security/integrity/ima/ima_main.c

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