security/integrity/ima/ima_appraise.c

   1 /*
   2  * Copyright (C) 2011 IBM Corporation
   3  *
   4  * Author:
   5  * Mimi Zohar <zohar@us.ibm.com>
   6  *
   7  * This program is free software; you can redistribute it and/or modify
   8  * it under the terms of the GNU General Public License as published by
   9  * the Free Software Foundation, version 2 of the License.
  10  */
  11 #include <linux/module.h>
  12 #include <linux/file.h>
  13 #include <linux/fs.h>
  14 #include <linux/xattr.h>
  15 #include <linux/magic.h>
  16 #include <linux/ima.h>
  17 #include <linux/evm.h>
  18
  19 #include "ima.h"
  20
  21 static int __init default_appraise_setup(char *str)
  22 {
  23 #ifdef CONFIG_IMA_APPRAISE_BOOTPARAM
  24         if (strncmp(str, "off", 3) == 0)
  25                 ima_appraise = 0;
  26         else if (strncmp(str, "log", 3) == 0)
  27                 ima_appraise = IMA_APPRAISE_LOG;
  28         else if (strncmp(str, "fix", 3) == 0)
  29                 ima_appraise = IMA_APPRAISE_FIX;
  30 #endif
  31         return 1;
  32 }
  33
  34 __setup("ima_appraise=", default_appraise_setup);
  35
  36 /*
  37  * is_ima_appraise_enabled - return appraise status
  38  *
  39  * Only return enabled, if not in ima_appraise="fix" or "log" modes.
  40  */
  41 bool is_ima_appraise_enabled(void)
  42 {
  43         return ima_appraise & IMA_APPRAISE_ENFORCE;
  44 }
  45
  46 /*
  47  * ima_must_appraise - set appraise flag
  48  *
  49  * Return 1 to appraise or hash
  50  */
  51 int ima_must_appraise(struct inode *inode, int mask, enum ima_hooks func)
  52 {
  53         if (!ima_appraise)
  54                 return 0;
  55
  56         return ima_match_policy(inode, func, mask, IMA_APPRAISE | IMA_HASH,
  57                                 NULL);
  58 }
  59
  60 static int ima_fix_xattr(struct dentry *dentry,
  61                          struct integrity_iint_cache *iint)
  62 {
  63         int rc, offset;
  64         u8 algo = iint->ima_hash->algo;
  65
  66         if (algo <= HASH_ALGO_SHA1) {
  67                 offset = 1;
  68                 iint->ima_hash->xattr.sha1.type = IMA_XATTR_DIGEST;
  69         } else {
  70                 offset = 0;
  71                 iint->ima_hash->xattr.ng.type = IMA_XATTR_DIGEST_NG;
  72                 iint->ima_hash->xattr.ng.algo = algo;
  73         }
  74         rc = __vfs_setxattr_noperm(dentry, XATTR_NAME_IMA,
  75                                    &iint->ima_hash->xattr.data[offset],
  76                                    (sizeof(iint->ima_hash->xattr) - offset) +
  77                                    iint->ima_hash->length, 0);
  78         return rc;
  79 }
  80
  81 /* Return specific func appraised cached result */
  82 enum integrity_status ima_get_cache_status(struct integrity_iint_cache *iint,
  83                                            enum ima_hooks func)
  84 {
  85         switch (func) {
  86         case MMAP_CHECK:
  87                 return iint->ima_mmap_status;
  88         case BPRM_CHECK:
  89                 return iint->ima_bprm_status;
  90         case FILE_CHECK:
  91         case POST_SETATTR:
  92                 return iint->ima_file_status;
  93         case MODULE_CHECK ... MAX_CHECK - 1:
  94         default:
  95                 return iint->ima_read_status;
  96         }
  97 }
  98
  99 static void ima_set_cache_status(struct integrity_iint_cache *iint,
 100                                  enum ima_hooks func,
 101                                  enum integrity_status status)
 102 {
 103         switch (func) {
 104         case MMAP_CHECK:
 105                 iint->ima_mmap_status = status;
 106                 break;
 107         case BPRM_CHECK:
 108                 iint->ima_bprm_status = status;
 109                 break;
 110         case FILE_CHECK:
 111         case POST_SETATTR:
 112                 iint->ima_file_status = status;
 113                 break;
 114         case MODULE_CHECK ... MAX_CHECK - 1:
 115         default:
 116                 iint->ima_read_status = status;
