security/integrity/ima/ima_main.c

   1 /*
   2  * Integrity Measurement Architecture
   3  *
   4  * Copyright (C) 2005,2006,2007,2008 IBM Corporation
   5  *
   6  * Authors:
   7  * Reiner Sailer <sailer@watson.ibm.com>
   8  * Serge Hallyn <serue@us.ibm.com>
   9  * Kylene Hall <kylene@us.ibm.com>
  10  * Mimi Zohar <zohar@us.ibm.com>
  11  *
  12  * This program is free software; you can redistribute it and/or
  13  * modify it under the terms of the GNU General Public License as
  14  * published by the Free Software Foundation, version 2 of the
  15  * License.
  16  *
  17  * File: ima_main.c
  18  *      implements the IMA hooks: ima_bprm_check, ima_file_mmap,
  19  *      and ima_file_check.
  20  */
  21
  22 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  23
  24 #include <linux/module.h>
  25 #include <linux/file.h>
  26 #include <linux/binfmts.h>
  27 #include <linux/mount.h>
  28 #include <linux/mman.h>
  29 #include <linux/slab.h>
  30 #include <linux/xattr.h>
  31 #include <linux/ima.h>
  32 #include <linux/iversion.h>
  33 #include <linux/fs.h>
  34
  35 #include "ima.h"
  36
  37 #ifdef CONFIG_IMA_APPRAISE
  38 int ima_appraise = IMA_APPRAISE_ENFORCE;
  39 #else
  40 int ima_appraise;
  41 #endif
  42
  43 int ima_hash_algo = HASH_ALGO_SHA1;
  44 static int hash_setup_done;
  45
  46 static int __init hash_setup(char *str)
  47 {
  48         struct ima_template_desc *template_desc = ima_template_desc_current();
  49         int i;
  50
  51         if (hash_setup_done)
  52                 return 1;
  53
  54         if (strcmp(template_desc->name, IMA_TEMPLATE_IMA_NAME) == 0) {
  55                 if (strncmp(str, "sha1", 4) == 0)
  56                         ima_hash_algo = HASH_ALGO_SHA1;
  57                 else if (strncmp(str, "md5", 3) == 0)
  58                         ima_hash_algo = HASH_ALGO_MD5;
  59                 else
  60                         return 1;
  61                 goto out;
  62         }
  63
  64         i = match_string(hash_algo_name, HASH_ALGO__LAST, str);
  65         if (i < 0)
  66                 return 1;
  67
  68         ima_hash_algo = i;
  69 out:
  70         hash_setup_done = 1;
  71         return 1;
  72 }
  73 __setup("ima_hash=", hash_setup);
  74
  75 /*
  76  * ima_rdwr_violation_check
  77  *
  78  * Only invalidate the PCR for measured files:
  79  *      - Opening a file for write when already open for read,
  80  *        results in a time of measure, time of use (ToMToU) error.
  81  *      - Opening a file for read when already open for write,
  82  *        could result in a file measurement error.
