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 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  18
  19 #include <linux/module.h>
  20 #include <linux/crypto.h>
  21 #include <linux/audit.h>
  22 #include <linux/xattr.h>
  23 #include <linux/integrity.h>
  24 #include <linux/evm.h>
  25 #include <crypto/hash.h>
  26 #include "evm.h"
  27
  28 int evm_initialized;
  29
  30 static char *integrity_status_msg[] = {
  31         "pass", "fail", "no_label", "no_xattrs", "unknown"
  32 };
  33 char *evm_hmac = "hmac(sha1)";
  34 char *evm_hash = "sha1";
  35 int evm_hmac_version = CONFIG_EVM_HMAC_VERSION;
  36
  37 char *evm_config_xattrnames[] = {
  38 #ifdef CONFIG_SECURITY_SELINUX
  39         XATTR_NAME_SELINUX,
  40 #endif
  41 #ifdef CONFIG_SECURITY_SMACK
  42         XATTR_NAME_SMACK,
  43 #endif
  44 #ifdef CONFIG_IMA_APPRAISE
  45         XATTR_NAME_IMA,
  46 #endif
  47         XATTR_NAME_CAPS,
  48         NULL
  49 };
  50
  51 static int evm_fixmode;
  52 static int __init evm_set_fixmode(char *str)
  53 {
  54         if (strncmp(str, "fix", 3) == 0)
  55                 evm_fixmode = 1;
  56         return 0;
  57 }
  58 __setup("evm=", evm_set_fixmode);
  59
  60 static int evm_find_protected_xattrs(struct dentry *dentry)
  61 {
  62         struct inode *inode = dentry->d_inode;
  63         char **xattr;
  64         int error;
  65         int count = 0;
  66
  67         if (!inode->i_op->getxattr)
  68                 return -EOPNOTSUPP;
  69
  70         for (xattr = evm_config_xattrnames; *xattr != NULL; xattr++) {
  71                 error = inode->i_op->getxattr(dentry, *xattr, NULL, 0);
  72                 if (error < 0) {
  73                         if (error == -ENODATA)
  74                                 continue;
  75                         return error;
  76                 }
  77                 count++;
  78         }
  79
  80         return count;
  81 }
  82
  83 /*
  84  * evm_verify_hmac - calculate and compare the HMAC with the EVM xattr
  85  *
  86  * Compute the HMAC on the dentry's protected set of extended attributes
  87  * and compare it against the stored security.evm xattr.
  88  *
  89  * For performance:
  90  * - use the previoulsy retrieved xattr value and length to calculate the
  91  *   HMAC.)
  92  * - cache the verification result in the iint, when available.
  93  *
  94  * Returns integrity status
  95  */
  96 static enum integrity_status evm_verify_hmac(struct dentry *dentry,
  97                                              const char *xattr_name,
  98                                              char *xattr_value,
  99                                              size_t xattr_value_len,
 100                                              struct integrity_iint_cache *iint)
 101 {
 102         struct evm_ima_xattr_data *xattr_data = NULL;
 103         struct evm_ima_xattr_data calc;
 104         enum integrity_status evm_status = INTEGRITY_PASS;
 105         int rc, xattr_len;
 106
 107         if (iint && iint->evm_status == INTEGRITY_PASS)
 108                 return iint->evm_status;
 109
 110         /* if status is not PASS, try to check again - against -ENOMEM */
 111
 112         /* first need to know the sig type */
 113         rc = vfs_getxattr_alloc(dentry, XATTR_NAME_EVM, (char **)&xattr_data, 0,
 114                                 GFP_NOFS);
 115         if (rc <= 0) {
 116                 if (rc == 0)
 117                         evm_status = INTEGRITY_FAIL; /* empty */
 118                 else if (rc == -ENODATA) {
 119                         rc = evm_find_protected_xattrs(dentry);
 120                         if (rc > 0)
 121                                 evm_status = INTEGRITY_NOLABEL;
 122                         else if (rc == 0)
 123                                 evm_status = INTEGRITY_NOXATTRS; /* new file */
 124                 }
 125                 goto out;
 126         }
 127
 128         xattr_len = rc;
 129
 130         /* check value type */
 131         switch (xattr_data->type) {
 132         case EVM_XATTR_HMAC:
 133                 rc = evm_calc_hmac(dentry, xattr_name, xattr_value,
 134                                    xattr_value_len, calc.digest);
 135                 if (rc)
 136                         break;
 137                 rc = memcmp(xattr_data->digest, calc.digest,
 138                             sizeof(calc.digest));
 139                 if (rc)
 140                         rc = -EINVAL;
 141                 break;
 142         case EVM_IMA_XATTR_DIGSIG:
 143                 rc = evm_calc_hash(dentry, xattr_name, xattr_value,
 144                                 xattr_value_len, calc.digest);
 145                 if (rc)
 146                         break;
 147                 rc = integrity_digsig_verify(INTEGRITY_KEYRING_EVM,
 148                                         (const char *)xattr_data, xattr_len,
 149                                         calc.digest, sizeof(calc.digest));
 150                 if (!rc) {
 151                         /* we probably want to replace rsa with hmac here */
 152                         evm_update_evmxattr(dentry, xattr_name, xattr_value,
 153                                    xattr_value_len);
 154                 }
 155                 break;
 156         default:
 157                 rc = -EINVAL;
 158                 break;
 159         }
 160
 161         if (rc)
 162                 evm_status = (rc == -ENODATA) ?
