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
  31 #include "ima.h"
  32
  33 int ima_initialized;
  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         for (i = 0; i < HASH_ALGO__LAST; i++) {
  63                 if (strcmp(str, hash_algo_name[i]) == 0) {
  64                         ima_hash_algo = i;
  65                         break;
  66                 }
  67         }
  68         if (i == HASH_ALGO__LAST)
  69                 return 1;
  70 out:
  71         hash_setup_done = 1;
  72         return 1;
  73 }
  74 __setup("ima_hash=", hash_setup);
  75
  76 /*
  77  * ima_rdwr_violation_check
  78  *
  79  * Only invalidate the PCR for measured files:
  80  *      - Opening a file for write when already open for read,
  81  *        results in a time of measure, time of use (ToMToU) error.
  82  *      - Opening a file for read when already open for write,
  83  *        could result in a file measurement error.
  84  *
  85  */
  86 static void ima_rdwr_violation_check(struct file *file,
  87                                      struct integrity_iint_cache *iint,
  88                                      int must_measure,
  89                                      char **pathbuf,
  90                                      const char **pathname)
  91 {
  92         struct inode *inode = file_inode(file);
  93         char filename[NAME_MAX];
  94         fmode_t mode = file->f_mode;
  95         bool send_tomtou = false, send_writers = false;
  96
  97         if (mode & FMODE_WRITE) {
  98                 if (atomic_read(&inode->i_readcount) && IS_IMA(inode)) {
  99                         if (!iint)
 100                                 iint = integrity_iint_find(inode);
 101                         /* IMA_MEASURE is set from reader side */
 102                         if (iint && (iint->flags & IMA_MEASURE))
 103                                 send_tomtou = true;
 104                 }
 105         } else {
 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
 128         if (!(mode & FMODE_WRITE))
 129                 return;
 130
 131         inode_lock(inode);
 132         if (atomic_read(&inode->i_writecount) == 1) {
 133                 if ((iint->version != inode->i_version) ||
 134                     (iint->flags & IMA_NEW_FILE)) {
 135                         iint->flags &= ~(IMA_DONE_MASK | IMA_NEW_FILE);
 136                         iint->measured_pcrs = 0;
 137                         if (iint->flags & IMA_APPRAISE)
 138                                 ima_update_xattr(iint, file);
 139                 }
 140         }
 141         inode_unlock(inode);
 142 }
 143
 144 /**
 145  * ima_file_free - called on __fput()
 146  * @file: pointer to file structure being freed
 147  *
 148  * Flag files that changed, based on i_version
 149  */
 150 void ima_file_free(struct file *file)
 151 {
 152         struct inode *inode = file_inode(file);
 153         struct integrity_iint_cache *iint;
 154
 155         if (!ima_policy_flag || !S_ISREG(inode->i_mode))
 156                 return;
 157
 158         iint = integrity_iint_find(inode);
 159         if (!iint)
 160                 return;
 161
 162         ima_check_last_writer(iint, inode, file);
 163 }
 164
 165 static int process_measurement(struct file *file, char *buf, loff_t size,
 166                                int mask, enum ima_hooks func, int opened)
 167 {
 168         struct inode *inode = file_inode(file);
 169         struct integrity_iint_cache *iint = NULL;
 170         struct ima_template_desc *template_desc;
 171         char *pathbuf = NULL;
 172         char filename[NAME_MAX];
 173         const char *pathname = NULL;
 174         int rc = -ENOMEM, action, must_appraise;
 175         int pcr = CONFIG_IMA_MEASURE_PCR_IDX;
 176         struct evm_ima_xattr_data *xattr_value = NULL;
 177         int xattr_len = 0;
 178         bool violation_check;
 179         enum hash_algo hash_algo;
 180
 181         if (!ima_policy_flag || !S_ISREG(inode->i_mode))
 182                 return 0;
 183
 184         /* Return an IMA_MEASURE, IMA_APPRAISE, IMA_AUDIT action
 185          * bitmask based on the appraise/audit/measurement policy.
