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 <linux/magic.h>
  26
  27 #include <crypto/hash.h>
  28 #include <crypto/algapi.h>
  29 #include "evm.h"
  30
  31 int evm_initialized;
  32
  33 static char *integrity_status_msg[] = {
  34         "pass", "pass_immutable", "fail", "no_label", "no_xattrs", "unknown"
  35 };
  36 char *evm_hmac = "hmac(sha1)";
  37 char *evm_hash = "sha1";
  38 int evm_hmac_attrs;
  39
  40 char *evm_config_xattrnames[] = {
  41 #ifdef CONFIG_SECURITY_SELINUX
  42         XATTR_NAME_SELINUX,
  43 #endif
  44 #ifdef CONFIG_SECURITY_SMACK
  45         XATTR_NAME_SMACK,
  46 #ifdef CONFIG_EVM_EXTRA_SMACK_XATTRS
  47         XATTR_NAME_SMACKEXEC,
  48         XATTR_NAME_SMACKTRANSMUTE,
  49         XATTR_NAME_SMACKMMAP,
  50 #endif
  51 #endif
  52 #ifdef CONFIG_SECURITY_APPARMOR
  53         XATTR_NAME_APPARMOR,
  54 #endif
  55 #ifdef CONFIG_IMA_APPRAISE
  56         XATTR_NAME_IMA,
  57 #endif
  58         XATTR_NAME_CAPS,
  59         NULL
  60 };
  61
  62 static int evm_fixmode;
  63 static int __init evm_set_fixmode(char *str)
  64 {
  65         if (strncmp(str, "fix", 3) == 0)
  66                 evm_fixmode = 1;
  67         return 0;
  68 }
  69 __setup("evm=", evm_set_fixmode);
  70
  71 static void __init evm_init_config(void)
  72 {
  73 #ifdef CONFIG_EVM_ATTR_FSUUID
  74         evm_hmac_attrs |= EVM_ATTR_FSUUID;
  75 #endif
  76         pr_info("HMAC attrs: 0x%x\n", evm_hmac_attrs);
  77 }
  78
  79 static bool evm_key_loaded(void)
  80 {
  81         return (bool)(evm_initialized & EVM_KEY_MASK);
  82 }
  83
  84 static int evm_find_protected_xattrs(struct dentry *dentry)
  85 {
  86         struct inode *inode = d_backing_inode(dentry);
  87         char **xattr;
  88         int error;
  89         int count = 0;
  90
  91         if (!(inode->i_opflags & IOP_XATTR))
  92                 return -EOPNOTSUPP;
  93
  94         for (xattr = evm_config_xattrnames; *xattr != NULL; xattr++) {
  95                 error = __vfs_getxattr(dentry, inode, *xattr, NULL, 0);
  96                 if (error < 0) {
  97                         if (error == -ENODATA)
  98                                 continue;
  99                         return error;
 100                 }
 101                 count++;
 102         }
 103
 104         return count;
 105 }
 106
 107 /*
 108  * evm_verify_hmac - calculate and compare the HMAC with the EVM xattr
 109  *
 110  * Compute the HMAC on the dentry's protected set of extended attributes
 111  * and compare it against the stored security.evm xattr.
 112  *
 113  * For performance:
 114  * - use the previoulsy retrieved xattr value and length to calculate the
 115  *   HMAC.)
 116  * - cache the verification result in the iint, when available.
