summaryrefslogtreecommitdiffstats
path: root/security/integrity/evm/evm_crypto.c
blob: 0450d79afdc8fc7dd85d77f35b82ea921957f6d7 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
// SPDX-License-Identifier: GPL-2.0-only
/*
 * Copyright (C) 2005-2010 IBM Corporation
 *
 * Authors:
 * Mimi Zohar <zohar@us.ibm.com>
 * Kylene Hall <kjhall@us.ibm.com>
 *
 * File: evm_crypto.c
 *	 Using root's kernel master key (kmk), calculate the HMAC
 */

#define pr_fmt(fmt) "EVM: "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, *tmp_tfm = NULL;
	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 {
		if (hash_algo >= HASH_ALGO__LAST)
			return ERR_PTR(-EINVAL);

		tfm = &evm_tfm[hash_algo];
		algo = hash_algo_name[hash_algo];
	}

	if (*tfm)
		goto alloc;
	mutex_lock(&mutex);
	if (*tfm)
		goto unlock;

	tmp_tfm = crypto_alloc_shash(algo, 0, CRYPTO_NOLOAD);
	if (IS_ERR(tmp_tfm)) {
		pr_err("Can not allocate %s (reason: %ld)\n", algo,
		       PTR_ERR(tmp_tfm));
		mutex_unlock(&mutex);
		return ERR_CAST(tmp_tfm);
	}
	if (type == EVM_XATTR_HMAC) {
		rc = crypto_shash_setkey(tmp_tfm, evmkey, evmkey_len);
		if (rc) {
			crypto_free_shash(tmp_tfm);
			mutex_unlock(&mutex);
			return ERR_PTR(rc);
		}
	}
	*tfm = tmp_tfm;
unlock:
	mutex_unlock(&mutex);
alloc:
	desc = kmalloc(sizeof(*desc) + crypto_shash_descsize(*tfm),
			GFP_KERNEL);
	if (!desc) {
		crypto_free_shash(tmp_tfm);
		return ERR_PTR(-ENOMEM);
	}

	desc->tfm = *tfm;

	rc = crypto_shash_init(desc);
	if (rc) {
		crypto_free_shash(tmp_tfm);
		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, (u8 *)&inode->i_sb->s_uuid, UUID_SIZE);
	crypto_shash_final(desc, digest);

	pr_debug("hmac_misc: (%zu) [%*phN]\n", sizeof(struct h_misc),
		 (int)sizeof(struct h_misc), &hmac_misc);
}

/*
 * Dump large security xattr values as a continuous ascii hexademical string.
 * (pr_debug is limited to 64 bytes.)
 */
static void dump_security_xattr(const char *prefix, const void *src,
				size_t count)
{
#if defined(DEBUG) || defined(CONFIG_DYNAMIC_DEBUG)
	char *asciihex, *p;

	p = asciihex = kmalloc(count * 2 + 1, GFP_KERNEL);
	if (!asciihex)
		return;

	p = bin2hex(p, src, count);
	*p = 0;
	pr_debug("%s: (%zu) %.*s\n", prefix, count, (int)count * 2, asciihex);
	kfree(asciihex);
#endif
}

/*
 * 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, user_space_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_lockless(xattr, &evm_config_xattrnames, list) {
		bool is_ima = false;

		if (strcmp(xattr->name, XATTR_NAME_IMA) == 0)
			is_ima = true;

		/*
		 * Skip non-enabled xattrs for locally calculated
		 * signatures/HMACs.
		 */
		if (type != EVM_XATTR_PORTABLE_DIGSIG && !xattr->enabled)
			continue;

