xref: /openbmc/linux/security/integrity/evm/evm_main.c (revision 9c6d26df1fae6ad4718d51c48e6517913304ed27)
1 /*
2  * Copyright (C) 2005-2010 IBM Corporation
3  *
4  * Author:
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_main.c
13  *	implements evm_inode_setxattr, evm_inode_post_setxattr,
14  *	evm_inode_removexattr, and evm_verifyxattr
15  */
16 
17 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
18 
19 #include <linux/module.h>
20 #include <linux/crypto.h>
21 #include <linux/audit.h>
22 #include <linux/xattr.h>
23 #include <linux/integrity.h>
24 #include <linux/evm.h>
25 #include <linux/magic.h>
26 
27 #include <crypto/hash.h>
28 #include <crypto/algapi.h>
29 #include "evm.h"
30 
31 int evm_initialized;
32 
33 static const char * const integrity_status_msg[] = {
34 	"pass", "pass_immutable", "fail", "no_label", "no_xattrs", "unknown"
35 };
36 int evm_hmac_attrs;
37 
38 char *evm_config_xattrnames[] = {
39 #ifdef CONFIG_SECURITY_SELINUX
40 	XATTR_NAME_SELINUX,
41 #endif
42 #ifdef CONFIG_SECURITY_SMACK
43 	XATTR_NAME_SMACK,
44 #ifdef CONFIG_EVM_EXTRA_SMACK_XATTRS
45 	XATTR_NAME_SMACKEXEC,
46 	XATTR_NAME_SMACKTRANSMUTE,
47 	XATTR_NAME_SMACKMMAP,
48 #endif
49 #endif
50 #ifdef CONFIG_SECURITY_APPARMOR
51 	XATTR_NAME_APPARMOR,
52 #endif
53 #ifdef CONFIG_IMA_APPRAISE
54 	XATTR_NAME_IMA,
55 #endif
56 	XATTR_NAME_CAPS,
57 	NULL
58 };
59 
60 static int evm_fixmode;
61 static int __init evm_set_fixmode(char *str)
62 {
63 	if (strncmp(str, "fix", 3) == 0)
64 		evm_fixmode = 1;
65 	return 0;
66 }
67 __setup("evm=", evm_set_fixmode);
68 
69 static void __init evm_init_config(void)
70 {
71 #ifdef CONFIG_EVM_ATTR_FSUUID
72 	evm_hmac_attrs |= EVM_ATTR_FSUUID;
73 #endif
74 	pr_info("HMAC attrs: 0x%x\n", evm_hmac_attrs);
75 }
76 
77 static bool evm_key_loaded(void)
78 {
79 	return (bool)(evm_initialized & EVM_KEY_MASK);
80 }
81 
82 static int evm_find_protected_xattrs(struct dentry *dentry)
83 {
84 	struct inode *inode = d_backing_inode(dentry);
85 	char **xattr;
86 	int error;
87 	int count = 0;
88 
89 	if (!(inode->i_opflags & IOP_XATTR))
90 		return -EOPNOTSUPP;
91 
92 	for (xattr = evm_config_xattrnames; *xattr != NULL; xattr++) {
93 		error = __vfs_getxattr(dentry, inode, *xattr, NULL, 0);
94 		if (error < 0) {
95 			if (error == -ENODATA)
96 				continue;
97 			return error;
98 		}
99 		count++;
100 	}
101 
102 	return count;
103 }
104 
105 /*
106  * evm_verify_hmac - calculate and compare the HMAC with the EVM xattr
107  *
108  * Compute the HMAC on the dentry's protected set of extended attributes
109  * and compare it against the stored security.evm xattr.
110  *
111  * For performance:
112  * - use the previoulsy retrieved xattr value and length to calculate the
113  *   HMAC.)
114  * - cache the verification result in the iint, when available.
