/*
* Copyright (C) 2005-2010 IBM Corporation
*
* Author:
* Mimi Zohar <zohar@us.ibm.com>
* Kylene Hall <kjhall@us.ibm.com>
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, version 2 of the License.
*
* File: evm_main.c
* implements evm_inode_setxattr, evm_inode_post_setxattr,
* evm_inode_removexattr, and evm_verifyxattr
*/
#include <linux/module.h>
#include <linux/crypto.h>
#include <linux/xattr.h>
#include <linux/integrity.h>
#include <linux/evm.h>
#include "evm.h"
int evm_initialized;
char *evm_hmac = "hmac(sha1)";
char *evm_config_xattrnames[] = {
#ifdef CONFIG_SECURITY_SELINUX
XATTR_NAME_SELINUX,
#endif
#ifdef CONFIG_SECURITY_SMACK
XATTR_NAME_SMACK,
#endif
XATTR_NAME_CAPS,
NULL
};
/*
* evm_verify_hmac - calculate and compare the HMAC with the EVM xattr
*
* Compute the HMAC on the dentry's protected set of extended attributes
* and compare it against the stored security.evm xattr. (For performance,
* use the previoulsy retrieved xattr value and length to calculate the
* HMAC.)
*
* Returns integrity status
*/
static enum integrity_status evm_verify_hmac(struct dentry *dentry,
const char *xattr_name,
char *xattr_value,
size_t xattr_value_len,
struct integrity_iint_cache *iint)
{
struct evm_ima_xattr_data xattr_data;
int rc;
if (iint->hmac_status != INTEGRITY_UNKNOWN)
return iint->hmac_status;
rc = evm_calc_hmac(dentry, xattr_name, xattr_value,
xattr_value_len, xattr_data.digest);
if (rc < 0)
return INTEGRITY_UNKNOWN;
xattr_data.type = EVM_XATTR_HMAC;
rc = vfs_xattr_cmp(dentry, XATTR_NAME_EVM, (u8 *)&xattr_data,
sizeof xattr_data, GFP_NOFS);
if (rc < 0)
goto err_out;
iint->hmac_status = INTEGRITY_PASS;
return iint->hmac_status;
err_out:
switch (rc) {
case -ENODATA: /* file not labelled */
iint->hmac_status = INTEGRITY_NOLABEL;
break;
case -EINVAL:
iint->hmac_status = INTEGRITY_FAIL;
break;
default:
iint->hmac_status = INTEGRITY_UNKNOWN;
}
return iint->hmac_status;
}
static int evm_protected_xattr(const char *req_xattr_name)
{
char **xattrname;
int namelen;
int found = 0;
namelen = strlen(req_xattr_name);
for (xattrname = evm_config_xattrnames; *xattrname != NULL; xattrname++) {
if ((strlen(*xattrname) == namelen)
&& (strncmp(req_xattr_name, *xattrname, namelen) == 0)) {
found = 1;
break;
}
}
return found;
}
/**
* evm_verifyxattr - verify the integrity of the requested xattr
* @dentry: object of the verify xattr
* @xattr_name: requested xattr
* @xattr_value: requested xattr value
* @xattr_value_len: requested xattr value length
*
* Calculate the HMAC for the given dentry and verify it against the stored
* security.evm xattr. For performance, use the xattr value and length
* previously retrieved to calculate the HMAC.
*
* Returns the xattr integrity status.
*
* This function requires the caller to lock the inode's i_mutex before it
* is executed.
*/
enum integrity_status evm_verifyxattr(struct dentry *dentry,
const char *xattr_name,
void *xattr_value, size_t xattr_value_len)
{
struct inode *inode = dentry->d_inode;
struct integrity_iint_cache *iint;
enum integrity_status status;
if (!evm_initialized || !evm_protected_xattr(xattr_name))
return INTEGRITY_UNKNOWN;
iint = integrity_iint_find(inode);
if (!iint)
return INTEGRITY_UNKNOWN;
status = evm_verify_hmac(dentry, xattr_name, xattr_value,
xattr_value_len, iint);
return status;
}
EXPORT_SYMBOL_GPL(evm_verifyxattr);
/*
* evm_protect_xattr - protect the EVM extended attribute
*
* Prevent security.evm from being modified or removed.