		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;

			if (req_xattr_value_len < 64)
				pr_debug("%s: (%zu) [%*phN]\n", req_xattr_name,
					 req_xattr_value_len,
					 (int)req_xattr_value_len,
					 req_xattr_value);
			else
				dump_security_xattr(req_xattr_name,
						    req_xattr_value,
						    req_xattr_value_len);
			continue;
		}
		size = vfs_getxattr_alloc(&init_user_ns, dentry, xattr->name,
					  &xattr_value, xattr_size, GFP_NOFS);
		if (size == -ENOMEM) {
			error = -ENOMEM;
			goto out;
		}
		if (size < 0)
			continue;

		user_space_size = vfs_getxattr(&init_user_ns, dentry,
					       xattr->name, NULL, 0);
		if (user_space_size != size)
			pr_debug("file %s: xattr %s size mismatch (kernel: %d, user: %d)\n",
				 dentry->d_name.name, xattr->name, size,
				 user_space_size);
		error = 0;
		xattr_size = size;
		crypto_shash_update(desc, (const u8 *)xattr_value, xattr_size);
		if (is_ima)
			ima_present = true;

		if (xattr_size < 64)
			pr_debug("%s: (%zu) [%*phN]", xattr->name, xattr_size,
				 (int)xattr_size, xattr_value);
		else
			dump_security_xattr(xattr->name, xattr_value,
					    xattr_size);
	}
	hmac_add_misc(desc, inode, type, data->digest);

	/* Portable EVM signatures must include an IMA hash */
	if (type == EVM_XATTR_PORTABLE_DIGSIG && !ima_present)
		error = -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)
{
	const struct evm_ima_xattr_data *xattr_data = NULL;
	struct integrity_iint_cache *iint;
	int rc = 0;

	iint = integrity_iint_find(inode);
	if (iint && (iint->flags & EVM_IMMUTABLE_DIGSIG))
		return 1;

	/* Do this the hard way */
	rc = vfs_getxattr_alloc(&init_user_ns, dentry, XATTR_NAME_EVM,
				(char **)&xattr_data, 0, GFP_NOFS);
	if (rc <= 0) {
		if (rc == -ENODATA)
			return 0;
		return rc;
	}
	if (xattr_data->type == EVM_XATTR_PORTABLE_DIGSIG)
		rc = 1;
	else
		rc = 0;

	kfree(xattr_data);
	return rc;
}


/*
 * 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 = d_backing_inode(dentry);
	struct evm_digest data;
	int rc = 0;

	/*
	 * Don't permit any transformation of the EVM xattr if the signature
	 * is of an immutable type
	 */
	rc = evm_is_immutable(dentry, inode);
	if (rc < 0)
		return rc;
	if (rc)
		return -EPERM;

	data.hdr.algo = HASH_ALGO_SHA1;
	rc = evm_calc_hmac(dentry, xattr_name, xattr_value,
			   xattr_value_len, &data);
	if (rc == 0) {
		data.hdr.xattr.sha1.type = EVM_XATTR_HMAC;
		rc = __vfs_setxattr_noperm(&init_user_ns, dentry,
					   XATTR_NAME_EVM,
					   &data.hdr.xattr.data[1],
					   SHA1_DIGEST_SIZE + 1, 0);
	} else if (rc == -ENODATA && (inode->i_opflags & IOP_XATTR)) {
		rc = __vfs_removexattr(&init_user_ns, dentry, XATTR_NAME_EVM);
	}
	return rc;
}

int evm_init_hmac(struct inode *inode, const struct xattr *lsm_xattr,
		  char *hmac_val)
{
	struct shash_desc *desc;

	desc = init_desc(EVM_XATTR_HMAC, HASH_ALGO_SHA1);
	if (IS_ERR(desc)) {
		pr_info("init_desc failed\n");
		return PTR_ERR(desc);
	}

	crypto_shash_update(desc, lsm_xattr->value, lsm_xattr->value_len);
	hmac_add_misc(desc, inode, EVM_XATTR_HMAC, hmac_val);
	kfree(desc);
	return 0;
}

/*
 * 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;

	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[0];

	rc = evm_set_key(ekp->decrypted_data, ekp->decrypted_datalen);

	/* burn the original key contents */
	memset(ekp->decrypted_data, 0, ekp->decrypted_datalen);
	up_read(&evm_key->sem);
	key_put(evm_key);
	return rc;
}