115  *
116  * Returns integrity status
117  */
118 static enum integrity_status evm_verify_hmac(struct dentry *dentry,
119 					     const char *xattr_name,
120 					     char *xattr_value,
121 					     size_t xattr_value_len,
122 					     struct integrity_iint_cache *iint)
123 {
124 	struct evm_ima_xattr_data *xattr_data = NULL;
125 	struct evm_ima_xattr_data calc;
126 	enum integrity_status evm_status = INTEGRITY_PASS;
127 	struct inode *inode;
128 	int rc, xattr_len;
129 
130 	if (iint && (iint->evm_status == INTEGRITY_PASS ||
131 		     iint->evm_status == INTEGRITY_PASS_IMMUTABLE))
132 		return iint->evm_status;
133 
134 	/* if status is not PASS, try to check again - against -ENOMEM */
135 
136 	/* first need to know the sig type */
137 	rc = vfs_getxattr_alloc(dentry, XATTR_NAME_EVM, (char **)&xattr_data, 0,
138 				GFP_NOFS);
139 	if (rc <= 0) {
140 		evm_status = INTEGRITY_FAIL;
141 		if (rc == -ENODATA) {
142 			rc = evm_find_protected_xattrs(dentry);
143 			if (rc > 0)
144 				evm_status = INTEGRITY_NOLABEL;
145 			else if (rc == 0)
146 				evm_status = INTEGRITY_NOXATTRS; /* new file */
147 		} else if (rc == -EOPNOTSUPP) {
148 			evm_status = INTEGRITY_UNKNOWN;
149 		}
150 		goto out;
151 	}
152 
153 	xattr_len = rc;
154 
155 	/* check value type */
156 	switch (xattr_data->type) {
157 	case EVM_XATTR_HMAC:
158 		if (xattr_len != sizeof(struct evm_ima_xattr_data)) {
159 			evm_status = INTEGRITY_FAIL;
160 			goto out;
161 		}
162 		rc = evm_calc_hmac(dentry, xattr_name, xattr_value,
163 				   xattr_value_len, calc.digest);
164 		if (rc)
165 			break;
166 		rc = crypto_memneq(xattr_data->digest, calc.digest,
167 			    sizeof(calc.digest));
168 		if (rc)
169 			rc = -EINVAL;
170 		break;
171 	case EVM_IMA_XATTR_DIGSIG:
172 	case EVM_XATTR_PORTABLE_DIGSIG:
173 		rc = evm_calc_hash(dentry, xattr_name, xattr_value,
174 				   xattr_value_len, xattr_data->type,
175 				   calc.digest);
176 		if (rc)
177 			break;
178 		rc = integrity_digsig_verify(INTEGRITY_KEYRING_EVM,
179 					(const char *)xattr_data, xattr_len,
180 					calc.digest, sizeof(calc.digest));
181 		if (!rc) {
182 			inode = d_backing_inode(dentry);
183 
184 			if (xattr_data->type == EVM_XATTR_PORTABLE_DIGSIG) {
185 				if (iint)
186 					iint->flags |= EVM_IMMUTABLE_DIGSIG;
187 				evm_status = INTEGRITY_PASS_IMMUTABLE;
188 			} else if (!IS_RDONLY(inode) &&
189 				   !(inode->i_sb->s_readonly_remount) &&
190 				   !IS_IMMUTABLE(inode)) {
191 				evm_update_evmxattr(dentry, xattr_name,
192 						    xattr_value,
193 						    xattr_value_len);
194 			}
195 		}
196 		break;
197 	default:
198 		rc = -EINVAL;
199 		break;
200 	}
201 
202 	if (rc)
203 		evm_status = (rc == -ENODATA) ?
204 				INTEGRITY_NOXATTRS : INTEGRITY_FAIL;
205 out:
206 	if (iint)
207 		iint->evm_status = evm_status;
208 	kfree(xattr_data);
209 	return evm_status;
210 }
211 
212 static int evm_protected_xattr(const char *req_xattr_name)
213 {
214 	char **xattrname;
215 	int namelen;
216 	int found = 0;
217 
218 	namelen = strlen(req_xattr_name);
219 	for (xattrname = evm_config_xattrnames; *xattrname != NULL; xattrname++) {
220 		if ((strlen(*xattrname) == namelen)
221 		    && (strncmp(req_xattr_name, *xattrname, namelen) == 0)) {
222 			found = 1;
223 			break;
224 		}
225 		if (strncmp(req_xattr_name,
226 			    *xattrname + XATTR_SECURITY_PREFIX_LEN,
227 			    strlen(req_xattr_name)) == 0) {
228 			found = 1;
229 			break;
230 		}
231 	}
232 	return found;
233 }
234 
235 /**
236  * evm_verifyxattr - verify the integrity of the requested xattr
237  * @dentry: object of the verify xattr
238  * @xattr_name: requested xattr
239  * @xattr_value: requested xattr value
240  * @xattr_value_len: requested xattr value length
241  *
242  * Calculate the HMAC for the given dentry and verify it against the stored
243  * security.evm xattr. For performance, use the xattr value and length
244  * previously retrieved to calculate the HMAC.
