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 <crypto/algapi.h>
  27 #include "evm.h"
  28
  29 int evm_initialized;
  30
  31 static char *integrity_status_msg[] = {
  32         "pass", "pass_immutable", "fail", "no_label", "no_xattrs", "unknown"
  33 };
  34 char *evm_hmac = "hmac(sha1)";
  35 char *evm_hash = "sha1";
  36 int evm_hmac_attrs;
  37
  38 char *evm_config_xattrnames[] = {
  39 #ifdef CONFIG_SECURITY_SELINUX
  40         XATTR_NAME_SELINUX,
  41 #endif
  42 #ifdef CONFIG_SECURITY_SMACK
  43         XATTR_NAME_SMACK,
  44 #ifdef CONFIG_EVM_EXTRA_SMACK_XATTRS
  45         XATTR_NAME_SMACKEXEC,
  46         XATTR_NAME_SMACKTRANSMUTE,
  47         XATTR_NAME_SMACKMMAP,
  48 #endif
  49 #endif
  50 #ifdef CONFIG_IMA_APPRAISE
  51         XATTR_NAME_IMA,
  52 #endif
  53         XATTR_NAME_CAPS,
  54         NULL
  55 };
  56
  57 static int evm_fixmode;
  58 static int __init evm_set_fixmode(char *str)
  59 {
  60         if (strncmp(str, "fix", 3) == 0)
  61                 evm_fixmode = 1;
  62         return 0;
  63 }
  64 __setup("evm=", evm_set_fixmode);
  65
  66 static void __init evm_init_config(void)
  67 {
  68 #ifdef CONFIG_EVM_ATTR_FSUUID
  69         evm_hmac_attrs |= EVM_ATTR_FSUUID;
  70 #endif
  71         pr_info("HMAC attrs: 0x%x\n", evm_hmac_attrs);
  72 }
  73
  74 static int evm_find_protected_xattrs(struct dentry *dentry)
  75 {
  76         struct inode *inode = d_backing_inode(dentry);
  77         char **xattr;
  78         int error;
  79         int count = 0;
  80
  81         if (!(inode->i_opflags & IOP_XATTR))
  82                 return -EOPNOTSUPP;
  83
  84         for (xattr = evm_config_xattrnames; *xattr != NULL; xattr++) {
  85                 error = __vfs_getxattr(dentry, inode, *xattr, NULL, 0);
  86                 if (error < 0) {
  87                         if (error == -ENODATA)
  88                                 continue;
  89                         return error;
  90                 }
  91                 count++;
  92         }
  93
  94         return count;
  95 }
  96
  97 /*
  98  * evm_verify_hmac - calculate and compare the HMAC with the EVM xattr
  99  *
 100  * Compute the HMAC on the dentry's protected set of extended attributes
 101  * and compare it against the stored security.evm xattr.
 102  *
 103  * For performance:
 104  * - use the previoulsy retrieved xattr value and length to calculate the
 105  *   HMAC.)
 106  * - cache the verification result in the iint, when available.