 163                                 INTEGRITY_NOXATTRS : INTEGRITY_FAIL;
 164 out:
 165         if (iint)
 166                 iint->evm_status = evm_status;
 167         kfree(xattr_data);
 168         return evm_status;
 169 }
 170
 171 static int evm_protected_xattr(const char *req_xattr_name)
 172 {
 173         char **xattrname;
 174         int namelen;
 175         int found = 0;
 176
 177         namelen = strlen(req_xattr_name);
 178         for (xattrname = evm_config_xattrnames; *xattrname != NULL; xattrname++) {
 179                 if ((strlen(*xattrname) == namelen)
 180                     && (strncmp(req_xattr_name, *xattrname, namelen) == 0)) {
 181                         found = 1;
 182                         break;
 183                 }
 184                 if (strncmp(req_xattr_name,
 185                             *xattrname + XATTR_SECURITY_PREFIX_LEN,
 186                             strlen(req_xattr_name)) == 0) {
 187                         found = 1;
 188                         break;
 189                 }
 190         }
 191         return found;
 192 }
 193
 194 /**
 195  * evm_verifyxattr - verify the integrity of the requested xattr
 196  * @dentry: object of the verify xattr
 197  * @xattr_name: requested xattr
 198  * @xattr_value: requested xattr value
 199  * @xattr_value_len: requested xattr value length
 200  *
 201  * Calculate the HMAC for the given dentry and verify it against the stored
 202  * security.evm xattr. For performance, use the xattr value and length
 203  * previously retrieved to calculate the HMAC.
 204  *
 205  * Returns the xattr integrity status.
 206  *
 207  * This function requires the caller to lock the inode's i_mutex before it
 208  * is executed.
 209  */
 210 enum integrity_status evm_verifyxattr(struct dentry *dentry,
 211                                       const char *xattr_name,
 212                                       void *xattr_value, size_t xattr_value_len,
 213                                       struct integrity_iint_cache *iint)
 214 {
 215         if (!evm_initialized || !evm_protected_xattr(xattr_name))
 216                 return INTEGRITY_UNKNOWN;
 217
 218         if (!iint) {
 219                 iint = integrity_iint_find(dentry->d_inode);
 220                 if (!iint)
 221                         return INTEGRITY_UNKNOWN;
 222         }
 223         return evm_verify_hmac(dentry, xattr_name, xattr_value,
 224                                  xattr_value_len, iint);
 225 }
 226 EXPORT_SYMBOL_GPL(evm_verifyxattr);
 227
 228 /*
 229  * evm_verify_current_integrity - verify the dentry's metadata integrity
 230  * @dentry: pointer to the affected dentry
 231  *
 232  * Verify and return the dentry's metadata integrity. The exceptions are
 233  * before EVM is initialized or in 'fix' mode.
 234  */
 235 static enum integrity_status evm_verify_current_integrity(struct dentry *dentry)
 236 {
 237         struct inode *inode = dentry->d_inode;
 238
 239         if (!evm_initialized || !S_ISREG(inode->i_mode) || evm_fixmode)
 240                 return 0;
 241         return evm_verify_hmac(dentry, NULL, NULL, 0, NULL);
 242 }
 243
 244 /*
 245  * evm_protect_xattr - protect the EVM extended attribute
 246  *
 247  * Prevent security.evm from being modified or removed without the
 248  * necessary permissions or when the existing value is invalid.
