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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);