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/hash_info.h>
29 #include <crypto/algapi.h>
30 #include "evm.h"
31 
32 int evm_initialized;
33 
34 static const char * const integrity_status_msg[] = {
35 	"pass", "pass_immutable", "fail", "no_label", "no_xattrs", "unknown"
36 };
37 int evm_hmac_attrs;
38 
39 static struct xattr_list evm_config_default_xattrnames[] = {
40 #ifdef CONFIG_SECURITY_SELINUX
41 	{.name = XATTR_NAME_SELINUX},
42 #endif
43 #ifdef CONFIG_SECURITY_SMACK
44 	{.name = XATTR_NAME_SMACK},
45 #ifdef CONFIG_EVM_EXTRA_SMACK_XATTRS
46 	{.name = XATTR_NAME_SMACKEXEC},
47 	{.name = XATTR_NAME_SMACKTRANSMUTE},
48 	{.name = XATTR_NAME_SMACKMMAP},
49 #endif
50 #endif
51 #ifdef CONFIG_SECURITY_APPARMOR
52 	{.name = XATTR_NAME_APPARMOR},
53 #endif
54 #ifdef CONFIG_IMA_APPRAISE
55 	{.name = XATTR_NAME_IMA},
56 #endif
57 	{.name = XATTR_NAME_CAPS},
58 };
59 
60 LIST_HEAD(evm_config_xattrnames);
61 
62 static int evm_fixmode;
63 static int __init evm_set_fixmode(char *str)
64 {
65 	if (strncmp(str, "fix", 3) == 0)
66 		evm_fixmode = 1;
67 	return 0;
68 }
69 __setup("evm=", evm_set_fixmode);
70 
71 static void __init evm_init_config(void)
72 {
73 	int i, xattrs;
74 
75 	xattrs = ARRAY_SIZE(evm_config_default_xattrnames);
76 
77 	pr_info("Initialising EVM extended attributes:\n");
78 	for (i = 0; i < xattrs; i++) {
79 		pr_info("%s\n", evm_config_default_xattrnames[i].name);
80 		list_add_tail(&evm_config_default_xattrnames[i].list,
81 			      &evm_config_xattrnames);
82 	}
83 
84 #ifdef CONFIG_EVM_ATTR_FSUUID
85 	evm_hmac_attrs |= EVM_ATTR_FSUUID;
86 #endif
87 	pr_info("HMAC attrs: 0x%x\n", evm_hmac_attrs);
88 }
89 
90 static bool evm_key_loaded(void)
91 {
92 	return (bool)(evm_initialized & EVM_KEY_MASK);
93 }
94 
95 static int evm_find_protected_xattrs(struct dentry *dentry)
96 {
97 	struct inode *inode = d_backing_inode(dentry);
98 	struct xattr_list *xattr;
99 	int error;
100 	int count = 0;
101 
102 	if (!(inode->i_opflags & IOP_XATTR))
103 		return -EOPNOTSUPP;
104 
105 	list_for_each_entry_rcu(xattr, &evm_config_xattrnames, list) {
106 		error = __vfs_getxattr(dentry, inode, xattr->name, NULL, 0);
107 		if (error < 0) {
108 			if (error == -ENODATA)
109 				continue;
110 			return error;
111 		}
112 		count++;
113 	}
114 
115 	return count;
116 }
117 
118 /*
119  * evm_verify_hmac - calculate and compare the HMAC with the EVM xattr
120  *
121  * Compute the HMAC on the dentry's protected set of extended attributes
122  * and compare it against the stored security.evm xattr.
123  *
124  * For performance:
125  * - use the previoulsy retrieved xattr value and length to calculate the
126  *   HMAC.)
127  * - cache the verification result in the iint, when available.
