1/*
  2 * Copyright (C) 2005-2010 IBM Corporation
  3 *
  4 * Authors:
  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_crypto.c
 13 *	 Using root's kernel master key (kmk), calculate the HMAC
 14 */
 15
 16#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
 17
 18#include <linux/module.h>
 19#include <linux/crypto.h>
 20#include <linux/xattr.h>
 21#include <linux/evm.h>
 22#include <keys/encrypted-type.h>
 23#include <crypto/hash.h>
 24#include "evm.h"
 25
 26#define EVMKEY "evm-key"
 27#define MAX_KEY_SIZE 128
 28static unsigned char evmkey[MAX_KEY_SIZE];
 29static int evmkey_len = MAX_KEY_SIZE;
 30
 31struct crypto_shash *hmac_tfm;
 32struct crypto_shash *hash_tfm;
 33
 34static DEFINE_MUTEX(mutex);
 35
 36#define EVM_SET_KEY_BUSY 0
 37
 38static unsigned long evm_set_key_flags;
 39
 40/**
 41 * evm_set_key() - set EVM HMAC key from the kernel
 42 * @key: pointer to a buffer with the key data
 43 * @size: length of the key data
 44 *
 45 * This function allows setting the EVM HMAC key from the kernel
 46 * without using the "encrypted" key subsystem keys. It can be used
 47 * by the crypto HW kernel module which has its own way of managing
 48 * keys.
 49 *
 50 * key length should be between 32 and 128 bytes long
 51 */
 52int evm_set_key(void *key, size_t keylen)
 53{
 54	int rc;
 55
 56	rc = -EBUSY;
 57	if (test_and_set_bit(EVM_SET_KEY_BUSY, &evm_set_key_flags))
 58		goto busy;
 59	rc = -EINVAL;
 60	if (keylen > MAX_KEY_SIZE)
 61		goto inval;
 62	memcpy(evmkey, key, keylen);
 63	evm_initialized |= EVM_INIT_HMAC;
 64	pr_info("key initialized\n");
 65	return 0;
 66inval:
 67	clear_bit(EVM_SET_KEY_BUSY, &evm_set_key_flags);
 68busy:
 69	pr_err("key initialization failed\n");
 70	return rc;
 71}
 72EXPORT_SYMBOL_GPL(evm_set_key);
 73
 74static struct shash_desc *init_desc(char type)
 75{
 76	long rc;
 77	char *algo;
 78	struct crypto_shash **tfm;
 79	struct shash_desc *desc;
 80
 81	if (type == EVM_XATTR_HMAC) {
 82		if (!(evm_initialized & EVM_INIT_HMAC)) {
 83			pr_err("HMAC key is not set\n");
 84			return ERR_PTR(-ENOKEY);
 85		}
 86		tfm = &hmac_tfm;
 87		algo = evm_hmac;
 88	} else {
 89		tfm = &hash_tfm;
 90		algo = evm_hash;
 91	}
 92
 93	if (*tfm == NULL) {
 94		mutex_lock(&mutex);
 95		if (*tfm)
 96			goto out;
 97		*tfm = crypto_alloc_shash(algo, 0, CRYPTO_ALG_ASYNC);
 98		if (IS_ERR(*tfm)) {
 99			rc = PTR_ERR(*tfm);
100			pr_err("Can not allocate %s (reason: %ld)\n", algo, rc);
101			*tfm = NULL;
102			mutex_unlock(&mutex);
103			return ERR_PTR(rc);
104		}
105		if (type == EVM_XATTR_HMAC) {
106			rc = crypto_shash_setkey(*tfm, evmkey, evmkey_len);
107			if (rc) {
108				crypto_free_shash(*tfm);
109				*tfm = NULL;
110				mutex_unlock(&mutex);
111				return ERR_PTR(rc);
112			}
113		}
114out:
115		mutex_unlock(&mutex);
116	}
117
118	desc = kmalloc(sizeof(*desc) + crypto_shash_descsize(*tfm),
119			GFP_KERNEL);
120	if (!desc)
121		return ERR_PTR(-ENOMEM);
122
123	desc->tfm = *tfm;
124	desc->flags = CRYPTO_TFM_REQ_MAY_SLEEP;
125
126	rc = crypto_shash_init(desc);
127	if (rc) {
128		kfree(desc);
129		return ERR_PTR(rc);
130	}
131	return desc;
132}
133
134/* Protect against 'cutting & pasting' security.evm xattr, include inode
135 * specific info.
136 *
137 * (Additional directory/file metadata needs to be added for more complete
138 * protection.)
139 */
140static void hmac_add_misc(struct shash_desc *desc, struct inode *inode,
141			  char *digest)
142{
143	struct h_misc {
144		unsigned long ino;
145		__u32 generation;
146		uid_t uid;
147		gid_t gid;
148		umode_t mode;
149	} hmac_misc;
150
151	memset(&hmac_misc, 0, sizeof(hmac_misc));
152	hmac_misc.ino = inode->i_ino;
153	hmac_misc.generation = inode->i_generation;
154	hmac_misc.uid = from_kuid(&init_user_ns, inode->i_uid);
155	hmac_misc.gid = from_kgid(&init_user_ns, inode->i_gid);
156	hmac_misc.mode = inode->i_mode;
157	crypto_shash_update(desc, (const u8 *)&hmac_misc, sizeof(hmac_misc));
158	if (evm_hmac_attrs & EVM_ATTR_FSUUID)
159		crypto_shash_update(desc, inode->i_sb->s_uuid,
160				    sizeof(inode->i_sb->s_uuid));
161	crypto_shash_final(desc, digest);
162}
163
164/*
165 * Calculate the HMAC value across the set of protected security xattrs.