245  *
246  * Returns the xattr integrity status.
247  *
248  * This function requires the caller to lock the inode's i_mutex before it
249  * is executed.
250  */
251 enum integrity_status evm_verifyxattr(struct dentry *dentry,
252 				      const char *xattr_name,
253 				      void *xattr_value, size_t xattr_value_len,
254 				      struct integrity_iint_cache *iint)
255 {
256 	if (!evm_key_loaded() || !evm_protected_xattr(xattr_name))
257 		return INTEGRITY_UNKNOWN;
258 
259 	if (!iint) {
260 		iint = integrity_iint_find(d_backing_inode(dentry));
261 		if (!iint)
262 			return INTEGRITY_UNKNOWN;
263 	}
264 	return evm_verify_hmac(dentry, xattr_name, xattr_value,
265 				 xattr_value_len, iint);
266 }
267 EXPORT_SYMBOL_GPL(evm_verifyxattr);
268 
269 /*
270  * evm_verify_current_integrity - verify the dentry's metadata integrity
271  * @dentry: pointer to the affected dentry
272  *
273  * Verify and return the dentry's metadata integrity. The exceptions are
274  * before EVM is initialized or in 'fix' mode.
275  */
276 static enum integrity_status evm_verify_current_integrity(struct dentry *dentry)
277 {
278 	struct inode *inode = d_backing_inode(dentry);
279 
280 	if (!evm_key_loaded() || !S_ISREG(inode->i_mode) || evm_fixmode)
281 		return 0;
282 	return evm_verify_hmac(dentry, NULL, NULL, 0, NULL);
283 }
284 
285 /*
286  * evm_protect_xattr - protect the EVM extended attribute
287  *
288  * Prevent security.evm from being modified or removed without the
289  * necessary permissions or when the existing value is invalid.
290  *
291  * The posix xattr acls are 'system' prefixed, which normally would not
292  * affect security.evm.  An interesting side affect of writing posix xattr
293  * acls is their modifying of the i_mode, which is included in security.evm.
294  * For posix xattr acls only, permit security.evm, even if it currently
295  * doesn't exist, to be updated unless the EVM signature is immutable.
296  */
297 static int evm_protect_xattr(struct dentry *dentry, const char *xattr_name,
298 			     const void *xattr_value, size_t xattr_value_len)
299 {
300 	enum integrity_status evm_status;
301 
302 	if (strcmp(xattr_name, XATTR_NAME_EVM) == 0) {
303 		if (!capable(CAP_SYS_ADMIN))
304 			return -EPERM;
305 	} else if (!evm_protected_xattr(xattr_name)) {
306 		if (!posix_xattr_acl(xattr_name))
307 			return 0;
308 		evm_status = evm_verify_current_integrity(dentry);
309 		if ((evm_status == INTEGRITY_PASS) ||
310 		    (evm_status == INTEGRITY_NOXATTRS))
311 			return 0;
312 		goto out;
313 	}
314 
315 	evm_status = evm_verify_current_integrity(dentry);
316 	if (evm_status == INTEGRITY_NOXATTRS) {
317 		struct integrity_iint_cache *iint;
318 
319 		iint = integrity_iint_find(d_backing_inode(dentry));
320 		if (iint && (iint->flags & IMA_NEW_FILE))
321 			return 0;
322 
323 		/* exception for pseudo filesystems */
324 		if (dentry->d_sb->s_magic == TMPFS_MAGIC
325 		    || dentry->d_sb->s_magic == SYSFS_MAGIC)
326 			return 0;
327 
328 		integrity_audit_msg(AUDIT_INTEGRITY_METADATA,
329 				    dentry->d_inode, dentry->d_name.name,
330 				    "update_metadata",
331 				    integrity_status_msg[evm_status],
332 				    -EPERM, 0);
333 	}
334 out:
335 	if (evm_status != INTEGRITY_PASS)
336 		integrity_audit_msg(AUDIT_INTEGRITY_METADATA, d_backing_inode(dentry),
337 				    dentry->d_name.name, "appraise_metadata",
338 				    integrity_status_msg[evm_status],
339 				    -EPERM, 0);
340 	return evm_status == INTEGRITY_PASS ? 0 : -EPERM;
341 }
342 
343 /**
344  * evm_inode_setxattr - protect the EVM extended attribute
345  * @dentry: pointer to the affected dentry
346  * @xattr_name: pointer to the affected extended attribute name
347  * @xattr_value: pointer to the new extended attribute value
348  * @xattr_value_len: pointer to the new extended attribute value length
349  *
350  * Before allowing the 'security.evm' protected xattr to be updated,
351  * verify the existing value is valid.  As only the kernel should have
352  * access to the EVM encrypted key needed to calculate the HMAC, prevent
353  * userspace from writing HMAC value.  Writing 'security.evm' requires
354  * requires CAP_SYS_ADMIN privileges.
