summaryrefslogtreecommitdiff
path: root/security/integrity/evm/evm_main.c
blob: 40220124364caa075019cef979a4a13387955835 (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
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
/*
 * Copyright (C) 2005-2010 IBM Corporation
 *
 * Author:
 * 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_main.c
 *	implements evm_inode_setxattr, evm_inode_post_setxattr,
 *	evm_inode_removexattr, and evm_verifyxattr
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/module.h>
#include <linux/crypto.h>
#include <linux/audit.h>
#include <linux/xattr.h>
#include <linux/integrity.h>
#include <linux/evm.h>
#include <crypto/hash.h>
#include "evm.h"

int evm_initialized;

static char *integrity_status_msg[] = {
	"pass", "fail", "no_label", "no_xattrs", "unknown"
};
char *evm_hmac = "hmac(sha1)";
char *evm_hash = "sha1";
int evm_hmac_attrs;

char *evm_config_xattrnames[] = {
#ifdef CONFIG_SECURITY_SELINUX
	XATTR_NAME_SELINUX,
#endif
#ifdef CONFIG_SECURITY_SMACK
	XATTR_NAME_SMACK,
#ifdef CONFIG_EVM_EXTRA_SMACK_XATTRS
	XATTR_NAME_SMACKEXEC,
	XATTR_NAME_SMACKTRANSMUTE,
	XATTR_NAME_SMACKMMAP,
#endif
#endif
#ifdef CONFIG_IMA_APPRAISE
	XATTR_NAME_IMA,
#endif
	XATTR_NAME_CAPS,
	NULL
};

static int evm_fixmode;
static int __init evm_set_fixmode(char *str)
{
	if (strncmp(str, "fix", 3) == 0)
		evm_fixmode = 1;
	return 0;
}
__setup("evm=", evm_set_fixmode);

static void __init evm_init_config(void)
{
#ifdef CONFIG_EVM_ATTR_FSUUID
	evm_hmac_attrs |= EVM_ATTR_FSUUID;
#endif
	pr_info("HMAC attrs: 0x%x\n", evm_hmac_attrs);
}

static int evm_find_protected_xattrs(struct dentry *dentry)
{
	struct inode *inode = dentry->d_inode;
	char **xattr;
	int error;
	int count = 0;

	if (!inode->i_op->getxattr)
		return -EOPNOTSUPP;

	for (xattr = evm_config_xattrnames; *xattr != NULL; xattr++) {
		error = inode->i_op->getxattr(dentry, *xattr, NULL, 0);
		if (error < 0) {
			if (error == -ENODATA)
				continue;
			return error;
		}
		count++;
	}

	return count;
}

/*
 * evm_verify_hmac - calculate and compare the HMAC with the EVM xattr
 *
 * Compute the HMAC on the dentry's protected set of extended attributes
 * and compare it against the stored security.evm xattr.
 *
 * For performance:
 * - use the previoulsy retrieved xattr value and length to calculate the
 *   HMAC.)
 * - cache the verification result in the iint, when available.
 *
 * Returns integrity status
 */
static enum integrity_status evm_verify_hmac(struct dentry *dentry,
					     const char *xattr_name,
					     char *xattr_value,
					     size_t xattr_value_len,
					     struct integrity_iint_cache *iint)
{
	struct evm_ima_xattr_data *xattr_data = NULL;
	struct evm_ima_xattr_data calc;
	enum integrity_status evm_status = INTEGRITY_PASS;
	int rc, xattr_len;

	if (iint && iint->evm_status == INTEGRITY_PASS)
		return iint->evm_status;

	/* if status is not PASS, try to check again - against -ENOMEM */

	/* first need to know the sig type */
	rc = vfs_getxattr_alloc(dentry, XATTR_NAME_EVM, (char **)&xattr_data, 0,
				GFP_NOFS);
	if (rc <= 0) {
		evm_status = INTEGRITY_FAIL;
		if (rc == -ENODATA) {
			rc = evm_find_protected_xattrs(dentry);
			if (rc > 0)
				evm_status = INTEGRITY_NOLABEL;
			else if (rc == 0)
				evm_status = INTEGRITY_NOXATTRS; /* new file */
		} else if (rc == -EOPNOTSUPP) {
			evm_status = INTEGRITY_UNKNOWN;
		}
		goto out;
	}

	xattr_len = rc;