 117  *
 118  * Returns integrity status
 119  */
 120 static enum integrity_status evm_verify_hmac(struct dentry *dentry,
 121                                              const char *xattr_name,
 122                                              char *xattr_value,
 123                                              size_t xattr_value_len,
 124                                              struct integrity_iint_cache *iint)
 125 {
 126         struct evm_ima_xattr_data *xattr_data = NULL;
 127         struct evm_ima_xattr_data calc;
 128         enum integrity_status evm_status = INTEGRITY_PASS;
 129         int rc, xattr_len;
 130
 131         if (iint && (iint->evm_status == INTEGRITY_PASS ||
 132                      iint->evm_status == INTEGRITY_PASS_IMMUTABLE))
 133                 return iint->evm_status;
 134
 135         /* if status is not PASS, try to check again - against -ENOMEM */
 136
 137         /* first need to know the sig type */
 138         rc = vfs_getxattr_alloc(dentry, XATTR_NAME_EVM, (char **)&xattr_data, 0,
 139                                 GFP_NOFS);
 140         if (rc <= 0) {
 141                 evm_status = INTEGRITY_FAIL;
 142                 if (rc == -ENODATA) {
 143                         rc = evm_find_protected_xattrs(dentry);
 144                         if (rc > 0)
 145                                 evm_status = INTEGRITY_NOLABEL;
 146                         else if (rc == 0)
 147                                 evm_status = INTEGRITY_NOXATTRS; /* new file */
 148                 } else if (rc == -EOPNOTSUPP) {
 149                         evm_status = INTEGRITY_UNKNOWN;
 150                 }
 151                 goto out;
 152         }
 153
 154         xattr_len = rc;
 155
 156         /* check value type */
 157         switch (xattr_data->type) {
 158         case EVM_XATTR_HMAC:
 159                 if (xattr_len != sizeof(struct evm_ima_xattr_data)) {
 160                         evm_status = INTEGRITY_FAIL;
 161                         goto out;
 162                 }
 163                 rc = evm_calc_hmac(dentry, xattr_name, xattr_value,
 164                                    xattr_value_len, calc.digest);
 165                 if (rc)
 166                         break;
 167                 rc = crypto_memneq(xattr_data->digest, calc.digest,
 168                             sizeof(calc.digest));
 169                 if (rc)
 170                         rc = -EINVAL;
 171                 break;
 172         case EVM_IMA_XATTR_DIGSIG:
 173         case EVM_XATTR_PORTABLE_DIGSIG:
 174                 rc = evm_calc_hash(dentry, xattr_name, xattr_value,
 175                                    xattr_value_len, xattr_data->type,
 176                                    calc.digest);
 177                 if (rc)
 178                         break;
 179                 rc = integrity_digsig_verify(INTEGRITY_KEYRING_EVM,
 180                                         (const char *)xattr_data, xattr_len,
 181                                         calc.digest, sizeof(calc.digest));
 182                 if (!rc) {
 183                         if (xattr_data->type == EVM_XATTR_PORTABLE_DIGSIG) {
 184                                 if (iint)
 185                                         iint->flags |= EVM_IMMUTABLE_DIGSIG;
 186                                 evm_status = INTEGRITY_PASS_IMMUTABLE;
 187                         } else if (!IS_RDONLY(d_backing_inode(dentry)) &&
 188                                    !IS_IMMUTABLE(d_backing_inode(dentry))) {
 189                                 evm_update_evmxattr(dentry, xattr_name,
 190                                                     xattr_value,
 191                                                     xattr_value_len);
 192                         }
 193                 }
 194                 break;
 195         default:
 196                 rc = -EINVAL;
 197                 break;
 198         }
 199
 200         if (rc)
 201                 evm_status = (rc == -ENODATA) ?
 202                                 INTEGRITY_NOXATTRS : INTEGRITY_FAIL;
 203 out:
 204         if (iint)
 205                 iint->evm_status = evm_status;
 206         kfree(xattr_data);
 207         return evm_status;
 208 }
 209
 210 static int evm_protected_xattr(const char *req_xattr_name)
 211 {
 212         char **xattrname;
 213         int namelen;
 214         int found = 0;
 215
 216         namelen = strlen(req_xattr_name);
 217         for (xattrname = evm_config_xattrnames; *xattrname != NULL; xattrname++) {
 218                 if ((strlen(*xattrname) == namelen)
 219                     && (strncmp(req_xattr_name, *xattrname, namelen) == 0)) {
 220                         found = 1;
 221                         break;
 222                 }
 223                 if (strncmp(req_xattr_name,
 224                             *xattrname + XATTR_SECURITY_PREFIX_LEN,
 225                             strlen(req_xattr_name)) == 0) {
 226                         found = 1;
 227                         break;
 228                 }
 229         }
 230         return found;
 231 }
 232
 233 /**
 234  * evm_verifyxattr - verify the integrity of the requested xattr
 235  * @dentry: object of the verify xattr
 236  * @xattr_name: requested xattr
 237  * @xattr_value: requested xattr value
 238  * @xattr_value_len: requested xattr value length
 239  *
 240  * Calculate the HMAC for the given dentry and verify it against the stored
 241  * security.evm xattr. For performance, use the xattr value and length
 242  * previously retrieved to calculate the HMAC.
 243  *
 244  * Returns the xattr integrity status.
 245  *
 246  * This function requires the caller to lock the inode's i_mutex before it
 247  * is executed.