 107  *
 108  * Returns integrity status
 109  */
 110 static enum integrity_status evm_verify_hmac(struct dentry *dentry,
 111                                              const char *xattr_name,
 112                                              char *xattr_value,
 113                                              size_t xattr_value_len,
 114                                              struct integrity_iint_cache *iint)
 115 {
 116         struct evm_ima_xattr_data *xattr_data = NULL;
 117         struct evm_ima_xattr_data calc;
 118         enum integrity_status evm_status = INTEGRITY_PASS;
 119         int rc, xattr_len;
 120
 121         if (iint && (iint->evm_status == INTEGRITY_PASS ||
 122                      iint->evm_status == INTEGRITY_PASS_IMMUTABLE))
 123                 return iint->evm_status;
 124
 125         /* if status is not PASS, try to check again - against -ENOMEM */
 126
 127         /* first need to know the sig type */
 128         rc = vfs_getxattr_alloc(dentry, XATTR_NAME_EVM, (char **)&xattr_data, 0,
 129                                 GFP_NOFS);
 130         if (rc <= 0) {
 131                 evm_status = INTEGRITY_FAIL;
 132                 if (rc == -ENODATA) {
 133                         rc = evm_find_protected_xattrs(dentry);
 134                         if (rc > 0)
 135                                 evm_status = INTEGRITY_NOLABEL;
 136                         else if (rc == 0)
 137                                 evm_status = INTEGRITY_NOXATTRS; /* new file */
 138                 } else if (rc == -EOPNOTSUPP) {
 139                         evm_status = INTEGRITY_UNKNOWN;
 140                 }
 141                 goto out;
 142         }
 143
 144         xattr_len = rc;
 145
 146         /* check value type */
 147         switch (xattr_data->type) {
 148         case EVM_XATTR_HMAC:
 149                 rc = evm_calc_hmac(dentry, xattr_name, xattr_value,
 150                                    xattr_value_len, calc.digest);
 151                 if (rc)
 152                         break;
 153                 rc = crypto_memneq(xattr_data->digest, calc.digest,
 154                             sizeof(calc.digest));
 155                 if (rc)
 156                         rc = -EINVAL;
 157                 break;
 158         case EVM_IMA_XATTR_DIGSIG:
 159         case EVM_XATTR_PORTABLE_DIGSIG:
 160                 rc = evm_calc_hash(dentry, xattr_name, xattr_value,
 161                                    xattr_value_len, xattr_data->type,
 162                                    calc.digest);
 163                 if (rc)
 164                         break;
 165                 rc = integrity_digsig_verify(INTEGRITY_KEYRING_EVM,
 166                                         (const char *)xattr_data, xattr_len,
 167                                         calc.digest, sizeof(calc.digest));
 168                 if (!rc) {
 169                         if (xattr_data->type == EVM_XATTR_PORTABLE_DIGSIG) {
 170                                 if (iint)
 171                                         iint->flags |= EVM_IMMUTABLE_DIGSIG;
 172                                 evm_status = INTEGRITY_PASS_IMMUTABLE;
 173                         } else if (!IS_RDONLY(d_backing_inode(dentry)) &&
 174                                    !IS_IMMUTABLE(d_backing_inode(dentry))) {
 175                                 evm_update_evmxattr(dentry, xattr_name,
 176                                                     xattr_value,
 177                                                     xattr_value_len);
 178                         }
 179                 }
 180                 break;
 181         default:
 182                 rc = -EINVAL;
 183                 break;
 184         }
 185
 186         if (rc)
 187                 evm_status = (rc == -ENODATA) ?
 188                                 INTEGRITY_NOXATTRS : INTEGRITY_FAIL;
 189 out:
 190         if (iint)
 191                 iint->evm_status = evm_status;
 192         kfree(xattr_data);
 193         return evm_status;
 194 }
 195
 196 static int evm_protected_xattr(const char *req_xattr_name)
 197 {
 198         char **xattrname;
 199         int namelen;
 200         int found = 0;
 201
 202         namelen = strlen(req_xattr_name);
 203         for (xattrname = evm_config_xattrnames; *xattrname != NULL; xattrname++) {
 204                 if ((strlen(*xattrname) == namelen)
 205                     && (strncmp(req_xattr_name, *xattrname, namelen) == 0)) {
 206                         found = 1;
 207                         break;
 208                 }
 209                 if (strncmp(req_xattr_name,
 210                             *xattrname + XATTR_SECURITY_PREFIX_LEN,
 211                             strlen(req_xattr_name)) == 0) {
 212                         found = 1;
 213                         break;
 214                 }
 215         }
 216         return found;
 217 }
 218
 219 /**
 220  * evm_verifyxattr - verify the integrity of the requested xattr
 221  * @dentry: object of the verify xattr
 222  * @xattr_name: requested xattr
 223  * @xattr_value: requested xattr value
 224  * @xattr_value_len: requested xattr value length
 225  *
 226  * Calculate the HMAC for the given dentry and verify it against the stored
 227  * security.evm xattr. For performance, use the xattr value and length
 228  * previously retrieved to calculate the HMAC.
 229  *
 230  * Returns the xattr integrity status.
 231  *
 232  * This function requires the caller to lock the inode's i_mutex before it
 233  * is executed.
