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1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * Copyright (C) 2005-2010 IBM Corporation
4 *
5 * Author:
6 * Mimi Zohar <zohar@us.ibm.com>
7 * Kylene Hall <kjhall@us.ibm.com>
8 *
9 * File: evm_main.c
10 * implements evm_inode_setxattr, evm_inode_post_setxattr,
11 * evm_inode_removexattr, and evm_verifyxattr
12 */
13
14#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
15
16#include <linux/init.h>
17#include <linux/crypto.h>
18#include <linux/audit.h>
19#include <linux/xattr.h>
20#include <linux/integrity.h>
21#include <linux/evm.h>
22#include <linux/magic.h>
23
24#include <crypto/hash.h>
25#include <crypto/hash_info.h>
26#include <crypto/algapi.h>
27#include "evm.h"
28
29int evm_initialized;
30
31static const char * const integrity_status_msg[] = {
32 "pass", "pass_immutable", "fail", "no_label", "no_xattrs", "unknown"
33};
34int evm_hmac_attrs;
35
36static struct xattr_list evm_config_default_xattrnames[] = {
37#ifdef CONFIG_SECURITY_SELINUX
38 {.name = XATTR_NAME_SELINUX},
39#endif
40#ifdef CONFIG_SECURITY_SMACK
41 {.name = XATTR_NAME_SMACK},
42#ifdef CONFIG_EVM_EXTRA_SMACK_XATTRS
43 {.name = XATTR_NAME_SMACKEXEC},
44 {.name = XATTR_NAME_SMACKTRANSMUTE},
45 {.name = XATTR_NAME_SMACKMMAP},
46#endif
47#endif
48#ifdef CONFIG_SECURITY_APPARMOR
49 {.name = XATTR_NAME_APPARMOR},
50#endif
51#ifdef CONFIG_IMA_APPRAISE
52 {.name = XATTR_NAME_IMA},
53#endif
54 {.name = XATTR_NAME_CAPS},
55};
56
57LIST_HEAD(evm_config_xattrnames);
58
59static int evm_fixmode;
60static int __init evm_set_fixmode(char *str)
61{
62 if (strncmp(str, "fix", 3) == 0)
63 evm_fixmode = 1;
64 return 0;
65}
66__setup("evm=", evm_set_fixmode);
67
68static void __init evm_init_config(void)
69{
70 int i, xattrs;
71
72 xattrs = ARRAY_SIZE(evm_config_default_xattrnames);
73
74 pr_info("Initialising EVM extended attributes:\n");
75 for (i = 0; i < xattrs; i++) {
76 pr_info("%s\n", evm_config_default_xattrnames[i].name);
77 list_add_tail(&evm_config_default_xattrnames[i].list,
78 &evm_config_xattrnames);
79 }
80
81#ifdef CONFIG_EVM_ATTR_FSUUID
82 evm_hmac_attrs |= EVM_ATTR_FSUUID;
83#endif
84 pr_info("HMAC attrs: 0x%x\n", evm_hmac_attrs);
85}
86
87static bool evm_key_loaded(void)
88{
89 return (bool)(evm_initialized & EVM_KEY_MASK);
90}
91
92static int evm_find_protected_xattrs(struct dentry *dentry)
93{
94 struct inode *inode = d_backing_inode(dentry);
95 struct xattr_list *xattr;
96 int error;
97 int count = 0;
98
99 if (!(inode->i_opflags & IOP_XATTR))
100 return -EOPNOTSUPP;
101
102 list_for_each_entry_rcu(xattr, &evm_config_xattrnames, list) {
103 error = __vfs_getxattr(dentry, inode, xattr->name, NULL, 0);
104 if (error < 0) {
105 if (error == -ENODATA)
106 continue;
107 return error;
108 }
109 count++;
110 }
111
112 return count;
113}
114
115/*
116 * evm_verify_hmac - calculate and compare the HMAC with the EVM xattr
117 *
118 * Compute the HMAC on the dentry's protected set of extended attributes
119 * and compare it against the stored security.evm xattr.
120 *
121 * For performance:
122 * - use the previoulsy retrieved xattr value and length to calculate the
123 * HMAC.)
124 * - cache the verification result in the iint, when available.