 186          * Included is the appraise submask.
 187          */
 188         action = ima_get_action(inode, mask, func, &pcr);
 189         violation_check = ((func == FILE_CHECK || func == MMAP_CHECK) &&
 190                            (ima_policy_flag & IMA_MEASURE));
 191         if (!action && !violation_check)
 192                 return 0;
 193
 194         must_appraise = action & IMA_APPRAISE;
 195
 196         /*  Is the appraise rule hook specific?  */
 197         if (action & IMA_FILE_APPRAISE)
 198                 func = FILE_CHECK;
 199
 200         inode_lock(inode);
 201
 202         if (action) {
 203                 iint = integrity_inode_get(inode);
 204                 if (!iint)
 205                         goto out;
 206         }
 207
 208         if (violation_check) {
 209                 ima_rdwr_violation_check(file, iint, action & IMA_MEASURE,
 210                                          &pathbuf, &pathname);
 211                 if (!action) {
 212                         rc = 0;
 213                         goto out_free;
 214                 }
 215         }
 216
 217         /* Determine if already appraised/measured based on bitmask
 218          * (IMA_MEASURE, IMA_MEASURED, IMA_XXXX_APPRAISE, IMA_XXXX_APPRAISED,
 219          *  IMA_AUDIT, IMA_AUDITED)
 220          */
 221         iint->flags |= action;
 222         action &= IMA_DO_MASK;
 223         action &= ~((iint->flags & (IMA_DONE_MASK ^ IMA_MEASURED)) >> 1);
 224
 225         /* If target pcr is already measured, unset IMA_MEASURE action */
 226         if ((action & IMA_MEASURE) && (iint->measured_pcrs & (0x1 << pcr)))
 227                 action ^= IMA_MEASURE;
 228
 229         /* Nothing to do, just return existing appraised status */
 230         if (!action) {
 231                 if (must_appraise)
 232                         rc = ima_get_cache_status(iint, func);
 233                 goto out_digsig;
 234         }
 235
 236         template_desc = ima_template_desc_current();
 237         if ((action & IMA_APPRAISE_SUBMASK) ||
 238                     strcmp(template_desc->name, IMA_TEMPLATE_IMA_NAME) != 0)
 239                 /* read 'security.ima' */
 240                 xattr_len = ima_read_xattr(file_dentry(file), &xattr_value);
 241
 242         hash_algo = ima_get_hash_algo(xattr_value, xattr_len);
 243
 244         rc = ima_collect_measurement(iint, file, buf, size, hash_algo);
 245         if (rc != 0 && rc != -EBADF && rc != -EINVAL)
 246                 goto out_digsig;
 247
 248         if (!pathbuf)   /* ima_rdwr_violation possibly pre-fetched */
 249                 pathname = ima_d_path(&file->f_path, &pathbuf, filename);
 250
 251         if (action & IMA_MEASURE)
 252                 ima_store_measurement(iint, file, pathname,
 253                                       xattr_value, xattr_len, pcr);
 254         if (rc == 0 && (action & IMA_APPRAISE_SUBMASK))
 255                 rc = ima_appraise_measurement(func, iint, file, pathname,
 256                                               xattr_value, xattr_len, opened);
 257         if (action & IMA_AUDIT)
 258                 ima_audit_measurement(iint, pathname);
 259
 260         if ((file->f_flags & O_DIRECT) && (iint->flags & IMA_PERMIT_DIRECTIO))
 261                 rc = 0;
 262 out_digsig:
 263         if ((mask & MAY_WRITE) && (iint->flags & IMA_DIGSIG) &&
 264              !(iint->flags & IMA_NEW_FILE))
 265                 rc = -EACCES;
 266         kfree(xattr_value);
 267 out_free:
 268         if (pathbuf)
 269                 __putname(pathbuf);
 270 out:
 271         inode_unlock(inode);
 272         if ((rc && must_appraise) && (ima_appraise & IMA_APPRAISE_ENFORCE))
 273                 return -EACCES;
 274         return 0;
 275 }
 276
 277 /**
 278  * ima_file_mmap - based on policy, collect/store measurement.
