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 #include <linux/module.h>
  20 #include <linux/file.h>
  21 #include <linux/binfmts.h>
  22 #include <linux/mount.h>
  23 #include <linux/mman.h>
  24 #include <linux/slab.h>
  25 #include <linux/xattr.h>
  26 #include <linux/ima.h>
  27
  28 #include "ima.h"
  29
  30 int ima_initialized;
  31
  32 #ifdef CONFIG_IMA_APPRAISE
  33 int ima_appraise = IMA_APPRAISE_ENFORCE;
  34 #else
  35 int ima_appraise;
  36 #endif
  37
  38 int ima_hash_algo = HASH_ALGO_SHA1;
  39 static int hash_setup_done;
  40
  41 static int __init hash_setup(char *str)
  42 {
  43         struct ima_template_desc *template_desc = ima_template_desc_current();
  44         int i;
  45
  46         if (hash_setup_done)
  47                 return 1;
  48
  49         if (strcmp(template_desc->name, IMA_TEMPLATE_IMA_NAME) == 0) {
  50                 if (strncmp(str, "sha1", 4) == 0)
  51                         ima_hash_algo = HASH_ALGO_SHA1;
  52                 else if (strncmp(str, "md5", 3) == 0)
  53                         ima_hash_algo = HASH_ALGO_MD5;
  54                 goto out;
  55         }
  56
  57         for (i = 0; i < HASH_ALGO__LAST; i++) {
  58                 if (strcmp(str, hash_algo_name[i]) == 0) {
  59                         ima_hash_algo = i;
  60                         break;
  61                 }
  62         }
  63 out:
  64         hash_setup_done = 1;
  65         return 1;
  66 }
  67 __setup("ima_hash=", hash_setup);
  68
  69 /*
  70  * ima_rdwr_violation_check
  71  *
  72  * Only invalidate the PCR for measured files:
  73  *      - Opening a file for write when already open for read,
  74  *        results in a time of measure, time of use (ToMToU) error.
  75  *      - Opening a file for read when already open for write,
  76  *        could result in a file measurement error.
  77  *
  78  */
  79 static void ima_rdwr_violation_check(struct file *file,
  80                                      struct integrity_iint_cache *iint,
  81                                      int must_measure,
  82                                      char **pathbuf,
  83                                      const char **pathname)
  84 {
  85         struct inode *inode = file_inode(file);
  86         char filename[NAME_MAX];
  87         fmode_t mode = file->f_mode;
  88         bool send_tomtou = false, send_writers = false;
  89
  90         if (mode & FMODE_WRITE) {
  91                 if (atomic_read(&inode->i_readcount) && IS_IMA(inode)) {
  92                         if (!iint)
  93                                 iint = integrity_iint_find(inode);
  94                         /* IMA_MEASURE is set from reader side */
  95                         if (iint && (iint->flags & IMA_MEASURE))
  96                                 send_tomtou = true;
  97                 }
  98         } else {
  99                 if ((atomic_read(&inode->i_writecount) > 0) && must_measure)
 100                         send_writers = true;
 101         }
 102
 103         if (!send_tomtou && !send_writers)
 104                 return;
 105
 106         *pathname = ima_d_path(&file->f_path, pathbuf, filename);
 107
 108         if (send_tomtou)
 109                 ima_add_violation(file, *pathname, iint,
 110                                   "invalid_pcr", "ToMToU");
 111         if (send_writers)
 112                 ima_add_violation(file, *pathname, iint,
 113                                   "invalid_pcr", "open_writers");
 114 }
 115
 116 static void ima_check_last_writer(struct integrity_iint_cache *iint,
 117                                   struct inode *inode, struct file *file)
 118 {
 119         fmode_t mode = file->f_mode;
 120
 121         if (!(mode & FMODE_WRITE))
 122                 return;
 123
 124         inode_lock(inode);
 125         if (atomic_read(&inode->i_writecount) == 1) {
 126                 if ((iint->version != inode->i_version) ||
 127                     (iint->flags & IMA_NEW_FILE)) {
 128                         iint->flags &= ~(IMA_DONE_MASK | IMA_NEW_FILE);