128  *
129  * Returns integrity status
130  */
131 static enum integrity_status evm_verify_hmac(struct dentry *dentry,
132 					     const char *xattr_name,
133 					     char *xattr_value,
134 					     size_t xattr_value_len,
135 					     struct integrity_iint_cache *iint)
136 {
137 	struct evm_ima_xattr_data *xattr_data = NULL;
138 	struct signature_v2_hdr *hdr;
139 	enum integrity_status evm_status = INTEGRITY_PASS;
140 	struct evm_digest digest;
141 	struct inode *inode;
142 	int rc, xattr_len;
143 
144 	if (iint && (iint->evm_status == INTEGRITY_PASS ||
145 		     iint->evm_status == INTEGRITY_PASS_IMMUTABLE))
146 		return iint->evm_status;
147 
148 	/* if status is not PASS, try to check again - against -ENOMEM */
149 
150 	/* first need to know the sig type */
151 	rc = vfs_getxattr_alloc(dentry, XATTR_NAME_EVM, (char **)&xattr_data, 0,
152 				GFP_NOFS);
153 	if (rc <= 0) {
154 		evm_status = INTEGRITY_FAIL;
155 		if (rc == -ENODATA) {
156 			rc = evm_find_protected_xattrs(dentry);
157 			if (rc > 0)
158 				evm_status = INTEGRITY_NOLABEL;
159 			else if (rc == 0)
160 				evm_status = INTEGRITY_NOXATTRS; /* new file */
161 		} else if (rc == -EOPNOTSUPP) {
162 			evm_status = INTEGRITY_UNKNOWN;
163 		}
164 		goto out;
165 	}
166 
167 	xattr_len = rc;
168 
169 	/* check value type */
170 	switch (xattr_data->type) {
171 	case EVM_XATTR_HMAC:
172 		if (xattr_len != sizeof(struct evm_ima_xattr_data)) {
173 			evm_status = INTEGRITY_FAIL;
174 			goto out;
175 		}
176 
177 		digest.hdr.algo = HASH_ALGO_SHA1;
178 		rc = evm_calc_hmac(dentry, xattr_name, xattr_value,
179 				   xattr_value_len, &digest);
180 		if (rc)
181 			break;
182 		rc = crypto_memneq(xattr_data->digest, digest.digest,
183 				   SHA1_DIGEST_SIZE);
184 		if (rc)
185 			rc = -EINVAL;
186 		break;
187 	case EVM_IMA_XATTR_DIGSIG:
188 	case EVM_XATTR_PORTABLE_DIGSIG:
189 		hdr = (struct signature_v2_hdr *)xattr_data;
190 		digest.hdr.algo = hdr->hash_algo;
191 		rc = evm_calc_hash(dentry, xattr_name, xattr_value,
192 				   xattr_value_len, xattr_data->type, &digest);
193 		if (rc)
194 			break;
195 		rc = integrity_digsig_verify(INTEGRITY_KEYRING_EVM,
196 					(const char *)xattr_data, xattr_len,
197 					digest.digest, digest.hdr.length);
198 		if (!rc) {
199 			inode = d_backing_inode(dentry);
200 
201 			if (xattr_data->type == EVM_XATTR_PORTABLE_DIGSIG) {
202 				if (iint)
203 					iint->flags |= EVM_IMMUTABLE_DIGSIG;
204 				evm_status = INTEGRITY_PASS_IMMUTABLE;
205 			} else if (!IS_RDONLY(inode) &&
206 				   !(inode->i_sb->s_readonly_remount) &&
207 				   !IS_IMMUTABLE(inode)) {
208 				evm_update_evmxattr(dentry, xattr_name,
209 						    xattr_value,
210 						    xattr_value_len);
211 			}
212 		}
213 		break;
214 	default:
215 		rc = -EINVAL;
216 		break;
217 	}
218 
219 	if (rc)
220 		evm_status = (rc == -ENODATA) ?
221 				INTEGRITY_NOXATTRS : INTEGRITY_FAIL;
222 out:
223 	if (iint)
224 		iint->evm_status = evm_status;
225 	kfree(xattr_data);
226 	return evm_status;
227 }
228 
229 static int evm_protected_xattr(const char *req_xattr_name)
230 {
231 	int namelen;
232 	int found = 0;
233 	struct xattr_list *xattr;
234 
235 	namelen = strlen(req_xattr_name);
236 	list_for_each_entry_rcu(xattr, &evm_config_xattrnames, list) {
237 		if ((strlen(xattr->name) == namelen)
238 		    && (strncmp(req_xattr_name, xattr->name, namelen) == 0)) {
239 			found = 1;
240 			break;
241 		}
242 		if (strncmp(req_xattr_name,
243 			    xattr->name + XATTR_SECURITY_PREFIX_LEN,
244 			    strlen(req_xattr_name)) == 0) {
245 			found = 1;
246 			break;
247 		}
248 	}
249 
250 	return found;
251 }
252 
253 /**
254  * evm_verifyxattr - verify the integrity of the requested xattr
255  * @dentry: object of the verify xattr
256  * @xattr_name: requested xattr
257  * @xattr_value: requested xattr value
258  * @xattr_value_len: requested xattr value length
259  *
260  * Calculate the HMAC for the given dentry and verify it against the stored
261  * security.evm xattr. For performance, use the xattr value and length
262  * previously retrieved to calculate the HMAC.
