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
28 static unsigned char evmkey[MAX_KEY_SIZE];
29 static int evmkey_len = MAX_KEY_SIZE;
30
31 struct crypto_shash *hmac_tfm;
32 struct crypto_shash *hash_tfm;
33
34 static DEFINE_MUTEX(mutex);
35
36 #define EVM_SET_KEY_BUSY 0
37
38 static 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 */
evm_set_key(void * key,size_t keylen)52 int 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;
66 inval:
67 clear_bit(EVM_SET_KEY_BUSY, &evm_set_key_flags);
68 busy:
69 pr_err("key initialization failed\n");
70 return rc;
71 }
72 EXPORT_SYMBOL_GPL(evm_set_key);
73
init_desc(char type)74 static 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,
98 CRYPTO_ALG_ASYNC | CRYPTO_NOLOAD);
99 if (IS_ERR(*tfm)) {
100 rc = PTR_ERR(*tfm);
101 pr_err("Can not allocate %s (reason: %ld)\n", algo, rc);
102 *tfm = NULL;
103 mutex_unlock(&mutex);
104 return ERR_PTR(rc);
105 }
106 if (type == EVM_XATTR_HMAC) {
107 rc = crypto_shash_setkey(*tfm, evmkey, evmkey_len);
108 if (rc) {
109 crypto_free_shash(*tfm);
110 *tfm = NULL;
111 mutex_unlock(&mutex);
112 return ERR_PTR(rc);
113 }
114 }
115 out:
116 mutex_unlock(&mutex);
117 }
118
119 desc = kmalloc(sizeof(*desc) + crypto_shash_descsize(*tfm),
120 GFP_KERNEL);
121 if (!desc)
122 return ERR_PTR(-ENOMEM);
123
124 desc->tfm = *tfm;
125 desc->flags = CRYPTO_TFM_REQ_MAY_SLEEP;
126
127 rc = crypto_shash_init(desc);
128 if (rc) {
129 kfree(desc);
130 return ERR_PTR(rc);
131 }
132 return desc;
133 }
134
135 /* Protect against 'cutting & pasting' security.evm xattr, include inode
136 * specific info.
137 *
138 * (Additional directory/file metadata needs to be added for more complete
139 * protection.)
140 */
hmac_add_misc(struct shash_desc * desc,struct inode * inode,char type,char * digest)141 static void hmac_add_misc(struct shash_desc *desc, struct inode *inode,
142 char type, char *digest)
143 {
144 struct h_misc {
145 unsigned long ino;
146 __u32 generation;
147 uid_t uid;
148 gid_t gid;
149 umode_t mode;
150 } hmac_misc;
151
152 memset(&hmac_misc, 0, sizeof(hmac_misc));
153 /* Don't include the inode or generation number in portable
154 * signatures
155 */
156 if (type != EVM_XATTR_PORTABLE_DIGSIG) {
157 hmac_misc.ino = inode->i_ino;
158 hmac_misc.generation = inode->i_generation;
159 }
160 /* The hmac uid and gid must be encoded in the initial user
161 * namespace (not the filesystems user namespace) as encoding
162 * them in the filesystems user namespace allows an attack
163 * where first they are written in an unprivileged fuse mount
164 * of a filesystem and then the system is tricked to mount the
165 * filesystem for real on next boot and trust it because
166 * everything is signed.
167 */
168 hmac_misc.uid = from_kuid(&init_user_ns, inode->i_uid);
169 hmac_misc.gid = from_kgid(&init_user_ns, inode->i_gid);
170 hmac_misc.mode = inode->i_mode;
171 crypto_shash_update(desc, (const u8 *)&hmac_misc, sizeof(hmac_misc));
172 if ((evm_hmac_attrs & EVM_ATTR_FSUUID) &&
173 type != EVM_XATTR_PORTABLE_DIGSIG)
174 crypto_shash_update(desc, &inode->i_sb->s_uuid.b[0],
175 sizeof(inode->i_sb->s_uuid));
176 crypto_shash_final(desc, digest);
177 }
178
179 /*
180 * Calculate the HMAC value across the set of protected security xattrs.
181 *
182 * Instead of retrieving the requested xattr, for performance, calculate
183 * the hmac using the requested xattr value. Don't alloc/free memory for
184 * each xattr, but attempt to re-use the previously allocated memory.
