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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#include <linux/module.h>
17#include <linux/crypto.h>
18#include <linux/xattr.h>
19#include <keys/encrypted-type.h>
20#include <crypto/hash.h>
21#include "evm.h"
22
23#define EVMKEY "evm-key"
24#define MAX_KEY_SIZE 128
25static unsigned char evmkey[MAX_KEY_SIZE];
26static int evmkey_len = MAX_KEY_SIZE;
27
28struct crypto_shash *hmac_tfm;
29struct crypto_shash *hash_tfm;
30
31static DEFINE_MUTEX(mutex);
32
33static struct shash_desc *init_desc(char type)
34{
35 long rc;
36 char *algo;
37 struct crypto_shash **tfm;
38 struct shash_desc *desc;
39
40 if (type == EVM_XATTR_HMAC) {
41 tfm = &hmac_tfm;
42 algo = evm_hmac;
43 } else {
44 tfm = &hash_tfm;
45 algo = evm_hash;
46 }
47
48 if (*tfm == NULL) {
49 mutex_lock(&mutex);
50 if (*tfm)
51 goto out;
52 *tfm = crypto_alloc_shash(algo, 0, CRYPTO_ALG_ASYNC);
53 if (IS_ERR(*tfm)) {
54 rc = PTR_ERR(*tfm);
55 pr_err("Can not allocate %s (reason: %ld)\n", algo, rc);
56 *tfm = NULL;
57 mutex_unlock(&mutex);
58 return ERR_PTR(rc);
59 }
60 if (type == EVM_XATTR_HMAC) {
61 rc = crypto_shash_setkey(*tfm, evmkey, evmkey_len);
62 if (rc) {
63 crypto_free_shash(*tfm);
64 *tfm = NULL;
65 mutex_unlock(&mutex);
66 return ERR_PTR(rc);
67 }
68 }
69out:
70 mutex_unlock(&mutex);
71 }
72
73 desc = kmalloc(sizeof(*desc) + crypto_shash_descsize(*tfm),
74 GFP_KERNEL);
75 if (!desc)
76 return ERR_PTR(-ENOMEM);
77
78 desc->tfm = *tfm;
79 desc->flags = CRYPTO_TFM_REQ_MAY_SLEEP;
80
81 rc = crypto_shash_init(desc);
82 if (rc) {
83 kfree(desc);
84 return ERR_PTR(rc);
85 }
86 return desc;
87}
88
89/* Protect against 'cutting & pasting' security.evm xattr, include inode
90 * specific info.
91 *
92 * (Additional directory/file metadata needs to be added for more complete
93 * protection.)
94 */
95static void hmac_add_misc(struct shash_desc *desc, struct inode *inode,
96 char *digest)
97{
98 struct h_misc {
99 unsigned long ino;
100 __u32 generation;
101 uid_t uid;
102 gid_t gid;
103 umode_t mode;
104 } hmac_misc;
105
106 memset(&hmac_misc, 0, sizeof hmac_misc);
107 hmac_misc.ino = inode->i_ino;
108 hmac_misc.generation = inode->i_generation;
109 hmac_misc.uid = inode->i_uid;
110 hmac_misc.gid = inode->i_gid;
111 hmac_misc.mode = inode->i_mode;
112 crypto_shash_update(desc, (const u8 *)&hmac_misc, sizeof hmac_misc);
113 crypto_shash_final(desc, digest);
114}
115
116/*
117 * Calculate the HMAC value across the set of protected security xattrs.
118 *
119 * Instead of retrieving the requested xattr, for performance, calculate
120 * the hmac using the requested xattr value. Don't alloc/free memory for
121 * each xattr, but attempt to re-use the previously allocated memory.