125 *
126 * Returns integrity status
127 */
128static enum integrity_status evm_verify_hmac(struct dentry *dentry,
129 const char *xattr_name,
130 char *xattr_value,
131 size_t xattr_value_len,
132 struct integrity_iint_cache *iint)
133{
134 struct evm_ima_xattr_data *xattr_data = NULL;
135 struct signature_v2_hdr *hdr;
136 enum integrity_status evm_status = INTEGRITY_PASS;
137 struct evm_digest digest;
138 struct inode *inode;
139 int rc, xattr_len;
140
141 if (iint && (iint->evm_status == INTEGRITY_PASS ||
142 iint->evm_status == INTEGRITY_PASS_IMMUTABLE))
143 return iint->evm_status;
144
145 /* if status is not PASS, try to check again - against -ENOMEM */
146
147 /* first need to know the sig type */
148 rc = vfs_getxattr_alloc(dentry, XATTR_NAME_EVM, (char **)&xattr_data, 0,
149 GFP_NOFS);
150 if (rc <= 0) {
151 evm_status = INTEGRITY_FAIL;
152 if (rc == -ENODATA) {
153 rc = evm_find_protected_xattrs(dentry);
154 if (rc > 0)
155 evm_status = INTEGRITY_NOLABEL;
156 else if (rc == 0)
157 evm_status = INTEGRITY_NOXATTRS; /* new file */
158 } else if (rc == -EOPNOTSUPP) {
159 evm_status = INTEGRITY_UNKNOWN;
160 }
161 goto out;
162 }
163
164 xattr_len = rc;
165
166 /* check value type */
167 switch (xattr_data->type) {
168 case EVM_XATTR_HMAC:
169 if (xattr_len != sizeof(struct evm_xattr)) {
170 evm_status = INTEGRITY_FAIL;
171 goto out;
172 }
173
174 digest.hdr.algo = HASH_ALGO_SHA1;
175 rc = evm_calc_hmac(dentry, xattr_name, xattr_value,
176 xattr_value_len, &digest);
177 if (rc)
178 break;
179 rc = crypto_memneq(xattr_data->data, digest.digest,
180 SHA1_DIGEST_SIZE);
181 if (rc)
182 rc = -EINVAL;
183 break;
184 case EVM_IMA_XATTR_DIGSIG:
185 case EVM_XATTR_PORTABLE_DIGSIG:
186 hdr = (struct signature_v2_hdr *)xattr_data;
187 digest.hdr.algo = hdr->hash_algo;
188 rc = evm_calc_hash(dentry, xattr_name, xattr_value,
189 xattr_value_len, xattr_data->type, &digest);
190 if (rc)
191 break;
192 rc = integrity_digsig_verify(INTEGRITY_KEYRING_EVM,
193 (const char *)xattr_data, xattr_len,
194 digest.digest, digest.hdr.length);
195 if (!rc) {
196 inode = d_backing_inode(dentry);
197
198 if (xattr_data->type == EVM_XATTR_PORTABLE_DIGSIG) {
199 if (iint)
200 iint->flags |= EVM_IMMUTABLE_DIGSIG;
201 evm_status = INTEGRITY_PASS_IMMUTABLE;
202 } else if (!IS_RDONLY(inode) &&
203 !(inode->i_sb->s_readonly_remount) &&
204 !IS_IMMUTABLE(inode)) {
205 evm_update_evmxattr(dentry, xattr_name,
206 xattr_value,
207 xattr_value_len);
208 }
209 }
210 break;
211 default:
212 rc = -EINVAL;
213 break;
214 }
215
216 if (rc)
217 evm_status = (rc == -ENODATA) ?
218 INTEGRITY_NOXATTRS : INTEGRITY_FAIL;
219out:
220 if (iint)
221 iint->evm_status = evm_status;
222 kfree(xattr_data);
223 return evm_status;
224}
225
226static int evm_protected_xattr(const char *req_xattr_name)
227{
228 int namelen;
229 int found = 0;
230 struct xattr_list *xattr;
231
232 namelen = strlen(req_xattr_name);
233 list_for_each_entry_rcu(xattr, &evm_config_xattrnames, list) {
234 if ((strlen(xattr->name) == namelen)
235 && (strncmp(req_xattr_name, xattr->name, namelen) == 0)) {
236 found = 1;
237 break;
238 }
239 if (strncmp(req_xattr_name,
240 xattr->name + XATTR_SECURITY_PREFIX_LEN,
241 strlen(req_xattr_name)) == 0) {
242 found = 1;
243 break;
244 }
245 }
246
247 return found;
248}
249
250/**
251 * evm_verifyxattr - verify the integrity of the requested xattr
252 * @dentry: object of the verify xattr
253 * @xattr_name: requested xattr
254 * @xattr_value: requested xattr value
255 * @xattr_value_len: requested xattr value length
256 *
257 * Calculate the HMAC for the given dentry and verify it against the stored
258 * security.evm xattr. For performance, use the xattr value and length
259 * previously retrieved to calculate the HMAC.
260 *
261 * Returns the xattr integrity status.
262 *
263 * This function requires the caller to lock the inode's i_mutex before it
264 * is executed.
265 */
266enum integrity_status evm_verifyxattr(struct dentry *dentry,
267 const char *xattr_name,
268 void *xattr_value, size_t xattr_value_len,
269 struct integrity_iint_cache *iint)
270{
271 if (!evm_key_loaded() || !evm_protected_xattr(xattr_name))
272 return INTEGRITY_UNKNOWN;
273
274 if (!iint) {
275 iint = integrity_iint_find(d_backing_inode(dentry));
276 if (!iint)
277 return INTEGRITY_UNKNOWN;
278 }
279 return evm_verify_hmac(dentry, xattr_name, xattr_value,
280 xattr_value_len, iint);
281}
282EXPORT_SYMBOL_GPL(evm_verifyxattr);
283
284/*
285 * evm_verify_current_integrity - verify the dentry's metadata integrity
286 * @dentry: pointer to the affected dentry
287 *
288 * Verify and return the dentry's metadata integrity. The exceptions are
289 * before EVM is initialized or in 'fix' mode.
290 */
291static enum integrity_status evm_verify_current_integrity(struct dentry *dentry)
292{
293 struct inode *inode = d_backing_inode(dentry);
294
295 if (!evm_key_loaded() || !S_ISREG(inode->i_mode) || evm_fixmode)
296 return 0;
297 return evm_verify_hmac(dentry, NULL, NULL, 0, NULL);
298}
299
300/*
301 * evm_protect_xattr - protect the EVM extended attribute
302 *
303 * Prevent security.evm from being modified or removed without the
304 * necessary permissions or when the existing value is invalid.
