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
  29 char *evm_config_xattrnames[] = {
  30 #ifdef CONFIG_SECURITY_SELINUX
  31         XATTR_NAME_SELINUX,
  32 #endif
  33 #ifdef CONFIG_SECURITY_SMACK
  34         XATTR_NAME_SMACK,
  35 #endif
  36         XATTR_NAME_CAPS,
  37         NULL
  38 };
  39
  40 static int evm_fixmode;
  41 static int __init evm_set_fixmode(char *str)
  42 {
  43         if (strncmp(str, "fix", 3) == 0)
  44                 evm_fixmode = 1;
  45         return 0;
  46 }
  47 __setup("evm=", evm_set_fixmode);
  48
  49 /*
  50  * evm_verify_hmac - calculate and compare the HMAC with the EVM xattr
  51  *
  52  * Compute the HMAC on the dentry's protected set of extended attributes
  53  * and compare it against the stored security.evm xattr.
  54  *
  55  * For performance:
  56  * - use the previoulsy retrieved xattr value and length to calculate the
  57  *   HMAC.)
  58  * - cache the verification result in the iint, when available.
  59  *
  60  * Returns integrity status
  61  */
  62 static enum integrity_status evm_verify_hmac(struct dentry *dentry,
  63                                              const char *xattr_name,
  64                                              char *xattr_value,
  65                                              size_t xattr_value_len,
  66                                              struct integrity_iint_cache *iint)
  67 {
  68         struct evm_ima_xattr_data xattr_data;
  69         enum integrity_status evm_status = INTEGRITY_PASS;
  70         int rc;
  71
  72         if (iint && iint->evm_status == INTEGRITY_PASS)
  73                 return iint->evm_status;
  74
  75         /* if status is not PASS, try to check again - against -ENOMEM */
  76
  77         rc = evm_calc_hmac(dentry, xattr_name, xattr_value,
  78                            xattr_value_len, xattr_data.digest);
  79         if (rc < 0) {
  80                 evm_status = (rc == -ENODATA)
  81                     ? INTEGRITY_NOXATTRS : INTEGRITY_FAIL;
  82                 goto out;
  83         }
  84
  85         xattr_data.type = EVM_XATTR_HMAC;
  86         rc = vfs_xattr_cmp(dentry, XATTR_NAME_EVM, (u8 *)&xattr_data,
  87                            sizeof xattr_data, GFP_NOFS);
  88         if (rc < 0)
  89                 evm_status = (rc == -ENODATA)
  90                     ? INTEGRITY_NOLABEL : INTEGRITY_FAIL;
  91 out:
  92         if (iint)
  93                 iint->evm_status = evm_status;
  94         return evm_status;
  95 }
  96
  97 static int evm_protected_xattr(const char *req_xattr_name)
  98 {
  99         char **xattrname;
 100         int namelen;
 101         int found = 0;
 102
 103         namelen = strlen(req_xattr_name);
 104         for (xattrname = evm_config_xattrnames; *xattrname != NULL; xattrname++) {
 105                 if ((strlen(*xattrname) == namelen)
 106                     && (strncmp(req_xattr_name, *xattrname, namelen) == 0)) {
 107                         found = 1;
 108                         break;
 109                 }
 110                 if (strncmp(req_xattr_name,
 111                             *xattrname + XATTR_SECURITY_PREFIX_LEN,
 112                             strlen(req_xattr_name)) == 0) {
 113                         found = 1;
 114                         break;
 115                 }
 116         }
 117         return found;
 118 }
 119
 120 /**
 121  * evm_verifyxattr - verify the integrity of the requested xattr
 122  * @dentry: object of the verify xattr
 123  * @xattr_name: requested xattr
 124  * @xattr_value: requested xattr value
 125  * @xattr_value_len: requested xattr value length
 126  *
 127  * Calculate the HMAC for the given dentry and verify it against the stored
 128  * security.evm xattr. For performance, use the xattr value and length
 129  * previously retrieved to calculate the HMAC.
 130  *
 131  * Returns the xattr integrity status.
 132  *
 133  * This function requires the caller to lock the inode's i_mutex before it
 134  * is executed.
 135  */
 136 enum integrity_status evm_verifyxattr(struct dentry *dentry,
 137                                       const char *xattr_name,
 138                                       void *xattr_value, size_t xattr_value_len,
 139                                       struct integrity_iint_cache *iint)
 140 {
 141         if (!evm_initialized || !evm_protected_xattr(xattr_name))
 142                 return INTEGRITY_UNKNOWN;
 143
 144         if (!iint) {
 145                 iint = integrity_iint_find(dentry->d_inode);
 146                 if (!iint)
 147                         return INTEGRITY_UNKNOWN;
 148         }
 149         return evm_verify_hmac(dentry, xattr_name, xattr_value,
 150                                  xattr_value_len, iint);
 151 }
 152 EXPORT_SYMBOL_GPL(evm_verifyxattr);
 153
 154 /*
 155  * evm_verify_current_integrity - verify the dentry's metadata integrity
 156  * @dentry: pointer to the affected dentry
 157  *
 158  * Verify and return the dentry's metadata integrity. The exceptions are
 159  * before EVM is initialized or in 'fix' mode.