166 *
167 * Instead of retrieving the requested xattr, for performance, calculate
168 * the hmac using the requested xattr value. Don't alloc/free memory for
169 * each xattr, but attempt to re-use the previously allocated memory.
170 */
171static int evm_calc_hmac_or_hash(struct dentry *dentry,
172				const char *req_xattr_name,
173				const char *req_xattr_value,
174				size_t req_xattr_value_len,
175				char type, char *digest)
176{
177	struct inode *inode = d_backing_inode(dentry);
178	struct shash_desc *desc;
179	char **xattrname;
180	size_t xattr_size = 0;
181	char *xattr_value = NULL;
182	int error;
183	int size;
184
185	if (!inode->i_op->getxattr)
186		return -EOPNOTSUPP;
187	desc = init_desc(type);
188	if (IS_ERR(desc))
189		return PTR_ERR(desc);
190
191	error = -ENODATA;
192	for (xattrname = evm_config_xattrnames; *xattrname != NULL; xattrname++) {
193		if ((req_xattr_name && req_xattr_value)
194		    && !strcmp(*xattrname, req_xattr_name)) {
195			error = 0;
196			crypto_shash_update(desc, (const u8 *)req_xattr_value,
197					     req_xattr_value_len);
198			continue;
199		}
200		size = vfs_getxattr_alloc(dentry, *xattrname,
201					  &xattr_value, xattr_size, GFP_NOFS);
202		if (size == -ENOMEM) {
203			error = -ENOMEM;
204			goto out;
205		}
206		if (size < 0)
207			continue;
208
209		error = 0;
210		xattr_size = size;
211		crypto_shash_update(desc, (const u8 *)xattr_value, xattr_size);
212	}
213	hmac_add_misc(desc, inode, digest);
214
215out:
216	kfree(xattr_value);
217	kfree(desc);
218	return error;
219}
220
221int evm_calc_hmac(struct dentry *dentry, const char *req_xattr_name,
222		  const char *req_xattr_value, size_t req_xattr_value_len,
223		  char *digest)
224{
225	return evm_calc_hmac_or_hash(dentry, req_xattr_name, req_xattr_value,
226				req_xattr_value_len, EVM_XATTR_HMAC, digest);
227}
228
229int evm_calc_hash(struct dentry *dentry, const char *req_xattr_name,
230		  const char *req_xattr_value, size_t req_xattr_value_len,
231		  char *digest)
232{
233	return evm_calc_hmac_or_hash(dentry, req_xattr_name, req_xattr_value,
234				req_xattr_value_len, IMA_XATTR_DIGEST, digest);
235}
236
237/*
238 * Calculate the hmac and update security.evm xattr
239 *
240 * Expects to be called with i_mutex locked.
241 */
242int evm_update_evmxattr(struct dentry *dentry, const char *xattr_name,
243			const char *xattr_value, size_t xattr_value_len)
244{
245	struct inode *inode = d_backing_inode(dentry);
246	struct evm_ima_xattr_data xattr_data;
247	int rc = 0;
248
249	rc = evm_calc_hmac(dentry, xattr_name, xattr_value,
250			   xattr_value_len, xattr_data.digest);
251	if (rc == 0) {
252		xattr_data.type = EVM_XATTR_HMAC;
253		rc = __vfs_setxattr_noperm(dentry, XATTR_NAME_EVM,
254					   &xattr_data,
255					   sizeof(xattr_data), 0);
256	} else if (rc == -ENODATA && inode->i_op->removexattr) {
257		rc = inode->i_op->removexattr(dentry, XATTR_NAME_EVM);
258	}
259	return rc;
260}
261
262int evm_init_hmac(struct inode *inode, const struct xattr *lsm_xattr,
263		  char *hmac_val)
264{
265	struct shash_desc *desc;
266
267	desc = init_desc(EVM_XATTR_HMAC);
268	if (IS_ERR(desc)) {
269		pr_info("init_desc failed\n");
270		return PTR_ERR(desc);
271	}
272
273	crypto_shash_update(desc, lsm_xattr->value, lsm_xattr->value_len);
274	hmac_add_misc(desc, inode, hmac_val);
275	kfree(desc);
276	return 0;
277}
278
279/*
280 * Get the key from the TPM for the SHA1-HMAC
281 */
282int evm_init_key(void)
283{
284	struct key *evm_key;
285	struct encrypted_key_payload *ekp;
286	int rc;
287
288	evm_key = request_key(&key_type_encrypted, EVMKEY, NULL);
289	if (IS_ERR(evm_key))
290		return -ENOENT;
291
292	down_read(&evm_key->sem);
293	ekp = evm_key->payload.data[0];
294
295	rc = evm_set_key(ekp->decrypted_data, ekp->decrypted_datalen);
296
297	/* burn the original key contents */
298	memset(ekp->decrypted_data, 0, ekp->decrypted_datalen);
299	up_read(&evm_key->sem);
300	key_put(evm_key);
301	return rc;
302}