 117                 break;
 118         }
 119 }
 120
 121 static void ima_cache_flags(struct integrity_iint_cache *iint,
 122                              enum ima_hooks func)
 123 {
 124         switch (func) {
 125         case MMAP_CHECK:
 126                 iint->flags |= (IMA_MMAP_APPRAISED | IMA_APPRAISED);
 127                 break;
 128         case BPRM_CHECK:
 129                 iint->flags |= (IMA_BPRM_APPRAISED | IMA_APPRAISED);
 130                 break;
 131         case FILE_CHECK:
 132         case POST_SETATTR:
 133                 iint->flags |= (IMA_FILE_APPRAISED | IMA_APPRAISED);
 134                 break;
 135         case MODULE_CHECK ... MAX_CHECK - 1:
 136         default:
 137                 iint->flags |= (IMA_READ_APPRAISED | IMA_APPRAISED);
 138                 break;
 139         }
 140 }
 141
 142 enum hash_algo ima_get_hash_algo(struct evm_ima_xattr_data *xattr_value,
 143                                  int xattr_len)
 144 {
 145         struct signature_v2_hdr *sig;
 146         enum hash_algo ret;
 147
 148         if (!xattr_value || xattr_len < 2)
 149                 /* return default hash algo */
 150                 return ima_hash_algo;
 151
 152         switch (xattr_value->type) {
 153         case EVM_IMA_XATTR_DIGSIG:
 154                 sig = (typeof(sig))xattr_value;
 155                 if (sig->version != 2 || xattr_len <= sizeof(*sig))
 156                         return ima_hash_algo;
 157                 return sig->hash_algo;
 158                 break;
 159         case IMA_XATTR_DIGEST_NG:
 160                 ret = xattr_value->digest[0];
 161                 if (ret < HASH_ALGO__LAST)
 162                         return ret;
 163                 break;
 164         case IMA_XATTR_DIGEST:
 165                 /* this is for backward compatibility */
 166                 if (xattr_len == 21) {
 167                         unsigned int zero = 0;
 168                         if (!memcmp(&xattr_value->digest[16], &zero, 4))
 169                                 return HASH_ALGO_MD5;
 170                         else
 171                                 return HASH_ALGO_SHA1;
 172                 } else if (xattr_len == 17)
 173                         return HASH_ALGO_MD5;
 174                 break;
 175         }
 176
 177         /* return default hash algo */
 178         return ima_hash_algo;
 179 }
 180
 181 int ima_read_xattr(struct dentry *dentry,
 182                    struct evm_ima_xattr_data **xattr_value)
 183 {
 184         ssize_t ret;
 185
 186         ret = vfs_getxattr_alloc(dentry, XATTR_NAME_IMA, (char **)xattr_value,
 187                                  0, GFP_NOFS);
 188         if (ret == -EOPNOTSUPP)
 189                 ret = 0;
 190         return ret;
 191 }
 192
 193 /*
 194  * ima_appraise_measurement - appraise file measurement
 195  *
 196  * Call evm_verifyxattr() to verify the integrity of 'security.ima'.
 197  * Assuming success, compare the xattr hash with the collected measurement.
 198  *
 199  * Return 0 on success, error code otherwise
 200  */
 201 int ima_appraise_measurement(enum ima_hooks func,
 202                              struct integrity_iint_cache *iint,
 203                              struct file *file, const unsigned char *filename,
 204                              struct evm_ima_xattr_data *xattr_value,
 205                              int xattr_len, int opened)
 206 {
 207         static const char op[] = "appraise_data";
 208         char *cause = "unknown";
 209         struct dentry *dentry = file_dentry(file);
 210         struct inode *inode = d_backing_inode(dentry);
 211         enum integrity_status status = INTEGRITY_UNKNOWN;
 212         int rc = xattr_len, hash_start = 0;
 213
 214         if (!(inode->i_opflags & IOP_XATTR))
 215                 return INTEGRITY_UNKNOWN;
 216
 217         if (rc <= 0) {
 218                 if (rc && rc != -ENODATA)
 219                         goto out;
 220
 221                 cause = iint->flags & IMA_DIGSIG_REQUIRED ?