122 */
123static int evm_calc_hmac_or_hash(struct dentry *dentry,
124 const char *req_xattr_name,
125 const char *req_xattr_value,
126 size_t req_xattr_value_len,
127 char type, char *digest)
128{
129 struct inode *inode = dentry->d_inode;
130 struct shash_desc *desc;
131 char **xattrname;
132 size_t xattr_size = 0;
133 char *xattr_value = NULL;
134 int error;
135 int size;
136
137 if (!inode->i_op || !inode->i_op->getxattr)
138 return -EOPNOTSUPP;
139 desc = init_desc(type);
140 if (IS_ERR(desc))
141 return PTR_ERR(desc);
142
143 error = -ENODATA;
144 for (xattrname = evm_config_xattrnames; *xattrname != NULL; xattrname++) {
145 if ((req_xattr_name && req_xattr_value)
146 && !strcmp(*xattrname, req_xattr_name)) {
147 error = 0;
148 crypto_shash_update(desc, (const u8 *)req_xattr_value,
149 req_xattr_value_len);
150 continue;
151 }
152 size = vfs_getxattr_alloc(dentry, *xattrname,
153 &xattr_value, xattr_size, GFP_NOFS);
154 if (size == -ENOMEM) {
155 error = -ENOMEM;
156 goto out;
157 }
158 if (size < 0)
159 continue;
160
161 error = 0;
162 xattr_size = size;
163 crypto_shash_update(desc, (const u8 *)xattr_value, xattr_size);
164 }
165 hmac_add_misc(desc, inode, digest);
166
167out:
168 kfree(xattr_value);
169 kfree(desc);
170 return error;
171}
172
173int evm_calc_hmac(struct dentry *dentry, const char *req_xattr_name,
174 const char *req_xattr_value, size_t req_xattr_value_len,
175 char *digest)
176{
177 return evm_calc_hmac_or_hash(dentry, req_xattr_name, req_xattr_value,
178 req_xattr_value_len, EVM_XATTR_HMAC, digest);
179}
180
181int evm_calc_hash(struct dentry *dentry, const char *req_xattr_name,
182 const char *req_xattr_value, size_t req_xattr_value_len,
183 char *digest)
184{
185 return evm_calc_hmac_or_hash(dentry, req_xattr_name, req_xattr_value,
186 req_xattr_value_len, IMA_XATTR_DIGEST, digest);
187}
188
189/*
190 * Calculate the hmac and update security.evm xattr
191 *
192 * Expects to be called with i_mutex locked.
193 */
194int evm_update_evmxattr(struct dentry *dentry, const char *xattr_name,
195 const char *xattr_value, size_t xattr_value_len)
196{
197 struct inode *inode = dentry->d_inode;
198 struct evm_ima_xattr_data xattr_data;
199 int rc = 0;
200
201 rc = evm_calc_hmac(dentry, xattr_name, xattr_value,
202 xattr_value_len, xattr_data.digest);
203 if (rc == 0) {
204 xattr_data.type = EVM_XATTR_HMAC;
205 rc = __vfs_setxattr_noperm(dentry, XATTR_NAME_EVM,
206 &xattr_data,
207 sizeof(xattr_data), 0);
208 }
209 else if (rc == -ENODATA)
210 rc = inode->i_op->removexattr(dentry, XATTR_NAME_EVM);
211 return rc;
212}
213
214int evm_init_hmac(struct inode *inode, const struct xattr *lsm_xattr,
215 char *hmac_val)
216{
217 struct shash_desc *desc;
218
219 desc = init_desc(EVM_XATTR_HMAC);
220 if (IS_ERR(desc)) {
221 printk(KERN_INFO "init_desc failed\n");
222 return PTR_ERR(desc);
223 }
224
225 crypto_shash_update(desc, lsm_xattr->value, lsm_xattr->value_len);
226 hmac_add_misc(desc, inode, hmac_val);
227 kfree(desc);
228 return 0;
229}
230
231/*
232 * Get the key from the TPM for the SHA1-HMAC
233 */
234int evm_init_key(void)
235{
236 struct key *evm_key;
237 struct encrypted_key_payload *ekp;
238 int rc = 0;
239
240 evm_key = request_key(&key_type_encrypted, EVMKEY, NULL);
241 if (IS_ERR(evm_key))
242 return -ENOENT;
243
244 down_read(&evm_key->sem);
245 ekp = evm_key->payload.data;
246 if (ekp->decrypted_datalen > MAX_KEY_SIZE) {
247 rc = -EINVAL;
248 goto out;
249 }
250 memcpy(evmkey, ekp->decrypted_data, ekp->decrypted_datalen);
251out:
252 /* burn the original key contents */
253 memset(ekp->decrypted_data, 0, ekp->decrypted_datalen);
254 up_read(&evm_key->sem);
255 key_put(evm_key);
256 return rc;
257}