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 #include <linux/module.h>
  18 #include <linux/crypto.h>
  19 #include <linux/audit.h>
  20 #include <linux/xattr.h>
  21 #include <linux/integrity.h>
  22 #include <linux/evm.h>
  23 #include <crypto/hash.h>
  24 #include <crypto/algapi.h>
  25 #include "evm.h"
  26
  27 int evm_initialized;
  28
  29 static char *integrity_status_msg[] = {
  30         "pass", "fail", "no_label", "no_xattrs", "unknown"
  31 };
  32 char *evm_hmac = "hmac(sha1)";
  33 char *evm_hash = "sha1";
  34 int evm_hmac_version = CONFIG_EVM_HMAC_VERSION;
  35
  36 char *evm_config_xattrnames[] = {
  37 #ifdef CONFIG_SECURITY_SELINUX
  38         XATTR_NAME_SELINUX,
  39 #endif
  40 #ifdef CONFIG_SECURITY_SMACK
  41         XATTR_NAME_SMACK,
  42 #endif
  43 #ifdef CONFIG_IMA_APPRAISE
  44         XATTR_NAME_IMA,
  45 #endif
  46         XATTR_NAME_CAPS,
  47         NULL
  48 };
  49
  50 static int evm_fixmode;
  51 static int __init evm_set_fixmode(char *str)
  52 {
  53         if (strncmp(str, "fix", 3) == 0)
  54                 evm_fixmode = 1;
  55         return 0;
  56 }
  57 __setup("evm=", evm_set_fixmode);
  58
  59 static int evm_find_protected_xattrs(struct dentry *dentry)
  60 {
  61         struct inode *inode = dentry->d_inode;
  62         char **xattr;
  63         int error;
  64         int count = 0;
  65
  66         if (!inode->i_op || !inode->i_op->getxattr)
  67                 return -EOPNOTSUPP;
  68
  69         for (xattr = evm_config_xattrnames; *xattr != NULL; xattr++) {
  70                 error = inode->i_op->getxattr(dentry, *xattr, NULL, 0);
  71                 if (error < 0) {
  72                         if (error == -ENODATA)
  73                                 continue;
  74                         return error;
  75                 }
  76                 count++;
  77         }
  78
  79         return count;
  80 }
  81
  82 /*
  83  * evm_verify_hmac - calculate and compare the HMAC with the EVM xattr
  84  *
  85  * Compute the HMAC on the dentry's protected set of extended attributes
  86  * and compare it against the stored security.evm xattr.
  87  *
  88  * For performance:
  89  * - use the previoulsy retrieved xattr value and length to calculate the
  90  *   HMAC.)
  91  * - cache the verification result in the iint, when available.
  92  *
  93  * Returns integrity status
  94  */
  95 static enum integrity_status evm_verify_hmac(struct dentry *dentry,
  96                                              const char *xattr_name,
  97                                              char *xattr_value,
  98                                              size_t xattr_value_len,
  99                                              struct integrity_iint_cache *iint)
 100 {
 101         struct evm_ima_xattr_data *xattr_data = NULL;
 102         struct evm_ima_xattr_data calc;
 103         enum integrity_status evm_status = INTEGRITY_PASS;
 104         int rc, xattr_len;
 105
 106         if (iint && iint->evm_status == INTEGRITY_PASS)
 107                 return iint->evm_status;
 108
 109         /* if status is not PASS, try to check again - against -ENOMEM */
 110
 111         /* first need to know the sig type */
 112         rc = vfs_getxattr_alloc(dentry, XATTR_NAME_EVM, (char **)&xattr_data, 0,
 113                                 GFP_NOFS);
 114         if (rc <= 0) {
 115                 if (rc == 0)
 116                         evm_status = INTEGRITY_FAIL; /* empty */
 117                 else if (rc == -ENODATA) {
 118                         rc = evm_find_protected_xattrs(dentry);
 119                         if (rc > 0)
 120                                 evm_status = INTEGRITY_NOLABEL;
 121                         else if (rc == 0)
 122                                 evm_status = INTEGRITY_NOXATTRS; /* new file */
 123                 }
 124                 goto out;
 125         }
 126
 127         xattr_len = rc - 1;
 128
 129         /* check value type */
 130         switch (xattr_data->type) {
 131         case EVM_XATTR_HMAC:
 132                 rc = evm_calc_hmac(dentry, xattr_name, xattr_value,
 133                                    xattr_value_len, calc.digest);
 134                 if (rc)
 135                         break;
 136                 rc = crypto_memneq(xattr_data->digest, calc.digest,
 137                             sizeof(calc.digest));
 138                 if (rc)
 139                         rc = -EINVAL;
 140                 break;
 141         case EVM_IMA_XATTR_DIGSIG:
 142                 rc = evm_calc_hash(dentry, xattr_name, xattr_value,
 143                                 xattr_value_len, calc.digest);
 144                 if (rc)
 145                         break;
 146                 rc = integrity_digsig_verify(INTEGRITY_KEYRING_EVM,
 147                                         xattr_data->digest, xattr_len,
 148                                         calc.digest, sizeof(calc.digest));
 149                 if (!rc) {
 150                         /* we probably want to replace rsa with hmac here */
 151                         evm_update_evmxattr(dentry, xattr_name, xattr_value,
 152                                    xattr_value_len);
 153                 }
 154                 break;
 155         default:
 156                 rc = -EINVAL;
 157                 break;
 158         }
 159
 160         if (rc)
 161                 evm_status = (rc == -ENODATA) ?
