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) ? 1 : 0;
  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) &&
 234             (status != INTEGRITY_PASS_IMMUTABLE) &&
 235             (status != INTEGRITY_UNKNOWN)) {
 236                 if ((status == INTEGRITY_NOLABEL)
 237                     || (status == INTEGRITY_NOXATTRS))
 238                         cause = "missing-HMAC";
 239                 else if (status == INTEGRITY_FAIL)
 240                         cause = "invalid-HMAC";
 241                 goto out;
 242         }
 243         switch (xattr_value->type) {
 244         case IMA_XATTR_DIGEST_NG:
 245                 /* first byte contains algorithm id */
 246                 hash_start = 1;
 247                 /* fall through */
 248         case IMA_XATTR_DIGEST:
 249                 if (iint->flags & IMA_DIGSIG_REQUIRED) {
 250                         cause = "IMA-signature-required";
 251                         status = INTEGRITY_FAIL;
 252                         break;
 253                 }
 254                 clear_bit(IMA_DIGSIG, &iint->atomic_flags);
 255                 if (xattr_len - sizeof(xattr_value->type) - hash_start >=
 256                                 iint->ima_hash->length)
 257                         /* xattr length may be longer. md5 hash in previous
 258                            version occupied 20 bytes in xattr, instead of 16
 259                          */
 260                         rc = memcmp(&xattr_value->digest[hash_start],
 261                                     iint->ima_hash->digest,
 262                                     iint->ima_hash->length);
 263                 else
 264                         rc = -EINVAL;
 265                 if (rc) {
 266                         cause = "invalid-hash";
 267                         status = INTEGRITY_FAIL;
 268                         break;
 269                 }
 270                 status = INTEGRITY_PASS;
 271                 break;
 272         case EVM_IMA_XATTR_DIGSIG:
 273                 set_bit(IMA_DIGSIG, &iint->atomic_flags);
 274                 rc = integrity_digsig_verify(INTEGRITY_KEYRING_IMA,
 275                                              (const char *)xattr_value, rc,
 276                                              iint->ima_hash->digest,
 277                                              iint->ima_hash->length);
 278                 if (rc == -EOPNOTSUPP) {
 279                         status = INTEGRITY_UNKNOWN;
 280                 } else if (rc) {
 281                         cause = "invalid-signature";
 282                         status = INTEGRITY_FAIL;
 283                 } else {
 284                         status = INTEGRITY_PASS;
 285                 }
 286                 break;
 287         default:
 288                 status = INTEGRITY_UNKNOWN;
 289                 cause = "unknown-ima-data";
 290                 break;
 291         }
 292
 293 out:
 294         if (status != INTEGRITY_PASS) {
 295                 if ((ima_appraise & IMA_APPRAISE_FIX) &&
 296                     (!xattr_value ||
 297                      xattr_value->type != EVM_IMA_XATTR_DIGSIG)) {
 298                         if (!ima_fix_xattr(dentry, iint))
 299                                 status = INTEGRITY_PASS;
 300                 } else if ((inode->i_size == 0) &&
 301                            (iint->flags & IMA_NEW_FILE) &&
 302                            (xattr_value &&
 303                             xattr_value->type == EVM_IMA_XATTR_DIGSIG)) {
 304                         status = INTEGRITY_PASS;
 305                 }
 306                 integrity_audit_msg(AUDIT_INTEGRITY_DATA, inode, filename,
 307                                     op, cause, rc, 0);
 308         } else {
 309                 ima_cache_flags(iint, func);
 310         }
 311         ima_set_cache_status(iint, func, status);
 312         return status;
 313 }
 314
 315 /*
 316  * ima_update_xattr - update 'security.ima' hash value
 317  */
 318 void ima_update_xattr(struct integrity_iint_cache *iint, struct file *file)
 319 {
 320         struct dentry *dentry = file_dentry(file);
 321         int rc = 0;
 322
 323         /* do not collect and update hash for digital signatures */
 324         if (test_bit(IMA_DIGSIG, &iint->atomic_flags))
 325                 return;
 326
 327         if (iint->ima_file_status != INTEGRITY_PASS)
 328                 return;
 329
 330         rc = ima_collect_measurement(iint, file, NULL, 0, ima_hash_algo);
 331         if (rc < 0)
 332                 return;
 333
 334         inode_lock(file_inode(file));
 335         ima_fix_xattr(dentry, iint);
 336         inode_unlock(file_inode(file));
 337 }
 338
 339 /**
 340  * ima_inode_post_setattr - reflect file metadata changes
 341  * @dentry: pointer to the affected dentry
 342  *
 343  * Changes to a dentry's metadata might result in needing to appraise.
