xref: /linux/security/integrity/ima/ima_appraise.c (revision a5fbeb615ca42f913ace3291d636e96feabcc545) 
1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3  * Copyright (C) 2011 IBM Corporation
4  *
5  * Author:
6  * Mimi Zohar <zohar@us.ibm.com>
7  */
8 #include <linux/init.h>
9 #include <linux/file.h>
10 #include <linux/fs.h>
11 #include <linux/xattr.h>
12 #include <linux/magic.h>
13 #include <linux/ima.h>
14 #include <linux/evm.h>
15 
16 #include "ima.h"
17 
18 static int __init default_appraise_setup(char *str)
19 {
20 #ifdef CONFIG_IMA_APPRAISE_BOOTPARAM
21 	if (strncmp(str, "off", 3) == 0)
22 		ima_appraise = 0;
23 	else if (strncmp(str, "log", 3) == 0)
24 		ima_appraise = IMA_APPRAISE_LOG;
25 	else if (strncmp(str, "fix", 3) == 0)
26 		ima_appraise = IMA_APPRAISE_FIX;
27 #endif
28 	return 1;
29 }
30 
31 __setup("ima_appraise=", default_appraise_setup);
32 
33 /*
34  * is_ima_appraise_enabled - return appraise status
35  *
36  * Only return enabled, if not in ima_appraise="fix" or "log" modes.
37  */
38 bool is_ima_appraise_enabled(void)
39 {
40 	return ima_appraise & IMA_APPRAISE_ENFORCE;
41 }
42 
43 /*
44  * ima_must_appraise - set appraise flag
45  *
46  * Return 1 to appraise or hash
47  */
48 int ima_must_appraise(struct inode *inode, int mask, enum ima_hooks func)
49 {
50 	u32 secid;
51 
52 	if (!ima_appraise)
53 		return 0;
54 
55 	security_task_getsecid(current, &secid);
56 	return ima_match_policy(inode, current_cred(), secid, func, mask,
57 				IMA_APPRAISE | IMA_HASH, NULL, NULL);
58 }
59 
60 static int ima_fix_xattr(struct dentry *dentry,
61 			 struct integrity_iint_cache *iint)
62 {
63 	int rc, offset;
64 	u8 algo = iint->ima_hash->algo;
65 
66 	if (algo <= HASH_ALGO_SHA1) {
67 		offset = 1;
68 		iint->ima_hash->xattr.sha1.type = IMA_XATTR_DIGEST;
69 	} else {
70 		offset = 0;
71 		iint->ima_hash->xattr.ng.type = IMA_XATTR_DIGEST_NG;
72 		iint->ima_hash->xattr.ng.algo = algo;
73 	}
74 	rc = __vfs_setxattr_noperm(dentry, XATTR_NAME_IMA,
75 				   &iint->ima_hash->xattr.data[offset],
76 				   (sizeof(iint->ima_hash->xattr) - offset) +
77 				   iint->ima_hash->length, 0);
78 	return rc;
79 }
80 
81 /* Return specific func appraised cached result */
82 enum integrity_status ima_get_cache_status(struct integrity_iint_cache *iint,
83 					   enum ima_hooks func)
84 {
85 	switch (func) {
86 	case MMAP_CHECK:
87 		return iint->ima_mmap_status;
88 	case BPRM_CHECK:
89 		return iint->ima_bprm_status;
90 	case CREDS_CHECK:
91 		return iint->ima_creds_status;
92 	case FILE_CHECK:
93 	case POST_SETATTR:
94 		return iint->ima_file_status;
95 	case MODULE_CHECK ... MAX_CHECK - 1:
96 	default:
97 		return iint->ima_read_status;
98 	}
99 }
100 
101 static void ima_set_cache_status(struct integrity_iint_cache *iint,
102 				 enum ima_hooks func,
103 				 enum integrity_status status)
104 {
105 	switch (func) {
106 	case MMAP_CHECK:
107 		iint->ima_mmap_status = status;
108 		break;
109 	case BPRM_CHECK:
110 		iint->ima_bprm_status = status;
111 		break;
112 	case CREDS_CHECK:
113 		iint->ima_creds_status = status;
114 		break;
115 	case FILE_CHECK:
116 	case POST_SETATTR:
117 		iint->ima_file_status = status;
118 		break;
119 	case MODULE_CHECK ... MAX_CHECK - 1:
120 	default:
121 		iint->ima_read_status = status;
122 		break;
123 	}
124 }
125 
126 static void ima_cache_flags(struct integrity_iint_cache *iint,
127 			     enum ima_hooks func)
128 {
129 	switch (func) {
130 	case MMAP_CHECK:
131 		iint->flags |= (IMA_MMAP_APPRAISED | IMA_APPRAISED);
132 		break;
133 	case BPRM_CHECK:
134 		iint->flags |= (IMA_BPRM_APPRAISED | IMA_APPRAISED);
135 		break;
136 	case CREDS_CHECK:
137 		iint->flags |= (IMA_CREDS_APPRAISED | IMA_APPRAISED);
138 		break;
139 	case FILE_CHECK:
140 	case POST_SETATTR:
141 		iint->flags |= (IMA_FILE_APPRAISED | IMA_APPRAISED);
142 		break;
