!ima_appraise)
  77                return 0;
  78
  79        security_task_getsecid_subj(current, &secid);
  80        return ima_match_policy(mnt_userns, inode, current_cred(), secid, func,
  81                                mask, IMA_APPRAISE | IMA_HASH, NULL, NULL, NULL);
  82}
  83
  84static int ima_fix_xattr(struct dentry *dentry,
  85                         struct integrity_iint_cache *iint)
  86{
  87        int rc, offset;
  88        u8 algo = iint->ima_hash->algo;
  89
  90        if (algo <= HASH_ALGO_SHA1) {
  91                offset = 1;
  92                iint->ima_hash->xattr.sha1.type = IMA_XATTR_DIGEST;
  93        } else {
  94                offset = 0;
  95                iint->ima_hash->xattr.ng.type = IMA_XATTR_DIGEST_NG;
  96                iint->ima_hash->xattr.ng.algo = algo;
  97        }
  98        rc = __vfs_setxattr_noperm(&init_user_ns, dentry, XATTR_NAME_IMA,
  99                                   &iint->ima_hash->xattr.data[offset],
 100                                   (sizeof(iint->ima_hash->xattr) - offset) +
 101                                   iint->ima_hash->length, 0);
 102        return rc;
 103}
 104
 105/* Return specific func appraised cached result */
 106enum integrity_status ima_get_cache_status(struct integrity_iint_cache *iint,
 107                                           enum ima_hooks func)
 108{
 109        switch (func) {
 110        case MMAP_CHECK:
 111                return iint->ima_mmap_status;
 112        case BPRM_CHECK:
 113                return iint->ima_bprm_status;
 114        case CREDS_CHECK:
 115                return iint->ima_creds_status;
 116        case FILE_CHECK:
 117        case POST_SETATTR:
 118                return iint->ima_file_status;
 119        case MODULE_CHECK ... MAX_CHECK - 1:
 120        default:
 121                return iint->ima_read_status;
 122        }
 123}
 124
 125static void ima_set_cache_status(struct integrity_iint_cache *iint,
 126                                 enum ima_hooks func,
 127                                 enum integrity_status status)
 128{
 129        switch (func) {
 130        case MMAP_CHECK:
 131                iint->ima_mmap_status = status;
 132                break;
 133        case BPRM_CHECK:
 134                iint->ima_bprm_status = status;
 135                break;
 136        case CREDS_CHECK:
 137                iint->ima_creds_status = status;
 138                break;
 139        case FILE_CHECK:
 140        case POST_SETATTR:
 141                iint->ima_file_status = status;
 142                break;
 143        case MODULE_CHECK ... MAX_CHECK - 1:
 144        default:
 145                iint->ima_read_status = status;
 146                break;
 147        }
 148}
 149
 150static void ima_cache_flags(struct integrity_iint_cache *iint,
 151                             enum ima_hooks func)
 152{
 153        switch (func) {
 154        case MMAP_CHECK:
 155                iint->flags |= (IMA_MMAP_APPRAISED | IMA_APPRAISED);
 156                break;
 157        case BPRM_CHECK:
 158                iint->flags |= (IMA_BPRM_APPRAISED | IMA_APPRAISED);
 159                break;
 160        case CREDS_CHECK:
 161                iint->flags |= (IMA_CREDS_APPRAISED | IMA_APPRAISED);
 162                break;
 163        case FILE_CHECK:
 164        case POST_SETATTR:
 165                iint->flags |= (IMA_FILE_APPRAISED | IMA_APPRAISED);
 166                break;
 167        case MODULE_CHECK ... MAX_CHECK - 1:
 168        default:
 169                iint->flags |= (IMA_READ_APPRAISED | IMA_APPRAISED);
 170                break;
 171        }
 172}
 173
 174enum hash_algo ima_get_hash_algo(struct evm_ima_xattr_data *xattr_value,
 175                                 int xattr_len)
 176{
 177        struct signature_v2_hdr *sig;
 178        enum hash_algo ret;
 179
 180        if (!xattr_value || xattr_len < 2)
 181                /* return default hash algo */
 182                return ima_hash_algo;
 183
 184        switch (xattr_value->type) {
 185        case EVM_IMA_XATTR_DIGSIG:
 186                sig = (typeof(sig))xattr_value;
 187                if (sig->version != 2 || xattr_len <= sizeof(*sig))
 188                        return ima_hash_algo;
 189                return sig->hash_algo;
 190                break;
 191        case IMA_XATTR_DIGEST_NG:
 192                /* first byte contains algorithm id */
 193                ret = xattr_value->data[0];
 194                if (ret < HASH_ALGO__LAST)
 195                        return ret;
 196                break;
 197        case IMA_XATTR_DIGEST:
 198                /* this is for backward compatibility */
 199                if (xattr_len == 21) {
 200                        unsigned int zero = 0;