  83  *
  84  */
  85 static void ima_rdwr_violation_check(struct file *file,
  86                                      struct integrity_iint_cache *iint,
  87                                      int must_measure,
  88                                      char **pathbuf,
  89                                      const char **pathname,
  90                                      char *filename)
  91 {
  92         struct inode *inode = file_inode(file);
  93         fmode_t mode = file->f_mode;
  94         bool send_tomtou = false, send_writers = false;
  95
  96         if (mode & FMODE_WRITE) {
  97                 if (atomic_read(&inode->i_readcount) && IS_IMA(inode)) {
  98                         if (!iint)
  99                                 iint = integrity_iint_find(inode);
 100                         /* IMA_MEASURE is set from reader side */
 101                         if (iint && test_bit(IMA_MUST_MEASURE,
 102                                                 &iint->atomic_flags))
 103                                 send_tomtou = true;
 104                 }
 105         } else {
 106                 if (must_measure)
 107                         set_bit(IMA_MUST_MEASURE, &iint->atomic_flags);
 108                 if (inode_is_open_for_write(inode) && must_measure)
 109                         send_writers = true;
 110         }
 111
 112         if (!send_tomtou && !send_writers)
 113                 return;
 114
 115         *pathname = ima_d_path(&file->f_path, pathbuf, filename);
 116
 117         if (send_tomtou)
 118                 ima_add_violation(file, *pathname, iint,
 119                                   "invalid_pcr", "ToMToU");
 120         if (send_writers)
 121                 ima_add_violation(file, *pathname, iint,
 122                                   "invalid_pcr", "open_writers");
 123 }
 124
 125 static void ima_check_last_writer(struct integrity_iint_cache *iint,
 126                                   struct inode *inode, struct file *file)
 127 {
 128         fmode_t mode = file->f_mode;
 129         bool update;
 130
 131         if (!(mode & FMODE_WRITE))
 132                 return;
 133
 134         mutex_lock(&iint->mutex);
 135         if (atomic_read(&inode->i_writecount) == 1) {
 136                 update = test_and_clear_bit(IMA_UPDATE_XATTR,
 137                                             &iint->atomic_flags);
 138                 if (!IS_I_VERSION(inode) ||
 139                     !inode_eq_iversion(inode, iint->version) ||
 140                     (iint->flags & IMA_NEW_FILE)) {
 141                         iint->flags &= ~(IMA_DONE_MASK | IMA_NEW_FILE);
 142                         iint->measured_pcrs = 0;
 143                         if (update)
 144                                 ima_update_xattr(iint, file);
 145                 }
 146         }
 147         mutex_unlock(&iint->mutex);
 148 }
 149
 150 /**
 151  * ima_file_free - called on __fput()
 152  * @file: pointer to file structure being freed
 153  *
 154  * Flag files that changed, based on i_version
 155  */
 156 void ima_file_free(struct file *file)
 157 {
 158         struct inode *inode = file_inode(file);
 159         struct integrity_iint_cache *iint;
 160
 161         if (!ima_policy_flag || !S_ISREG(inode->i_mode))
 162                 return;
 163
 164         iint = integrity_iint_find(inode);
 165         if (!iint)
 166                 return;
 167
 168         ima_check_last_writer(iint, inode, file);
 169 }
 170
 171 static int process_measurement(struct file *file, const struct cred *cred,
 172                                u32 secid, char *buf, loff_t size, int mask,
 173                                enum ima_hooks func)
 174 {
 175         struct inode *inode = file_inode(file);
 176         struct integrity_iint_cache *iint = NULL;
 177         struct ima_template_desc *template_desc;
 178         char *pathbuf = NULL;
 179         char filename[NAME_MAX];
 180         const char *pathname = NULL;
 181         int rc = 0, action, must_appraise = 0;
 182         int pcr = CONFIG_IMA_MEASURE_PCR_IDX;
 183         struct evm_ima_xattr_data *xattr_value = NULL;
 184         int xattr_len = 0;
 185         bool violation_check;
 186         enum hash_algo hash_algo;
 187
 188         if (!ima_policy_flag || !S_ISREG(inode->i_mode))
 189                 return 0;
 190
 191         /* Return an IMA_MEASURE, IMA_APPRAISE, IMA_AUDIT action
 192          * bitmask based on the appraise/audit/measurement policy.
 193          * Included is the appraise submask.
 194          */
 195         action = ima_get_action(inode, cred, secid, mask, func, &pcr);
 196         violation_check = ((func == FILE_CHECK || func == MMAP_CHECK) &&
 197                            (ima_policy_flag & IMA_MEASURE));
 198         if (!action && !violation_check)
 199                 return 0;
 200
 201         must_appraise = action & IMA_APPRAISE;
 202
 203         /*  Is the appraise rule hook specific?  */
 204         if (action & IMA_FILE_APPRAISE)
 205                 func = FILE_CHECK;
 206
 207         inode_lock(inode);
 208
 209         if (action) {
 210                 iint = integrity_inode_get(inode);
 211                 if (!iint)
 212                         rc = -ENOMEM;
 213         }
 214
 215         if (!rc && violation_check)
 216                 ima_rdwr_violation_check(file, iint, action & IMA_MEASURE,
 217                                          &pathbuf, &pathname, filename);
 218
 219         inode_unlock(inode);
 220
 221         if (rc)
 222                 goto out;
 223         if (!action)
 224                 goto out;
 225
 226         mutex_lock(&iint->mutex);
 227
 228         if (test_and_clear_bit(IMA_CHANGE_ATTR, &iint->atomic_flags))
 229                 /* reset appraisal flags if ima_inode_post_setattr was called */
 230                 iint->flags &= ~(IMA_APPRAISE | IMA_APPRAISED |
 231                                  IMA_APPRAISE_SUBMASK | IMA_APPRAISED_SUBMASK |
 232                                  IMA_ACTION_FLAGS);
 233
 234         /*
 235          * Re-evaulate the file if either the xattr has changed or the
 236          * kernel has no way of detecting file change on the filesystem.