305 *
306 * The posix xattr acls are 'system' prefixed, which normally would not
307 * affect security.evm. An interesting side affect of writing posix xattr
308 * acls is their modifying of the i_mode, which is included in security.evm.
309 * For posix xattr acls only, permit security.evm, even if it currently
310 * doesn't exist, to be updated unless the EVM signature is immutable.
311 */
312static int evm_protect_xattr(struct dentry *dentry, const char *xattr_name,
313 const void *xattr_value, size_t xattr_value_len)
314{
315 enum integrity_status evm_status;
316
317 if (strcmp(xattr_name, XATTR_NAME_EVM) == 0) {
318 if (!capable(CAP_SYS_ADMIN))
319 return -EPERM;
320 } else if (!evm_protected_xattr(xattr_name)) {
321 if (!posix_xattr_acl(xattr_name))
322 return 0;
323 evm_status = evm_verify_current_integrity(dentry);
324 if ((evm_status == INTEGRITY_PASS) ||
325 (evm_status == INTEGRITY_NOXATTRS))
326 return 0;
327 goto out;
328 }
329
330 evm_status = evm_verify_current_integrity(dentry);
331 if (evm_status == INTEGRITY_NOXATTRS) {
332 struct integrity_iint_cache *iint;
333
334 iint = integrity_iint_find(d_backing_inode(dentry));
335 if (iint && (iint->flags & IMA_NEW_FILE))
336 return 0;
337
338 /* exception for pseudo filesystems */
339 if (dentry->d_sb->s_magic == TMPFS_MAGIC
340 || dentry->d_sb->s_magic == SYSFS_MAGIC)
341 return 0;
342
343 integrity_audit_msg(AUDIT_INTEGRITY_METADATA,
344 dentry->d_inode, dentry->d_name.name,
345 "update_metadata",
346 integrity_status_msg[evm_status],
347 -EPERM, 0);
348 }
349out:
350 if (evm_status != INTEGRITY_PASS)
351 integrity_audit_msg(AUDIT_INTEGRITY_METADATA, d_backing_inode(dentry),
352 dentry->d_name.name, "appraise_metadata",
353 integrity_status_msg[evm_status],
354 -EPERM, 0);
355 return evm_status == INTEGRITY_PASS ? 0 : -EPERM;
356}
357
358/**
359 * evm_inode_setxattr - protect the EVM extended attribute
360 * @dentry: pointer to the affected dentry
361 * @xattr_name: pointer to the affected extended attribute name
362 * @xattr_value: pointer to the new extended attribute value
363 * @xattr_value_len: pointer to the new extended attribute value length
364 *
365 * Before allowing the 'security.evm' protected xattr to be updated,
366 * verify the existing value is valid. As only the kernel should have
367 * access to the EVM encrypted key needed to calculate the HMAC, prevent
368 * userspace from writing HMAC value. Writing 'security.evm' requires
369 * requires CAP_SYS_ADMIN privileges.
370 */
371int evm_inode_setxattr(struct dentry *dentry, const char *xattr_name,
372 const void *xattr_value, size_t xattr_value_len)
373{
374 const struct evm_ima_xattr_data *xattr_data = xattr_value;
375
376 /* Policy permits modification of the protected xattrs even though
377 * there's no HMAC key loaded
378 */
379 if (evm_initialized & EVM_ALLOW_METADATA_WRITES)
380 return 0;
381
382 if (strcmp(xattr_name, XATTR_NAME_EVM) == 0) {
383 if (!xattr_value_len)
384 return -EINVAL;
385 if (xattr_data->type != EVM_IMA_XATTR_DIGSIG &&
386 xattr_data->type != EVM_XATTR_PORTABLE_DIGSIG)
387 return -EPERM;
388 }
389 return evm_protect_xattr(dentry, xattr_name, xattr_value,
390 xattr_value_len);
391}
392
393/**
394 * evm_inode_removexattr - protect the EVM extended attribute
395 * @dentry: pointer to the affected dentry
396 * @xattr_name: pointer to the affected extended attribute name
397 *
398 * Removing 'security.evm' requires CAP_SYS_ADMIN privileges and that
399 * the current value is valid.
400 */
401int evm_inode_removexattr(struct dentry *dentry, const char *xattr_name)
402{
403 /* Policy permits modification of the protected xattrs even though
404 * there's no HMAC key loaded
405 */
406 if (evm_initialized & EVM_ALLOW_METADATA_WRITES)
407 return 0;
408
409 return evm_protect_xattr(dentry, xattr_name, NULL, 0);
410}
411
412static void evm_reset_status(struct inode *inode)
413{
414 struct integrity_iint_cache *iint;
415
416 iint = integrity_iint_find(inode);
417 if (iint)
418 iint->evm_status = INTEGRITY_UNKNOWN;
419}
420
421/**
422 * evm_inode_post_setxattr - update 'security.evm' to reflect the changes
423 * @dentry: pointer to the affected dentry
424 * @xattr_name: pointer to the affected extended attribute name
425 * @xattr_value: pointer to the new extended attribute value
426 * @xattr_value_len: pointer to the new extended attribute value length
427 *
428 * Update the HMAC stored in 'security.evm' to reflect the change.