 162                                 INTEGRITY_NOXATTRS : INTEGRITY_FAIL;
 163 out:
 164         if (iint)
 165                 iint->evm_status = evm_status;
 166         kfree(xattr_data);
 167         return evm_status;
 168 }
 169
 170 static int evm_protected_xattr(const char *req_xattr_name)
 171 {
 172         char **xattrname;
 173         int namelen;
 174         int found = 0;
 175
 176         namelen = strlen(req_xattr_name);
 177         for (xattrname = evm_config_xattrnames; *xattrname != NULL; xattrname++) {
 178                 if ((strlen(*xattrname) == namelen)
 179                     && (strncmp(req_xattr_name, *xattrname, namelen) == 0)) {
 180                         found = 1;
 181                         break;
 182                 }
 183                 if (strncmp(req_xattr_name,
 184                             *xattrname + XATTR_SECURITY_PREFIX_LEN,
 185                             strlen(req_xattr_name)) == 0) {
 186                         found = 1;
 187                         break;
 188                 }
 189         }
 190         return found;
 191 }
 192
 193 /**
 194  * evm_verifyxattr - verify the integrity of the requested xattr
 195  * @dentry: object of the verify xattr
 196  * @xattr_name: requested xattr
 197  * @xattr_value: requested xattr value
 198  * @xattr_value_len: requested xattr value length
 199  *
 200  * Calculate the HMAC for the given dentry and verify it against the stored
 201  * security.evm xattr. For performance, use the xattr value and length
 202  * previously retrieved to calculate the HMAC.
 203  *
 204  * Returns the xattr integrity status.
 205  *
 206  * This function requires the caller to lock the inode's i_mutex before it
 207  * is executed.
 208  */
 209 enum integrity_status evm_verifyxattr(struct dentry *dentry,
 210                                       const char *xattr_name,
 211                                       void *xattr_value, size_t xattr_value_len,
 212                                       struct integrity_iint_cache *iint)
 213 {
 214         if (!evm_initialized || !evm_protected_xattr(xattr_name))
 215                 return INTEGRITY_UNKNOWN;
 216
 217         if (!iint) {
 218                 iint = integrity_iint_find(dentry->d_inode);
 219                 if (!iint)
 220                         return INTEGRITY_UNKNOWN;
 221         }
 222         return evm_verify_hmac(dentry, xattr_name, xattr_value,
 223                                  xattr_value_len, iint);
 224 }
 225 EXPORT_SYMBOL_GPL(evm_verifyxattr);
 226
 227 /*
 228  * evm_verify_current_integrity - verify the dentry's metadata integrity
 229  * @dentry: pointer to the affected dentry
 230  *
 231  * Verify and return the dentry's metadata integrity. The exceptions are
 232  * before EVM is initialized or in 'fix' mode.
 233  */
 234 static enum integrity_status evm_verify_current_integrity(struct dentry *dentry)
 235 {
 236         struct inode *inode = dentry->d_inode;
 237
 238         if (!evm_initialized || !S_ISREG(inode->i_mode) || evm_fixmode)
 239                 return 0;
 240         return evm_verify_hmac(dentry, NULL, NULL, 0, NULL);
 241 }
 242
 243 /*
 244  * evm_protect_xattr - protect the EVM extended attribute
 245  *
 246  * Prevent security.evm from being modified or removed without the
 247  * necessary permissions or when the existing value is invalid.
 248  *
 249  * The posix xattr acls are 'system' prefixed, which normally would not
 250  * affect security.evm.  An interesting side affect of writing posix xattr
 251  * acls is their modifying of the i_mode, which is included in security.evm.