 237          * (Limited to privileged mounted filesystems.)
 238          */
 239         if (test_and_clear_bit(IMA_CHANGE_XATTR, &iint->atomic_flags) ||
 240             ((inode->i_sb->s_iflags & SB_I_IMA_UNVERIFIABLE_SIGNATURE) &&
 241              !(inode->i_sb->s_iflags & SB_I_UNTRUSTED_MOUNTER) &&
 242              !(action & IMA_FAIL_UNVERIFIABLE_SIGS))) {
 243                 iint->flags &= ~IMA_DONE_MASK;
 244                 iint->measured_pcrs = 0;
 245         }
 246
 247         /* Determine if already appraised/measured based on bitmask
 248          * (IMA_MEASURE, IMA_MEASURED, IMA_XXXX_APPRAISE, IMA_XXXX_APPRAISED,
 249          *  IMA_AUDIT, IMA_AUDITED)
 250          */
 251         iint->flags |= action;
 252         action &= IMA_DO_MASK;
 253         action &= ~((iint->flags & (IMA_DONE_MASK ^ IMA_MEASURED)) >> 1);
 254
 255         /* If target pcr is already measured, unset IMA_MEASURE action */
 256         if ((action & IMA_MEASURE) && (iint->measured_pcrs & (0x1 << pcr)))
 257                 action ^= IMA_MEASURE;
 258
 259         /* HASH sets the digital signature and update flags, nothing else */
 260         if ((action & IMA_HASH) &&
 261             !(test_bit(IMA_DIGSIG, &iint->atomic_flags))) {
 262                 xattr_len = ima_read_xattr(file_dentry(file), &xattr_value);
 263                 if ((xattr_value && xattr_len > 2) &&
 264                     (xattr_value->type == EVM_IMA_XATTR_DIGSIG))
 265                         set_bit(IMA_DIGSIG, &iint->atomic_flags);
 266                 iint->flags |= IMA_HASHED;
 267                 action ^= IMA_HASH;
 268                 set_bit(IMA_UPDATE_XATTR, &iint->atomic_flags);
 269         }
 270
 271         /* Nothing to do, just return existing appraised status */
 272         if (!action) {
 273                 if (must_appraise)
 274                         rc = ima_get_cache_status(iint, func);
 275                 goto out_locked;
 276         }
 277
 278         template_desc = ima_template_desc_current();
 279         if ((action & IMA_APPRAISE_SUBMASK) ||
 280                     strcmp(template_desc->name, IMA_TEMPLATE_IMA_NAME) != 0)
 281                 /* read 'security.ima' */
 282                 xattr_len = ima_read_xattr(file_dentry(file), &xattr_value);
 283
 284         hash_algo = ima_get_hash_algo(xattr_value, xattr_len);
 285
 286         rc = ima_collect_measurement(iint, file, buf, size, hash_algo);
 287         if (rc != 0 && rc != -EBADF && rc != -EINVAL)
 288                 goto out_locked;
 289
 290         if (!pathbuf)   /* ima_rdwr_violation possibly pre-fetched */
 291                 pathname = ima_d_path(&file->f_path, &pathbuf, filename);
 292
 293         if (action & IMA_MEASURE)
 294                 ima_store_measurement(iint, file, pathname,
 295                                       xattr_value, xattr_len, pcr);
 296         if (rc == 0 && (action & IMA_APPRAISE_SUBMASK)) {
 297                 inode_lock(inode);
 298                 rc = ima_appraise_measurement(func, iint, file, pathname,
 299                                               xattr_value, xattr_len);
 300                 inode_unlock(inode);
 301         }
 302         if (action & IMA_AUDIT)
 303                 ima_audit_measurement(iint, pathname);
 304
 305         if ((file->f_flags & O_DIRECT) && (iint->flags & IMA_PERMIT_DIRECTIO))
 306                 rc = 0;
 307 out_locked:
 308         if ((mask & MAY_WRITE) && test_bit(IMA_DIGSIG, &iint->atomic_flags) &&
 309              !(iint->flags & IMA_NEW_FILE))
 310                 rc = -EACCES;
 311         mutex_unlock(&iint->mutex);
 312         kfree(xattr_value);
 313 out:
 314         if (pathbuf)
 315                 __putname(pathbuf);
 316         if (must_appraise) {
 317                 if (rc && (ima_appraise & IMA_APPRAISE_ENFORCE))
 318                         return -EACCES;
 319                 if (file->f_mode & FMODE_WRITE)
 320                         set_bit(IMA_UPDATE_XATTR, &iint->atomic_flags);
 321         }
 322         return 0;
 323 }
 324
 325 /**
 326  * ima_file_mmap - based on policy, collect/store measurement.