263  *
264  * Returns the xattr integrity status.
265  *
266  * This function requires the caller to lock the inode's i_mutex before it
267  * is executed.
268  */
269 enum integrity_status evm_verifyxattr(struct dentry *dentry,
270 				      const char *xattr_name,
271 				      void *xattr_value, size_t xattr_value_len,
272 				      struct integrity_iint_cache *iint)
273 {
274 	if (!evm_key_loaded() || !evm_protected_xattr(xattr_name))
275 		return INTEGRITY_UNKNOWN;
276 
277 	if (!iint) {
278 		iint = integrity_iint_find(d_backing_inode(dentry));
279 		if (!iint)
280 			return INTEGRITY_UNKNOWN;
281 	}
282 	return evm_verify_hmac(dentry, xattr_name, xattr_value,
283 				 xattr_value_len, iint);
284 }
285 EXPORT_SYMBOL_GPL(evm_verifyxattr);
286 
287 /*
288  * evm_verify_current_integrity - verify the dentry's metadata integrity
289  * @dentry: pointer to the affected dentry
290  *
291  * Verify and return the dentry's metadata integrity. The exceptions are
292  * before EVM is initialized or in 'fix' mode.
293  */
294 static enum integrity_status evm_verify_current_integrity(struct dentry *dentry)
295 {
296 	struct inode *inode = d_backing_inode(dentry);
297 
298 	if (!evm_key_loaded() || !S_ISREG(inode->i_mode) || evm_fixmode)
299 		return 0;
300 	return evm_verify_hmac(dentry, NULL, NULL, 0, NULL);
301 }
302 
303 /*
304  * evm_protect_xattr - protect the EVM extended attribute
305  *
306  * Prevent security.evm from being modified or removed without the
307  * necessary permissions or when the existing value is invalid.
308  *
309  * The posix xattr acls are 'system' prefixed, which normally would not
310  * affect security.evm.  An interesting side affect of writing posix xattr
311  * acls is their modifying of the i_mode, which is included in security.evm.
312  * For posix xattr acls only, permit security.evm, even if it currently
313  * doesn't exist, to be updated unless the EVM signature is immutable.
314  */
315 static int evm_protect_xattr(struct dentry *dentry, const char *xattr_name,
316 			     const void *xattr_value, size_t xattr_value_len)
317 {
318 	enum integrity_status evm_status;
319 
320 	if (strcmp(xattr_name, XATTR_NAME_EVM) == 0) {
321 		if (!capable(CAP_SYS_ADMIN))
322 			return -EPERM;
323 	} else if (!evm_protected_xattr(xattr_name)) {
324 		if (!posix_xattr_acl(xattr_name))
325 			return 0;
326 		evm_status = evm_verify_current_integrity(dentry);
327 		if ((evm_status == INTEGRITY_PASS) ||
328 		    (evm_status == INTEGRITY_NOXATTRS))
329 			return 0;
330 		goto out;
331 	}
332 
333 	evm_status = evm_verify_current_integrity(dentry);
334 	if (evm_status == INTEGRITY_NOXATTRS) {
335 		struct integrity_iint_cache *iint;
336 
337 		iint = integrity_iint_find(d_backing_inode(dentry));
338 		if (iint && (iint->flags & IMA_NEW_FILE))
339 			return 0;
340 
341 		/* exception for pseudo filesystems */
342 		if (dentry->d_sb->s_magic == TMPFS_MAGIC
343 		    || dentry->d_sb->s_magic == SYSFS_MAGIC)
344 			return 0;
345 
346 		integrity_audit_msg(AUDIT_INTEGRITY_METADATA,
347 				    dentry->d_inode, dentry->d_name.name,
348 				    "update_metadata",
349 				    integrity_status_msg[evm_status],
350 				    -EPERM, 0);
351 	}
352 out:
353 	if (evm_status != INTEGRITY_PASS)
354 		integrity_audit_msg(AUDIT_INTEGRITY_METADATA, d_backing_inode(dentry),
355 				    dentry->d_name.name, "appraise_metadata",
356 				    integrity_status_msg[evm_status],
357 				    -EPERM, 0);
358 	return evm_status == INTEGRITY_PASS ? 0 : -EPERM;
359 }
360 
361 /**
362  * evm_inode_setxattr - protect the EVM extended attribute
363  * @dentry: pointer to the affected dentry
364  * @xattr_name: pointer to the affected extended attribute name
365  * @xattr_value: pointer to the new extended attribute value
366  * @xattr_value_len: pointer to the new extended attribute value length
367  *
368  * Before allowing the 'security.evm' protected xattr to be updated,
369  * verify the existing value is valid.  As only the kernel should have
370  * access to the EVM encrypted key needed to calculate the HMAC, prevent
371  * userspace from writing HMAC value.  Writing 'security.evm' requires
372  * requires CAP_SYS_ADMIN privileges.
