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