 160  */
 161 static enum integrity_status evm_verify_current_integrity(struct dentry *dentry)
 162 {
 163         struct inode *inode = dentry->d_inode;
 164
 165         if (!evm_initialized || !S_ISREG(inode->i_mode) || evm_fixmode)
 166                 return 0;
 167         return evm_verify_hmac(dentry, NULL, NULL, 0, NULL);
 168 }
 169
 170 /*
 171  * evm_protect_xattr - protect the EVM extended attribute
 172  *
 173  * Prevent security.evm from being modified or removed without the
 174  * necessary permissions or when the existing value is invalid.
 175  *
 176  * The posix xattr acls are 'system' prefixed, which normally would not
 177  * affect security.evm.  An interesting side affect of writing posix xattr
 178  * acls is their modifying of the i_mode, which is included in security.evm.
 179  * For posix xattr acls only, permit security.evm, even if it currently
 180  * doesn't exist, to be updated.
 181  */
 182 static int evm_protect_xattr(struct dentry *dentry, const char *xattr_name,
 183                              const void *xattr_value, size_t xattr_value_len)
 184 {
 185         enum integrity_status evm_status;
 186
 187         if (strcmp(xattr_name, XATTR_NAME_EVM) == 0) {
 188                 if (!capable(CAP_SYS_ADMIN))
 189                         return -EPERM;
 190         } else if (!evm_protected_xattr(xattr_name)) {
 191                 if (!posix_xattr_acl(xattr_name))
 192                         return 0;
 193                 evm_status = evm_verify_current_integrity(dentry);
 194                 if ((evm_status == INTEGRITY_PASS) ||
 195                     (evm_status == INTEGRITY_NOXATTRS))
 196                         return 0;
 197                 return -EPERM;
 198         }
 199         evm_status = evm_verify_current_integrity(dentry);
 200         return evm_status == INTEGRITY_PASS ? 0 : -EPERM;
 201 }
 202
 203 /**
 204  * evm_inode_setxattr - protect the EVM extended attribute
 205  * @dentry: pointer to the affected dentry
 206  * @xattr_name: pointer to the affected extended attribute name
 207  * @xattr_value: pointer to the new extended attribute value
 208  * @xattr_value_len: pointer to the new extended attribute value length
 209  *
 210  * Updating 'security.evm' requires CAP_SYS_ADMIN privileges and that
 211  * the current value is valid.
 212  */
 213 int evm_inode_setxattr(struct dentry *dentry, const char *xattr_name,
 214                        const void *xattr_value, size_t xattr_value_len)
 215 {
 216         return evm_protect_xattr(dentry, xattr_name, xattr_value,
 217                                  xattr_value_len);
 218 }
 219
 220 /**
 221  * evm_inode_removexattr - protect the EVM extended attribute
 222  * @dentry: pointer to the affected dentry
 223  * @xattr_name: pointer to the affected extended attribute name
 224  *
 225  * Removing 'security.evm' requires CAP_SYS_ADMIN privileges and that
 226  * the current value is valid.
 227  */
 228 int evm_inode_removexattr(struct dentry *dentry, const char *xattr_name)
 229 {
 230         return evm_protect_xattr(dentry, xattr_name, NULL, 0);
 231 }
 232
 233 /**
 234  * evm_inode_post_setxattr - update 'security.evm' to reflect the changes
 235  * @dentry: pointer to the affected dentry
 236  * @xattr_name: pointer to the affected extended attribute name
 237  * @xattr_value: pointer to the new extended attribute value
 238  * @xattr_value_len: pointer to the new extended attribute value length
 239  *
 240  * Update the HMAC stored in 'security.evm' to reflect the change.
 241  *
 242  * No need to take the i_mutex lock here, as this function is called from
 243  * __vfs_setxattr_noperm().  The caller of which has taken the inode's
 244  * i_mutex lock.