 279  * @file: pointer to the file to be measured (May be NULL)
 280  * @prot: contains the protection that will be applied by the kernel.
 281  *
 282  * Measure files being mmapped executable based on the ima_must_measure()
 283  * policy decision.
 284  *
 285  * On success return 0.  On integrity appraisal error, assuming the file
 286  * is in policy and IMA-appraisal is in enforcing mode, return -EACCES.
 287  */
 288 int ima_file_mmap(struct file *file, unsigned long prot)
 289 {
 290         if (file && (prot & PROT_EXEC))
 291                 return process_measurement(file, NULL, 0, MAY_EXEC,
 292                                            MMAP_CHECK, 0);
 293         return 0;
 294 }
 295
 296 /**
 297  * ima_bprm_check - based on policy, collect/store measurement.
 298  * @bprm: contains the linux_binprm structure
 299  *
 300  * The OS protects against an executable file, already open for write,
 301  * from being executed in deny_write_access() and an executable file,
 302  * already open for execute, from being modified in get_write_access().
 303  * So we can be certain that what we verify and measure here is actually
 304  * what is being executed.
 305  *
 306  * On success return 0.  On integrity appraisal error, assuming the file
 307  * is in policy and IMA-appraisal is in enforcing mode, return -EACCES.
 308  */
 309 int ima_bprm_check(struct linux_binprm *bprm)
 310 {
 311         return process_measurement(bprm->file, NULL, 0, MAY_EXEC,
 312                                    BPRM_CHECK, 0);
 313 }
 314
 315 /**
 316  * ima_path_check - based on policy, collect/store measurement.
 317  * @file: pointer to the file to be measured
 318  * @mask: contains MAY_READ, MAY_WRITE, MAY_EXEC or MAY_APPEND
 319  *
 320  * Measure files based on the ima_must_measure() policy decision.
 321  *
 322  * On success return 0.  On integrity appraisal error, assuming the file
 323  * is in policy and IMA-appraisal is in enforcing mode, return -EACCES.
 324  */
 325 int ima_file_check(struct file *file, int mask, int opened)
 326 {
 327         return process_measurement(file, NULL, 0,
 328                                    mask & (MAY_READ | MAY_WRITE | MAY_EXEC |
 329                                            MAY_APPEND), FILE_CHECK, opened);
 330 }
 331 EXPORT_SYMBOL_GPL(ima_file_check);
 332
 333 /**
 334  * ima_post_path_mknod - mark as a new inode
 335  * @dentry: newly created dentry
 336  *
 337  * Mark files created via the mknodat syscall as new, so that the
 338  * file data can be written later.
 339  */
 340 void ima_post_path_mknod(struct dentry *dentry)
 341 {
 342         struct integrity_iint_cache *iint;
 343         struct inode *inode = dentry->d_inode;
 344         int must_appraise;
 345
 346         must_appraise = ima_must_appraise(inode, MAY_ACCESS, FILE_CHECK);
 347         if (!must_appraise)
 348                 return;
 349
 350         iint = integrity_inode_get(inode);
 351         if (iint)
 352                 iint->flags |= IMA_NEW_FILE;
 353 }
 354
 355 /**
 356  * ima_read_file - pre-measure/appraise hook decision based on policy
 357  * @file: pointer to the file to be measured/appraised/audit
 358  * @read_id: caller identifier
 359  *
 360  * Permit reading a file based on policy. The policy rules are written
 361  * in terms of the policy identifier.  Appraising the integrity of
 362  * a file requires a file descriptor.
 363  *
 364  * For permission return 0, otherwise return -EACCES.