	/* check value type */
	switch (xattr_data->type) {
	case EVM_XATTR_HMAC:
		rc = evm_calc_hmac(dentry, xattr_name, xattr_value,
				   xattr_value_len, calc.digest);
		if (rc)
			break;
		rc = memcmp(xattr_data->digest, calc.digest,
			    sizeof(calc.digest));
		if (rc)
			rc = -EINVAL;
		break;
	case EVM_IMA_XATTR_DIGSIG:
		rc = evm_calc_hash(dentry, xattr_name, xattr_value,
				xattr_value_len, calc.digest);
		if (rc)
			break;
		rc = integrity_digsig_verify(INTEGRITY_KEYRING_EVM,
					(const char *)xattr_data, xattr_len,
					calc.digest, sizeof(calc.digest));
		if (!rc) {
			/* we probably want to replace rsa with hmac here */
			evm_update_evmxattr(dentry, xattr_name, xattr_value,
				   xattr_value_len);
		}
		break;
	default:
		rc = -EINVAL;
		break;
	}

	if (rc)
		evm_status = (rc == -ENODATA) ?
				INTEGRITY_NOXATTRS : INTEGRITY_FAIL;
out:
	if (iint)
		iint->evm_status = evm_status;
	kfree(xattr_data);
	return evm_status;
}

static int evm_protected_xattr(const char *req_xattr_name)
{
	char **xattrname;
	int namelen;
	int found = 0;

	namelen = strlen(req_xattr_name);
	for (xattrname = evm_config_xattrnames; *xattrname != NULL; xattrname++) {
		if ((strlen(*xattrname) == namelen)
		    && (strncmp(req_xattr_name, *xattrname, namelen) == 0)) {
			found = 1;
			break;
		}
		if (strncmp(req_xattr_name,
			    *xattrname + XATTR_SECURITY_PREFIX_LEN,
			    strlen(req_xattr_name)) == 0) {
			found = 1;
			break;
		}
	}
	return found;
}

/**
 * evm_verifyxattr - verify the integrity of the requested xattr
 * @dentry: object of the verify xattr
 * @xattr_name: requested xattr
 * @xattr_value: requested xattr value
 * @xattr_value_len: requested xattr value length
 *
 * Calculate the HMAC for the given dentry and verify it against the stored
 * security.evm xattr. For performance, use the xattr value and length
 * previously retrieved to calculate the HMAC.
 *
 * Returns the xattr integrity status.
 *
 * This function requires the caller to lock the inode's i_mutex before it
 * is executed.
 */
enum integrity_status evm_verifyxattr(struct dentry *dentry,
				      const char *xattr_name,
				      void *xattr_value, size_t xattr_value_len,
				      struct integrity_iint_cache *iint)
{
	if (!evm_initialized || !evm_protected_xattr(xattr_name))
		return INTEGRITY_UNKNOWN;

	if (!iint) {
		iint = integrity_iint_find(dentry->d_inode);
		if (!iint)
			return INTEGRITY_UNKNOWN;
	}
	return evm_verify_hmac(dentry, xattr_name, xattr_value,
				 xattr_value_len, iint);
}
EXPORT_SYMBOL_GPL(evm_verifyxattr);

/*
 * evm_verify_current_integrity - verify the dentry's metadata integrity
 * @dentry: pointer to the affected dentry
 *
 * Verify and return the dentry's metadata integrity. The exceptions are
 * before EVM is initialized or in 'fix' mode.
 */
static enum integrity_status evm_verify_current_integrity(struct dentry *dentry)
{
	struct inode *inode = dentry->d_inode;

	if (!evm_initialized || !S_ISREG(inode->i_mode) || evm_fixmode)
		return 0;
	return evm_verify_hmac(dentry, NULL, NULL, 0, NULL);
}