429 *
430 * No need to take the i_mutex lock here, as this function is called from
431 * __vfs_setxattr_noperm(). The caller of which has taken the inode's
432 * i_mutex lock.
433 */
434void evm_inode_post_setxattr(struct dentry *dentry, const char *xattr_name,
435 const void *xattr_value, size_t xattr_value_len)
436{
437 if (!evm_key_loaded() || (!evm_protected_xattr(xattr_name)
438 && !posix_xattr_acl(xattr_name)))
439 return;
440
441 evm_reset_status(dentry->d_inode);
442
443 evm_update_evmxattr(dentry, xattr_name, xattr_value, xattr_value_len);
444}
445
446/**
447 * evm_inode_post_removexattr - update 'security.evm' after removing the xattr
448 * @dentry: pointer to the affected dentry
449 * @xattr_name: pointer to the affected extended attribute name
450 *
451 * Update the HMAC stored in 'security.evm' to reflect removal of the xattr.
452 *
453 * No need to take the i_mutex lock here, as this function is called from
454 * vfs_removexattr() which takes the i_mutex.
455 */
456void evm_inode_post_removexattr(struct dentry *dentry, const char *xattr_name)
457{
458 if (!evm_key_loaded() || !evm_protected_xattr(xattr_name))
459 return;
460
461 evm_reset_status(dentry->d_inode);
462
463 evm_update_evmxattr(dentry, xattr_name, NULL, 0);
464}
465
466/**
467 * evm_inode_setattr - prevent updating an invalid EVM extended attribute
468 * @dentry: pointer to the affected dentry
469 *
470 * Permit update of file attributes when files have a valid EVM signature,
471 * except in the case of them having an immutable portable signature.
472 */
473int evm_inode_setattr(struct dentry *dentry, struct iattr *attr)
474{
475 unsigned int ia_valid = attr->ia_valid;
476 enum integrity_status evm_status;
477
478 /* Policy permits modification of the protected attrs even though
479 * there's no HMAC key loaded
480 */
481 if (evm_initialized & EVM_ALLOW_METADATA_WRITES)
482 return 0;
483
484 if (!(ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID)))
485 return 0;
486 evm_status = evm_verify_current_integrity(dentry);
487 if ((evm_status == INTEGRITY_PASS) ||
488 (evm_status == INTEGRITY_NOXATTRS))
489 return 0;
490 integrity_audit_msg(AUDIT_INTEGRITY_METADATA, d_backing_inode(dentry),
491 dentry->d_name.name, "appraise_metadata",
492 integrity_status_msg[evm_status], -EPERM, 0);
493 return -EPERM;
494}
495
496/**
497 * evm_inode_post_setattr - update 'security.evm' after modifying metadata
498 * @dentry: pointer to the affected dentry
499 * @ia_valid: for the UID and GID status
500 *
501 * For now, update the HMAC stored in 'security.evm' to reflect UID/GID
502 * changes.
503 *
504 * This function is called from notify_change(), which expects the caller
505 * to lock the inode's i_mutex.
506 */
507void evm_inode_post_setattr(struct dentry *dentry, int ia_valid)
508{
509 if (!evm_key_loaded())
510 return;
511
512 if (ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID))
513 evm_update_evmxattr(dentry, NULL, NULL, 0);
514}
515
516/*
517 * evm_inode_init_security - initializes security.evm
518 */
519int evm_inode_init_security(struct inode *inode,
520 const struct xattr *lsm_xattr,
521 struct xattr *evm_xattr)
522{
523 struct evm_xattr *xattr_data;
524 int rc;
525
526 if (!evm_key_loaded() || !evm_protected_xattr(lsm_xattr->name))
527 return 0;
528
529 xattr_data = kzalloc(sizeof(*xattr_data), GFP_NOFS);
530 if (!xattr_data)
531 return -ENOMEM;
532
533 xattr_data->data.type = EVM_XATTR_HMAC;
534 rc = evm_init_hmac(inode, lsm_xattr, xattr_data->digest);
535 if (rc < 0)
536 goto out;
537
538 evm_xattr->value = xattr_data;
539 evm_xattr->value_len = sizeof(*xattr_data);
540 evm_xattr->name = XATTR_EVM_SUFFIX;
541 return 0;
542out:
543 kfree(xattr_data);
544 return rc;
545}
546EXPORT_SYMBOL_GPL(evm_inode_init_security);
547
548#ifdef CONFIG_EVM_LOAD_X509
549void __init evm_load_x509(void)
