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