 249  *
 250  * The posix xattr acls are 'system' prefixed, which normally would not
 251  * affect security.evm.  An interesting side affect of writing posix xattr
 252  * acls is their modifying of the i_mode, which is included in security.evm.
 253  * For posix xattr acls only, permit security.evm, even if it currently
 254  * doesn't exist, to be updated.
 255  */
 256 static int evm_protect_xattr(struct dentry *dentry, const char *xattr_name,
 257                              const void *xattr_value, size_t xattr_value_len)
 258 {
 259         enum integrity_status evm_status;
 260
 261         if (strcmp(xattr_name, XATTR_NAME_EVM) == 0) {
 262                 if (!capable(CAP_SYS_ADMIN))
 263                         return -EPERM;
 264         } else if (!evm_protected_xattr(xattr_name)) {
 265                 if (!posix_xattr_acl(xattr_name))
 266                         return 0;
 267                 evm_status = evm_verify_current_integrity(dentry);
 268                 if ((evm_status == INTEGRITY_PASS) ||
 269                     (evm_status == INTEGRITY_NOXATTRS))
 270                         return 0;
 271                 goto out;
 272         }
 273         evm_status = evm_verify_current_integrity(dentry);
 274 out:
 275         if (evm_status != INTEGRITY_PASS)
 276                 integrity_audit_msg(AUDIT_INTEGRITY_METADATA, dentry->d_inode,
 277                                     dentry->d_name.name, "appraise_metadata",
 278                                     integrity_status_msg[evm_status],
 279                                     -EPERM, 0);
 280         return evm_status == INTEGRITY_PASS ? 0 : -EPERM;
 281 }
 282
 283 /**
 284  * evm_inode_setxattr - protect the EVM extended attribute
 285  * @dentry: pointer to the affected dentry
 286  * @xattr_name: pointer to the affected extended attribute name
 287  * @xattr_value: pointer to the new extended attribute value
 288  * @xattr_value_len: pointer to the new extended attribute value length
 289  *
 290  * Updating 'security.evm' requires CAP_SYS_ADMIN privileges and that
 291  * the current value is valid.
 292  */
 293 int evm_inode_setxattr(struct dentry *dentry, const char *xattr_name,
 294                        const void *xattr_value, size_t xattr_value_len)
 295 {
 296         return evm_protect_xattr(dentry, xattr_name, xattr_value,
 297                                  xattr_value_len);
 298 }
 299
 300 /**
 301  * evm_inode_removexattr - protect the EVM extended attribute
 302  * @dentry: pointer to the affected dentry
 303  * @xattr_name: pointer to the affected extended attribute name
 304  *
 305  * Removing 'security.evm' requires CAP_SYS_ADMIN privileges and that
 306  * the current value is valid.
 307  */
 308 int evm_inode_removexattr(struct dentry *dentry, const char *xattr_name)
 309 {
 310         return evm_protect_xattr(dentry, xattr_name, NULL, 0);
 311 }
 312
 313 /**
 314  * evm_inode_post_setxattr - update 'security.evm' to reflect the changes
 315  * @dentry: pointer to the affected dentry
 316  * @xattr_name: pointer to the affected extended attribute name
 317  * @xattr_value: pointer to the new extended attribute value
 318  * @xattr_value_len: pointer to the new extended attribute value length
 319  *
 320  * Update the HMAC stored in 'security.evm' to reflect the change.
 321  *
 322  * No need to take the i_mutex lock here, as this function is called from
 323  * __vfs_setxattr_noperm().  The caller of which has taken the inode's
 324  * i_mutex lock.
 325  */
 326 void evm_inode_post_setxattr(struct dentry *dentry, const char *xattr_name,
 327                              const void *xattr_value, size_t xattr_value_len)
 328 {
 329         if (!evm_initialized || (!evm_protected_xattr(xattr_name)
 330                                  && !posix_xattr_acl(xattr_name)))
 331                 return;
 332
 333         evm_update_evmxattr(dentry, xattr_name, xattr_value, xattr_value_len);
 334         return;
 335 }
 336
 337 /**
 338  * evm_inode_post_removexattr - update 'security.evm' after removing the xattr
 339  * @dentry: pointer to the affected dentry
 340  * @xattr_name: pointer to the affected extended attribute name
 341  *
 342  * Update the HMAC stored in 'security.evm' to reflect removal of the xattr.