 222                                 "IMA-signature-required" : "missing-hash";
 223                 status = INTEGRITY_NOLABEL;
 224                 if (opened & FILE_CREATED)
 225                         iint->flags |= IMA_NEW_FILE;
 226                 if ((iint->flags & IMA_NEW_FILE) &&
 227                     (!(iint->flags & IMA_DIGSIG_REQUIRED) ||
 228                      (inode->i_size == 0)))
 229                         status = INTEGRITY_PASS;
 230                 goto out;
 231         }
 232
 233         status = evm_verifyxattr(dentry, XATTR_NAME_IMA, xattr_value, rc, iint);
 234         if ((status != INTEGRITY_PASS) &&
 235             (status != INTEGRITY_PASS_IMMUTABLE) &&
 236             (status != INTEGRITY_UNKNOWN)) {
 237                 if ((status == INTEGRITY_NOLABEL)
 238                     || (status == INTEGRITY_NOXATTRS))
 239                         cause = "missing-HMAC";
 240                 else if (status == INTEGRITY_FAIL)
 241                         cause = "invalid-HMAC";
 242                 goto out;
 243         }
 244         switch (xattr_value->type) {
 245         case IMA_XATTR_DIGEST_NG:
 246                 /* first byte contains algorithm id */
 247                 hash_start = 1;
 248                 /* fall through */
 249         case IMA_XATTR_DIGEST:
 250                 if (iint->flags & IMA_DIGSIG_REQUIRED) {
 251                         cause = "IMA-signature-required";
 252                         status = INTEGRITY_FAIL;
 253                         break;
 254                 }
 255                 clear_bit(IMA_DIGSIG, &iint->atomic_flags);
 256                 if (xattr_len - sizeof(xattr_value->type) - hash_start >=
 257                                 iint->ima_hash->length)
 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->digest[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, rc,
 277                                              iint->ima_hash->digest,
 278                                              iint->ima_hash->length);
 279                 if (rc == -EOPNOTSUPP) {
 280                         status = INTEGRITY_UNKNOWN;
 281                 } else if (rc) {
 282                         cause = "invalid-signature";
 283                         status = INTEGRITY_FAIL;
 284                 } else {
 285                         status = INTEGRITY_PASS;
 286                 }
 287                 break;
 288         default:
 289                 status = INTEGRITY_UNKNOWN;
 290                 cause = "unknown-ima-data";
 291                 break;
 292         }
 293
 294 out:
 295         if (status != INTEGRITY_PASS) {
 296                 if ((ima_appraise & IMA_APPRAISE_FIX) &&
 297                     (!xattr_value ||
 298                      xattr_value->type != EVM_IMA_XATTR_DIGSIG)) {
 299                         if (!ima_fix_xattr(dentry, iint))
 300                                 status = INTEGRITY_PASS;
 301                 } else if ((inode->i_size == 0) &&
 302                            (iint->flags & IMA_NEW_FILE) &&
 303                            (xattr_value &&
 304                             xattr_value->type == EVM_IMA_XATTR_DIGSIG)) {
 305                         status = INTEGRITY_PASS;
 306                 }
 307                 integrity_audit_msg(AUDIT_INTEGRITY_DATA, inode, filename,
 308                                     op, cause, rc, 0);
 309         } else {
 310                 ima_cache_flags(iint, func);
 311         }
 312         ima_set_cache_status(iint, func, status);
 313         return status;
 314 }
 315
 316 /*
 317  * ima_update_xattr - update 'security.ima' hash value
 318  */
 319 void ima_update_xattr(struct integrity_iint_cache *iint, struct file *file)
 320 {
 321         struct dentry *dentry = file_dentry(file);
 322         int rc = 0;
 323
 324         /* do not collect and update hash for digital signatures */
 325         if (test_bit(IMA_DIGSIG, &iint->atomic_flags))
 326                 return;
 327
 328         if ((iint->ima_file_status != INTEGRITY_PASS) &&
 329             !(iint->flags & IMA_HASH))
 330                 return;
 331
 332         rc = ima_collect_measurement(iint, file, NULL, 0, ima_hash_algo);
 333         if (rc < 0)
 334                 return;
 335
 336         inode_lock(file_inode(file));
 337         ima_fix_xattr(dentry, iint);
 338         inode_unlock(file_inode(file));
 339 }
 340
 341 /**
 342  * ima_inode_post_setattr - reflect file metadata changes
 343  * @dentry: pointer to the affected dentry
 344  *
 345  * Changes to a dentry's metadata might result in needing to appraise.