355  */
356 int evm_inode_setxattr(struct dentry *dentry, const char *xattr_name,
357 		       const void *xattr_value, size_t xattr_value_len)
358 {
359 	const struct evm_ima_xattr_data *xattr_data = xattr_value;
360 
361 	/* Policy permits modification of the protected xattrs even though
362 	 * there's no HMAC key loaded
363 	 */
364 	if (evm_initialized & EVM_ALLOW_METADATA_WRITES)
365 		return 0;
366 
367 	if (strcmp(xattr_name, XATTR_NAME_EVM) == 0) {
368 		if (!xattr_value_len)
369 			return -EINVAL;
370 		if (xattr_data->type != EVM_IMA_XATTR_DIGSIG &&
371 		    xattr_data->type != EVM_XATTR_PORTABLE_DIGSIG)
372 			return -EPERM;
373 	}
374 	return evm_protect_xattr(dentry, xattr_name, xattr_value,
375 				 xattr_value_len);
376 }
377 
378 /**
379  * evm_inode_removexattr - protect the EVM extended attribute
380  * @dentry: pointer to the affected dentry
381  * @xattr_name: pointer to the affected extended attribute name
382  *
383  * Removing 'security.evm' requires CAP_SYS_ADMIN privileges and that
384  * the current value is valid.
385  */
386 int evm_inode_removexattr(struct dentry *dentry, const char *xattr_name)
387 {
388 	/* Policy permits modification of the protected xattrs even though
389 	 * there's no HMAC key loaded
390 	 */
391 	if (evm_initialized & EVM_ALLOW_METADATA_WRITES)
392 		return 0;
393 
394 	return evm_protect_xattr(dentry, xattr_name, NULL, 0);
395 }
396 
397 static void evm_reset_status(struct inode *inode)
398 {
399 	struct integrity_iint_cache *iint;
400 
401 	iint = integrity_iint_find(inode);
402 	if (iint)
403 		iint->evm_status = INTEGRITY_UNKNOWN;
404 }
405 
406 /**
407  * evm_inode_post_setxattr - update 'security.evm' to reflect the changes
408  * @dentry: pointer to the affected dentry
409  * @xattr_name: pointer to the affected extended attribute name
410  * @xattr_value: pointer to the new extended attribute value
411  * @xattr_value_len: pointer to the new extended attribute value length
412  *
413  * Update the HMAC stored in 'security.evm' to reflect the change.
414  *
415  * No need to take the i_mutex lock here, as this function is called from
416  * __vfs_setxattr_noperm().  The caller of which has taken the inode's
417  * i_mutex lock.
418  */
419 void evm_inode_post_setxattr(struct dentry *dentry, const char *xattr_name,
420 			     const void *xattr_value, size_t xattr_value_len)
421 {
422 	if (!evm_key_loaded() || (!evm_protected_xattr(xattr_name)
423 				  && !posix_xattr_acl(xattr_name)))
424 		return;
425 
426 	evm_reset_status(dentry->d_inode);
427 
428 	evm_update_evmxattr(dentry, xattr_name, xattr_value, xattr_value_len);
429 }
430 
431 /**
432  * evm_inode_post_removexattr - update 'security.evm' after removing the xattr
433  * @dentry: pointer to the affected dentry
434  * @xattr_name: pointer to the affected extended attribute name
435  *
436  * Update the HMAC stored in 'security.evm' to reflect removal of the xattr.
437  *
438  * No need to take the i_mutex lock here, as this function is called from
439  * vfs_removexattr() which takes the i_mutex.
440  */
441 void evm_inode_post_removexattr(struct dentry *dentry, const char *xattr_name)
442 {
443 	if (!evm_key_loaded() || !evm_protected_xattr(xattr_name))
444 		return;
445 
446 	evm_reset_status(dentry->d_inode);
447 
448 	evm_update_evmxattr(dentry, xattr_name, NULL, 0);
449 }
450 
451 /**
452  * evm_inode_setattr - prevent updating an invalid EVM extended attribute
453  * @dentry: pointer to the affected dentry
454  *
455  * Permit update of file attributes when files have a valid EVM signature,
456  * except in the case of them having an immutable portable signature.