373  */
374 int evm_inode_setxattr(struct dentry *dentry, const char *xattr_name,
375 		       const void *xattr_value, size_t xattr_value_len)
376 {
377 	const struct evm_ima_xattr_data *xattr_data = xattr_value;
378 
379 	/* Policy permits modification of the protected xattrs even though
380 	 * there's no HMAC key loaded
381 	 */
382 	if (evm_initialized & EVM_ALLOW_METADATA_WRITES)
383 		return 0;
384 
385 	if (strcmp(xattr_name, XATTR_NAME_EVM) == 0) {
386 		if (!xattr_value_len)
387 			return -EINVAL;
388 		if (xattr_data->type != EVM_IMA_XATTR_DIGSIG &&
389 		    xattr_data->type != EVM_XATTR_PORTABLE_DIGSIG)
390 			return -EPERM;
391 	}
392 	return evm_protect_xattr(dentry, xattr_name, xattr_value,
393 				 xattr_value_len);
394 }
395 
396 /**
397  * evm_inode_removexattr - protect the EVM extended attribute
398  * @dentry: pointer to the affected dentry
399  * @xattr_name: pointer to the affected extended attribute name
400  *
401  * Removing 'security.evm' requires CAP_SYS_ADMIN privileges and that
402  * the current value is valid.
403  */
404 int evm_inode_removexattr(struct dentry *dentry, const char *xattr_name)
405 {
406 	/* Policy permits modification of the protected xattrs even though
407 	 * there's no HMAC key loaded
408 	 */
409 	if (evm_initialized & EVM_ALLOW_METADATA_WRITES)
410 		return 0;
411 
412 	return evm_protect_xattr(dentry, xattr_name, NULL, 0);
413 }
414 
415 static void evm_reset_status(struct inode *inode)
416 {
417 	struct integrity_iint_cache *iint;
418 
419 	iint = integrity_iint_find(inode);
420 	if (iint)
421 		iint->evm_status = INTEGRITY_UNKNOWN;
422 }
423 
424 /**
425  * evm_inode_post_setxattr - update 'security.evm' to reflect the changes
426  * @dentry: pointer to the affected dentry
427  * @xattr_name: pointer to the affected extended attribute name
428  * @xattr_value: pointer to the new extended attribute value
429  * @xattr_value_len: pointer to the new extended attribute value length
430  *
431  * Update the HMAC stored in 'security.evm' to reflect the change.
432  *
433  * No need to take the i_mutex lock here, as this function is called from
434  * __vfs_setxattr_noperm().  The caller of which has taken the inode's
435  * i_mutex lock.
436  */
437 void evm_inode_post_setxattr(struct dentry *dentry, const char *xattr_name,
438 			     const void *xattr_value, size_t xattr_value_len)
439 {
440 	if (!evm_key_loaded() || (!evm_protected_xattr(xattr_name)
441 				  && !posix_xattr_acl(xattr_name)))
442 		return;
443 
444 	evm_reset_status(dentry->d_inode);
445 
446 	evm_update_evmxattr(dentry, xattr_name, xattr_value, xattr_value_len);
447 }
448 
449 /**
450  * evm_inode_post_removexattr - update 'security.evm' after removing the xattr
451  * @dentry: pointer to the affected dentry
452  * @xattr_name: pointer to the affected extended attribute name
453  *
454  * Update the HMAC stored in 'security.evm' to reflect removal of the xattr.
455  *
456  * No need to take the i_mutex lock here, as this function is called from
457  * vfs_removexattr() which takes the i_mutex.
458  */
459 void evm_inode_post_removexattr(struct dentry *dentry, const char *xattr_name)
460 {
461 	if (!evm_key_loaded() || !evm_protected_xattr(xattr_name))
462 		return;
463 
464 	evm_reset_status(dentry->d_inode);
465 
466 	evm_update_evmxattr(dentry, xattr_name, NULL, 0);
467 }
468 
469 /**
470  * evm_inode_setattr - prevent updating an invalid EVM extended attribute
471  * @dentry: pointer to the affected dentry
472  *
473  * Permit update of file attributes when files have a valid EVM signature,
474  * except in the case of them having an immutable portable signature.