 343  */
 344 void evm_inode_post_removexattr(struct dentry *dentry, const char *xattr_name)
 345 {
 346         struct inode *inode = dentry->d_inode;
 347
 348         if (!evm_initialized || !evm_protected_xattr(xattr_name))
 349                 return;
 350
 351         mutex_lock(&inode->i_mutex);
 352         evm_update_evmxattr(dentry, xattr_name, NULL, 0);
 353         mutex_unlock(&inode->i_mutex);
 354         return;
 355 }
 356
 357 /**
 358  * evm_inode_setattr - prevent updating an invalid EVM extended attribute
 359  * @dentry: pointer to the affected dentry
 360  */
 361 int evm_inode_setattr(struct dentry *dentry, struct iattr *attr)
 362 {
 363         unsigned int ia_valid = attr->ia_valid;
 364         enum integrity_status evm_status;
 365
 366         if (!(ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID)))
 367                 return 0;
 368         evm_status = evm_verify_current_integrity(dentry);
 369         if ((evm_status == INTEGRITY_PASS) ||
 370             (evm_status == INTEGRITY_NOXATTRS))
 371                 return 0;
 372         integrity_audit_msg(AUDIT_INTEGRITY_METADATA, dentry->d_inode,
 373                             dentry->d_name.name, "appraise_metadata",
 374                             integrity_status_msg[evm_status], -EPERM, 0);
 375         return -EPERM;
 376 }
 377
 378 /**
 379  * evm_inode_post_setattr - update 'security.evm' after modifying metadata
 380  * @dentry: pointer to the affected dentry
 381  * @ia_valid: for the UID and GID status
 382  *
 383  * For now, update the HMAC stored in 'security.evm' to reflect UID/GID
 384  * changes.
 385  *
 386  * This function is called from notify_change(), which expects the caller
 387  * to lock the inode's i_mutex.
 388  */
 389 void evm_inode_post_setattr(struct dentry *dentry, int ia_valid)
 390 {
 391         if (!evm_initialized)
 392                 return;
 393
 394         if (ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID))
 395                 evm_update_evmxattr(dentry, NULL, NULL, 0);
 396         return;
 397 }
 398
 399 /*
 400  * evm_inode_init_security - initializes security.evm
 401  */
 402 int evm_inode_init_security(struct inode *inode,
 403                                  const struct xattr *lsm_xattr,
 404                                  struct xattr *evm_xattr)
 405 {
 406         struct evm_ima_xattr_data *xattr_data;
 407         int rc;
 408
 409         if (!evm_initialized || !evm_protected_xattr(lsm_xattr->name))
 410                 return 0;
 411
 412         xattr_data = kzalloc(sizeof(*xattr_data), GFP_NOFS);
 413         if (!xattr_data)
 414                 return -ENOMEM;
 415
 416         xattr_data->type = EVM_XATTR_HMAC;
 417         rc = evm_init_hmac(inode, lsm_xattr, xattr_data->digest);
 418         if (rc < 0)
 419                 goto out;
 420
 421         evm_xattr->value = xattr_data;
 422         evm_xattr->value_len = sizeof(*xattr_data);
 423         evm_xattr->name = XATTR_EVM_SUFFIX;
 424         return 0;
 425 out:
 426         kfree(xattr_data);
 427         return rc;
 428 }
 429 EXPORT_SYMBOL_GPL(evm_inode_init_security);
 430
 431 static int __init init_evm(void)
 432 {
 433         int error;
 434
 435         error = evm_init_secfs();
 436         if (error < 0) {
 437                 pr_info("Error registering secfs\n");
 438                 goto err;
 439         }
 440
 441         return 0;
 442 err:
 443         return error;
 444 }
 445
 446 /*
 447  * evm_display_config - list the EVM protected security extended attributes
 448  */
 449 static int __init evm_display_config(void)
 450 {
 451         char **xattrname;
 452
 453         for (xattrname = evm_config_xattrnames; *xattrname != NULL; xattrname++)
 454                 pr_info("%s\n", *xattrname);
 455         return 0;
 456 }
 457
 458 pure_initcall(evm_display_config);
 459 late_initcall(init_evm);
 460
 461 MODULE_DESCRIPTION("Extended Verification Module");
 462 MODULE_LICENSE("GPL");