/*
 * evm_protect_xattr - protect the EVM extended attribute
 *
 * Prevent security.evm from being modified or removed without the
 * necessary permissions or when the existing value is invalid.
 *
 * The posix xattr acls are 'system' prefixed, which normally would not
 * affect security.evm.  An interesting side affect of writing posix xattr
 * acls is their modifying of the i_mode, which is included in security.evm.
 * For posix xattr acls only, permit security.evm, even if it currently
 * doesn't exist, to be updated.
 */
static int evm_protect_xattr(struct dentry *dentry, const char *xattr_name,
			     const void *xattr_value, size_t xattr_value_len)
{
	enum integrity_status evm_status;

	if (strcmp(xattr_name, XATTR_NAME_EVM) == 0) {
		if (!capable(CAP_SYS_ADMIN))
			return -EPERM;
	} else if (!evm_protected_xattr(xattr_name)) {
		if (!posix_xattr_acl(xattr_name))
			return 0;
		evm_status = evm_verify_current_integrity(dentry);
		if ((evm_status == INTEGRITY_PASS) ||
		    (evm_status == INTEGRITY_NOXATTRS))
			return 0;
		goto out;
	}
	evm_status = evm_verify_current_integrity(dentry);
out:
	if (evm_status != INTEGRITY_PASS)
		integrity_audit_msg(AUDIT_INTEGRITY_METADATA, dentry->d_inode,
				    dentry->d_name.name, "appraise_metadata",
				    integrity_status_msg[evm_status],
				    -EPERM, 0);
	return evm_status == INTEGRITY_PASS ? 0 : -EPERM;
}

/**
 * evm_inode_setxattr - protect the EVM extended attribute
 * @dentry: pointer to the affected dentry
 * @xattr_name: pointer to the affected extended attribute name
 * @xattr_value: pointer to the new extended attribute value
 * @xattr_value_len: pointer to the new extended attribute value length
 *
 * Before allowing the 'security.evm' protected xattr to be updated,
 * verify the existing value is valid.  As only the kernel should have
 * access to the EVM encrypted key needed to calculate the HMAC, prevent
 * userspace from writing HMAC value.  Writing 'security.evm' requires
 * requires CAP_SYS_ADMIN privileges.
 */
int evm_inode_setxattr(struct dentry *dentry, const char *xattr_name,
		       const void *xattr_value, size_t xattr_value_len)
{
	const struct evm_ima_xattr_data *xattr_data = xattr_value;

	if ((strcmp(xattr_name, XATTR_NAME_EVM) == 0)
	    && (xattr_data->type == EVM_XATTR_HMAC))
		return -EPERM;
	return evm_protect_xattr(dentry, xattr_name, xattr_value,
				 xattr_value_len);
}

/**
 * evm_inode_removexattr - protect the EVM extended attribute
 * @dentry: pointer to the affected dentry
 * @xattr_name: pointer to the affected extended attribute name
 *
 * Removing 'security.evm' requires CAP_SYS_ADMIN privileges and that
 * the current value is valid.
 */
int evm_inode_removexattr(struct dentry *dentry, const char *xattr_name)
{
	return evm_protect_xattr(dentry, xattr_name, NULL, 0);
}

/**
 * evm_inode_post_setxattr - update 'security.evm' to reflect the changes
 * @dentry: pointer to the affected dentry
 * @xattr_name: pointer to the affected extended attribute name
 * @xattr_value: pointer to the new extended attribute value
 * @xattr_value_len: pointer to the new extended attribute value length
 *
 * Update the HMAC stored in 'security.evm' to reflect the change.
 *
 * No need to take the i_mutex lock here, as this function is called from
 * __vfs_setxattr_noperm().  The caller of which has taken the inode's
 * i_mutex lock.
 */
void evm_inode_post_setxattr(struct dentry *dentry, const char *xattr_name,
			     const void *xattr_value, size_t xattr_value_len)
{
	if (!evm_initialized || (!evm_protected_xattr(xattr_name)
				 && !posix_xattr_acl(xattr_name)))
		return;

