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
  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, NULL);
  57 }
  58
  59 static int ima_fix_xattr(struct dentry *dentry,
  60                          struct integrity_iint_cache *iint)
  61 {
  62         int rc, offset;
  63         u8 algo = iint->ima_hash->algo;
  64
  65         if (algo <= HASH_ALGO_SHA1) {
  66                 offset = 1;
  67                 iint->ima_hash->xattr.sha1.type = IMA_XATTR_DIGEST;
  68         } else {
  69                 offset = 0;
  70                 iint->ima_hash->xattr.ng.type = IMA_XATTR_DIGEST_NG;
  71                 iint->ima_hash->xattr.ng.algo = algo;
  72         }
  73         rc = __vfs_setxattr_noperm(dentry, XATTR_NAME_IMA,
  74                                    &iint->ima_hash->xattr.data[offset],
  75                                    (sizeof(iint->ima_hash->xattr) - offset) +
  76                                    iint->ima_hash->length, 0);
  77         return rc;
  78 }
  79
  80 /* Return specific func appraised cached result */
  81 enum integrity_status ima_get_cache_status(struct integrity_iint_cache *iint,
  82                                            enum ima_hooks func)
  83 {
  84         switch (func) {
  85         case MMAP_CHECK:
  86                 return iint->ima_mmap_status;
  87         case BPRM_CHECK:
  88                 return iint->ima_bprm_status;
  89         case FILE_CHECK:
  90         case POST_SETATTR:
  91                 return iint->ima_file_status;
  92         case MODULE_CHECK ... MAX_CHECK - 1:
  93         default:
  94                 return iint->ima_read_status;
  95         }
  96 }
  97
  98 static void ima_set_cache_status(struct integrity_iint_cache *iint,
  99                                  enum ima_hooks func,
 100                                  enum integrity_status status)
 101 {
 102         switch (func) {
 103         case MMAP_CHECK:
 104                 iint->ima_mmap_status = status;
 105                 break;
 106         case BPRM_CHECK:
 107                 iint->ima_bprm_status = status;
 108                 break;
 109         case FILE_CHECK:
 110         case POST_SETATTR:
 111                 iint->ima_file_status = status;
 112                 break;
 113         case MODULE_CHECK ... MAX_CHECK - 1:
 114         default:
 115                 iint->ima_read_status = status;
 116                 break;
 117         }
 118 }
 119
 120 static void ima_cache_flags(struct integrity_iint_cache *iint,
 121                              enum ima_hooks func)
 122 {
 123         switch (func) {
 124         case MMAP_CHECK:
 125                 iint->flags |= (IMA_MMAP_APPRAISED | IMA_APPRAISED);
 126                 break;
 127         case BPRM_CHECK:
 128                 iint->flags |= (IMA_BPRM_APPRAISED | IMA_APPRAISED);
 129                 break;
 130         case FILE_CHECK:
 131         case POST_SETATTR:
 132                 iint->flags |= (IMA_FILE_APPRAISED | IMA_APPRAISED);
 133                 break;
 134         case MODULE_CHECK ... MAX_CHECK - 1:
 135         default:
 136                 iint->flags |= (IMA_READ_APPRAISED | IMA_APPRAISED);
 137                 break;
 138         }
 139 }
 140
 141 enum hash_algo ima_get_hash_algo(struct evm_ima_xattr_data *xattr_value,
 142                                  int xattr_len)
 143 {
 144         struct signature_v2_hdr *sig;
 145         enum hash_algo ret;
 146
 147         if (!xattr_value || xattr_len < 2)
 148                 /* return default hash algo */
 149                 return ima_hash_algo;
 150
 151         switch (xattr_value->type) {
 152         case EVM_IMA_XATTR_DIGSIG:
 153                 sig = (typeof(sig))xattr_value;
 154                 if (sig->version != 2 || xattr_len <= sizeof(*sig))
 155                         return ima_hash_algo;
 156                 return sig->hash_algo;
 157                 break;
 158         case IMA_XATTR_DIGEST_NG:
 159                 ret = xattr_value->digest[0];
 160                 if (ret < HASH_ALGO__LAST)
 161                         return ret;
 162                 break;
 163         case IMA_XATTR_DIGEST:
 164                 /* this is for backward compatibility */
 165                 if (xattr_len == 21) {
 166                         unsigned int zero = 0;
 167                         if (!memcmp(&xattr_value->digest[16], &zero, 4))
 168                                 return HASH_ALGO_MD5;
 169                         else
 170                                 return HASH_ALGO_SHA1;
 171                 } else if (xattr_len == 17)
 172                         return HASH_ALGO_MD5;
 173                 break;
 174         }
 175
 176         /* return default hash algo */
 177         return ima_hash_algo;
 178 }
 179
 180 int ima_read_xattr(struct dentry *dentry,
 181                    struct evm_ima_xattr_data **xattr_value)
 182 {
 183         ssize_t ret;
 184
 185         ret = vfs_getxattr_alloc(dentry, XATTR_NAME_IMA, (char **)xattr_value,
 186                                  0, GFP_NOFS);
 187         if (ret == -EOPNOTSUPP)
 188                 ret = 0;
 189         return ret;
 190 }
 191
 192 /*
 193  * ima_appraise_measurement - appraise file measurement
 194  *
 195  * Call evm_verifyxattr() to verify the integrity of 'security.ima'.