 252  * For posix xattr acls only, permit security.evm, even if it currently
 253  * doesn't exist, to be updated.
 254  */
 255 static int evm_protect_xattr(struct dentry *dentry, const char *xattr_name,
 256                              const void *xattr_value, size_t xattr_value_len)
 257 {
 258         enum integrity_status evm_status;
 259
 260         if (strcmp(xattr_name, XATTR_NAME_EVM) == 0) {
 261                 if (!capable(CAP_SYS_ADMIN))
 262                         return -EPERM;
 263         } else if (!evm_protected_xattr(xattr_name)) {
 264                 if (!posix_xattr_acl(xattr_name))
 265                         return 0;
 266                 evm_status = evm_verify_current_integrity(dentry);
 267                 if ((evm_status == INTEGRITY_PASS) ||
 268                     (evm_status == INTEGRITY_NOXATTRS))
 269                         return 0;
 270                 goto out;
 271         }
 272         evm_status = evm_verify_current_integrity(dentry);
 273 out:
 274         if (evm_status != INTEGRITY_PASS)
 275                 integrity_audit_msg(AUDIT_INTEGRITY_METADATA, dentry->d_inode,
 276                                     dentry->d_name.name, "appraise_metadata",
 277                                     integrity_status_msg[evm_status],
 278                                     -EPERM, 0);
 279         return evm_status == INTEGRITY_PASS ? 0 : -EPERM;
 280 }
 281
 282 /**
 283  * evm_inode_setxattr - protect the EVM extended attribute
 284  * @dentry: pointer to the affected dentry
 285  * @xattr_name: pointer to the affected extended attribute name
 286  * @xattr_value: pointer to the new extended attribute value
 287  * @xattr_value_len: pointer to the new extended attribute value length
 288  *
 289  * Before allowing the 'security.evm' protected xattr to be updated,
 290  * verify the existing value is valid.  As only the kernel should have
 291  * access to the EVM encrypted key needed to calculate the HMAC, prevent
 292  * userspace from writing HMAC value.  Writing 'security.evm' requires
 293  * requires CAP_SYS_ADMIN privileges.
 294  */
 295 int evm_inode_setxattr(struct dentry *dentry, const char *xattr_name,
 296                        const void *xattr_value, size_t xattr_value_len)
 297 {
 298         const struct evm_ima_xattr_data *xattr_data = xattr_value;
 299
 300         if (strcmp(xattr_name, XATTR_NAME_EVM) == 0) {
 301                 if (!xattr_value_len)
 302                         return -EINVAL;
 303                 if (xattr_data->type != EVM_IMA_XATTR_DIGSIG)
 304                         return -EPERM;
 305         }
 306         return evm_protect_xattr(dentry, xattr_name, xattr_value,
 307                                  xattr_value_len);
 308 }
 309
 310 /**
 311  * evm_inode_removexattr - protect the EVM extended attribute
 312  * @dentry: pointer to the affected dentry
 313  * @xattr_name: pointer to the affected extended attribute name
 314  *
 315  * Removing 'security.evm' requires CAP_SYS_ADMIN privileges and that
 316  * the current value is valid.
 317  */
 318 int evm_inode_removexattr(struct dentry *dentry, const char *xattr_name)
 319 {
 320         return evm_protect_xattr(dentry, xattr_name, NULL, 0);
 321 }
 322
 323 /**
 324  * evm_inode_post_setxattr - update 'security.evm' to reflect the changes
 325  * @dentry: pointer to the affected dentry
 326  * @xattr_name: pointer to the affected extended attribute name
 327  * @xattr_value: pointer to the new extended attribute value
 328  * @xattr_value_len: pointer to the new extended attribute value length
 329  *
 330  * Update the HMAC stored in 'security.evm' to reflect the change.
 331  *
 332  * No need to take the i_mutex lock here, as this function is called from
 333  * __vfs_setxattr_noperm().  The caller of which has taken the inode's
 334  * i_mutex lock.
 335  */
 336 void evm_inode_post_setxattr(struct dentry *dentry, const char *xattr_name,
 337                              const void *xattr_value, size_t xattr_value_len)
 338 {
 339         if (!evm_initialized || (!evm_protected_xattr(xattr_name)
 340                                  && !posix_xattr_acl(xattr_name)))
 341                 return;
 342
 343         evm_update_evmxattr(dentry, xattr_name, xattr_value, xattr_value_len);
 344         return;
 345 }
 346
 347 /**
 348  * evm_inode_post_removexattr - update 'security.evm' after removing the xattr
 349  * @dentry: pointer to the affected dentry
 350  * @xattr_name: pointer to the affected extended attribute name
 351  *
 352  * Update the HMAC stored in 'security.evm' to reflect removal of the xattr.
