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