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/*
* Copyright (C) 2005-2010 IBM Corporation
*
* Authors:
* 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_crypto.c
* Using root's kernel master key (kmk), calculate the HMAC
*/
#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
#include <linux/export.h>
#include <linux/crypto.h>
#include <linux/xattr.h>
#include <linux/evm.h>
#include <keys/encrypted-type.h>
#include <crypto/hash.h>
#include <crypto/hash_info.h>
#include "evm.h"
#define EVMKEY "evm-key"
#define MAX_KEY_SIZE 128
static unsigned char evmkey[MAX_KEY_SIZE];
static const int evmkey_len = MAX_KEY_SIZE;
struct crypto_shash *hmac_tfm;
static struct crypto_shash *evm_tfm[HASH_ALGO__LAST];
static DEFINE_MUTEX(mutex);
#define EVM_SET_KEY_BUSY 0
static unsigned long evm_set_key_flags;
static const char evm_hmac[] = "hmac(sha1)";
/**
* evm_set_key() - set EVM HMAC key from the kernel
* @key: pointer to a buffer with the key data
* @size: length of the key data
*
* This function allows setting the EVM HMAC key from the kernel
* without using the "encrypted" key subsystem keys. It can be used
* by the crypto HW kernel module which has its own way of managing
* keys.
*
* key length should be between 32 and 128 bytes long
*/
int evm_set_key(void *key, size_t keylen)
{
int rc;
rc = -EBUSY;
if (test_and_set_bit(EVM_SET_KEY_BUSY, &evm_set_key_flags))
goto busy;
rc = -EINVAL;
if (keylen > MAX_KEY_SIZE)
goto inval;
memcpy(evmkey, key, keylen);
evm_initialized |= EVM_INIT_HMAC;
pr_info("key initialized\n");
return 0;
inval:
clear_bit(EVM_SET_KEY_BUSY, &evm_set_key_flags);
busy:
pr_err("key initialization failed\n");
return rc;
}
EXPORT_SYMBOL_GPL(evm_set_key);
static struct shash_desc *init_desc(char type, uint8_t hash_algo)
{
long rc;
const char *algo;
struct crypto_shash **tfm;
struct shash_desc *desc;
if (type == EVM_XATTR_HMAC) {
if (!(evm_initialized & EVM_INIT_HMAC)) {
pr_err_once("HMAC key is not set\n");
return ERR_PTR(-ENOKEY);
}
tfm = &hmac_tfm;
algo = evm_hmac;
} else {
tfm = &evm_tfm[hash_algo];
algo = hash_algo_name[hash_algo];
}
if (*tfm == NULL) {
mutex_lock(&mutex);
if (*tfm)
goto out;
*tfm = crypto_alloc_shash(algo, 0, CRYPTO_NOLOAD);
if (IS_ERR(*tfm)) {
rc = PTR_ERR(*tfm);
pr_err("Can not allocate %s (reason: %ld)\n", algo, rc);
*tfm = NULL;
mutex_unlock(&mutex);
return ERR_PTR(rc);
}
if (type == EVM_XATTR_HMAC) {
rc = crypto_shash_setkey(*tfm, evmkey, evmkey_len);
if (rc) {
crypto_free_shash(*tfm);
*tfm = NULL;
mutex_unlock(&mutex);
return ERR_PTR(rc);
}
}
out:
mutex_unlock(&mutex);
}
desc = kmalloc(sizeof(*desc) + crypto_shash_descsize(*tfm),
GFP_KERNEL);
if (!desc)
return ERR_PTR(-ENOMEM);
desc->tfm = *tfm;
desc->flags = CRYPTO_TFM_REQ_MAY_SLEEP;
rc = crypto_shash_init(desc);
if (rc) {
kfree(desc);
return ERR_PTR(rc);
}
return desc;
}
/* Protect against 'cutting & pasting' security.evm xattr, include inode
* specific info.
*
* (Additional directory/file metadata needs to be added for more complete
* protection.)