 201                        if (!memcmp(&xattr_value->data[16], &zero, 4))
 202                                return HASH_ALGO_MD5;
 203                        else
 204                                return HASH_ALGO_SHA1;
 205                } else if (xattr_len == 17)
 206                        return HASH_ALGO_MD5;
 207                break;
 208        }
 209
 210        /* return default hash algo */
 211        return ima_hash_algo;
 212}
 213
 214int ima_read_xattr(struct dentry *dentry,
 215                   struct evm_ima_xattr_data **xattr_value)
 216{
 217        ssize_t ret;
 218
 219        ret = vfs_getxattr_alloc(&init_user_ns, dentry, XATTR_NAME_IMA,
 220                                 (char **)xattr_value, 0, GFP_NOFS);
 221        if (ret == -EOPNOTSUPP)
 222                ret = 0;
 223        return ret;
 224}
 225
 226/*
 227 * xattr_verify - verify xattr digest or signature
 228 *
 229 * Verify whether the hash or signature matches the file contents.
 230 *
 231 * Return 0 on success, error code otherwise.
 232 */
 233static int xattr_verify(enum ima_hooks func, struct integrity_iint_cache *iint,
 234                        struct evm_ima_xattr_data *xattr_value, int xattr_len,
 235                        enum integrity_status *status, const char **cause)
 236{
 237        int rc = -EINVAL, hash_start = 0;
 238
 239        switch (xattr_value->type) {
 240        case IMA_XATTR_DIGEST_NG:
 241                /* first byte contains algorithm id */
 242                hash_start = 1;
 243                fallthrough;
 244        case IMA_XATTR_DIGEST:
 245                if (*status != INTEGRITY_PASS_IMMUTABLE) {
 246                        if (iint->flags & IMA_DIGSIG_REQUIRED) {
 247                                *cause = "IMA-signature-required";
 248                                *status = INTEGRITY_FAIL;
 249                                break;
 250                        }
 251                        clear_bit(IMA_DIGSIG, &iint->atomic_flags);
 252                } else {
 253                        set_bit(IMA_DIGSIG, &iint->atomic_flags);
 254                }
 255                if (xattr_len - sizeof(xattr_value->type) - hash_start >=
 256                                iint->ima_hash->length)
 257                        /*
 258                         * xattr length may be longer. md5 hash in previous
 259                         * version occupied 20 bytes in xattr, instead of 16
 260                         */
 261                        rc = memcmp(&xattr_value->data[hash_start],
 262                                    iint->ima_hash->digest,
 263                                    iint->ima_hash->length);
 264                else
 265                        rc = -EINVAL;
 266                if (rc) {
 267                        *cause = "invalid-hash";
 268                        *status = INTEGRITY_FAIL;
 269                        break;
 270                }
 271                *status = INTEGRITY_PASS;
 272                break;
 273        case EVM_IMA_XATTR_DIGSIG:
 274                set_bit(IMA_DIGSIG, &iint->atomic_flags);
 275                rc = integrity_digsig_verify(INTEGRITY_KEYRING_IMA,
 276                                             (const char *)xattr_value,
 277                                             xattr_len,
 278                                             iint->ima_hash->digest,
 279                                             iint->ima_hash->length);
 280                if (rc == -EOPNOTSUPP) {
 281                        *status = INTEGRITY_UNKNOWN;
 282                        break;
 283                }
 284                if (IS_ENABLED(CONFIG_INTEGRITY_PLATFORM_KEYRING) && rc &&
 285                    func == KEXEC_KERNEL_CHECK)
 286                        rc = integrity_digsig_verify(INTEGRITY_KEYRING_PLATFORM,
 287                                                     (const char *)xattr_value,
 288                                                     xattr_len,
 289                                                     iint->ima_hash->digest,
 290                                                     iint->ima_hash->length);
 291                if (rc) {
 292                        *cause = "invalid-signature";
 293                        *status = INTEGRITY_FAIL;
 294                } else {
 295                        *status = INTEGRITY_PASS;
 296                }
 297                break;
 298        default:
 299                *status = INTEGRITY_UNKNOWN;
 300                *cause = "unknown-ima-data";
 301                break;
 302        }
 303
 304        return rc;
 305}
 306
 307/*
 308 * modsig_verify - verify modsig signature
 309 *
 310 * Verify whether the signature matches the file contents.