185 */
evm_calc_hmac_or_hash(struct dentry * dentry,const char * req_xattr_name,const char * req_xattr_value,size_t req_xattr_value_len,char type,char * digest)186 static int evm_calc_hmac_or_hash(struct dentry *dentry,
187 const char *req_xattr_name,
188 const char *req_xattr_value,
189 size_t req_xattr_value_len,
190 char type, char *digest)
191 {
192 struct inode *inode = d_backing_inode(dentry);
193 struct shash_desc *desc;
194 char **xattrname;
195 size_t xattr_size = 0;
196 char *xattr_value = NULL;
197 int error;
198 int size;
199 bool ima_present = false;
200
201 if (!(inode->i_opflags & IOP_XATTR))
202 return -EOPNOTSUPP;
203
204 desc = init_desc(type);
205 if (IS_ERR(desc))
206 return PTR_ERR(desc);
207
208 error = -ENODATA;
209 for (xattrname = evm_config_xattrnames; *xattrname != NULL; xattrname++) {
210 bool is_ima = false;
211
212 if (strcmp(*xattrname, XATTR_NAME_IMA) == 0)
213 is_ima = true;
214
215 if ((req_xattr_name && req_xattr_value)
216 && !strcmp(*xattrname, req_xattr_name)) {
217 error = 0;
218 crypto_shash_update(desc, (const u8 *)req_xattr_value,
219 req_xattr_value_len);
220 if (is_ima)
221 ima_present = true;
222 continue;
223 }
224 size = vfs_getxattr_alloc(dentry, *xattrname,
225 &xattr_value, xattr_size, GFP_NOFS);
226 if (size == -ENOMEM) {
227 error = -ENOMEM;
228 goto out;
229 }
230 if (size < 0)
231 continue;
232
233 error = 0;
234 xattr_size = size;
235 crypto_shash_update(desc, (const u8 *)xattr_value, xattr_size);
236 if (is_ima)
237 ima_present = true;
238 }
239 hmac_add_misc(desc, inode, type, digest);
240
241 /* Portable EVM signatures must include an IMA hash */
242 if (type == EVM_XATTR_PORTABLE_DIGSIG && !ima_present)
243 return -EPERM;
244 out:
245 kfree(xattr_value);
246 kfree(desc);
247 return error;
248 }
249
evm_calc_hmac(struct dentry * dentry,const char * req_xattr_name,const char * req_xattr_value,size_t req_xattr_value_len,char * digest)250 int evm_calc_hmac(struct dentry *dentry, const char *req_xattr_name,
251 const char *req_xattr_value, size_t req_xattr_value_len,
252 char *digest)
253 {
254 return evm_calc_hmac_or_hash(dentry, req_xattr_name, req_xattr_value,
255 req_xattr_value_len, EVM_XATTR_HMAC, digest);
256 }
257
evm_calc_hash(struct dentry * dentry,const char * req_xattr_name,const char * req_xattr_value,size_t req_xattr_value_len,char type,char * digest)258 int evm_calc_hash(struct dentry *dentry, const char *req_xattr_name,
259 const char *req_xattr_value, size_t req_xattr_value_len,
260 char type, char *digest)
261 {
262 return evm_calc_hmac_or_hash(dentry, req_xattr_name, req_xattr_value,
263 req_xattr_value_len, type, digest);
264 }
265
evm_is_immutable(struct dentry * dentry,struct inode * inode)266 static int evm_is_immutable(struct dentry *dentry, struct inode *inode)
267 {
268 const struct evm_ima_xattr_data *xattr_data = NULL;
269 struct integrity_iint_cache *iint;
270 int rc = 0;
271
272 iint = integrity_iint_find(inode);
273 if (iint && (iint->flags & EVM_IMMUTABLE_DIGSIG))
274 return 1;
275
276 /* Do this the hard way */
277 rc = vfs_getxattr_alloc(dentry, XATTR_NAME_EVM, (char **)&xattr_data, 0,
278 GFP_NOFS);
279 if (rc <= 0) {
280 if (rc == -ENODATA)
281 return 0;
282 return rc;
283 }
284 if (xattr_data->type == EVM_XATTR_PORTABLE_DIGSIG)
285 rc = 1;
286 else
287 rc = 0;
288
289 kfree(xattr_data);
290 return rc;
291 }
292
293
294 /*
295 * Calculate the hmac and update security.evm xattr
296 *
297 * Expects to be called with i_mutex locked.
298 */
evm_update_evmxattr(struct dentry * dentry,const char * xattr_name,const char * xattr_value,size_t xattr_value_len)299 int evm_update_evmxattr(struct dentry *dentry, const char *xattr_name,
300 const char *xattr_value, size_t xattr_value_len)
301 {
302 struct inode *inode = d_backing_inode(dentry);
303 struct evm_ima_xattr_data xattr_data;
304 int rc = 0;
305
306 /*
307 * Don't permit any transformation of the EVM xattr if the signature
308 * is of an immutable type
309 */
310 rc = evm_is_immutable(dentry, inode);
311 if (rc < 0)
312 return rc;
313 if (rc)
314 return -EPERM;
315
316 rc = evm_calc_hmac(dentry, xattr_name, xattr_value,
317 xattr_value_len, xattr_data.digest);
318 if (rc == 0) {
319 xattr_data.type = EVM_XATTR_HMAC;
320 rc = __vfs_setxattr_noperm(dentry, XATTR_NAME_EVM,
321 &xattr_data,
322 sizeof(xattr_data), 0);
323 } else if (rc == -ENODATA && (inode->i_opflags & IOP_XATTR)) {
324 rc = __vfs_removexattr(dentry, XATTR_NAME_EVM);
325 }
326 return rc;
327 }
328
evm_init_hmac(struct inode * inode,const struct xattr * lsm_xattr,char * hmac_val)329 int evm_init_hmac(struct inode *inode, const struct xattr *lsm_xattr,
330 char *hmac_val)
331 {
332 struct shash_desc *desc;
333
334 desc = init_desc(EVM_XATTR_HMAC);
335 if (IS_ERR(desc)) {
336 pr_info("init_desc failed\n");
337 return PTR_ERR(desc);
338 }
339
340 crypto_shash_update(desc, lsm_xattr->value, lsm_xattr->value_len);
341 hmac_add_misc(desc, inode, EVM_XATTR_HMAC, hmac_val);
342 kfree(desc);
343 return 0;
344 }
345
346 /*
347 * Get the key from the TPM for the SHA1-HMAC
348 */
evm_init_key(void)349 int evm_init_key(void)
350 {
351 struct key *evm_key;
352 struct encrypted_key_payload *ekp;
353 int rc;
354
355 evm_key = request_key(&key_type_encrypted, EVMKEY, NULL);
356 if (IS_ERR(evm_key))
357 return -ENOENT;
358
359 down_read(&evm_key->sem);
360 ekp = evm_key->payload.data[0];
361
362 rc = evm_set_key(ekp->decrypted_data, ekp->decrypted_datalen);
363
364 /* burn the original key contents */
365 memset(ekp->decrypted_data, 0, ekp->decrypted_datalen);
366 up_read(&evm_key->sem);
367 key_put(evm_key);
368 return rc;
369 }
370