475  */
476 int evm_inode_setattr(struct dentry *dentry, struct iattr *attr)
477 {
478 	unsigned int ia_valid = attr->ia_valid;
479 	enum integrity_status evm_status;
480 
481 	/* Policy permits modification of the protected attrs even though
482 	 * there's no HMAC key loaded
483 	 */
484 	if (evm_initialized & EVM_ALLOW_METADATA_WRITES)
485 		return 0;
486 
487 	if (!(ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID)))
488 		return 0;
489 	evm_status = evm_verify_current_integrity(dentry);
490 	if ((evm_status == INTEGRITY_PASS) ||
491 	    (evm_status == INTEGRITY_NOXATTRS))
492 		return 0;
493 	integrity_audit_msg(AUDIT_INTEGRITY_METADATA, d_backing_inode(dentry),
494 			    dentry->d_name.name, "appraise_metadata",
495 			    integrity_status_msg[evm_status], -EPERM, 0);
496 	return -EPERM;
497 }
498 
499 /**
500  * evm_inode_post_setattr - update 'security.evm' after modifying metadata
501  * @dentry: pointer to the affected dentry
502  * @ia_valid: for the UID and GID status
503  *
504  * For now, update the HMAC stored in 'security.evm' to reflect UID/GID
505  * changes.
506  *
507  * This function is called from notify_change(), which expects the caller
508  * to lock the inode's i_mutex.
509  */
510 void evm_inode_post_setattr(struct dentry *dentry, int ia_valid)
511 {
512 	if (!evm_key_loaded())
513 		return;
514 
515 	if (ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID))
516 		evm_update_evmxattr(dentry, NULL, NULL, 0);
517 }
518 
519 /*
520  * evm_inode_init_security - initializes security.evm
521  */
522 int evm_inode_init_security(struct inode *inode,
523 				 const struct xattr *lsm_xattr,
524 				 struct xattr *evm_xattr)
525 {
526 	struct evm_ima_xattr_data *xattr_data;
527 	int rc;
528 
529 	if (!evm_key_loaded() || !evm_protected_xattr(lsm_xattr->name))
530 		return 0;
531 
532 	xattr_data = kzalloc(sizeof(*xattr_data), GFP_NOFS);
533 	if (!xattr_data)
534 		return -ENOMEM;
535 
536 	xattr_data->type = EVM_XATTR_HMAC;
537 	rc = evm_init_hmac(inode, lsm_xattr, xattr_data->digest);
538 	if (rc < 0)
539 		goto out;
540 
541 	evm_xattr->value = xattr_data;
542 	evm_xattr->value_len = sizeof(*xattr_data);
543 	evm_xattr->name = XATTR_EVM_SUFFIX;
544 	return 0;
545 out:
546 	kfree(xattr_data);
547 	return rc;
548 }
549 EXPORT_SYMBOL_GPL(evm_inode_init_security);
550 
551 #ifdef CONFIG_EVM_LOAD_X509
552 void __init evm_load_x509(void)
553 {
554 	int rc;
555 
556 	rc = integrity_load_x509(INTEGRITY_KEYRING_EVM, CONFIG_EVM_X509_PATH);
557 	if (!rc)
558 		evm_initialized |= EVM_INIT_X509;
559 }
560 #endif
561 
562 static int __init init_evm(void)
563 {
564 	int error;
565 	struct list_head *pos, *q;
566 	struct xattr_list *xattr;
567 
568 	evm_init_config();
569 
570 	error = integrity_init_keyring(INTEGRITY_KEYRING_EVM);
571 	if (error)
572 		goto error;
573 
574 	error = evm_init_secfs();
575 	if (error < 0) {
576 		pr_info("Error registering secfs\n");
577 		goto error;
578 	}
579 
580 error:
581 	if (error != 0) {
582 		if (!list_empty(&evm_config_xattrnames)) {
583 			list_for_each_safe(pos, q, &evm_config_xattrnames) {
584 				xattr = list_entry(pos, struct xattr_list,
585 						   list);
586 				list_del(pos);
587 			}
588 		}
589 	}
590 
591 	return error;
592 }
593 
594 late_initcall(init_evm);
595 
596 MODULE_DESCRIPTION("Extended Verification Module");
597 MODULE_LICENSE("GPL");
598