 129                         iint->measured_pcrs = 0;
 130                         if (iint->flags & IMA_APPRAISE)
 131                                 ima_update_xattr(iint, file);
 132                 }
 133         }
 134         inode_unlock(inode);
 135 }
 136
 137 /**
 138  * ima_file_free - called on __fput()
 139  * @file: pointer to file structure being freed
 140  *
 141  * Flag files that changed, based on i_version
 142  */
 143 void ima_file_free(struct file *file)
 144 {
 145         struct inode *inode = file_inode(file);
 146         struct integrity_iint_cache *iint;
 147
 148         if (!ima_policy_flag || !S_ISREG(inode->i_mode))
 149                 return;
 150
 151         iint = integrity_iint_find(inode);
 152         if (!iint)
 153                 return;
 154
 155         ima_check_last_writer(iint, inode, file);
 156 }
 157
 158 static int process_measurement(struct file *file, char *buf, loff_t size,
 159                                int mask, enum ima_hooks func, int opened)
 160 {
 161         struct inode *inode = file_inode(file);
 162         struct integrity_iint_cache *iint = NULL;
 163         struct ima_template_desc *template_desc;
 164         char *pathbuf = NULL;
 165         char filename[NAME_MAX];
 166         const char *pathname = NULL;
 167         int rc = -ENOMEM, action, must_appraise;
 168         int pcr = CONFIG_IMA_MEASURE_PCR_IDX;
 169         struct evm_ima_xattr_data *xattr_value = NULL;
 170         int xattr_len = 0;
 171         bool violation_check;
 172         enum hash_algo hash_algo;
 173
 174         if (!ima_policy_flag || !S_ISREG(inode->i_mode))
 175                 return 0;
 176
 177         /* Return an IMA_MEASURE, IMA_APPRAISE, IMA_AUDIT action
 178          * bitmask based on the appraise/audit/measurement policy.
 179          * Included is the appraise submask.
 180          */
 181         action = ima_get_action(inode, mask, func, &pcr);
 182         violation_check = ((func == FILE_CHECK || func == MMAP_CHECK) &&
 183                            (ima_policy_flag & IMA_MEASURE));
 184         if (!action && !violation_check)
 185                 return 0;
 186
 187         must_appraise = action & IMA_APPRAISE;
 188
 189         /*  Is the appraise rule hook specific?  */
 190         if (action & IMA_FILE_APPRAISE)
 191                 func = FILE_CHECK;
 192
 193         inode_lock(inode);
 194
 195         if (action) {
 196                 iint = integrity_inode_get(inode);
 197                 if (!iint)
 198                         goto out;
 199         }
 200
 201         if (violation_check) {
 202                 ima_rdwr_violation_check(file, iint, action & IMA_MEASURE,
 203                                          &pathbuf, &pathname);
 204                 if (!action) {
 205                         rc = 0;
 206                         goto out_free;
 207                 }
 208         }
 209
 210         /* Determine if already appraised/measured based on bitmask
 211          * (IMA_MEASURE, IMA_MEASURED, IMA_XXXX_APPRAISE, IMA_XXXX_APPRAISED,
 212          *  IMA_AUDIT, IMA_AUDITED)
 213          */
 214         iint->flags |= action;
 215         action &= IMA_DO_MASK;
 216         action &= ~((iint->flags & (IMA_DONE_MASK ^ IMA_MEASURED)) >> 1);
 217
 218         /* If target pcr is already measured, unset IMA_MEASURE action */
 219         if ((action & IMA_MEASURE) && (iint->measured_pcrs & (0x1 << pcr)))
 220                 action ^= IMA_MEASURE;
 221
 222         /* Nothing to do, just return existing appraised status */
 223         if (!action) {
 224                 if (must_appraise)
 225                         rc = ima_get_cache_status(iint, func);
 226                 goto out_digsig;
 227         }
 228
 229         template_desc = ima_template_desc_current();
 230         if ((action & IMA_APPRAISE_SUBMASK) ||
 231                     strcmp(template_desc->name, IMA_TEMPLATE_IMA_NAME) != 0)
 232                 /* read 'security.ima' */
 233                 xattr_len = ima_read_xattr(file_dentry(file), &xattr_value);
 234