 234  */
 235 enum integrity_status evm_verifyxattr(struct dentry *dentry,
 236                                       const char *xattr_name,
 237                                       void *xattr_value, size_t xattr_value_len,
 238                                       struct integrity_iint_cache *iint)
 239 {
 240         if (!evm_initialized || !evm_protected_xattr(xattr_name))
 241                 return INTEGRITY_UNKNOWN;
 242
 243         if (!iint) {
 244                 iint = integrity_iint_find(d_backing_inode(dentry));
 245                 if (!iint)
 246                         return INTEGRITY_UNKNOWN;
 247         }
 248         return evm_verify_hmac(dentry, xattr_name, xattr_value,
 249                                  xattr_value_len, iint);
 250 }
 251 EXPORT_SYMBOL_GPL(evm_verifyxattr);
 252
 253 /*
 254  * evm_verify_current_integrity - verify the dentry's metadata integrity
 255  * @dentry: pointer to the affected dentry
 256  *
 257  * Verify and return the dentry's metadata integrity. The exceptions are
 258  * before EVM is initialized or in 'fix' mode.
 259  */
 260 static enum integrity_status evm_verify_current_integrity(struct dentry *dentry)
 261 {
 262         struct inode *inode = d_backing_inode(dentry);
 263
 264         if (!evm_initialized || !S_ISREG(inode->i_mode) || evm_fixmode)
 265                 return 0;
 266         return evm_verify_hmac(dentry, NULL, NULL, 0, NULL);
 267 }
 268
 269 /*
 270  * evm_protect_xattr - protect the EVM extended attribute
 271  *
 272  * Prevent security.evm from being modified or removed without the
 273  * necessary permissions or when the existing value is invalid.
 274  *
 275  * The posix xattr acls are 'system' prefixed, which normally would not
 276  * affect security.evm.  An interesting side affect of writing posix xattr
 277  * acls is their modifying of the i_mode, which is included in security.evm.
 278  * For posix xattr acls only, permit security.evm, even if it currently
 279  * doesn't exist, to be updated unless the EVM signature is immutable.
 280  */
 281 static int evm_protect_xattr(struct dentry *dentry, const char *xattr_name,
 282                              const void *xattr_value, size_t xattr_value_len)
 283 {
 284         enum integrity_status evm_status;
 285
 286         if (strcmp(xattr_name, XATTR_NAME_EVM) == 0) {
 287                 if (!capable(CAP_SYS_ADMIN))
 288                         return -EPERM;
 289         } else if (!evm_protected_xattr(xattr_name)) {
 290                 if (!posix_xattr_acl(xattr_name))
 291                         return 0;
 292                 evm_status = evm_verify_current_integrity(dentry);
 293                 if ((evm_status == INTEGRITY_PASS) ||
 294                     (evm_status == INTEGRITY_NOXATTRS))
 295                         return 0;
 296                 goto out;
 297         }
 298         evm_status = evm_verify_current_integrity(dentry);
 299         if (evm_status == INTEGRITY_NOXATTRS) {
 300                 struct integrity_iint_cache *iint;
 301
 302                 iint = integrity_iint_find(d_backing_inode(dentry));
 303                 if (iint && (iint->flags & IMA_NEW_FILE))
 304                         return 0;
 305
 306                 /* exception for pseudo filesystems */
 307                 if (dentry->d_sb->s_magic == TMPFS_MAGIC
 308                     || dentry->d_sb->s_magic == SYSFS_MAGIC)
 309                         return 0;
 310
 311                 integrity_audit_msg(AUDIT_INTEGRITY_METADATA,
 312                                     dentry->d_inode, dentry->d_name.name,
 313                                     "update_metadata",
 314                                     integrity_status_msg[evm_status],
 315                                     -EPERM, 0);
 316         }
 317 out:
 318         if (evm_status != INTEGRITY_PASS)
 319                 integrity_audit_msg(AUDIT_INTEGRITY_METADATA, d_backing_inode(dentry),
 320                                     dentry->d_name.name, "appraise_metadata",
 321                                     integrity_status_msg[evm_status],
 322                                     -EPERM, 0);
 323         return evm_status == INTEGRITY_PASS ? 0 : -EPERM;
 324 }
 325
 326 /**
 327  * evm_inode_setxattr - protect the EVM extended attribute
 328  * @dentry: pointer to the affected dentry
 329  * @xattr_name: pointer to the affected extended attribute name
 330  * @xattr_value: pointer to the new extended attribute value
 331  * @xattr_value_len: pointer to the new extended attribute value length
 332  *
 333  * Before allowing the 'security.evm' protected xattr to be updated,
 334  * verify the existing value is valid.  As only the kernel should have
 335  * access to the EVM encrypted key needed to calculate the HMAC, prevent
 336  * userspace from writing HMAC value.  Writing 'security.evm' requires
 337  * requires CAP_SYS_ADMIN privileges.