 346  *
 347  * This function is called from notify_change(), which expects the caller
 348  * to lock the inode's i_mutex.
 349  */
 350 void ima_inode_post_setattr(struct dentry *dentry)
 351 {
 352         struct inode *inode = d_backing_inode(dentry);
 353         struct integrity_iint_cache *iint;
 354         int action;
 355
 356         if (!(ima_policy_flag & IMA_APPRAISE) || !S_ISREG(inode->i_mode)
 357             || !(inode->i_opflags & IOP_XATTR))
 358                 return;
 359
 360         action = ima_must_appraise(inode, MAY_ACCESS, POST_SETATTR);
 361         if (!action)
 362                 __vfs_removexattr(dentry, XATTR_NAME_IMA);
 363         iint = integrity_iint_find(inode);
 364         if (iint) {
 365                 set_bit(IMA_CHANGE_ATTR, &iint->atomic_flags);
 366                 if (!action)
 367                         clear_bit(IMA_UPDATE_XATTR, &iint->atomic_flags);
 368         }
 369 }
 370
 371 /*
 372  * ima_protect_xattr - protect 'security.ima'
 373  *
 374  * Ensure that not just anyone can modify or remove 'security.ima'.
 375  */
 376 static int ima_protect_xattr(struct dentry *dentry, const char *xattr_name,
 377                              const void *xattr_value, size_t xattr_value_len)
 378 {
 379         if (strcmp(xattr_name, XATTR_NAME_IMA) == 0) {
 380                 if (!capable(CAP_SYS_ADMIN))
 381                         return -EPERM;
 382                 return 1;
 383         }
 384         return 0;
 385 }
 386
 387 static void ima_reset_appraise_flags(struct inode *inode, int digsig)
 388 {
 389         struct integrity_iint_cache *iint;
 390
 391         if (!(ima_policy_flag & IMA_APPRAISE) || !S_ISREG(inode->i_mode))
 392                 return;
 393
 394         iint = integrity_iint_find(inode);
 395         if (!iint)
 396                 return;
 397         iint->measured_pcrs = 0;
 398         set_bit(IMA_CHANGE_XATTR, &iint->atomic_flags);
 399         if (digsig)
 400                 set_bit(IMA_DIGSIG, &iint->atomic_flags);
 401         else
 402                 clear_bit(IMA_DIGSIG, &iint->atomic_flags);
 403 }
 404
 405 int ima_inode_setxattr(struct dentry *dentry, const char *xattr_name,
 406                        const void *xattr_value, size_t xattr_value_len)
 407 {
 408         const struct evm_ima_xattr_data *xvalue = xattr_value;
 409         int result;
 410
 411         result = ima_protect_xattr(dentry, xattr_name, xattr_value,
 412                                    xattr_value_len);
 413         if (result == 1) {
 414                 if (!xattr_value_len || (xvalue->type >= IMA_XATTR_LAST))
 415                         return -EINVAL;
 416                 ima_reset_appraise_flags(d_backing_inode(dentry),
 417                         xvalue->type == EVM_IMA_XATTR_DIGSIG);
 418                 result = 0;
 419         }
 420         return result;
 421 }
 422
 423 int ima_inode_removexattr(struct dentry *dentry, const char *xattr_name)
 424 {
 425         int result;
 426
 427         result = ima_protect_xattr(dentry, xattr_name, NULL, 0);
 428         if (result == 1) {
 429                 ima_reset_appraise_flags(d_backing_inode(dentry), 0);
 430                 result = 0;
 431         }
 432         return result;
 433 }