 327  * @file: pointer to the file to be measured (May be NULL)
 328  * @prot: contains the protection that will be applied by the kernel.
 329  *
 330  * Measure files being mmapped executable based on the ima_must_measure()
 331  * policy decision.
 332  *
 333  * On success return 0.  On integrity appraisal error, assuming the file
 334  * is in policy and IMA-appraisal is in enforcing mode, return -EACCES.
 335  */
 336 int ima_file_mmap(struct file *file, unsigned long prot)
 337 {
 338         u32 secid;
 339
 340         if (file && (prot & PROT_EXEC)) {
 341                 security_task_getsecid(current, &secid);
 342                 return process_measurement(file, current_cred(), secid, NULL,
 343                                            0, MAY_EXEC, MMAP_CHECK);
 344         }
 345
 346         return 0;
 347 }
 348
 349 /**
 350  * ima_bprm_check - based on policy, collect/store measurement.
 351  * @bprm: contains the linux_binprm structure
 352  *
 353  * The OS protects against an executable file, already open for write,
 354  * from being executed in deny_write_access() and an executable file,
 355  * already open for execute, from being modified in get_write_access().
 356  * So we can be certain that what we verify and measure here is actually
 357  * what is being executed.
 358  *
 359  * On success return 0.  On integrity appraisal error, assuming the file
 360  * is in policy and IMA-appraisal is in enforcing mode, return -EACCES.
 361  */
 362 int ima_bprm_check(struct linux_binprm *bprm)
 363 {
 364         int ret;
 365         u32 secid;
 366
 367         security_task_getsecid(current, &secid);
 368         ret = process_measurement(bprm->file, current_cred(), secid, NULL, 0,
 369                                   MAY_EXEC, BPRM_CHECK);
 370         if (ret)
 371                 return ret;
 372
 373         security_cred_getsecid(bprm->cred, &secid);
 374         return process_measurement(bprm->file, bprm->cred, secid, NULL, 0,
 375                                    MAY_EXEC, CREDS_CHECK);
 376 }
 377
 378 /**
 379  * ima_path_check - based on policy, collect/store measurement.
 380  * @file: pointer to the file to be measured
 381  * @mask: contains MAY_READ, MAY_WRITE, MAY_EXEC or MAY_APPEND
 382  *
 383  * Measure files based on the ima_must_measure() policy decision.
 384  *
 385  * On success return 0.  On integrity appraisal error, assuming the file
 386  * is in policy and IMA-appraisal is in enforcing mode, return -EACCES.
 387  */
 388 int ima_file_check(struct file *file, int mask)
 389 {
 390         u32 secid;
 391
 392         security_task_getsecid(current, &secid);
 393         return process_measurement(file, current_cred(), secid, NULL, 0,
 394                                    mask & (MAY_READ | MAY_WRITE | MAY_EXEC |
 395                                            MAY_APPEND), FILE_CHECK);
 396 }
 397 EXPORT_SYMBOL_GPL(ima_file_check);
 398
 399 /**
 400  * ima_post_create_tmpfile - mark newly created tmpfile as new
 401  * @file : newly created tmpfile
 402  *
 403  * No measuring, appraising or auditing of newly created tmpfiles is needed.
