security/integrity/evm/evm_main.c

   1 /*
   2  * Copyright (C) 2005-2010 IBM Corporation
   3  *
   4  * Author:
   5  * Mimi Zohar <zohar@us.ibm.com>
   6  * Kylene Hall <kjhall@us.ibm.com>
   7  *
   8  * This program is free software; you can redistribute it and/or modify
   9  * it under the terms of the GNU General Public License as published by
  10  * the Free Software Foundation, version 2 of the License.
  11  *
  12  * File: evm_main.c
  13  *      implements evm_inode_setxattr, evm_inode_post_setxattr,
  14  *      evm_inode_removexattr, and evm_verifyxattr
  15  */
  16
  17 #include <linux/module.h>
  18 #include <linux/crypto.h>
  19 #include <linux/xattr.h>
  20 #include <linux/integrity.h>
  21 #include <linux/evm.h>
  22 #include <crypto/hash.h>
  23 #include "evm.h"
  24
  25 int evm_initialized;
  26
  27 char *evm_hmac = "hmac(sha1)";
  28 char *evm_hash = "sha1";
  29
  30 char *evm_config_xattrnames[] = {
  31 #ifdef CONFIG_SECURITY_SELINUX
  32         XATTR_NAME_SELINUX,
  33 #endif
  34 #ifdef CONFIG_SECURITY_SMACK
  35         XATTR_NAME_SMACK,
  36 #endif
  37         XATTR_NAME_CAPS,
  38         NULL
  39 };
  40
  41 static int evm_fixmode;
  42 static int __init evm_set_fixmode(char *str)
  43 {
  44         if (strncmp(str, "fix", 3) == 0)
  45                 evm_fixmode = 1;
  46         return 0;
  47 }
  48 __setup("evm=", evm_set_fixmode);
  49
  50 static int evm_find_protected_xattrs(struct dentry *dentry)
  51 {
  52         struct inode *inode = dentry->d_inode;
  53         char **xattr;
  54         int error;
  55         int count = 0;
  56
  57         if (!inode->i_op || !inode->i_op->getxattr)
  58                 return -EOPNOTSUPP;
  59
  60         for (xattr = evm_config_xattrnames; *xattr != NULL; xattr++) {
  61                 error = inode->i_op->getxattr(dentry, *xattr, NULL, 0);
  62                 if (error < 0) {
  63                         if (error == -ENODATA)
  64                                 continue;
  65                         return error;
  66                 }
  67                 count++;
  68         }
  69
  70         return count;
  71 }
  72
  73 /*
  74  * evm_verify_hmac - calculate and compare the HMAC with the EVM xattr
  75  *
  76  * Compute the HMAC on the dentry's protected set of extended attributes
  77  * and compare it against the stored security.evm xattr.
  78  *
  79  * For performance:
  80  * - use the previoulsy retrieved xattr value and length to calculate the
  81  *   HMAC.)
  82  * - cache the verification result in the iint, when available.
  83  *
  84  * Returns integrity status
  85  */
  86 static enum integrity_status evm_verify_hmac(struct dentry *dentry,
  87                                              const char *xattr_name,
  88                                              char *xattr_value,
  89                                              size_t xattr_value_len,
  90                                              struct integrity_iint_cache *iint)
  91 {
  92         struct evm_ima_xattr_data *xattr_data = NULL;
  93         struct evm_ima_xattr_data calc;
  94         enum integrity_status evm_status = INTEGRITY_PASS;
  95         int rc, xattr_len;
  96
  97         if (iint && iint->evm_status == INTEGRITY_PASS)
  98                 return iint->evm_status;
  99
 100         /* if status is not PASS, try to check again - against -ENOMEM */
 101
 102         /* first need to know the sig type */
 103         rc = vfs_getxattr_alloc(dentry, XATTR_NAME_EVM, (char **)&xattr_data, 0,
 104                                 GFP_NOFS);
 105         if (rc <= 0) {
 106                 if (rc == 0)
 107                         evm_status = INTEGRITY_FAIL; /* empty */
 108                 else if (rc == -ENODATA) {
 109                         rc = evm_find_protected_xattrs(dentry);
 110                         if (rc > 0)
 111                                 evm_status = INTEGRITY_NOLABEL;
 112                         else if (rc == 0)
 113                                 evm_status = INTEGRITY_NOXATTRS; /* new file */
 114                 }
 115                 goto out;
 116         }
 117
 118         xattr_len = rc - 1;
 119
 120         /* check value type */
 121         switch (xattr_data->type) {