 196  * Assuming success, compare the xattr hash with the collected measurement.
 197  *
 198  * Return 0 on success, error code otherwise
 199  */
 200 int ima_appraise_measurement(enum ima_hooks func,
 201                              struct integrity_iint_cache *iint,
 202                              struct file *file, const unsigned char *filename,
 203                              struct evm_ima_xattr_data *xattr_value,
 204                              int xattr_len, int opened)
 205 {
 206         static const char op[] = "appraise_data";
 207         char *cause = "unknown";
 208         struct dentry *dentry = file_dentry(file);
 209         struct inode *inode = d_backing_inode(dentry);
 210         enum integrity_status status = INTEGRITY_UNKNOWN;
 211         int rc = xattr_len, hash_start = 0;
 212
 213         if (!(inode->i_opflags & IOP_XATTR))
 214                 return INTEGRITY_UNKNOWN;
 215
 216         if (rc <= 0) {
 217                 if (rc && rc != -ENODATA)
 218                         goto out;
 219
 220                 cause = iint->flags & IMA_DIGSIG_REQUIRED ?
 221                                 "IMA-signature-required" : "missing-hash";
 222                 status = INTEGRITY_NOLABEL;
 223                 if (opened & FILE_CREATED)
 224                         iint->flags |= IMA_NEW_FILE;
 225                 if ((iint->flags & IMA_NEW_FILE) &&
 226                     (!(iint->flags & IMA_DIGSIG_REQUIRED) ||
 227                      (inode->i_size == 0)))
 228                         status = INTEGRITY_PASS;
 229                 goto out;
 230         }
 231
 232         status = evm_verifyxattr(dentry, XATTR_NAME_IMA, xattr_value, rc, iint);
 233         if ((status != INTEGRITY_PASS) && (status != INTEGRITY_UNKNOWN)) {
 234                 if ((status == INTEGRITY_NOLABEL)
 235                     || (status == INTEGRITY_NOXATTRS))
 236                         cause = "missing-HMAC";
 237                 else if (status == INTEGRITY_FAIL)
 238                         cause = "invalid-HMAC";
 239                 goto out;
 240         }
 241         switch (xattr_value->type) {
 242         case IMA_XATTR_DIGEST_NG:
 243                 /* first byte contains algorithm id */
 244                 hash_start = 1;
 245                 /* fall through */
 246         case IMA_XATTR_DIGEST:
 247                 if (iint->flags & IMA_DIGSIG_REQUIRED) {
 248                         cause = "IMA-signature-required";
 249                         status = INTEGRITY_FAIL;
 250                         break;
 251                 }
 252                 if (xattr_len - sizeof(xattr_value->type) - hash_start >=
 253                                 iint->ima_hash->length)
 254                         /* xattr length may be longer. md5 hash in previous
 255                            version occupied 20 bytes in xattr, instead of 16
 256                          */
 257                         rc = memcmp(&xattr_value->digest[hash_start],
 258                                     iint->ima_hash->digest,
 259                                     iint->ima_hash->length);
 260                 else
 261                         rc = -EINVAL;
 262                 if (rc) {
 263                         cause = "invalid-hash";
 264                         status = INTEGRITY_FAIL;
 265                         break;
 266                 }
 267                 status = INTEGRITY_PASS;
 268                 break;
 269         case EVM_IMA_XATTR_DIGSIG:
 270                 iint->flags |= IMA_DIGSIG;
 271                 rc = integrity_digsig_verify(INTEGRITY_KEYRING_IMA,
 272                                              (const char *)xattr_value, rc,
 273                                              iint->ima_hash->digest,
 274                                              iint->ima_hash->length);
 275                 if (rc == -EOPNOTSUPP) {
 276                         status = INTEGRITY_UNKNOWN;
 277                 } else if (rc) {
 278                         cause = "invalid-signature";
 279                         status = INTEGRITY_FAIL;
 280                 } else {
 281                         status = INTEGRITY_PASS;
 282                 }
 283                 break;
 284         default:
 285                 status = INTEGRITY_UNKNOWN;
 286                 cause = "unknown-ima-data";
 287                 break;
 288         }
 289
 290 out:
 291         if (status != INTEGRITY_PASS) {
 292                 if ((ima_appraise & IMA_APPRAISE_FIX) &&
 293                     (!xattr_value ||
 294                      xattr_value->type != EVM_IMA_XATTR_DIGSIG)) {
 295                         if (!ima_fix_xattr(dentry, iint))
 296                                 status = INTEGRITY_PASS;
 297                 } else if ((inode->i_size == 0) &&
 298                            (iint->flags & IMA_NEW_FILE) &&
 299                            (xattr_value &&
 300                             xattr_value->type == EVM_IMA_XATTR_DIGSIG)) {
 301                         status = INTEGRITY_PASS;
 302                 }
 303                 integrity_audit_msg(AUDIT_INTEGRITY_DATA, inode, filename,
 304                                     op, cause, rc, 0);
 305         } else {
 306                 ima_cache_flags(iint, func);
 307         }
 308         ima_set_cache_status(iint, func, status);
 309         return status;
 310 }
 311
 312 /*
 313  * ima_update_xattr - update 'security.ima' hash value
 314  */
 315 void ima_update_xattr(struct integrity_iint_cache *iint, struct file *file)
 316 {
 317         struct dentry *dentry = file_dentry(file);
 318         int rc = 0;
 319
 320         /* do not collect and update hash for digital signatures */
 321         if (iint->flags & IMA_DIGSIG)
 322                 return;
 323
 324         if (iint->ima_file_status != INTEGRITY_PASS)
 325                 return;
 326
 327         rc = ima_collect_measurement(iint, file, NULL, 0, ima_hash_algo);
 328         if (rc < 0)
 329                 return;
 330
 331         ima_fix_xattr(dentry, iint);
 332 }
 333
 334 /**
 335  * ima_inode_post_setattr - reflect file metadata changes
 336  * @dentry: pointer to the affected dentry
 337  *
 338  * Changes to a dentry's metadata might result in needing to appraise.