 338  */
 339 int evm_inode_setxattr(struct dentry *dentry, const char *xattr_name,
 340                        const void *xattr_value, size_t xattr_value_len)
 341 {
 342         const struct evm_ima_xattr_data *xattr_data = xattr_value;
 343
 344         if (strcmp(xattr_name, XATTR_NAME_EVM) == 0) {
 345                 if (!xattr_value_len)
 346                         return -EINVAL;
 347                 if (xattr_data->type != EVM_IMA_XATTR_DIGSIG &&
 348                     xattr_data->type != EVM_XATTR_PORTABLE_DIGSIG)
 349                         return -EPERM;
 350         }
 351         return evm_protect_xattr(dentry, xattr_name, xattr_value,
 352                                  xattr_value_len);
 353 }
 354
 355 /**
 356  * evm_inode_removexattr - protect the EVM extended attribute
 357  * @dentry: pointer to the affected dentry
 358  * @xattr_name: pointer to the affected extended attribute name
 359  *
 360  * Removing 'security.evm' requires CAP_SYS_ADMIN privileges and that
 361  * the current value is valid.
 362  */
 363 int evm_inode_removexattr(struct dentry *dentry, const char *xattr_name)
 364 {
 365         return evm_protect_xattr(dentry, xattr_name, NULL, 0);
 366 }
 367
 368 static void evm_reset_status(struct inode *inode)
 369 {
 370         struct integrity_iint_cache *iint;
 371
 372         iint = integrity_iint_find(inode);
 373         if (iint)
 374                 iint->evm_status = INTEGRITY_UNKNOWN;
 375 }
 376
 377 /**
 378  * evm_inode_post_setxattr - update 'security.evm' to reflect the changes
 379  * @dentry: pointer to the affected dentry
 380  * @xattr_name: pointer to the affected extended attribute name
 381  * @xattr_value: pointer to the new extended attribute value
 382  * @xattr_value_len: pointer to the new extended attribute value length
 383  *
 384  * Update the HMAC stored in 'security.evm' to reflect the change.
 385  *
 386  * No need to take the i_mutex lock here, as this function is called from
 387  * __vfs_setxattr_noperm().  The caller of which has taken the inode's
 388  * i_mutex lock.
 389  */
 390 void evm_inode_post_setxattr(struct dentry *dentry, const char *xattr_name,
 391                              const void *xattr_value, size_t xattr_value_len)
 392 {
 393         if (!evm_initialized || (!evm_protected_xattr(xattr_name)
 394                                  && !posix_xattr_acl(xattr_name)))
 395                 return;
 396
 397         evm_reset_status(dentry->d_inode);
 398
 399         evm_update_evmxattr(dentry, xattr_name, xattr_value, xattr_value_len);
 400 }
 401
 402 /**
 403  * evm_inode_post_removexattr - update 'security.evm' after removing the xattr
 404  * @dentry: pointer to the affected dentry
 405  * @xattr_name: pointer to the affected extended attribute name
 406  *
 407  * Update the HMAC stored in 'security.evm' to reflect removal of the xattr.
 408  *
 409  * No need to take the i_mutex lock here, as this function is called from
 410  * vfs_removexattr() which takes the i_mutex.
 411  */
 412 void evm_inode_post_removexattr(struct dentry *dentry, const char *xattr_name)
 413 {
 414         if (!evm_initialized || !evm_protected_xattr(xattr_name))
 415                 return;
 416
 417         evm_reset_status(dentry->d_inode);
 418
 419         evm_update_evmxattr(dentry, xattr_name, NULL, 0);
 420 }
 421
 422 /**
 423  * evm_inode_setattr - prevent updating an invalid EVM extended attribute
 424  * @dentry: pointer to the affected dentry
 425  *
 426  * Permit update of file attributes when files have a valid EVM signature,
 427  * except in the case of them having an immutable portable signature.