 311 *
 312 * Return 0 on success, error code otherwise.
 313 */
 314static int modsig_verify(enum ima_hooks func, const struct modsig *modsig,
 315                         enum integrity_status *status, const char **cause)
 316{
 317        int rc;
 318
 319        rc = integrity_modsig_verify(INTEGRITY_KEYRING_IMA, modsig);
 320        if (IS_ENABLED(CONFIG_INTEGRITY_PLATFORM_KEYRING) && rc &&
 321            func == KEXEC_KERNEL_CHECK)
 322                rc = integrity_modsig_verify(INTEGRITY_KEYRING_PLATFORM,
 323                                             modsig);
 324        if (rc) {
 325                *cause = "invalid-signature";
 326                *status = INTEGRITY_FAIL;
 327        } else {
 328                *status = INTEGRITY_PASS;
 329        }
 330
 331        return rc;
 332}
 333
 334/*
 335 * ima_check_blacklist - determine if the binary is blacklisted.
 336 *
 337 * Add the hash of the blacklisted binary to the measurement list, based
 338 * on policy.
 339 *
 340 * Returns -EPERM if the hash is blacklisted.
 341 */
 342int ima_check_blacklist(struct integrity_iint_cache *iint,
 343                        const struct modsig *modsig, int pcr)
 344{
 345        enum hash_algo hash_algo;
 346        const u8 *digest = NULL;
 347        u32 digestsize = 0;
 348        int rc = 0;
 349
 350        if (!(iint->flags & IMA_CHECK_BLACKLIST))
 351                return 0;
 352
 353        if (iint->flags & IMA_MODSIG_ALLOWED && modsig) {
 354                ima_get_modsig_digest(modsig, &hash_algo, &digest, &digestsize);
 355
 356                rc = is_binary_blacklisted(digest, digestsize);
 357                if ((rc == -EPERM) && (iint->flags & IMA_MEASURE))
 358                        process_buffer_measurement(&init_user_ns, NULL, digest, digestsize,
 359                                                   "blacklisted-hash", NONE,
 360                                                   pcr, NULL, false);
 361        }
 362
 363        return rc;
 364}
 365
 366/*
 367 * ima_appraise_measurement - appraise file measurement
 368 *
 369 * Call evm_verifyxattr() to verify the integrity of 'security.ima'.
 370 * Assuming success, compare the xattr hash with the collected measurement.
 371 *
 372 * Return 0 on success, error code otherwise
 373 */
 374int ima_appraise_measurement(enum ima_hooks func,
 375                             struct integrity_iint_cache *iint,
 376                             struct file *file, const unsigned char *filename,
 377                             struct evm_ima_xattr_data *xattr_value,
 378                             int xattr_len, const struct modsig *modsig)
 379{
 380        static const char op[] = "appraise_data";
 381        const char *cause = "unknown";
 382        struct dentry *dentry = file_dentry(file);
 383        struct inode *inode = d_backing_inode(dentry);
 384        enum integrity_status status = INTEGRITY_UNKNOWN;
 385        int rc = xattr_len;
 386        bool try_modsig = iint->flags & IMA_MODSIG_ALLOWED && modsig;
 387
 388        /* If not appraising a modsig, we need an xattr. */
 389        if (!(inode->i_opflags & IOP_XATTR) && !try_modsig)
 390                return INTEGRITY_UNKNOWN;
 391
 392        /* If reading the xattr failed and there's no modsig, error out. */
 393        if (rc <= 0 && !try_modsig) {
 394                if (rc && rc != -ENODATA)
 395                        goto out;
 396
 397                cause = iint->flags & IMA_DIGSIG_REQUIRED ?