 122         case EVM_XATTR_HMAC:
 123                 rc = evm_calc_hmac(dentry, xattr_name, xattr_value,
 124                                    xattr_value_len, calc.digest);
 125                 if (rc)
 126                         break;
 127                 rc = memcmp(xattr_data->digest, calc.digest,
 128                             sizeof(calc.digest));
 129                 if (rc)
 130                         rc = -EINVAL;
 131                 break;
 132         case EVM_IMA_XATTR_DIGSIG:
 133                 rc = evm_calc_hash(dentry, xattr_name, xattr_value,
 134                                 xattr_value_len, calc.digest);
 135                 if (rc)
 136                         break;
 137                 rc = integrity_digsig_verify(INTEGRITY_KEYRING_EVM,
 138                                         xattr_data->digest, xattr_len,
 139                                         calc.digest, sizeof(calc.digest));
 140                 if (!rc) {
 141                         /* we probably want to replace rsa with hmac here */
 142                         evm_update_evmxattr(dentry, xattr_name, xattr_value,
 143                                    xattr_value_len);
 144                 }
 145                 break;
 146         default:
 147                 rc = -EINVAL;
 148                 break;
 149         }
 150
 151         if (rc)
 152                 evm_status = (rc == -ENODATA) ?
 153                                 INTEGRITY_NOXATTRS : INTEGRITY_FAIL;
 154 out:
 155         if (iint)
 156                 iint->evm_status = evm_status;
 157         kfree(xattr_data);
 158         return evm_status;
 159 }
 160
 161 static int evm_protected_xattr(const char *req_xattr_name)
 162 {
 163         char **xattrname;
 164         int namelen;
 165         int found = 0;
 166
 167         namelen = strlen(req_xattr_name);
 168         for (xattrname = evm_config_xattrnames; *xattrname != NULL; xattrname++) {
 169                 if ((strlen(*xattrname) == namelen)
 170                     && (strncmp(req_xattr_name, *xattrname, namelen) == 0)) {
 171                         found = 1;
 172                         break;
 173                 }
 174                 if (strncmp(req_xattr_name,
 175                             *xattrname + XATTR_SECURITY_PREFIX_LEN,
 176                             strlen(req_xattr_name)) == 0) {
 177                         found = 1;
 178                         break;
 179                 }
 180         }
 181         return found;
 182 }
 183
 184 /**
 185  * evm_verifyxattr - verify the integrity of the requested xattr
 186  * @dentry: object of the verify xattr
 187  * @xattr_name: requested xattr
 188  * @xattr_value: requested xattr value
 189  * @xattr_value_len: requested xattr value length
 190  *
 191  * Calculate the HMAC for the given dentry and verify it against the stored
 192  * security.evm xattr. For performance, use the xattr value and length
 193  * previously retrieved to calculate the HMAC.
 194  *
 195  * Returns the xattr integrity status.
 196  *
 197  * This function requires the caller to lock the inode's i_mutex before it
 198  * is executed.
 199  */
 200 enum integrity_status evm_verifyxattr(struct dentry *dentry,
 201                                       const char *xattr_name,
 202                                       void *xattr_value, size_t xattr_value_len,
 203                                       struct integrity_iint_cache *iint)
 204 {
 205         if (!evm_initialized || !evm_protected_xattr(xattr_name))
 206                 return INTEGRITY_UNKNOWN;
 207
 208         if (!iint) {
 209                 iint = integrity_iint_find(dentry->d_inode);
 210                 if (!iint)
 211                         return INTEGRITY_UNKNOWN;
 212         }
 213         return evm_verify_hmac(dentry, xattr_name, xattr_value,
 214                                  xattr_value_len, iint);
 215 }
 216 EXPORT_SYMBOL_GPL(evm_verifyxattr);
 217
 218 /*
 219  * evm_verify_current_integrity - verify the dentry's metadata integrity
 220  * @dentry: pointer to the affected dentry
 221  *
 222  * Verify and return the dentry's metadata integrity. The exceptions are
 223  * before EVM is initialized or in 'fix' mode.