	evm_update_evmxattr(dentry, xattr_name, xattr_value, xattr_value_len);
}

/**
 * evm_inode_post_removexattr - update 'security.evm' after removing the xattr
 * @dentry: pointer to the affected dentry
 * @xattr_name: pointer to the affected extended attribute name
 *
 * Update the HMAC stored in 'security.evm' to reflect removal of the xattr.
 */
void evm_inode_post_removexattr(struct dentry *dentry, const char *xattr_name)
{
	struct inode *inode = dentry->d_inode;

	if (!evm_initialized || !evm_protected_xattr(xattr_name))
		return;

	mutex_lock(&inode->i_mutex);
	evm_update_evmxattr(dentry, xattr_name, NULL, 0);
	mutex_unlock(&inode->i_mutex);
}

/**
 * evm_inode_setattr - prevent updating an invalid EVM extended attribute
 * @dentry: pointer to the affected dentry
 */
int evm_inode_setattr(struct dentry *dentry, struct iattr *attr)
{
	unsigned int ia_valid = attr->ia_valid;
	enum integrity_status evm_status;

	if (!(ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID)))
		return 0;
	evm_status = evm_verify_current_integrity(dentry);
	if ((evm_status == INTEGRITY_PASS) ||
	    (evm_status == INTEGRITY_NOXATTRS))
		return 0;
	integrity_audit_msg(AUDIT_INTEGRITY_METADATA, dentry->d_inode,
			    dentry->d_name.name, "appraise_metadata",
			    integrity_status_msg[evm_status], -EPERM, 0);
	return -EPERM;
}

/**
 * evm_inode_post_setattr - update 'security.evm' after modifying metadata
 * @dentry: pointer to the affected dentry
 * @ia_valid: for the UID and GID status
 *
 * For now, update the HMAC stored in 'security.evm' to reflect UID/GID
 * changes.
 *
 * This function is called from notify_change(), which expects the caller
 * to lock the inode's i_mutex.
 */
void evm_inode_post_setattr(struct dentry *dentry, int ia_valid)
{
	if (!evm_initialized)
		return;

	if (ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID))
		evm_update_evmxattr(dentry, NULL, NULL, 0);
}

/*
 * evm_inode_init_security - initializes security.evm
 */
int evm_inode_init_security(struct inode *inode,
				 const struct xattr *lsm_xattr,
				 struct xattr *evm_xattr)
{
	struct evm_ima_xattr_data *xattr_data;
	int rc;

	if (!evm_initialized || !evm_protected_xattr(lsm_xattr->name))
		return 0;

	xattr_data = kzalloc(sizeof(*xattr_data), GFP_NOFS);
	if (!xattr_data)
		return -ENOMEM;

	xattr_data->type = EVM_XATTR_HMAC;
	rc = evm_init_hmac(inode, lsm_xattr, xattr_data->digest);
	if (rc < 0)
		goto out;

	evm_xattr->value = xattr_data;
	evm_xattr->value_len = sizeof(*xattr_data);
	evm_xattr->name = XATTR_EVM_SUFFIX;
	return 0;
out:
	kfree(xattr_data);
	return rc;
}
EXPORT_SYMBOL_GPL(evm_inode_init_security);

static int __init init_evm(void)
{
	int error;

	evm_init_config();

	error = evm_init_secfs();
	if (error < 0) {
		pr_info("Error registering secfs\n");
		goto err;
	}

	return 0;
err:
	return error;
}

/*
 * evm_display_config - list the EVM protected security extended attributes
 */
static int __init evm_display_config(void)
{
	char **xattrname;

	for (xattrname = evm_config_xattrnames; *xattrname != NULL; xattrname++)
		pr_info("%s\n", *xattrname);
	return 0;
}

pure_initcall(evm_display_config);
late_initcall(init_evm);

MODULE_DESCRIPTION("Extended Verification Module");
MODULE_LICENSE("GPL");