 248  */
 249 enum integrity_status evm_verifyxattr(struct dentry *dentry,
 250                                       const char *xattr_name,
 251                                       void *xattr_value, size_t xattr_value_len,
 252                                       struct integrity_iint_cache *iint)
 253 {
 254         if (!evm_key_loaded() || !evm_protected_xattr(xattr_name))
 255                 return INTEGRITY_UNKNOWN;
 256
 257         if (!iint) {
 258                 iint = integrity_iint_find(d_backing_inode(dentry));
 259                 if (!iint)
 260                         return INTEGRITY_UNKNOWN;
 261         }
 262         return evm_verify_hmac(dentry, xattr_name, xattr_value,
 263                                  xattr_value_len, iint);
 264 }
 265 EXPORT_SYMBOL_GPL(evm_verifyxattr);
 266
 267 /*
 268  * evm_verify_current_integrity - verify the dentry's metadata integrity
 269  * @dentry: pointer to the affected dentry
 270  *
 271  * Verify and return the dentry's metadata integrity. The exceptions are
 272  * before EVM is initialized or in 'fix' mode.
 273  */
 274 static enum integrity_status evm_verify_current_integrity(struct dentry *dentry)
 275 {
 276         struct inode *inode = d_backing_inode(dentry);
 277
 278         if (!evm_key_loaded() || !S_ISREG(inode->i_mode) || evm_fixmode)
 279                 return 0;
 280         return evm_verify_hmac(dentry, NULL, NULL, 0, NULL);
 281 }
 282
 283 /*
 284  * evm_protect_xattr - protect the EVM extended attribute
 285  *
 286  * Prevent security.evm from being modified or removed without the
 287  * necessary permissions or when the existing value is invalid.
 288  *
 289  * The posix xattr acls are 'system' prefixed, which normally would not
 290  * affect security.evm.  An interesting side affect of writing posix xattr
 291  * acls is their modifying of the i_mode, which is included in security.evm.
 292  * For posix xattr acls only, permit security.evm, even if it currently
 293  * doesn't exist, to be updated unless the EVM signature is immutable.
 294  */
 295 static int evm_protect_xattr(struct dentry *dentry, const char *xattr_name,
 296                              const void *xattr_value, size_t xattr_value_len)
 297 {
 298         enum integrity_status evm_status;
 299
 300         if (strcmp(xattr_name, XATTR_NAME_EVM) == 0) {
 301                 if (!capable(CAP_SYS_ADMIN))
 302                         return -EPERM;
 303         } else if (!evm_protected_xattr(xattr_name)) {
 304                 if (!posix_xattr_acl(xattr_name))
 305                         return 0;
 306                 evm_status = evm_verify_current_integrity(dentry);
 307                 if ((evm_status == INTEGRITY_PASS) ||
 308                     (evm_status == INTEGRITY_NOXATTRS))
 309                         return 0;
 310                 goto out;
 311         }
 312
 313         evm_status = evm_verify_current_integrity(dentry);
 314         if (evm_status == INTEGRITY_NOXATTRS) {
 315                 struct integrity_iint_cache *iint;
 316
 317                 iint = integrity_iint_find(d_backing_inode(dentry));
 318                 if (iint && (iint->flags & IMA_NEW_FILE))
 319                         return 0;
 320
 321                 /* exception for pseudo filesystems */
 322                 if (dentry->d_sb->s_magic == TMPFS_MAGIC
 323                     || dentry->d_sb->s_magic == SYSFS_MAGIC)
 324                         return 0;
 325
 326                 integrity_audit_msg(AUDIT_INTEGRITY_METADATA,
 327                                     dentry->d_inode, dentry->d_name.name,
 328                                     "update_metadata",
 329                                     integrity_status_msg[evm_status],
 330                                     -EPERM, 0);
 331         }
 332 out:
 333         if (evm_status != INTEGRITY_PASS)
 334                 integrity_audit_msg(AUDIT_INTEGRITY_METADATA, d_backing_inode(dentry),
 335                                     dentry->d_name.name, "appraise_metadata",
 336                                     integrity_status_msg[evm_status],
 337                                     -EPERM, 0);
 338         return evm_status == INTEGRITY_PASS ? 0 : -EPERM;
 339 }
 340
 341 /**
 342  * evm_inode_setxattr - protect the EVM extended attribute
 343  * @dentry: pointer to the affected dentry
 344  * @xattr_name: pointer to the affected extended attribute name
 345  * @xattr_value: pointer to the new extended attribute value
 346  * @xattr_value_len: pointer to the new extended attribute value length
 347  *
 348  * Before allowing the 'security.evm' protected xattr to be updated,
 349  * verify the existing value is valid.  As only the kernel should have
 350  * access to the EVM encrypted key needed to calculate the HMAC, prevent
 351  * userspace from writing HMAC value.  Writing 'security.evm' requires
 352  * requires CAP_SYS_ADMIN privileges.
