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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
*/
#include <linux/module.h>
#include <linux/crypto.h>
#include <linux/xattr.h>
#include <linux/scatterlist.h>
#include <keys/encrypted-type.h>
#include "evm.h"
#define EVMKEY "evm-key"
#define MAX_KEY_SIZE 128
static unsigned char evmkey[MAX_KEY_SIZE];
static int evmkey_len = MAX_KEY_SIZE;
static int init_desc(struct hash_desc *desc)
{
int rc;
desc->tfm = crypto_alloc_hash(evm_hmac, 0, CRYPTO_ALG_ASYNC);
if (IS_ERR(desc->tfm)) {
pr_info("Can not allocate %s (reason: %ld)\n",
evm_hmac, PTR_ERR(desc->tfm));
rc = PTR_ERR(desc->tfm);
return rc;
}
desc->flags = 0;
rc = crypto_hash_setkey(desc->tfm, evmkey, evmkey_len);
if (rc)
goto out;
rc = crypto_hash_init(desc);
out:
if (rc)
crypto_free_hash(desc->tfm);
return rc;
}
/* 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 hash_desc *desc, struct inode *inode,
char *digest)
{
struct h_misc {
unsigned long ino;
__u32 generation;
uid_t uid;
gid_t gid;
umode_t mode;
} hmac_misc;
struct scatterlist sg[1];
memset(&hmac_misc, 0, sizeof hmac_misc);
hmac_misc.ino = inode->i_ino;
hmac_misc.generation = inode->i_generation;
hmac_misc.uid = inode->i_uid;
hmac_misc.gid = inode->i_gid;
hmac_misc.mode = inode->i_mode;
sg_init_one(sg, &hmac_misc, sizeof hmac_misc);
crypto_hash_update(desc, sg, sizeof hmac_misc);
crypto_hash_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.
*/
int evm_calc_hmac(struct dentry *dentry, const char *req_xattr_name,
const char *req_xattr_value, size_t req_xattr_value_len,
char *digest)
{
struct inode *inode = dentry->d_inode;
struct hash_desc desc;
struct scatterlist sg[1];
char **xattrname;
size_t xattr_size = 0;
char *xattr_value = NULL;
int error;
int size;
if (!inode->i_op || !inode->i_op->getxattr)
return -EOPNOTSUPP;
error = init_desc(&desc);
if (error)
return error;
error = -ENODATA;
for (xattrname = evm_config_xattrnames; *xattrname != NULL; xattrname++) {
if ((req_xattr_name && req_xattr_value)
&& !strcmp(*xattrname, req_xattr_name)) {
error = 0;
sg_init_one(sg, req_xattr_value, req_xattr_value_len);
crypto_hash_update(&desc, sg, req_xattr_value_len);
continue;
}
size = vfs_getxattr_alloc(dentry, *xattrname,
&xattr_value, xattr_size, GFP_NOFS);
if (size == -ENOMEM) {
error = -ENOMEM;
goto out;
}
if (size < 0)
continue;
error = 0;
xattr_size = size;
sg_init_one(sg, xattr_value, xattr_size);
crypto_hash_update(&desc, sg, xattr_size);
}
hmac_add_misc(&desc, inode, digest);
kfree(xattr_value);
out:
crypto_free_hash(desc.tfm);
return error;
}
/*
* Calculate the hmac and update security.evm xattr
*
* Expects to be called with i_mutex locked.
*/
int evm_update_evmxattr(struct dentry *dentry, const char *xattr_name,
const char *xattr_value, size_t xattr_value_len)
{
struct inode *inode = dentry->d_inode;
u8 hmac[SHA1_DIGEST_SIZE];
int rc = 0;
rc = evm_calc_hmac(dentry, xattr_name, xattr_value,
xattr_value_len, hmac);
if (rc == 0)
rc = __vfs_setxattr_noperm(dentry, XATTR_NAME_EVM,
hmac, SHA1_DIGEST_SIZE, 0);
else if (rc == -ENODATA)
rc = inode->i_op->removexattr(dentry, XATTR_NAME_EVM);
return rc;
}
/*
* Get the key from the TPM for the SHA1-HMAC
*/
int evm_init_key(void)
{
struct key *evm_key;
struct encrypted_key_payload *ekp;
int rc = 0;
evm_key = request_key(&key_type_encrypted, EVMKEY, NULL);
if (IS_ERR(evm_key))
return -ENOENT;
down_read(&evm_key->sem);
ekp = evm_key->payload.data;
if (ekp->decrypted_datalen > MAX_KEY_SIZE) {
rc = -EINVAL;
goto out;
}
memcpy(evmkey, ekp->decrypted_data, ekp->decrypted_datalen);
out:
/* burn the original key contents */
memset(ekp->decrypted_data, 0, ekp->decrypted_datalen);
up_read(&evm_key->sem);
key_put(evm_key);
return rc;
}
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