 224  */
 225 static enum integrity_status evm_verify_current_integrity(struct dentry *dentry)
 226 {
 227         struct inode *inode = dentry->d_inode;
 228
 229         if (!evm_initialized || !S_ISREG(inode->i_mode) || evm_fixmode)
 230                 return 0;
 231         return evm_verify_hmac(dentry, NULL, NULL, 0, NULL);
 232 }
 233
 234 /*
 235  * evm_protect_xattr - protect the EVM extended attribute
 236  *
 237  * Prevent security.evm from being modified or removed without the
 238  * necessary permissions or when the existing value is invalid.
 239  *
 240  * The posix xattr acls are 'system' prefixed, which normally would not
 241  * affect security.evm.  An interesting side affect of writing posix xattr
 242  * acls is their modifying of the i_mode, which is included in security.evm.
 243  * For posix xattr acls only, permit security.evm, even if it currently
 244  * doesn't exist, to be updated.
 245  */
 246 static int evm_protect_xattr(struct dentry *dentry, const char *xattr_name,
 247                              const void *xattr_value, size_t xattr_value_len)
 248 {
 249         enum integrity_status evm_status;
 250
 251         if (strcmp(xattr_name, XATTR_NAME_EVM) == 0) {
 252                 if (!capable(CAP_SYS_ADMIN))
 253                         return -EPERM;
 254         } else if (!evm_protected_xattr(xattr_name)) {
 255                 if (!posix_xattr_acl(xattr_name))
 256                         return 0;
 257                 evm_status = evm_verify_current_integrity(dentry);
 258                 if ((evm_status == INTEGRITY_PASS) ||
 259                     (evm_status == INTEGRITY_NOXATTRS))
 260                         return 0;
 261                 return -EPERM;
 262         }
 263         evm_status = evm_verify_current_integrity(dentry);
 264         return evm_status == INTEGRITY_PASS ? 0 : -EPERM;
 265 }
 266
 267 /**
 268  * evm_inode_setxattr - protect the EVM extended attribute
 269  * @dentry: pointer to the affected dentry
 270  * @xattr_name: pointer to the affected extended attribute name
 271  * @xattr_value: pointer to the new extended attribute value
 272  * @xattr_value_len: pointer to the new extended attribute value length
 273  *
 274  * Updating 'security.evm' requires CAP_SYS_ADMIN privileges and that
 275  * the current value is valid.
 276  */
 277 int evm_inode_setxattr(struct dentry *dentry, const char *xattr_name,
 278                        const void *xattr_value, size_t xattr_value_len)
 279 {
 280         return evm_protect_xattr(dentry, xattr_name, xattr_value,
 281                                  xattr_value_len);
 282 }
 283
 284 /**
 285  * evm_inode_removexattr - protect the EVM extended attribute
 286  * @dentry: pointer to the affected dentry
 287  * @xattr_name: pointer to the affected extended attribute name
 288  *
 289  * Removing 'security.evm' requires CAP_SYS_ADMIN privileges and that
 290  * the current value is valid.
 291  */
 292 int evm_inode_removexattr(struct dentry *dentry, const char *xattr_name)
 293 {
 294         return evm_protect_xattr(dentry, xattr_name, NULL, 0);
 295 }
 296
 297 /**
 298  * evm_inode_post_setxattr - update 'security.evm' to reflect the changes
 299  * @dentry: pointer to the affected dentry
 300  * @xattr_name: pointer to the affected extended attribute name
 301  * @xattr_value: pointer to the new extended attribute value
 302  * @xattr_value_len: pointer to the new extended attribute value length
 303  *
 304  * Update the HMAC stored in 'security.evm' to reflect the change.
 305  *
 306  * No need to take the i_mutex lock here, as this function is called from
 307  * __vfs_setxattr_noperm().  The caller of which has taken the inode's
 308  * i_mutex lock.
 309  */
 310 void evm_inode_post_setxattr(struct dentry *dentry, const char *xattr_name,
 311                              const void *xattr_value, size_t xattr_value_len)
 312 {
 313         if (!evm_initialized || (!evm_protected_xattr(xattr_name)
 314                                  && !posix_xattr_acl(xattr_name)))
 315                 return;
 316
 317         evm_update_evmxattr(dentry, xattr_name, xattr_value, xattr_value_len);
 318         return;
 319 }
 320
 321 /**
 322  * evm_inode_post_removexattr - update 'security.evm' after removing the xattr
 323  * @dentry: pointer to the affected dentry
 324  * @xattr_name: pointer to the affected extended attribute name
 325  *
 326  * Update the HMAC stored in 'security.evm' to reflect removal of the xattr.