 235         hash_algo = ima_get_hash_algo(xattr_value, xattr_len);
 236
 237         rc = ima_collect_measurement(iint, file, buf, size, hash_algo);
 238         if (rc != 0) {
 239                 if (file->f_flags & O_DIRECT)
 240                         rc = (iint->flags & IMA_PERMIT_DIRECTIO) ? 0 : -EACCES;
 241                 goto out_digsig;
 242         }
 243
 244         if (!pathbuf)   /* ima_rdwr_violation possibly pre-fetched */
 245                 pathname = ima_d_path(&file->f_path, &pathbuf, filename);
 246
 247         if (action & IMA_MEASURE)
 248                 ima_store_measurement(iint, file, pathname,
 249                                       xattr_value, xattr_len, pcr);
 250         if (action & IMA_APPRAISE_SUBMASK)
 251                 rc = ima_appraise_measurement(func, iint, file, pathname,
 252                                               xattr_value, xattr_len, opened);
 253         if (action & IMA_AUDIT)
 254                 ima_audit_measurement(iint, pathname);
 255
 256 out_digsig:
 257         if ((mask & MAY_WRITE) && (iint->flags & IMA_DIGSIG) &&
 258              !(iint->flags & IMA_NEW_FILE))
 259                 rc = -EACCES;
 260         kfree(xattr_value);
 261 out_free:
 262         if (pathbuf)
 263                 __putname(pathbuf);
 264 out:
 265         inode_unlock(inode);
 266         if ((rc && must_appraise) && (ima_appraise & IMA_APPRAISE_ENFORCE))
 267                 return -EACCES;
 268         return 0;
 269 }
 270
 271 /**
 272  * ima_file_mmap - based on policy, collect/store measurement.
 273  * @file: pointer to the file to be measured (May be NULL)
 274  * @prot: contains the protection that will be applied by the kernel.
 275  *
 276  * Measure files being mmapped executable based on the ima_must_measure()
 277  * policy decision.
 278  *
 279  * On success return 0.  On integrity appraisal error, assuming the file
 280  * is in policy and IMA-appraisal is in enforcing mode, return -EACCES.
 281  */
 282 int ima_file_mmap(struct file *file, unsigned long prot)
 283 {
 284         if (file && (prot & PROT_EXEC))
 285                 return process_measurement(file, NULL, 0, MAY_EXEC,
 286                                            MMAP_CHECK, 0);
 287         return 0;
 288 }
 289
 290 /**
 291  * ima_bprm_check - based on policy, collect/store measurement.
 292  * @bprm: contains the linux_binprm structure
 293  *
 294  * The OS protects against an executable file, already open for write,
 295  * from being executed in deny_write_access() and an executable file,
 296  * already open for execute, from being modified in get_write_access().
 297  * So we can be certain that what we verify and measure here is actually
 298  * what is being executed.
 299  *
 300  * On success return 0.  On integrity appraisal error, assuming the file
 301  * is in policy and IMA-appraisal is in enforcing mode, return -EACCES.
 302  */
 303 int ima_bprm_check(struct linux_binprm *bprm)
 304 {
 305         return process_measurement(bprm->file, NULL, 0, MAY_EXEC,
 306                                    BPRM_CHECK, 0);
 307 }
 308
 309 /**
 310  * ima_path_check - based on policy, collect/store measurement.
 311  * @file: pointer to the file to be measured
 312  * @mask: contains MAY_READ, MAY_WRITE, MAY_EXEC or MAY_APPEND
 313  *
 314  * Measure files based on the ima_must_measure() policy decision.
 315  *
 316  * On success return 0.  On integrity appraisal error, assuming the file
 317  * is in policy and IMA-appraisal is in enforcing mode, return -EACCES.
 318  */
 319 int ima_file_check(struct file *file, int mask, int opened)
 320 {
 321         return process_measurement(file, NULL, 0,
 322                                    mask & (MAY_READ | MAY_WRITE | MAY_EXEC |
 323                                            MAY_APPEND), FILE_CHECK, opened);
 324 }
 325 EXPORT_SYMBOL_GPL(ima_file_check);
 326
 327 /**
 328  * ima_post_path_mknod - mark as a new inode
 329  * @dentry: newly created dentry
 330  *
 331  * Mark files created via the mknodat syscall as new, so that the
 332  * file data can be written later.