 365  */
 366 int ima_read_file(struct file *file, enum kernel_read_file_id read_id)
 367 {
 368         bool sig_enforce = is_module_sig_enforced();
 369
 370         if (!file && read_id == READING_MODULE) {
 371                 if (!sig_enforce && (ima_appraise & IMA_APPRAISE_MODULES) &&
 372                     (ima_appraise & IMA_APPRAISE_ENFORCE))
 373                         return -EACCES; /* INTEGRITY_UNKNOWN */
 374                 return 0;       /* We rely on module signature checking */
 375         }
 376         return 0;
 377 }
 378
 379 static int read_idmap[READING_MAX_ID] = {
 380         [READING_FIRMWARE] = FIRMWARE_CHECK,
 381         [READING_FIRMWARE_PREALLOC_BUFFER] = FIRMWARE_CHECK,
 382         [READING_MODULE] = MODULE_CHECK,
 383         [READING_KEXEC_IMAGE] = KEXEC_KERNEL_CHECK,
 384         [READING_KEXEC_INITRAMFS] = KEXEC_INITRAMFS_CHECK,
 385         [READING_POLICY] = POLICY_CHECK
 386 };
 387
 388 /**
 389  * ima_post_read_file - in memory collect/appraise/audit measurement
 390  * @file: pointer to the file to be measured/appraised/audit
 391  * @buf: pointer to in memory file contents
 392  * @size: size of in memory file contents
 393  * @read_id: caller identifier
 394  *
 395  * Measure/appraise/audit in memory file based on policy.  Policy rules
 396  * are written in terms of a policy identifier.
 397  *
 398  * On success return 0.  On integrity appraisal error, assuming the file
 399  * is in policy and IMA-appraisal is in enforcing mode, return -EACCES.
 400  */
 401 int ima_post_read_file(struct file *file, void *buf, loff_t size,
 402                        enum kernel_read_file_id read_id)
 403 {
 404         enum ima_hooks func;
 405
 406         if (!file && read_id == READING_FIRMWARE) {
 407                 if ((ima_appraise & IMA_APPRAISE_FIRMWARE) &&
 408                     (ima_appraise & IMA_APPRAISE_ENFORCE))
 409                         return -EACCES; /* INTEGRITY_UNKNOWN */
 410                 return 0;
 411         }
 412
 413         if (!file && read_id == READING_MODULE) /* MODULE_SIG_FORCE enabled */
 414                 return 0;
 415
 416         /* permit signed certs */
 417         if (!file && read_id == READING_X509_CERTIFICATE)
 418                 return 0;
 419
 420         if (!file || !buf || size == 0) { /* should never happen */
 421                 if (ima_appraise & IMA_APPRAISE_ENFORCE)
 422                         return -EACCES;
 423                 return 0;
 424         }
 425
 426         func = read_idmap[read_id] ?: FILE_CHECK;
 427         return process_measurement(file, buf, size, MAY_READ, func, 0);
 428 }
 429
 430 static int __init init_ima(void)
 431 {
 432         int error;
 433
 434         ima_init_template_list();
 435         hash_setup(CONFIG_IMA_DEFAULT_HASH);
 436         error = ima_init();
 437
 438         if (error && strcmp(hash_algo_name[ima_hash_algo],
 439                             CONFIG_IMA_DEFAULT_HASH) != 0) {
 440                 pr_info("Allocating %s failed, going to use default hash algorithm %s\n",
 441                         hash_algo_name[ima_hash_algo], CONFIG_IMA_DEFAULT_HASH);
 442                 hash_setup_done = 0;
 443                 hash_setup(CONFIG_IMA_DEFAULT_HASH);
 444                 error = ima_init();
 445         }
 446
 447         if (!error) {
 448                 ima_initialized = 1;
 449                 ima_update_policy_flag();
 450         }
 451         return error;
 452 }
 453
 454 late_initcall(init_ima);        /* Start IMA after the TPM is available */
 455
 456 MODULE_DESCRIPTION("Integrity Measurement Architecture");
 457 MODULE_LICENSE("GPL");