 404  * Skip calling process_measurement(), but indicate which newly, created
 405  * tmpfiles are in policy.
 406  */
 407 void ima_post_create_tmpfile(struct inode *inode)
 408 {
 409         struct integrity_iint_cache *iint;
 410         int must_appraise;
 411
 412         must_appraise = ima_must_appraise(inode, MAY_ACCESS, FILE_CHECK);
 413         if (!must_appraise)
 414                 return;
 415
 416         /* Nothing to do if we can't allocate memory */
 417         iint = integrity_inode_get(inode);
 418         if (!iint)
 419                 return;
 420
 421         /* needed for writing the security xattrs */
 422         set_bit(IMA_UPDATE_XATTR, &iint->atomic_flags);
 423         iint->ima_file_status = INTEGRITY_PASS;
 424 }
 425
 426 /**
 427  * ima_post_path_mknod - mark as a new inode
 428  * @dentry: newly created dentry
 429  *
 430  * Mark files created via the mknodat syscall as new, so that the
 431  * file data can be written later.
 432  */
 433 void ima_post_path_mknod(struct dentry *dentry)
 434 {
 435         struct integrity_iint_cache *iint;
 436         struct inode *inode = dentry->d_inode;
 437         int must_appraise;
 438
 439         must_appraise = ima_must_appraise(inode, MAY_ACCESS, FILE_CHECK);
 440         if (!must_appraise)
 441                 return;
 442
 443         /* Nothing to do if we can't allocate memory */
 444         iint = integrity_inode_get(inode);
 445         if (!iint)
 446                 return;
 447
 448         /* needed for re-opening empty files */
 449         iint->flags |= IMA_NEW_FILE;
 450 }
 451
 452 /**
 453  * ima_read_file - pre-measure/appraise hook decision based on policy
 454  * @file: pointer to the file to be measured/appraised/audit
 455  * @read_id: caller identifier
 456  *
 457  * Permit reading a file based on policy. The policy rules are written
 458  * in terms of the policy identifier.  Appraising the integrity of
 459  * a file requires a file descriptor.
 460  *
 461  * For permission return 0, otherwise return -EACCES.
 462  */
 463 int ima_read_file(struct file *file, enum kernel_read_file_id read_id)
 464 {
 465         /*
 466          * READING_FIRMWARE_PREALLOC_BUFFER
 467          *
 468          * Do devices using pre-allocated memory run the risk of the
 469          * firmware being accessible to the device prior to the completion
 470          * of IMA's signature verification any more than when using two
 471          * buffers?
 472          */
 473         return 0;
 474 }
 475
 476 static const int read_idmap[READING_MAX_ID] = {
 477         [READING_FIRMWARE] = FIRMWARE_CHECK,
 478         [READING_FIRMWARE_PREALLOC_BUFFER] = FIRMWARE_CHECK,
 479         [READING_MODULE] = MODULE_CHECK,
 480         [READING_KEXEC_IMAGE] = KEXEC_KERNEL_CHECK,
 481         [READING_KEXEC_INITRAMFS] = KEXEC_INITRAMFS_CHECK,
 482         [READING_POLICY] = POLICY_CHECK
 483 };
 484
 485 /**
 486  * ima_post_read_file - in memory collect/appraise/audit measurement
 487  * @file: pointer to the file to be measured/appraised/audit
 488  * @buf: pointer to in memory file contents
 489  * @size: size of in memory file contents
 490  * @read_id: caller identifier
 491  *
 492  * Measure/appraise/audit in memory file based on policy.  Policy rules
 493  * are written in terms of a policy identifier.
 494  *
 495  * On success return 0.  On integrity appraisal error, assuming the file
 496  * is in policy and IMA-appraisal is in enforcing mode, return -EACCES.
