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