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