 497  */
 498 int ima_post_read_file(struct file *file, void *buf, loff_t size,
 499                        enum kernel_read_file_id read_id)
 500 {
 501         enum ima_hooks func;
 502         u32 secid;
 503
 504         if (!file && read_id == READING_FIRMWARE) {
 505                 if ((ima_appraise & IMA_APPRAISE_FIRMWARE) &&
 506                     (ima_appraise & IMA_APPRAISE_ENFORCE)) {
 507                         pr_err("Prevent firmware loading_store.\n");
 508                         return -EACCES; /* INTEGRITY_UNKNOWN */
 509                 }
 510                 return 0;
 511         }
 512
 513         /* permit signed certs */
 514         if (!file && read_id == READING_X509_CERTIFICATE)
 515                 return 0;
 516
 517         if (!file || !buf || size == 0) { /* should never happen */
 518                 if (ima_appraise & IMA_APPRAISE_ENFORCE)
 519                         return -EACCES;
 520                 return 0;
 521         }
 522
 523         func = read_idmap[read_id] ?: FILE_CHECK;
 524         security_task_getsecid(current, &secid);
 525         return process_measurement(file, current_cred(), secid, buf, size,
 526                                    MAY_READ, func);
 527 }
 528
 529 /**
 530  * ima_load_data - appraise decision based on policy
 531  * @id: kernel load data caller identifier
 532  *
 533  * Callers of this LSM hook can not measure, appraise, or audit the
 534  * data provided by userspace.  Enforce policy rules requring a file
 535  * signature (eg. kexec'ed kernel image).
 536  *
 537  * For permission return 0, otherwise return -EACCES.
 538  */
 539 int ima_load_data(enum kernel_load_data_id id)
 540 {
 541         bool ima_enforce, sig_enforce;
 542
 543         ima_enforce =
 544                 (ima_appraise & IMA_APPRAISE_ENFORCE) == IMA_APPRAISE_ENFORCE;
 545
 546         switch (id) {
 547         case LOADING_KEXEC_IMAGE:
 548                 if (IS_ENABLED(CONFIG_KEXEC_VERIFY_SIG)
 549                     && arch_ima_get_secureboot()) {
 550                         pr_err("impossible to appraise a kernel image without a file descriptor; try using kexec_file_load syscall.\n");
 551                         return -EACCES;
 552                 }
 553
 554                 if (ima_enforce && (ima_appraise & IMA_APPRAISE_KEXEC)) {
 555                         pr_err("impossible to appraise a kernel image without a file descriptor; try using kexec_file_load syscall.\n");
 556                         return -EACCES; /* INTEGRITY_UNKNOWN */
 557                 }
 558                 break;
 559         case LOADING_FIRMWARE:
 560                 if (ima_enforce && (ima_appraise & IMA_APPRAISE_FIRMWARE)) {
 561                         pr_err("Prevent firmware sysfs fallback loading.\n");
 562                         return -EACCES; /* INTEGRITY_UNKNOWN */
 563                 }
 564                 break;
 565         case LOADING_MODULE:
 566                 sig_enforce = is_module_sig_enforced();
 567
 568                 if (ima_enforce && (!sig_enforce
 569                                     && (ima_appraise & IMA_APPRAISE_MODULES))) {
 570                         pr_err("impossible to appraise a module without a file descriptor. sig_enforce kernel parameter might help\n");
 571                         return -EACCES; /* INTEGRITY_UNKNOWN */
 572                 }
 573         default:
 574                 break;
 575         }
 576         return 0;
 577 }
 578
 579 static int __init init_ima(void)
 580 {
 581         int error;
 582
 583         ima_init_template_list();
 584         hash_setup(CONFIG_IMA_DEFAULT_HASH);
 585         error = ima_init();
 586
 587         if (error && strcmp(hash_algo_name[ima_hash_algo],
 588                             CONFIG_IMA_DEFAULT_HASH) != 0) {
 589                 pr_info("Allocating %s failed, going to use default hash algorithm %s\n",
 590                         hash_algo_name[ima_hash_algo], CONFIG_IMA_DEFAULT_HASH);
 591                 hash_setup_done = 0;
 592                 hash_setup(CONFIG_IMA_DEFAULT_HASH);
 593                 error = ima_init();
 594         }
 595
 596         if (!error)
 597                 ima_update_policy_flag();
 598
 599         return error;
 600 }
 601
 602 late_initcall(init_ima);        /* Start IMA after the TPM is available */