457  */
458 int evm_inode_setattr(struct dentry *dentry, struct iattr *attr)
459 {
460 	unsigned int ia_valid = attr->ia_valid;
461 	enum integrity_status evm_status;
462 
463 	/* Policy permits modification of the protected attrs even though
464 	 * there's no HMAC key loaded
465 	 */
466 	if (evm_initialized & EVM_ALLOW_METADATA_WRITES)
467 		return 0;
468 
469 	if (!(ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID)))
470 		return 0;
471 	evm_status = evm_verify_current_integrity(dentry);
472 	if ((evm_status == INTEGRITY_PASS) ||
473 	    (evm_status == INTEGRITY_NOXATTRS))
474 		return 0;
475 	integrity_audit_msg(AUDIT_INTEGRITY_METADATA, d_backing_inode(dentry),
476 			    dentry->d_name.name, "appraise_metadata",
477 			    integrity_status_msg[evm_status], -EPERM, 0);
478 	return -EPERM;
479 }
480 
481 /**
482  * evm_inode_post_setattr - update 'security.evm' after modifying metadata
483  * @dentry: pointer to the affected dentry
484  * @ia_valid: for the UID and GID status
485  *
486  * For now, update the HMAC stored in 'security.evm' to reflect UID/GID
487  * changes.
488  *
489  * This function is called from notify_change(), which expects the caller
490  * to lock the inode's i_mutex.
491  */
492 void evm_inode_post_setattr(struct dentry *dentry, int ia_valid)
493 {
494 	if (!evm_key_loaded())
495 		return;
496 
497 	if (ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID))
498 		evm_update_evmxattr(dentry, NULL, NULL, 0);
499 }
500 
501 /*
502  * evm_inode_init_security - initializes security.evm
503  */
504 int evm_inode_init_security(struct inode *inode,
505 				 const struct xattr *lsm_xattr,
506 				 struct xattr *evm_xattr)
507 {
508 	struct evm_ima_xattr_data *xattr_data;
509 	int rc;
510 
511 	if (!evm_key_loaded() || !evm_protected_xattr(lsm_xattr->name))
512 		return 0;
513 
514 	xattr_data = kzalloc(sizeof(*xattr_data), GFP_NOFS);
515 	if (!xattr_data)
516 		return -ENOMEM;
517 
518 	xattr_data->type = EVM_XATTR_HMAC;
519 	rc = evm_init_hmac(inode, lsm_xattr, xattr_data->digest);
520 	if (rc < 0)
521 		goto out;
522 
523 	evm_xattr->value = xattr_data;
524 	evm_xattr->value_len = sizeof(*xattr_data);
525 	evm_xattr->name = XATTR_EVM_SUFFIX;
526 	return 0;
527 out:
528 	kfree(xattr_data);
529 	return rc;
530 }
531 EXPORT_SYMBOL_GPL(evm_inode_init_security);
532 
533 #ifdef CONFIG_EVM_LOAD_X509
534 void __init evm_load_x509(void)
535 {
536 	int rc;
537 
538 	rc = integrity_load_x509(INTEGRITY_KEYRING_EVM, CONFIG_EVM_X509_PATH);
539 	if (!rc)
540 		evm_initialized |= EVM_INIT_X509;
541 }
542 #endif
543 
544 static int __init init_evm(void)
545 {
546 	int error;
547 
548 	evm_init_config();
549 
550 	error = integrity_init_keyring(INTEGRITY_KEYRING_EVM);
551 	if (error)
552 		return error;
553 
554 	error = evm_init_secfs();
555 	if (error < 0) {
556 		pr_info("Error registering secfs\n");
557 		return error;
558 	}
559 
560 	return 0;
561 }
562 
563 /*
564  * evm_display_config - list the EVM protected security extended attributes
565  */
566 static int __init evm_display_config(void)
567 {
568 	char **xattrname;
569 
570 	for (xattrname = evm_config_xattrnames; *xattrname != NULL; xattrname++)
571 		pr_info("%s\n", *xattrname);
572 	return 0;
573 }
574 
575 pure_initcall(evm_display_config);
576 late_initcall(init_evm);
577 
578 MODULE_DESCRIPTION("Extended Verification Module");
579 MODULE_LICENSE("GPL");
580