 353  */
 354 int evm_inode_setxattr(struct dentry *dentry, const char *xattr_name,
 355                        const void *xattr_value, size_t xattr_value_len)
 356 {
 357         const struct evm_ima_xattr_data *xattr_data = xattr_value;
 358
 359         /* Policy permits modification of the protected xattrs even though
 360          * there's no HMAC key loaded
 361          */
 362         if (evm_initialized & EVM_ALLOW_METADATA_WRITES)
 363                 return 0;
 364
 365         if (strcmp(xattr_name, XATTR_NAME_EVM) == 0) {
 366                 if (!xattr_value_len)
 367                         return -EINVAL;
 368                 if (xattr_data->type != EVM_IMA_XATTR_DIGSIG &&
 369                     xattr_data->type != EVM_XATTR_PORTABLE_DIGSIG)
 370                         return -EPERM;
 371         }
 372         return evm_protect_xattr(dentry, xattr_name, xattr_value,
 373                                  xattr_value_len);
 374 }
 375
 376 /**
 377  * evm_inode_removexattr - protect the EVM extended attribute
 378  * @dentry: pointer to the affected dentry
 379  * @xattr_name: pointer to the affected extended attribute name
 380  *
 381  * Removing 'security.evm' requires CAP_SYS_ADMIN privileges and that
 382  * the current value is valid.
 383  */
 384 int evm_inode_removexattr(struct dentry *dentry, const char *xattr_name)
 385 {
 386         /* Policy permits modification of the protected xattrs even though
 387          * there's no HMAC key loaded
 388          */
 389         if (evm_initialized & EVM_ALLOW_METADATA_WRITES)
 390                 return 0;
 391
 392         return evm_protect_xattr(dentry, xattr_name, NULL, 0);
 393 }
 394
 395 static void evm_reset_status(struct inode *inode)
 396 {
 397         struct integrity_iint_cache *iint;
 398
 399         iint = integrity_iint_find(inode);
 400         if (iint)
 401                 iint->evm_status = INTEGRITY_UNKNOWN;
 402 }
 403
 404 /**
 405  * evm_inode_post_setxattr - update 'security.evm' to reflect the changes
 406  * @dentry: pointer to the affected dentry
 407  * @xattr_name: pointer to the affected extended attribute name
 408  * @xattr_value: pointer to the new extended attribute value
 409  * @xattr_value_len: pointer to the new extended attribute value length
 410  *
 411  * Update the HMAC stored in 'security.evm' to reflect the change.
 412  *
 413  * No need to take the i_mutex lock here, as this function is called from
 414  * __vfs_setxattr_noperm().  The caller of which has taken the inode's
 415  * i_mutex lock.
 416  */
 417 void evm_inode_post_setxattr(struct dentry *dentry, const char *xattr_name,
 418                              const void *xattr_value, size_t xattr_value_len)
 419 {
 420         if (!evm_key_loaded() || (!evm_protected_xattr(xattr_name)
 421                                   && !posix_xattr_acl(xattr_name)))
 422                 return;
 423
 424         evm_reset_status(dentry->d_inode);
 425
 426         evm_update_evmxattr(dentry, xattr_name, xattr_value, xattr_value_len);
 427 }
 428
 429 /**
 430  * evm_inode_post_removexattr - update 'security.evm' after removing the xattr
 431  * @dentry: pointer to the affected dentry
 432  * @xattr_name: pointer to the affected extended attribute name
 433  *
 434  * Update the HMAC stored in 'security.evm' to reflect removal of the xattr.
 435  *
 436  * No need to take the i_mutex lock here, as this function is called from
 437  * vfs_removexattr() which takes the i_mutex.
 438  */
 439 void evm_inode_post_removexattr(struct dentry *dentry, const char *xattr_name)
 440 {
 441         if (!evm_key_loaded() || !evm_protected_xattr(xattr_name))
 442                 return;
 443
 444         evm_reset_status(dentry->d_inode);
 445
 446         evm_update_evmxattr(dentry, xattr_name, NULL, 0);
 447 }
 448
 449 /**
 450  * evm_inode_setattr - prevent updating an invalid EVM extended attribute
 451  * @dentry: pointer to the affected dentry
 452  *
 453  * Permit update of file attributes when files have a valid EVM signature,
 454  * except in the case of them having an immutable portable signature.
