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