 428  */
 429 int evm_inode_setattr(struct dentry *dentry, struct iattr *attr)
 430 {
 431         unsigned int ia_valid = attr->ia_valid;
 432         enum integrity_status evm_status;
 433
 434         if (!(ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID)))
 435                 return 0;
 436         evm_status = evm_verify_current_integrity(dentry);
 437         if ((evm_status == INTEGRITY_PASS) ||
 438             (evm_status == INTEGRITY_NOXATTRS))
 439                 return 0;
 440         integrity_audit_msg(AUDIT_INTEGRITY_METADATA, d_backing_inode(dentry),
 441                             dentry->d_name.name, "appraise_metadata",
 442                             integrity_status_msg[evm_status], -EPERM, 0);
 443         return -EPERM;
 444 }
 445
 446 /**
 447  * evm_inode_post_setattr - update 'security.evm' after modifying metadata
 448  * @dentry: pointer to the affected dentry
 449  * @ia_valid: for the UID and GID status
 450  *
 451  * For now, update the HMAC stored in 'security.evm' to reflect UID/GID
 452  * changes.
 453  *
 454  * This function is called from notify_change(), which expects the caller
 455  * to lock the inode's i_mutex.
 456  */
 457 void evm_inode_post_setattr(struct dentry *dentry, int ia_valid)
 458 {
 459         if (!evm_initialized)
 460                 return;
 461
 462         if (ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID))
 463                 evm_update_evmxattr(dentry, NULL, NULL, 0);
 464 }
 465
 466 /*
 467  * evm_inode_init_security - initializes security.evm
 468  */
 469 int evm_inode_init_security(struct inode *inode,
 470                                  const struct xattr *lsm_xattr,
 471                                  struct xattr *evm_xattr)
 472 {
 473         struct evm_ima_xattr_data *xattr_data;
 474         int rc;
 475
 476         if (!evm_initialized || !evm_protected_xattr(lsm_xattr->name))
 477                 return 0;
 478
 479         xattr_data = kzalloc(sizeof(*xattr_data), GFP_NOFS);
 480         if (!xattr_data)
 481                 return -ENOMEM;
 482
 483         xattr_data->type = EVM_XATTR_HMAC;
 484         rc = evm_init_hmac(inode, lsm_xattr, xattr_data->digest);
 485         if (rc < 0)
 486                 goto out;
 487
 488         evm_xattr->value = xattr_data;
 489         evm_xattr->value_len = sizeof(*xattr_data);
 490         evm_xattr->name = XATTR_EVM_SUFFIX;
 491         return 0;
 492 out:
 493         kfree(xattr_data);
 494         return rc;
 495 }
 496 EXPORT_SYMBOL_GPL(evm_inode_init_security);
 497
 498 #ifdef CONFIG_EVM_LOAD_X509
 499 void __init evm_load_x509(void)
 500 {
 501         int rc;
 502
 503         rc = integrity_load_x509(INTEGRITY_KEYRING_EVM, CONFIG_EVM_X509_PATH);
 504         if (!rc)
 505                 evm_initialized |= EVM_INIT_X509;
 506 }
 507 #endif
 508
 509 static int __init init_evm(void)
 510 {
 511         int error;
 512
 513         evm_init_config();
 514
 515         error = integrity_init_keyring(INTEGRITY_KEYRING_EVM);
 516         if (error)
 517                 return error;
 518
 519         error = evm_init_secfs();
 520         if (error < 0) {
 521                 pr_info("Error registering secfs\n");
 522                 return error;
 523         }
 524
 525         return 0;
 526 }
 527
 528 /*
 529  * evm_display_config - list the EVM protected security extended attributes
 530  */
 531 static int __init evm_display_config(void)
 532 {
 533         char **xattrname;
 534
 535         for (xattrname = evm_config_xattrnames; *xattrname != NULL; xattrname++)
 536                 pr_info("%s\n", *xattrname);
 537         return 0;
 538 }
 539
 540 pure_initcall(evm_display_config);
 541 late_initcall(init_evm);
 542
 543 MODULE_DESCRIPTION("Extended Verification Module");
 544 MODULE_LICENSE("GPL");