550{
551 int rc;
552
553 rc = integrity_load_x509(INTEGRITY_KEYRING_EVM, CONFIG_EVM_X509_PATH);
554 if (!rc)
555 evm_initialized |= EVM_INIT_X509;
556}
557#endif
558
559static int __init init_evm(void)
560{
561 int error;
562 struct list_head *pos, *q;
563
564 evm_init_config();
565
566 error = integrity_init_keyring(INTEGRITY_KEYRING_EVM);
567 if (error)
568 goto error;
569
570 error = evm_init_secfs();
571 if (error < 0) {
572 pr_info("Error registering secfs\n");
573 goto error;
574 }
575
576error:
577 if (error != 0) {
578 if (!list_empty(&evm_config_xattrnames)) {
579 list_for_each_safe(pos, q, &evm_config_xattrnames)
580 list_del(pos);
581 }
582 }
583
584 return error;
585}
586
587late_initcall(init_evm);
1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * Copyright (C) 2005-2010 IBM Corporation
4 *
5 * Author:
6 * Mimi Zohar <zohar@us.ibm.com>
7 * Kylene Hall <kjhall@us.ibm.com>
8 *
9 * File: evm_main.c
10 * implements evm_inode_setxattr, evm_inode_post_setxattr,
11 * evm_inode_removexattr, and evm_verifyxattr
12 */
13
14#include <linux/init.h>
15#include <linux/crypto.h>
16#include <linux/audit.h>
17#include <linux/xattr.h>
18#include <linux/integrity.h>
19#include <linux/evm.h>
20#include <linux/magic.h>
21
22#include <crypto/hash.h>
23#include <crypto/hash_info.h>
24#include <crypto/algapi.h>
25#include "evm.h"
26
27int evm_initialized;
28
29static const char * const integrity_status_msg[] = {
30 "pass", "pass_immutable", "fail", "no_label", "no_xattrs", "unknown"
31};
32int evm_hmac_attrs;
33
34static struct xattr_list evm_config_default_xattrnames[] = {
35#ifdef CONFIG_SECURITY_SELINUX
36 {.name = XATTR_NAME_SELINUX},
37#endif
38#ifdef CONFIG_SECURITY_SMACK
39 {.name = XATTR_NAME_SMACK},
40#ifdef CONFIG_EVM_EXTRA_SMACK_XATTRS
41 {.name = XATTR_NAME_SMACKEXEC},
42 {.name = XATTR_NAME_SMACKTRANSMUTE},
43 {.name = XATTR_NAME_SMACKMMAP},
44#endif
45#endif
46#ifdef CONFIG_SECURITY_APPARMOR
47 {.name = XATTR_NAME_APPARMOR},
48#endif
49#ifdef CONFIG_IMA_APPRAISE
50 {.name = XATTR_NAME_IMA},
51#endif
52 {.name = XATTR_NAME_CAPS},
53};
54
55LIST_HEAD(evm_config_xattrnames);
56
57static int evm_fixmode;
58static int __init evm_set_fixmode(char *str)
59{
60 if (strncmp(str, "fix", 3) == 0)
61 evm_fixmode = 1;
62 return 0;
63}
64__setup("evm=", evm_set_fixmode);
65
66static void __init evm_init_config(void)
67{
68 int i, xattrs;
69
70 xattrs = ARRAY_SIZE(evm_config_default_xattrnames);
71
72 pr_info("Initialising EVM extended attributes:\n");
73 for (i = 0; i < xattrs; i++) {
74 pr_info("%s\n", evm_config_default_xattrnames[i].name);
75 list_add_tail(&evm_config_default_xattrnames[i].list,
76 &evm_config_xattrnames);
77 }
78
79#ifdef CONFIG_EVM_ATTR_FSUUID
80 evm_hmac_attrs |= EVM_ATTR_FSUUID;
81#endif
82 pr_info("HMAC attrs: 0x%x\n", evm_hmac_attrs);
83}
84
85static bool evm_key_loaded(void)
86{
87 return (bool)(evm_initialized & EVM_KEY_MASK);
88}
89
90static int evm_find_protected_xattrs(struct dentry *dentry)
91{
92 struct inode *inode = d_backing_inode(dentry);
93 struct xattr_list *xattr;
94 int error;
95 int count = 0;
96
97 if (!(inode->i_opflags & IOP_XATTR))
98 return -EOPNOTSUPP;
99
100 list_for_each_entry_lockless(xattr, &evm_config_xattrnames, list) {
101 error = __vfs_getxattr(dentry, inode, xattr->name, NULL, 0);
102 if (error < 0) {
103 if (error == -ENODATA)
104 continue;
105 return error;
106 }
107 count++;
108 }
109
110 return count;
111}
112
113/*
114 * evm_verify_hmac - calculate and compare the HMAC with the EVM xattr
115 *
116 * Compute the HMAC on the dentry's protected set of extended attributes
117 * and compare it against the stored security.evm xattr.
118 *
119 * For performance:
120 * - use the previoulsy retrieved xattr value and length to calculate the
121 * HMAC.)
122 * - cache the verification result in the iint, when available.