 245  */
 246 void evm_inode_post_setxattr(struct dentry *dentry, const char *xattr_name,
 247                              const void *xattr_value, size_t xattr_value_len)
 248 {
 249         if (!evm_initialized || (!evm_protected_xattr(xattr_name)
 250                                  && !posix_xattr_acl(xattr_name)))
 251                 return;
 252
 253         evm_update_evmxattr(dentry, xattr_name, xattr_value, xattr_value_len);
 254         return;
 255 }
 256
 257 /**
 258  * evm_inode_post_removexattr - update 'security.evm' after removing the xattr
 259  * @dentry: pointer to the affected dentry
 260  * @xattr_name: pointer to the affected extended attribute name
 261  *
 262  * Update the HMAC stored in 'security.evm' to reflect removal of the xattr.
 263  */
 264 void evm_inode_post_removexattr(struct dentry *dentry, const char *xattr_name)
 265 {
 266         struct inode *inode = dentry->d_inode;
 267
 268         if (!evm_initialized || !evm_protected_xattr(xattr_name))
 269                 return;
 270
 271         mutex_lock(&inode->i_mutex);
 272         evm_update_evmxattr(dentry, xattr_name, NULL, 0);
 273         mutex_unlock(&inode->i_mutex);
 274         return;
 275 }
 276
 277 /**
 278  * evm_inode_setattr - prevent updating an invalid EVM extended attribute
 279  * @dentry: pointer to the affected dentry
 280  */
 281 int evm_inode_setattr(struct dentry *dentry, struct iattr *attr)
 282 {
 283         unsigned int ia_valid = attr->ia_valid;
 284         enum integrity_status evm_status;
 285
 286         if (!(ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID)))
 287                 return 0;
 288         evm_status = evm_verify_current_integrity(dentry);
 289         if ((evm_status == INTEGRITY_PASS) ||
 290             (evm_status == INTEGRITY_NOXATTRS))
 291                 return 0;
 292         return -EPERM;
 293 }
 294
 295 /**
 296  * evm_inode_post_setattr - update 'security.evm' after modifying metadata
 297  * @dentry: pointer to the affected dentry
 298  * @ia_valid: for the UID and GID status
 299  *
 300  * For now, update the HMAC stored in 'security.evm' to reflect UID/GID
 301  * changes.
 302  *
 303  * This function is called from notify_change(), which expects the caller
 304  * to lock the inode's i_mutex.
 305  */
 306 void evm_inode_post_setattr(struct dentry *dentry, int ia_valid)
 307 {
 308         if (!evm_initialized)
 309                 return;
 310
 311         if (ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID))
 312                 evm_update_evmxattr(dentry, NULL, NULL, 0);
 313         return;
 314 }
 315
 316 /*
 317  * evm_inode_init_security - initializes security.evm
 318  */
 319 int evm_inode_init_security(struct inode *inode,
 320                                  const struct xattr *lsm_xattr,
 321                                  struct xattr *evm_xattr)
 322 {
 323         struct evm_ima_xattr_data *xattr_data;
 324         int rc;
 325
 326         if (!evm_initialized || !evm_protected_xattr(lsm_xattr->name))
 327                 return 0;
 328
 329         xattr_data = kzalloc(sizeof(*xattr_data), GFP_NOFS);
 330         if (!xattr_data)
 331                 return -ENOMEM;
 332
 333         xattr_data->type = EVM_XATTR_HMAC;
 334         rc = evm_init_hmac(inode, lsm_xattr, xattr_data->digest);
 335         if (rc < 0)
 336                 goto out;
 337
 338         evm_xattr->value = xattr_data;
 339         evm_xattr->value_len = sizeof(*xattr_data);
 340         evm_xattr->name = kstrdup(XATTR_EVM_SUFFIX, GFP_NOFS);
 341         return 0;
 342 out:
 343         kfree(xattr_data);
 344         return rc;
 345 }
 346 EXPORT_SYMBOL_GPL(evm_inode_init_security);
 347
 348 static int __init init_evm(void)
 349 {
 350         int error;
 351
 352         error = evm_init_secfs();
 353         if (error < 0) {
 354                 printk(KERN_INFO "EVM: Error registering secfs\n");
 355                 goto err;
 356         }
 357 err:
 358         return error;
 359 }
 360
 361 static void __exit cleanup_evm(void)
 362 {
 363         evm_cleanup_secfs();
 364         if (hmac_tfm)
 365                 crypto_free_shash(hmac_tfm);
 366 }
 367
 368 /*
 369  * evm_display_config - list the EVM protected security extended attributes
 370  */
 371 static int __init evm_display_config(void)
 372 {
 373         char **xattrname;
 374
 375         for (xattrname = evm_config_xattrnames; *xattrname != NULL; xattrname++)
 376                 printk(KERN_INFO "EVM: %s\n", *xattrname);
 377         return 0;
 378 }
 379
 380 pure_initcall(evm_display_config);
 381 late_initcall(init_evm);
 382
 383 MODULE_DESCRIPTION("Extended Verification Module");
 384 MODULE_LICENSE("GPL");