 339  *
 340  * This function is called from notify_change(), which expects the caller
 341  * to lock the inode's i_mutex.
 342  */
 343 void ima_inode_post_setattr(struct dentry *dentry)
 344 {
 345         struct inode *inode = d_backing_inode(dentry);
 346         struct integrity_iint_cache *iint;
 347         int must_appraise;
 348
 349         if (!(ima_policy_flag & IMA_APPRAISE) || !S_ISREG(inode->i_mode)
 350             || !(inode->i_opflags & IOP_XATTR))
 351                 return;
 352
 353         must_appraise = ima_must_appraise(inode, MAY_ACCESS, POST_SETATTR);
 354         iint = integrity_iint_find(inode);
 355         if (iint) {
 356                 iint->flags &= ~(IMA_APPRAISE | IMA_APPRAISED |
 357                                  IMA_APPRAISE_SUBMASK | IMA_APPRAISED_SUBMASK |
 358                                  IMA_ACTION_RULE_FLAGS);
 359                 if (must_appraise)
 360                         iint->flags |= IMA_APPRAISE;
 361         }
 362         if (!must_appraise)
 363                 __vfs_removexattr(dentry, XATTR_NAME_IMA);
 364 }
 365
 366 /*
 367  * ima_protect_xattr - protect 'security.ima'
 368  *
 369  * Ensure that not just anyone can modify or remove 'security.ima'.
 370  */
 371 static int ima_protect_xattr(struct dentry *dentry, const char *xattr_name,
 372                              const void *xattr_value, size_t xattr_value_len)
 373 {
 374         if (strcmp(xattr_name, XATTR_NAME_IMA) == 0) {
 375                 if (!capable(CAP_SYS_ADMIN))
 376                         return -EPERM;
 377                 return 1;
 378         }
 379         return 0;
 380 }
 381
 382 static void ima_reset_appraise_flags(struct inode *inode, int digsig)
 383 {
 384         struct integrity_iint_cache *iint;
 385
 386         if (!(ima_policy_flag & IMA_APPRAISE) || !S_ISREG(inode->i_mode))
 387                 return;
 388
 389         iint = integrity_iint_find(inode);
 390         if (!iint)
 391                 return;
 392
 393         iint->flags &= ~IMA_DONE_MASK;
 394         iint->measured_pcrs = 0;
 395         if (digsig)
 396                 iint->flags |= IMA_DIGSIG;
 397         return;
 398 }
 399
 400 int ima_inode_setxattr(struct dentry *dentry, const char *xattr_name,
 401                        const void *xattr_value, size_t xattr_value_len)
 402 {
 403         const struct evm_ima_xattr_data *xvalue = xattr_value;
 404         int result;
 405
 406         result = ima_protect_xattr(dentry, xattr_name, xattr_value,
 407                                    xattr_value_len);
 408         if (result == 1) {
 409                 if (!xattr_value_len || (xvalue->type >= IMA_XATTR_LAST))
 410                         return -EINVAL;
 411                 ima_reset_appraise_flags(d_backing_inode(dentry),
 412                         xvalue->type == EVM_IMA_XATTR_DIGSIG);
 413                 result = 0;
 414         }
 415         return result;
 416 }
 417
 418 int ima_inode_removexattr(struct dentry *dentry, const char *xattr_name)
 419 {
 420         int result;
 421
 422         result = ima_protect_xattr(dentry, xattr_name, NULL, 0);
 423         if (result == 1) {
 424                 ima_reset_appraise_flags(d_backing_inode(dentry), 0);
 425                 result = 0;
 426         }
 427         return result;
 428 }