123 *
124 * Returns integrity status
125 */
126static enum integrity_status evm_verify_hmac(struct dentry *dentry,
127 const char *xattr_name,
128 char *xattr_value,
129 size_t xattr_value_len,
130 struct integrity_iint_cache *iint)
131{
132 struct evm_ima_xattr_data *xattr_data = NULL;
133 struct signature_v2_hdr *hdr;
134 enum integrity_status evm_status = INTEGRITY_PASS;
135 struct evm_digest digest;
136 struct inode *inode;
137 int rc, xattr_len;
138
139 if (iint && (iint->evm_status == INTEGRITY_PASS ||
140 iint->evm_status == INTEGRITY_PASS_IMMUTABLE))
141 return iint->evm_status;
142
143 /* if status is not PASS, try to check again - against -ENOMEM */
144
145 /* first need to know the sig type */
146 rc = vfs_getxattr_alloc(dentry, XATTR_NAME_EVM, (char **)&xattr_data, 0,
147 GFP_NOFS);
148 if (rc <= 0) {
149 evm_status = INTEGRITY_FAIL;
150 if (rc == -ENODATA) {
151 rc = evm_find_protected_xattrs(dentry);
152 if (rc > 0)
153 evm_status = INTEGRITY_NOLABEL;
154 else if (rc == 0)
155 evm_status = INTEGRITY_NOXATTRS; /* new file */
156 } else if (rc == -EOPNOTSUPP) {
157 evm_status = INTEGRITY_UNKNOWN;
158 }
159 goto out;
160 }
161
162 xattr_len = rc;
163
164 /* check value type */
165 switch (xattr_data->type) {
166 case EVM_XATTR_HMAC:
167 if (xattr_len != sizeof(struct evm_xattr)) {
168 evm_status = INTEGRITY_FAIL;
169 goto out;
170 }
171
172 digest.hdr.algo = HASH_ALGO_SHA1;
173 rc = evm_calc_hmac(dentry, xattr_name, xattr_value,
174 xattr_value_len, &digest);
175 if (rc)
176 break;
177 rc = crypto_memneq(xattr_data->data, digest.digest,
178 SHA1_DIGEST_SIZE);
179 if (rc)
180 rc = -EINVAL;
181 break;
182 case EVM_IMA_XATTR_DIGSIG:
183 case EVM_XATTR_PORTABLE_DIGSIG:
184 hdr = (struct signature_v2_hdr *)xattr_data;
185 digest.hdr.algo = hdr->hash_algo;
186 rc = evm_calc_hash(dentry, xattr_name, xattr_value,
187 xattr_value_len, xattr_data->type, &digest);
188 if (rc)
189 break;
190 rc = integrity_digsig_verify(INTEGRITY_KEYRING_EVM,
191 (const char *)xattr_data, xattr_len,
192 digest.digest, digest.hdr.length);
193 if (!rc) {
194 inode = d_backing_inode(dentry);
195
196 if (xattr_data->type == EVM_XATTR_PORTABLE_DIGSIG) {
197 if (iint)
198 iint->flags |= EVM_IMMUTABLE_DIGSIG;
199 evm_status = INTEGRITY_PASS_IMMUTABLE;
200 } else if (!IS_RDONLY(inode) &&
201 !(inode->i_sb->s_readonly_remount) &&
202 !IS_IMMUTABLE(inode)) {
203 evm_update_evmxattr(dentry, xattr_name,
204 xattr_value,
205 xattr_value_len);
206 }
207 }
208 break;
209 default:
210 rc = -EINVAL;
211 break;
212 }
213
214 if (rc)
215 evm_status = (rc == -ENODATA) ?
216 INTEGRITY_NOXATTRS : INTEGRITY_FAIL;
217out:
218 if (iint)
219 iint->evm_status = evm_status;
220 kfree(xattr_data);
221 return evm_status;
222}
223
224static int evm_protected_xattr(const char *req_xattr_name)
225{
226 int namelen;
227 int found = 0;
228 struct xattr_list *xattr;
229
230 namelen = strlen(req_xattr_name);
231 list_for_each_entry_lockless(xattr, &evm_config_xattrnames, list) {
232 if ((strlen(xattr->name) == namelen)
233 && (strncmp(req_xattr_name, xattr->name, namelen) == 0)) {
234 found = 1;
235 break;
236 }
237 if (strncmp(req_xattr_name,
238 xattr->name + XATTR_SECURITY_PREFIX_LEN,
239 strlen(req_xattr_name)) == 0) {
240 found = 1;
241 break;
242 }
243 }
244
245 return found;
246}
247
248/**
249 * evm_verifyxattr - verify the integrity of the requested xattr
250 * @dentry: object of the verify xattr
251 * @xattr_name: requested xattr
252 * @xattr_value: requested xattr value
253 * @xattr_value_len: requested xattr value length
254 *
255 * Calculate the HMAC for the given dentry and verify it against the stored
256 * security.evm xattr. For performance, use the xattr value and length
257 * previously retrieved to calculate the HMAC.
258 *
259 * Returns the xattr integrity status.
260 *
261 * This function requires the caller to lock the inode's i_mutex before it
262 * is executed.
263 */
264enum integrity_status evm_verifyxattr(struct dentry *dentry,
265 const char *xattr_name,
266 void *xattr_value, size_t xattr_value_len,
267 struct integrity_iint_cache *iint)
268{
269 if (!evm_key_loaded() || !evm_protected_xattr(xattr_name))
270 return INTEGRITY_UNKNOWN;
271
272 if (!iint) {
273 iint = integrity_iint_find(d_backing_inode(dentry));
274 if (!iint)
275 return INTEGRITY_UNKNOWN;
276 }
277 return evm_verify_hmac(dentry, xattr_name, xattr_value,
278 xattr_value_len, iint);
279}
280EXPORT_SYMBOL_GPL(evm_verifyxattr);
281
282/*
283 * evm_verify_current_integrity - verify the dentry's metadata integrity
284 * @dentry: pointer to the affected dentry
285 *
286 * Verify and return the dentry's metadata integrity. The exceptions are
287 * before EVM is initialized or in 'fix' mode.
288 */
289static enum integrity_status evm_verify_current_integrity(struct dentry *dentry)
290{
291 struct inode *inode = d_backing_inode(dentry);
292
293 if (!evm_key_loaded() || !S_ISREG(inode->i_mode) || evm_fixmode)
294 return 0;
295 return evm_verify_hmac(dentry, NULL, NULL, 0, NULL);
296}
297
298/*
299 * evm_protect_xattr - protect the EVM extended attribute
300 *
301 * Prevent security.evm from being modified or removed without the
302 * necessary permissions or when the existing value is invalid.