 455  */
 456 int evm_inode_setattr(struct dentry *dentry, struct iattr *attr)
 457 {
 458         unsigned int ia_valid = attr->ia_valid;
 459         enum integrity_status evm_status;
 460
 461         /* Policy permits modification of the protected attrs even though
 462          * there's no HMAC key loaded
 463          */
 464         if (evm_initialized & EVM_ALLOW_METADATA_WRITES)
 465                 return 0;
 466
 467         if (!(ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID)))
 468                 return 0;
 469         evm_status = evm_verify_current_integrity(dentry);
 470         if ((evm_status == INTEGRITY_PASS) ||
 471             (evm_status == INTEGRITY_NOXATTRS))
 472                 return 0;
 473         integrity_audit_msg(AUDIT_INTEGRITY_METADATA, d_backing_inode(dentry),
 474                             dentry->d_name.name, "appraise_metadata",
 475                             integrity_status_msg[evm_status], -EPERM, 0);
 476         return -EPERM;
 477 }
 478
 479 /**
 480  * evm_inode_post_setattr - update 'security.evm' after modifying metadata
 481  * @dentry: pointer to the affected dentry
 482  * @ia_valid: for the UID and GID status
 483  *
 484  * For now, update the HMAC stored in 'security.evm' to reflect UID/GID
 485  * changes.
 486  *
 487  * This function is called from notify_change(), which expects the caller
 488  * to lock the inode's i_mutex.
 489  */
 490 void evm_inode_post_setattr(struct dentry *dentry, int ia_valid)
 491 {
 492         if (!evm_key_loaded())
 493                 return;
 494
 495         if (ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID))
 496                 evm_update_evmxattr(dentry, NULL, NULL, 0);
 497 }
 498
 499 /*
 500  * evm_inode_init_security - initializes security.evm
 501  */
 502 int evm_inode_init_security(struct inode *inode,
 503                                  const struct xattr *lsm_xattr,
 504                                  struct xattr *evm_xattr)
 505 {
 506         struct evm_ima_xattr_data *xattr_data;
 507         int rc;
 508
 509         if (!evm_key_loaded() || !evm_protected_xattr(lsm_xattr->name))
 510                 return 0;
 511
 512         xattr_data = kzalloc(sizeof(*xattr_data), GFP_NOFS);
 513         if (!xattr_data)
 514                 return -ENOMEM;
 515
 516         xattr_data->type = EVM_XATTR_HMAC;
 517         rc = evm_init_hmac(inode, lsm_xattr, xattr_data->digest);
 518         if (rc < 0)
 519                 goto out;
 520
 521         evm_xattr->value = xattr_data;
 522         evm_xattr->value_len = sizeof(*xattr_data);
 523         evm_xattr->name = XATTR_EVM_SUFFIX;
 524         return 0;
 525 out:
 526         kfree(xattr_data);
 527         return rc;
 528 }
 529 EXPORT_SYMBOL_GPL(evm_inode_init_security);
 530
 531 #ifdef CONFIG_EVM_LOAD_X509
 532 void __init evm_load_x509(void)
 533 {
 534         int rc;
 535
 536         rc = integrity_load_x509(INTEGRITY_KEYRING_EVM, CONFIG_EVM_X509_PATH);
 537         if (!rc)
 538                 evm_initialized |= EVM_INIT_X509;
 539 }
 540 #endif
 541
 542 static int __init init_evm(void)
 543 {
 544         int error;
 545
 546         evm_init_config();
 547
 548         error = integrity_init_keyring(INTEGRITY_KEYRING_EVM);
 549         if (error)
 550                 return error;
 551
 552         error = evm_init_secfs();
 553         if (error < 0) {
 554                 pr_info("Error registering secfs\n");
 555                 return error;
 556         }
 557
 558         return 0;
 559 }
 560
 561 /*
 562  * evm_display_config - list the EVM protected security extended attributes
 563  */
 564 static int __init evm_display_config(void)
 565 {
 566         char **xattrname;
 567
 568         for (xattrname = evm_config_xattrnames; *xattrname != NULL; xattrname++)
 569                 pr_info("%s\n", *xattrname);
 570         return 0;
 571 }
 572
 573 pure_initcall(evm_display_config);
 574 late_initcall(init_evm);
 575
 576 MODULE_DESCRIPTION("Extended Verification Module");
 577 MODULE_LICENSE("GPL");