 333  */
 334 void ima_post_path_mknod(struct dentry *dentry)
 335 {
 336         struct integrity_iint_cache *iint;
 337         struct inode *inode = dentry->d_inode;
 338         int must_appraise;
 339
 340         must_appraise = ima_must_appraise(inode, MAY_ACCESS, FILE_CHECK);
 341         if (!must_appraise)
 342                 return;
 343
 344         iint = integrity_inode_get(inode);
 345         if (iint)
 346                 iint->flags |= IMA_NEW_FILE;
 347 }
 348
 349 /**
 350  * ima_read_file - pre-measure/appraise hook decision based on policy
 351  * @file: pointer to the file to be measured/appraised/audit
 352  * @read_id: caller identifier
 353  *
 354  * Permit reading a file based on policy. The policy rules are written
 355  * in terms of the policy identifier.  Appraising the integrity of
 356  * a file requires a file descriptor.
 357  *
 358  * For permission return 0, otherwise return -EACCES.
 359  */
 360 int ima_read_file(struct file *file, enum kernel_read_file_id read_id)
 361 {
 362         if (!file && read_id == READING_MODULE) {
 363 #ifndef CONFIG_MODULE_SIG_FORCE
 364                 if ((ima_appraise & IMA_APPRAISE_MODULES) &&
 365                     (ima_appraise & IMA_APPRAISE_ENFORCE))
 366                         return -EACCES; /* INTEGRITY_UNKNOWN */
 367 #endif
 368                 return 0;       /* We rely on module signature checking */
 369         }
 370         return 0;
 371 }
 372
 373 static int read_idmap[READING_MAX_ID] = {
 374         [READING_FIRMWARE] = FIRMWARE_CHECK,
 375         [READING_MODULE] = MODULE_CHECK,
 376         [READING_KEXEC_IMAGE] = KEXEC_KERNEL_CHECK,
 377         [READING_KEXEC_INITRAMFS] = KEXEC_INITRAMFS_CHECK,
 378         [READING_POLICY] = POLICY_CHECK
 379 };
 380
 381 /**
 382  * ima_post_read_file - in memory collect/appraise/audit measurement
 383  * @file: pointer to the file to be measured/appraised/audit
 384  * @buf: pointer to in memory file contents
 385  * @size: size of in memory file contents
 386  * @read_id: caller identifier
 387  *
 388  * Measure/appraise/audit in memory file based on policy.  Policy rules
 389  * are written in terms of a policy identifier.
 390  *
 391  * On success return 0.  On integrity appraisal error, assuming the file
 392  * is in policy and IMA-appraisal is in enforcing mode, return -EACCES.
 393  */
 394 int ima_post_read_file(struct file *file, void *buf, loff_t size,
 395                        enum kernel_read_file_id read_id)
 396 {
 397         enum ima_hooks func;
 398
 399         if (!file && read_id == READING_FIRMWARE) {
 400                 if ((ima_appraise & IMA_APPRAISE_FIRMWARE) &&
 401                     (ima_appraise & IMA_APPRAISE_ENFORCE))
 402                         return -EACCES; /* INTEGRITY_UNKNOWN */
 403                 return 0;
 404         }
 405
 406         if (!file && read_id == READING_MODULE) /* MODULE_SIG_FORCE enabled */
 407                 return 0;
 408
 409         if (!file || !buf || size == 0) { /* should never happen */
 410                 if (ima_appraise & IMA_APPRAISE_ENFORCE)
 411                         return -EACCES;
 412                 return 0;
 413         }
 414
 415         func = read_idmap[read_id] ?: FILE_CHECK;
 416         return process_measurement(file, buf, size, MAY_READ, func, 0);
 417 }
 418
 419 static int __init init_ima(void)
 420 {
 421         int error;
 422
 423         ima_init_template_list();
 424         hash_setup(CONFIG_IMA_DEFAULT_HASH);
 425         error = ima_init();
 426         if (!error) {
 427                 ima_initialized = 1;
 428                 ima_update_policy_flag();
 429         }
 430         return error;
 431 }
 432
 433 late_initcall(init_ima);        /* Start IMA after the TPM is available */
 434
 435 MODULE_DESCRIPTION("Integrity Measurement Architecture");
 436 MODULE_LICENSE("GPL");