303 *
304 * The posix xattr acls are 'system' prefixed, which normally would not
305 * affect security.evm. An interesting side affect of writing posix xattr
306 * acls is their modifying of the i_mode, which is included in security.evm.
307 * For posix xattr acls only, permit security.evm, even if it currently
308 * doesn't exist, to be updated unless the EVM signature is immutable.
309 */
310static int evm_protect_xattr(struct dentry *dentry, const char *xattr_name,
311 const void *xattr_value, size_t xattr_value_len)
312{
313 enum integrity_status evm_status;
314
315 if (strcmp(xattr_name, XATTR_NAME_EVM) == 0) {
316 if (!capable(CAP_SYS_ADMIN))
317 return -EPERM;
318 } else if (!evm_protected_xattr(xattr_name)) {
319 if (!posix_xattr_acl(xattr_name))
320 return 0;
321 evm_status = evm_verify_current_integrity(dentry);
322 if ((evm_status == INTEGRITY_PASS) ||
323 (evm_status == INTEGRITY_NOXATTRS))
324 return 0;
325 goto out;
326 }
327
328 evm_status = evm_verify_current_integrity(dentry);
329 if (evm_status == INTEGRITY_NOXATTRS) {
330 struct integrity_iint_cache *iint;
331
332 iint = integrity_iint_find(d_backing_inode(dentry));
333 if (iint && (iint->flags & IMA_NEW_FILE))
334 return 0;
335
336 /* exception for pseudo filesystems */
337 if (dentry->d_sb->s_magic == TMPFS_MAGIC
338 || dentry->d_sb->s_magic == SYSFS_MAGIC)
339 return 0;
340
341 integrity_audit_msg(AUDIT_INTEGRITY_METADATA,
342 dentry->d_inode, dentry->d_name.name,
343 "update_metadata",
344 integrity_status_msg[evm_status],
345 -EPERM, 0);
346 }
347out:
348 if (evm_status != INTEGRITY_PASS)
349 integrity_audit_msg(AUDIT_INTEGRITY_METADATA, d_backing_inode(dentry),
350 dentry->d_name.name, "appraise_metadata",
351 integrity_status_msg[evm_status],
352 -EPERM, 0);
353 return evm_status == INTEGRITY_PASS ? 0 : -EPERM;
354}
355
356/**
357 * evm_inode_setxattr - protect the EVM extended attribute
358 * @dentry: pointer to the affected dentry
359 * @xattr_name: pointer to the affected extended attribute name
360 * @xattr_value: pointer to the new extended attribute value
361 * @xattr_value_len: pointer to the new extended attribute value length
362 *
363 * Before allowing the 'security.evm' protected xattr to be updated,
364 * verify the existing value is valid. As only the kernel should have
365 * access to the EVM encrypted key needed to calculate the HMAC, prevent
366 * userspace from writing HMAC value. Writing 'security.evm' requires
367 * requires CAP_SYS_ADMIN privileges.
368 */
369int evm_inode_setxattr(struct dentry *dentry, const char *xattr_name,
370 const void *xattr_value, size_t xattr_value_len)
371{
372 const struct evm_ima_xattr_data *xattr_data = xattr_value;
373
374 /* Policy permits modification of the protected xattrs even though
375 * there's no HMAC key loaded
376 */
377 if (evm_initialized & EVM_ALLOW_METADATA_WRITES)
378 return 0;
379
380 if (strcmp(xattr_name, XATTR_NAME_EVM) == 0) {
381 if (!xattr_value_len)
382 return -EINVAL;
383 if (xattr_data->type != EVM_IMA_XATTR_DIGSIG &&
384 xattr_data->type != EVM_XATTR_PORTABLE_DIGSIG)
385 return -EPERM;
386 }
387 return evm_protect_xattr(dentry, xattr_name, xattr_value,
388 xattr_value_len);
389}
390
391/**
392 * evm_inode_removexattr - protect the EVM extended attribute
393 * @dentry: pointer to the affected dentry
394 * @xattr_name: pointer to the affected extended attribute name
395 *
396 * Removing 'security.evm' requires CAP_SYS_ADMIN privileges and that
397 * the current value is valid.
398 */
399int evm_inode_removexattr(struct dentry *dentry, const char *xattr_name)
400{
401 /* Policy permits modification of the protected xattrs even though
402 * there's no HMAC key loaded
403 */
404 if (evm_initialized & EVM_ALLOW_METADATA_WRITES)
405 return 0;
406
407 return evm_protect_xattr(dentry, xattr_name, NULL, 0);
408}
409
410static void evm_reset_status(struct inode *inode)
411{
412 struct integrity_iint_cache *iint;
413
414 iint = integrity_iint_find(inode);
415 if (iint)
416 iint->evm_status = INTEGRITY_UNKNOWN;
417}
418
419/**
420 * evm_inode_post_setxattr - update 'security.evm' to reflect the changes
421 * @dentry: pointer to the affected dentry
422 * @xattr_name: pointer to the affected extended attribute name
423 * @xattr_value: pointer to the new extended attribute value
424 * @xattr_value_len: pointer to the new extended attribute value length
425 *
426 * Update the HMAC stored in 'security.evm' to reflect the change.