 398                                "IMA-signature-required" : "missing-hash";
 399                status = INTEGRITY_NOLABEL;
 400                if (file->f_mode & FMODE_CREATED)
 401                        iint->flags |= IMA_NEW_FILE;
 402                if ((iint->flags & IMA_NEW_FILE) &&
 403                    (!(iint->flags & IMA_DIGSIG_REQUIRED) ||
 404                     (inode->i_size == 0)))
 405                        status = INTEGRITY_PASS;
 406                goto out;
 407        }
 408
 409        status = evm_verifyxattr(dentry, XATTR_NAME_IMA, xattr_value, rc, iint);
 410        switch (status) {
 411        case INTEGRITY_PASS:
 412        case INTEGRITY_PASS_IMMUTABLE:
 413        case INTEGRITY_UNKNOWN:
 414                break;
 415        case INTEGRITY_NOXATTRS:        /* No EVM protected xattrs. */
 416                /* It's fine not to have xattrs when using a modsig. */
 417                if (try_modsig)
 418                        break;
 419                fallthrough;
 420        case INTEGRITY_NOLABEL:         /* No security.evm xattr. */
 421                cause = "missing-HMAC";
 422                goto out;
 423        case INTEGRITY_FAIL_IMMUTABLE:
 424                set_bit(IMA_DIGSIG, &iint->atomic_flags);
 425                cause = "invalid-fail-immutable";
 426                goto out;
 427        case INTEGRITY_FAIL:            /* Invalid HMAC/signature. */
 428                cause = "invalid-HMAC";
 429                goto out;
 430        default:
 431                WARN_ONCE(true, "Unexpected integrity status %d\n", status);
 432        }
 433
 434        if (xattr_value)
 435                rc = xattr_verify(func, iint, xattr_value, xattr_len, &status,
 436                                  &cause);
 437
 438        /*
 439         * If we have a modsig and either no imasig or the imasig's key isn't
 440         * known, then try verifying the modsig.
 441         */
 442        if (try_modsig &&
 443            (!xattr_value || xattr_value->type == IMA_XATTR_DIGEST_NG ||
 444             rc == -ENOKEY))
 445                rc = modsig_verify(func, modsig, &status, &cause);
 446
 447out:
 448        /*
 449         * File signatures on some filesystems can not be properly verified.
 450         * When such filesystems are mounted by an untrusted mounter or on a
 451         * system not willing to accept such a risk, fail the file signature
 452         * verification.
 453         */
 454        if ((inode->i_sb->s_iflags & SB_I_IMA_UNVERIFIABLE_SIGNATURE) &&
 455            ((inode->i_sb->s_iflags & SB_I_UNTRUSTED_MOUNTER) ||
 456             (iint->flags & IMA_FAIL_UNVERIFIABLE_SIGS))) {
 457                status = INTEGRITY_FAIL;
 458                cause = "unverifiable-signature";
 459                integrity_audit_msg(AUDIT_INTEGRITY_DATA, inode, filename,
 460                                    op, cause, rc, 0);
 461        } else if (status != INTEGRITY_PASS) {
 462                /* Fix mode, but don't replace file signatures. */
 463                if ((ima_appraise & IMA_APPRAISE_FIX) && !try_modsig &&
 464                    (!xattr_value ||
 465                     xattr_value->type != EVM_IMA_XATTR_DIGSIG)) {
 466                        if (!ima_fix_xattr(dentry, iint))
 467                                status = INTEGRITY_PASS;
 468                }
 469
 470                /*
 471                 * Permit new files with file/EVM portable signatures, but
 472                 * without data.
 473                 */
 474                if (inode->i_size == 0 && iint->flags & IMA_NEW_FILE &&
 475                    test_bit(IMA_DIGSIG, &iint->atomic_flags)) {
 476                        status = INTEGRITY_PASS;
 477                }
 478
 479                integrity_audit_msg(AUDIT_INTEGRITY_DATA, inode, filename,
 480                                    op, cause, rc, 0);
 481        } else {
 482                ima_cache_flags(iint, func);
 483        }
 484
 485        ima_set_cache_status(iint, func, status);
 486        return status;
 487}
 488
 489/*
 490 * ima_update_xattr - update 'security.ima' hash value
 491 */
 492void ima_update_xattr(struct integrity_iint_cache *iint, struct file *file)
 493{
 494        struct dentry *dentry = file_dentry(file);
 495        int rc = 0;
 496
 497        /* do not collect and update hash for digital signatures */
 498        if (test_bit(IMA_DIGSIG, &iint->atomic_flags))
 499                return;
 500
 501        if ((iint->ima_file_status != INTEGRITY_PASS) &&
 502            !(iint->flags & IMA_HASH))
 503                return;
 504
 505        rc = ima_collect_measurement(iint, file, NULL, 0, ima_hash_algo, NULL);
 506        if (rc < 0)
 507                return;
 508
 509        inode_lock(file_inode(file));
 510        ima_fix_xattr(dentry, iint);
 511        inode_unlock(file_inode(file));
 512}
 513
 514/**
 515 * ima_inode_post_setattr - reflect file metadata changes
 516 * @mnt_userns: user namespace of the mount the inode was found from
 517 * @dentry: pointer to the affected dentry
 518 *
 519 * Changes to a dentry's metadata might result in needing to appraise.