*/
static int evm_protect_xattr(struct dentry *dentry, const char *xattr_name,
const void *xattr_value, size_t xattr_value_len)
{
if (strcmp(xattr_name, XATTR_NAME_EVM) == 0) {
if (!capable(CAP_SYS_ADMIN))
return -EPERM;
}
return 0;
}
/**
* evm_inode_setxattr - protect the EVM extended attribute
* @dentry: pointer to the affected dentry
* @xattr_name: pointer to the affected extended attribute name
* @xattr_value: pointer to the new extended attribute value
* @xattr_value_len: pointer to the new extended attribute value length
*
* Prevent 'security.evm' from being modified
*/
int evm_inode_setxattr(struct dentry *dentry, const char *xattr_name,
const void *xattr_value, size_t xattr_value_len)
{
return evm_protect_xattr(dentry, xattr_name, xattr_value,
xattr_value_len);
}
/**
* evm_inode_removexattr - protect the EVM extended attribute
* @dentry: pointer to the affected dentry
* @xattr_name: pointer to the affected extended attribute name
*
* Prevent 'security.evm' from being removed.
*/
int evm_inode_removexattr(struct dentry *dentry, const char *xattr_name)
{
return evm_protect_xattr(dentry, xattr_name, NULL, 0);
}
/**
* evm_inode_post_setxattr - update 'security.evm' to reflect the changes
* @dentry: pointer to the affected dentry
* @xattr_name: pointer to the affected extended attribute name
* @xattr_value: pointer to the new extended attribute value
* @xattr_value_len: pointer to the new extended attribute value length
*
* Update the HMAC stored in 'security.evm' to reflect the change.
*
* No need to take the i_mutex lock here, as this function is called from
* __vfs_setxattr_noperm(). The caller of which has taken the inode's
* i_mutex lock.
*/
void evm_inode_post_setxattr(struct dentry *dentry, const char *xattr_name,
const void *xattr_value, size_t xattr_value_len)
{
if (!evm_initialized || !evm_protected_xattr(xattr_name))
return;
evm_update_evmxattr(dentry, xattr_name, xattr_value, xattr_value_len);
return;
}
/**
* evm_inode_post_removexattr - update 'security.evm' after removing the xattr
* @dentry: pointer to the affected dentry
* @xattr_name: pointer to the affected extended attribute name
*
* Update the HMAC stored in 'security.evm' to reflect removal of the xattr.
*/
void evm_inode_post_removexattr(struct dentry *dentry, const char *xattr_name)
{
struct inode *inode = dentry->d_inode;
if (!evm_initialized || !evm_protected_xattr(xattr_name))
return;
mutex_lock(&inode->i_mutex);
evm_update_evmxattr(dentry, xattr_name, NULL, 0);
mutex_unlock(&inode->i_mutex);
return;
}
/**
* evm_inode_post_setattr - update 'security.evm' after modifying metadata
* @dentry: pointer to the affected dentry
* @ia_valid: for the UID and GID status
*
* For now, update the HMAC stored in 'security.evm' to reflect UID/GID
* changes.
*
* This function is called from notify_change(), which expects the caller
* to lock the inode's i_mutex.
*/
void evm_inode_post_setattr(struct dentry *dentry, int ia_valid)
{
if (!evm_initialized)
return;
if (ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID))
evm_update_evmxattr(dentry, NULL, NULL, 0);
return;
}
static struct crypto_hash *tfm_hmac; /* preload crypto alg */
static int __init init_evm(void)
{
int error;
tfm_hmac = crypto_alloc_hash(evm_hmac, 0, CRYPTO_ALG_ASYNC);
error = evm_init_secfs();
if (error < 0) {
printk(KERN_INFO "EVM: Error registering secfs\n");
goto err;
}
err:
return error;
}
static void __exit cleanup_evm(void)
{
evm_cleanup_secfs();
crypto_free_hash(tfm_hmac);
}
/*
* evm_display_config - list the EVM protected security extended attributes
*/
static int __init evm_display_config(void)
{
char **xattrname;
for (xattrname = evm_config_xattrnames; *xattrname != NULL; xattrname++)
printk(KERN_INFO "EVM: %s\n", *xattrname);
return 0;
}
pure_initcall(evm_display_config);
late_initcall(init_evm);
MODULE_DESCRIPTION("Extended Verification Module");
MODULE_LICENSE("GPL");