*/
static void hmac_add_misc(struct shash_desc *desc, struct inode *inode,
char type, char *digest)
{
struct h_misc {
unsigned long ino;
__u32 generation;
uid_t uid;
gid_t gid;
umode_t mode;
} hmac_misc;
memset(&hmac_misc, 0, sizeof(hmac_misc));
/* Don't include the inode or generation number in portable
* signatures
*/
if (type != EVM_XATTR_PORTABLE_DIGSIG) {
hmac_misc.ino = inode->i_ino;
hmac_misc.generation = inode->i_generation;
}
/* The hmac uid and gid must be encoded in the initial user
* namespace (not the filesystems user namespace) as encoding
* them in the filesystems user namespace allows an attack
* where first they are written in an unprivileged fuse mount
* of a filesystem and then the system is tricked to mount the
* filesystem for real on next boot and trust it because
* everything is signed.
*/
hmac_misc.uid = from_kuid(&init_user_ns, inode->i_uid);
hmac_misc.gid = from_kgid(&init_user_ns, inode->i_gid);
hmac_misc.mode = inode->i_mode;
crypto_shash_update(desc, (const u8 *)&hmac_misc, sizeof(hmac_misc));
if ((evm_hmac_attrs & EVM_ATTR_FSUUID) &&
type != EVM_XATTR_PORTABLE_DIGSIG)
crypto_shash_update(desc, &inode->i_sb->s_uuid.b[0],
sizeof(inode->i_sb->s_uuid));
crypto_shash_final(desc, digest);
}
/*
* Calculate the HMAC value across the set of protected security xattrs.
*
* Instead of retrieving the requested xattr, for performance, calculate
* the hmac using the requested xattr value. Don't alloc/free memory for
* each xattr, but attempt to re-use the previously allocated memory.
*/
static int evm_calc_hmac_or_hash(struct dentry *dentry,
const char *req_xattr_name,
const char *req_xattr_value,
size_t req_xattr_value_len,
uint8_t type, struct evm_digest *data)
{
struct inode *inode = d_backing_inode(dentry);
struct xattr_list *xattr;
struct shash_desc *desc;
size_t xattr_size = 0;
char *xattr_value = NULL;
int error;
int size;
bool ima_present = false;
if (!(inode->i_opflags & IOP_XATTR) ||
inode->i_sb->s_user_ns != &init_user_ns)
return -EOPNOTSUPP;
desc = init_desc(type, data->hdr.algo);
if (IS_ERR(desc))
return PTR_ERR(desc);
data->hdr.length = crypto_shash_digestsize(desc->tfm);
error = -ENODATA;
list_for_each_entry_rcu(xattr, &evm_config_xattrnames, list) {
bool is_ima = false;
if (strcmp(xattr->name, XATTR_NAME_IMA) == 0)
is_ima = true;
if ((req_xattr_name && req_xattr_value)
&& !strcmp(xattr->name, req_xattr_name)) {
error = 0;
crypto_shash_update(desc, (const u8 *)req_xattr_value,
req_xattr_value_len);
if (is_ima)
ima_present = true;
continue;
}
size = vfs_getxattr_alloc(dentry, xattr->name,
&xattr_value, xattr_size, GFP_NOFS);
if (size == -ENOMEM) {
error = -ENOMEM;
goto out;
}
if (size < 0)
continue;
error = 0;
xattr_size = size;
crypto_shash_update(desc, (const u8 *)xattr_value, xattr_size);
if (is_ima)
ima_present = true;
}
hmac_add_misc(desc, inode, type, data->digest);
/* Portable EVM signatures must include an IMA hash */
if (type == EVM_XATTR_PORTABLE_DIGSIG && !ima_present)
return -EPERM;
out:
kfree(xattr_value);
kfree(desc);
return error;
}
int evm_calc_hmac(struct dentry *dentry, const char *req_xattr_name,
const char *req_xattr_value, size_t req_xattr_value_len,
struct evm_digest *data)
{
return evm_calc_hmac_or_hash(dentry, req_xattr_name, req_xattr_value,
req_xattr_value_len, EVM_XATTR_HMAC, data);
}
int evm_calc_hash(struct dentry *dentry, const char *req_xattr_name,
const char *req_xattr_value, size_t req_xattr_value_len,
char type, struct evm_digest *data)
{
return evm_calc_hmac_or_hash(dentry, req_xattr_name, req_xattr_value,
req_xattr_value_len, type, data);
}
static int evm_is_immutable(struct dentry *dentry, struct inode *inode<
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