 344  *
 345  * This function is called from notify_change(), which expects the caller
 346  * to lock the inode's i_mutex.
 347  */
 348 void ima_inode_post_setattr(struct dentry *dentry)
 349 {
 350         struct inode *inode = d_backing_inode(dentry);
 351         struct integrity_iint_cache *iint;
 352         int must_appraise;
 353
 354         if (!(ima_policy_flag & IMA_APPRAISE) || !S_ISREG(inode->i_mode)
 355             || !(inode->i_opflags & IOP_XATTR))
 356                 return;
 357
 358         must_appraise = ima_must_appraise(inode, MAY_ACCESS, POST_SETATTR);
 359         if (!must_appraise)
 360                 __vfs_removexattr(dentry, XATTR_NAME_IMA);
 361         iint = integrity_iint_find(inode);
 362         if (iint) {
 363                 set_bit(IMA_CHANGE_ATTR, &iint->atomic_flags);
 364                 if (!must_appraise)
 365                         clear_bit(IMA_UPDATE_XATTR, &iint->atomic_flags);
 366         }
 367 }
 368
 369 /*
 370  * ima_protect_xattr - protect 'security.ima'
 371  *
 372  * Ensure that not just anyone can modify or remove 'security.ima'.
 373  */
 374 static int ima_protect_xattr(struct dentry *dentry, const char *xattr_name,
 375                              const void *xattr_value, size_t xattr_value_len)
 376 {
 377         if (strcmp(xattr_name, XATTR_NAME_IMA) == 0) {
 378                 if (!capable(CAP_SYS_ADMIN))
 379                         return -EPERM;
 380                 return 1;
 381         }
 382         return 0;
 383 }
 384
 385 static void ima_reset_appraise_flags(struct inode *inode, int digsig)
 386 {
 387         struct integrity_iint_cache *iint;
 388
 389         if (!(ima_policy_flag & IMA_APPRAISE) || !S_ISREG(inode->i_mode))
 390                 return;
 391
 392         iint = integrity_iint_find(inode);
 393         if (!iint)
 394                 return;
 395         iint->measured_pcrs = 0;
 396         set_bit(IMA_CHANGE_XATTR, &iint->atomic_flags);
 397         if (digsig)
 398                 set_bit(IMA_DIGSIG, &iint->atomic_flags);
 399         else
 400                 clear_bit(IMA_DIGSIG, &iint->atomic_flags);
 401 }
 402
 403 int ima_inode_setxattr(struct dentry *dentry, const char *xattr_name,
 404                        const void *xattr_value, size_t xattr_value_len)
 405 {
 406         const struct evm_ima_xattr_data *xvalue = xattr_value;
 407         int result;
 408
 409         result = ima_protect_xattr(dentry, xattr_name, xattr_value,
 410                                    xattr_value_len);
 411         if (result == 1) {
 412                 if (!xattr_value_len || (xvalue->type >= IMA_XATTR_LAST))
 413                         return -EINVAL;
 414                 ima_reset_appraise_flags(d_backing_inode(dentry),
 415                          (xvalue->type == EVM_IMA_XATTR_DIGSIG) ? 1 : 0);
 416                 result = 0;
 417         }
 418         return result;
 419 }
 420
 421 int ima_inode_removexattr(struct dentry *dentry, const char *xattr_name)
 422 {
 423         int result;
 424
 425         result = ima_protect_xattr(dentry, xattr_name, NULL, 0);
 426         if (result == 1) {
 427                 ima_reset_appraise_flags(d_backing_inode(dentry), 0);
 428                 result = 0;
 429         }
 430         return result;
 431 }