427 *
428 * No need to take the i_mutex lock here, as this function is called from
429 * __vfs_setxattr_noperm(). The caller of which has taken the inode's
430 * i_mutex lock.
431 */
432void evm_inode_post_setxattr(struct dentry *dentry, const char *xattr_name,
433 const void *xattr_value, size_t xattr_value_len)
434{
435 if (!evm_key_loaded() || (!evm_protected_xattr(xattr_name)
436 && !posix_xattr_acl(xattr_name)))
437 return;
438
439 evm_reset_status(dentry->d_inode);
440
441 evm_update_evmxattr(dentry, xattr_name, xattr_value, xattr_value_len);
442}
443
444/**
445 * evm_inode_post_removexattr - update 'security.evm' after removing the xattr
446 * @dentry: pointer to the affected dentry
447 * @xattr_name: pointer to the affected extended attribute name
448 *
449 * Update the HMAC stored in 'security.evm' to reflect removal of the xattr.
450 *
451 * No need to take the i_mutex lock here, as this function is called from
452 * vfs_removexattr() which takes the i_mutex.
453 */
454void evm_inode_post_removexattr(struct dentry *dentry, const char *xattr_name)
455{
456 if (!evm_key_loaded() || !evm_protected_xattr(xattr_name))
457 return;
458
459 evm_reset_status(dentry->d_inode);
460
461 evm_update_evmxattr(dentry, xattr_name, NULL, 0);
462}
463
464/**
465 * evm_inode_setattr - prevent updating an invalid EVM extended attribute
466 * @dentry: pointer to the affected dentry
467 *
468 * Permit update of file attributes when files have a valid EVM signature,
469 * except in the case of them having an immutable portable signature.
470 */
471int evm_inode_setattr(struct dentry *dentry, struct iattr *attr)
472{
473 unsigned int ia_valid = attr->ia_valid;
474 enum integrity_status evm_status;
475
476 /* Policy permits modification of the protected attrs even though
477 * there's no HMAC key loaded
478 */
479 if (evm_initialized & EVM_ALLOW_METADATA_WRITES)
480 return 0;
481
482 if (!(ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID)))
483 return 0;
484 evm_status = evm_verify_current_integrity(dentry);
485 if ((evm_status == INTEGRITY_PASS) ||
486 (evm_status == INTEGRITY_NOXATTRS))
487 return 0;
488 integrity_audit_msg(AUDIT_INTEGRITY_METADATA, d_backing_inode(dentry),
489 dentry->d_name.name, "appraise_metadata",
490 integrity_status_msg[evm_status], -EPERM, 0);
491 return -EPERM;
492}
493
494/**
495 * evm_inode_post_setattr - update 'security.evm' after modifying metadata
496 * @dentry: pointer to the affected dentry
497 * @ia_valid: for the UID and GID status
498 *
499 * For now, update the HMAC stored in 'security.evm' to reflect UID/GID
500 * changes.
501 *
502 * This function is called from notify_change(), which expects the caller
503 * to lock the inode's i_mutex.
504 */
505void evm_inode_post_setattr(struct dentry *dentry, int ia_valid)
506{
507 if (!evm_key_loaded())
508 return;
509
510 if (ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID))
511 evm_update_evmxattr(dentry, NULL, NULL, 0);
512}
513
514/*
515 * evm_inode_init_security - initializes security.evm
516 */
517int evm_inode_init_security(struct inode *inode,
518 const struct xattr *lsm_xattr,
519 struct xattr *evm_xattr)
520{
521 struct evm_xattr *xattr_data;
522 int rc;
523
524 if (!evm_key_loaded() || !evm_protected_xattr(lsm_xattr->name))
525 return 0;
526
527 xattr_data = kzalloc(sizeof(*xattr_data), GFP_NOFS);
528 if (!xattr_data)
529 return -ENOMEM;
530
531 xattr_data->data.type = EVM_XATTR_HMAC;
532 rc = evm_init_hmac(inode, lsm_xattr, xattr_data->digest);
533 if (rc < 0)
534 goto out;
535
536 evm_xattr->value = xattr_data;
537 evm_xattr->value_len = sizeof(*xattr_data);
538 evm_xattr->name = XATTR_EVM_SUFFIX;
539 return 0;
540out:
541 kfree(xattr_data);
542 return rc;
543}
544EXPORT_SYMBOL_GPL(evm_inode_init_security);
545
546#ifdef CONFIG_EVM_LOAD_X509
547void __init evm_load_x509(void)
548{
549 int rc;
550
551 rc = integrity_load_x509(INTEGRITY_KEYRING_EVM, CONFIG_EVM_X509_PATH);
552 if (!rc)
553 evm_initialized |= EVM_INIT_X509;
554}
555#endif
556
557static int __init init_evm(void)
558{
559 int error;
560 struct list_head *pos, *q;
561
562 evm_init_config();
563
564 error = integrity_init_keyring(INTEGRITY_KEYRING_EVM);
565 if (error)
566 goto error;
567
568 error = evm_init_secfs();
569 if (error < 0) {
570 pr_info("Error registering secfs\n");
571 goto error;
572 }
573
574error:
575 if (error != 0) {
576 if (!list_empty(&evm_config_xattrnames)) {
577 list_for_each_safe(pos, q, &evm_config_xattrnames)
578 list_del(pos);
579 }
580 }
581
582 return error;
583}
584
585late_initcall(init_evm);