 353  */
 354 void evm_inode_post_removexattr(struct dentry *dentry, const char *xattr_name)
 355 {
 356         struct inode *inode = dentry->d_inode;
 357
 358         if (!evm_initialized || !evm_protected_xattr(xattr_name))
 359                 return;
 360
 361         mutex_lock(&inode->i_mutex);
 362         evm_update_evmxattr(dentry, xattr_name, NULL, 0);
 363         mutex_unlock(&inode->i_mutex);
 364         return;
 365 }
 366
 367 /**
 368  * evm_inode_setattr - prevent updating an invalid EVM extended attribute
 369  * @dentry: pointer to the affected dentry
 370  */
 371 int evm_inode_setattr(struct dentry *dentry, struct iattr *attr)
 372 {
 373         unsigned int ia_valid = attr->ia_valid;
 374         enum integrity_status evm_status;
 375
 376         if (!(ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID)))
 377                 return 0;
 378         evm_status = evm_verify_current_integrity(dentry);
 379         if ((evm_status == INTEGRITY_PASS) ||
 380             (evm_status == INTEGRITY_NOXATTRS))
 381                 return 0;
 382         integrity_audit_msg(AUDIT_INTEGRITY_METADATA, dentry->d_inode,
 383                             dentry->d_name.name, "appraise_metadata",
 384                             integrity_status_msg[evm_status], -EPERM, 0);
 385         return -EPERM;
 386 }
 387
 388 /**
 389  * evm_inode_post_setattr - update 'security.evm' after modifying metadata
 390  * @dentry: pointer to the affected dentry
 391  * @ia_valid: for the UID and GID status
 392  *
 393  * For now, update the HMAC stored in 'security.evm' to reflect UID/GID
 394  * changes.
 395  *
 396  * This function is called from notify_change(), which expects the caller
 397  * to lock the inode's i_mutex.
 398  */
 399 void evm_inode_post_setattr(struct dentry *dentry, int ia_valid)
 400 {
 401         if (!evm_initialized)
 402                 return;
 403
 404         if (ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID))
 405                 evm_update_evmxattr(dentry, NULL, NULL, 0);
 406         return;
 407 }
 408
 409 /*
 410  * evm_inode_init_security - initializes security.evm
 411  */
 412 int evm_inode_init_security(struct inode *inode,
 413                                  const struct xattr *lsm_xattr,
 414                                  struct xattr *evm_xattr)
 415 {
 416         struct evm_ima_xattr_data *xattr_data;
 417         int rc;
 418
 419         if (!evm_initialized || !evm_protected_xattr(lsm_xattr->name))
 420                 return 0;
 421
 422         xattr_data = kzalloc(sizeof(*xattr_data), GFP_NOFS);
 423         if (!xattr_data)
 424                 return -ENOMEM;
 425
 426         xattr_data->type = EVM_XATTR_HMAC;
 427         rc = evm_init_hmac(inode, lsm_xattr, xattr_data->digest);
 428         if (rc < 0)
 429                 goto out;
 430
 431         evm_xattr->value = xattr_data;
 432         evm_xattr->value_len = sizeof(*xattr_data);
 433         evm_xattr->name = XATTR_EVM_SUFFIX;
 434         return 0;
 435 out:
 436         kfree(xattr_data);
 437         return rc;
 438 }
 439 EXPORT_SYMBOL_GPL(evm_inode_init_security);
 440
 441 static int __init init_evm(void)
 442 {
 443         int error;
 444
 445         error = evm_init_secfs();
 446         if (error < 0) {
 447                 printk(KERN_INFO "EVM: Error registering secfs\n");
 448                 goto err;
 449         }
 450
 451         return 0;
 452 err:
 453         return error;
 454 }
 455
 456 /*
 457  * evm_display_config - list the EVM protected security extended attributes
 458  */
 459 static int __init evm_display_config(void)
 460 {
 461         char **xattrname;
 462
 463         for (xattrname = evm_config_xattrnames; *xattrname != NULL; xattrname++)
 464                 printk(KERN_INFO "EVM: %s\n", *xattrname);
 465         return 0;
 466 }
 467
 468 pure_initcall(evm_display_config);
 469 late_initcall(init_evm);
 470
 471 MODULE_DESCRIPTION("Extended Verification Module");
 472 MODULE_LICENSE("GPL");