 520 *
 521 * This function is called from notify_change(), which expects the caller
 522 * to lock the inode's i_mutex.
 523 */
 524void ima_inode_post_setattr(struct user_namespace *mnt_userns,
 525                            struct dentry *dentry)
 526{
 527        struct inode *inode = d_backing_inode(dentry);
 528        struct integrity_iint_cache *iint;
 529        int action;
 530
 531        if (!(ima_policy_flag & IMA_APPRAISE) || !S_ISREG(inode->i_mode)
 532            || !(inode->i_opflags & IOP_XATTR))
 533                return;
 534
 535        action = ima_must_appraise(mnt_userns, inode, MAY_ACCESS, POST_SETATTR);
 536        iint = integrity_iint_find(inode);
 537        if (iint) {
 538                set_bit(IMA_CHANGE_ATTR, &iint->atomic_flags);
 539                if (!action)
 540                        clear_bit(IMA_UPDATE_XATTR, &iint->atomic_flags);
 541        }
 542}
 543
 544/*
 545 * ima_protect_xattr - protect 'security.ima'
 546 *
 547 * Ensure that not just anyone can modify or remove 'security.ima'.
 548 */
 549static int ima_protect_xattr(struct dentry *dentry, const char *xattr_name,
 550                             const void *xattr_value, size_t xattr_value_len)
 551{
 552        if (strcmp(xattr_name, XATTR_NAME_IMA) == 0) {
 553                if (!capable(CAP_SYS_ADMIN))
 554                        return -EPERM;
 555                return 1;
 556        }
 557        return 0;
 558}
 559
 560static void ima_reset_appraise_flags(struct inode *inode, int digsig)
 561{
 562        struct integrity_iint_cache *iint;
 563
 564        if (!(ima_policy_flag & IMA_APPRAISE) || !S_ISREG(inode->i_mode))
 565                return;
 566
 567        iint = integrity_iint_find(inode);
 568        if (!iint)
 569                return;
 570        iint->measured_pcrs = 0;
 571        set_bit(IMA_CHANGE_XATTR, &iint->atomic_flags);
 572        if (digsig)
 573                set_bit(IMA_DIGSIG, &iint->atomic_flags);
 574        else
 575                clear_bit(IMA_DIGSIG, &iint->atomic_flags);
 576}
 577
 578int ima_inode_setxattr(struct dentry *dentry, const char *xattr_name,
 579                       const void *xattr_value, size_t xattr_value_len)
 580{
 581        const struct evm_ima_xattr_data *xvalue = xattr_value;
 582        int digsig = 0;
 583        int result;
 584
 585        result = ima_protect_xattr(dentry, xattr_name, xattr_value,
 586                                   xattr_value_len);
 587        if (result == 1) {
 588                if (!xattr_value_len || (xvalue->type >= IMA_XATTR_LAST))
 589                        return -EINVAL;
 590                digsig = (xvalue->type == EVM_IMA_XATTR_DIGSIG);
 591        } else if (!strcmp(xattr_name, XATTR_NAME_EVM) && xattr_value_len > 0) {
 592                digsig = (xvalue->type == EVM_XATTR_PORTABLE_DIGSIG);
 593        }
 594        if (result == 1 || evm_revalidate_status(xattr_name)) {
 595                ima_reset_appraise_flags(d_backing_inode(dentry), digsig);
 596                if (result == 1)
 597                        result = 0;
 598        }
 599        return result;
 600}
 601
 602int ima_inode_removexattr(struct dentry *dentry, const char *xattr_name)
 603{
 604        int result;
 605
 606        result = ima_protect_xattr(dentry, xattr_name, NULL, 0);
 607        if (result == 1 || evm_revalidate_status(xattr_name)) {
 608                ima_reset_appraise_flags(d_backing_inode(dentry), 0);
 609                if (result == 1)
 610                        result = 0;
 611        }
 612        return result;
 613}
 614