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