 327  */
 328 void evm_inode_post_removexattr(struct dentry *dentry, const char *xattr_name)
 329 {
 330         struct inode *inode = dentry->d_inode;
 331
 332         if (!evm_initialized || !evm_protected_xattr(xattr_name))
 333                 return;
 334
 335         mutex_lock(&inode->i_mutex);
 336         evm_update_evmxattr(dentry, xattr_name, NULL, 0);
 337         mutex_unlock(&inode->i_mutex);
 338         return;
 339 }
 340
 341 /**
 342  * evm_inode_setattr - prevent updating an invalid EVM extended attribute
 343  * @dentry: pointer to the affected dentry
 344  */
 345 int evm_inode_setattr(struct dentry *dentry, struct iattr *attr)
 346 {
 347         unsigned int ia_valid = attr->ia_valid;
 348         enum integrity_status evm_status;
 349
 350         if (!(ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID)))
 351                 return 0;
 352         evm_status = evm_verify_current_integrity(dentry);
 353         if ((evm_status == INTEGRITY_PASS) ||
 354             (evm_status == INTEGRITY_NOXATTRS))
 355                 return 0;
 356         return -EPERM;
 357 }
 358
 359 /**
 360  * evm_inode_post_setattr - update 'security.evm' after modifying metadata
 361  * @dentry: pointer to the affected dentry
 362  * @ia_valid: for the UID and GID status
 363  *
 364  * For now, update the HMAC stored in 'security.evm' to reflect UID/GID
 365  * changes.
 366  *
 367  * This function is called from notify_change(), which expects the caller
 368  * to lock the inode's i_mutex.
 369  */
 370 void evm_inode_post_setattr(struct dentry *dentry, int ia_valid)
 371 {
 372         if (!evm_initialized)
 373                 return;
 374
 375         if (ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID))
 376                 evm_update_evmxattr(dentry, NULL, NULL, 0);
 377         return;
 378 }
 379
 380 /*
 381  * evm_inode_init_security - initializes security.evm
 382  */
 383 int evm_inode_init_security(struct inode *inode,
 384                                  const struct xattr *lsm_xattr,
 385                                  struct xattr *evm_xattr)
 386 {
 387         struct evm_ima_xattr_data *xattr_data;
 388         int rc;
 389
 390         if (!evm_initialized || !evm_protected_xattr(lsm_xattr->name))
 391                 return 0;
 392
 393         xattr_data = kzalloc(sizeof(*xattr_data), GFP_NOFS);
 394         if (!xattr_data)
 395                 return -ENOMEM;
 396
 397         xattr_data->type = EVM_XATTR_HMAC;
 398         rc = evm_init_hmac(inode, lsm_xattr, xattr_data->digest);
 399         if (rc < 0)
 400                 goto out;
 401
 402         evm_xattr->value = xattr_data;
 403         evm_xattr->value_len = sizeof(*xattr_data);
 404         evm_xattr->name = kstrdup(XATTR_EVM_SUFFIX, GFP_NOFS);
 405         return 0;
 406 out:
 407         kfree(xattr_data);
 408         return rc;
 409 }
 410 EXPORT_SYMBOL_GPL(evm_inode_init_security);
 411
 412 static int __init init_evm(void)
 413 {
 414         int error;
 415
 416         error = evm_init_secfs();
 417         if (error < 0) {
 418                 printk(KERN_INFO "EVM: Error registering secfs\n");
 419                 goto err;
 420         }
 421
 422         return 0;
 423 err:
 424         return error;
 425 }
 426
 427 static void __exit cleanup_evm(void)
 428 {
 429         evm_cleanup_secfs();
 430         if (hmac_tfm)
 431                 crypto_free_shash(hmac_tfm);
 432         if (hash_tfm)
 433                 crypto_free_shash(hash_tfm);
 434 }
 435
 436 /*
 437  * evm_display_config - list the EVM protected security extended attributes
 438  */
 439 static int __init evm_display_config(void)
 440 {
 441         char **xattrname;
 442
 443         for (xattrname = evm_config_xattrnames; *xattrname != NULL; xattrname++)
 444                 printk(KERN_INFO "EVM: %s\n", *xattrname);
 445         return 0;
 446 }
 447
 448 pure_initcall(evm_display_config);
 449 late_initcall(init_evm);
 450
 451 MODULE_DESCRIPTION("Extended Verification Module");
 452 MODULE_LICENSE("GPL");