143 	case MODULE_CHECK ... MAX_CHECK - 1:
144 	default:
145 		iint->flags |= (IMA_READ_APPRAISED | IMA_APPRAISED);
146 		break;
147 	}
148 }
149 
150 enum hash_algo ima_get_hash_algo(struct evm_ima_xattr_data *xattr_value,
151 				 int xattr_len)
152 {
153 	struct signature_v2_hdr *sig;
154 	enum hash_algo ret;
155 
156 	if (!xattr_value || xattr_len < 2)
157 		/* return default hash algo */
158 		return ima_hash_algo;
159 
160 	switch (xattr_value->type) {
161 	case EVM_IMA_XATTR_DIGSIG:
162 		sig = (typeof(sig))xattr_value;
163 		if (sig->version != 2 || xattr_len <= sizeof(*sig))
164 			return ima_hash_algo;
165 		return sig->hash_algo;
166 		break;
167 	case IMA_XATTR_DIGEST_NG:
168 		/* first byte contains algorithm id */
169 		ret = xattr_value->data[0];
170 		if (ret < HASH_ALGO__LAST)
171 			return ret;
172 		break;
173 	case IMA_XATTR_DIGEST:
174 		/* this is for backward compatibility */
175 		if (xattr_len == 21) {
176 			unsigned int zero = 0;
177 			if (!memcmp(&xattr_value->data[16], &zero, 4))
178 				return HASH_ALGO_MD5;
179 			else
180 				return HASH_ALGO_SHA1;
181 		} else if (xattr_len == 17)
182 			return HASH_ALGO_MD5;
183 		break;
184 	}
185 
186 	/* return default hash algo */
187 	return ima_hash_algo;
188 }
189 
190 int ima_read_xattr(struct dentry *dentry,
191 		   struct evm_ima_xattr_data **xattr_value)
192 {
193 	ssize_t ret;
194 
195 	ret = vfs_getxattr_alloc(dentry, XATTR_NAME_IMA, (char **)xattr_value,
196 				 0, GFP_NOFS);
197 	if (ret == -EOPNOTSUPP)
198 		ret = 0;
199 	return ret;
200 }
201 
202 /*
203  * xattr_verify - verify xattr digest or signature
204  *
205  * Verify whether the hash or signature matches the file contents.
206  *
207  * Return 0 on success, error code otherwise.
208  */
209 static int xattr_verify(enum ima_hooks func, struct integrity_iint_cache *iint,
210 			struct evm_ima_xattr_data *xattr_value, int xattr_len,
211 			enum integrity_status *status, const char **cause)
212 {
213 	int rc = -EINVAL, hash_start = 0;
214 
215 	switch (xattr_value->type) {
216 	case IMA_XATTR_DIGEST_NG:
217 		/* first byte contains algorithm id */
218 		hash_start = 1;
219 		/* fall through */
220 	case IMA_XATTR_DIGEST:
221 		if (iint->flags & IMA_DIGSIG_REQUIRED) {
222 			*cause = "IMA-signature-required";
223 			*status = INTEGRITY_FAIL;
224 			break;
225 		}
226 		clear_bit(IMA_DIGSIG, &iint->atomic_flags);
227 		if (xattr_len - sizeof(xattr_value->type) - hash_start >=
228 				iint->ima_hash->length)
229 			/*
230 			 * xattr length may be longer. md5 hash in previous
231 			 * version occupied 20 bytes in xattr, instead of 16
232 			 */
233 			rc = memcmp(&xattr_value->data[hash_start],
234 				    iint->ima_hash->digest,
235 				    iint->ima_hash->length);
236 		else
237 			rc = -EINVAL;
238 		if (rc) {
239 			*cause = "invalid-hash";
240 			*status = INTEGRITY_FAIL;
241 			break;
242 		}
243 		*status = INTEGRITY_PASS;
244 		break;
245 	case EVM_IMA_XATTR_DIGSIG:
246 		set_bit(IMA_DIGSIG, &iint->atomic_flags);
247 		rc = integrity_digsig_verify(INTEGRITY_KEYRING_IMA,
248 					     (const char *)xattr_value,
249 					     xattr_len,
250 					     iint->ima_hash->digest,
251 					     iint->ima_hash->length);
252 		if (rc == -EOPNOTSUPP) {
253 			*status = INTEGRITY_UNKNOWN;
254 			break;
255 		}
256 		if (IS_ENABLED(CONFIG_INTEGRITY_PLATFORM_KEYRING) && rc &&
257 		    func == KEXEC_KERNEL_CHECK)
258 			rc = integrity_digsig_verify(INTEGRITY_KEYRING_PLATFORM,
259 						     (const char *)xattr_value,
260 						     xattr_len,
261 						     iint->ima_hash->digest,
262 						     iint->ima_hash->length);
263 		if (rc) {
264 			*cause = "invalid-signature";
265 			*status = INTEGRITY_FAIL;
266 		} else {
267 			*status = INTEGRITY_PASS;
268 		}
269 		break;
270 	default:
271 		*status = INTEGRITY_UNKNOWN;
272 		*cause = "unknown-ima-data";
273 		break;
274 	}
275 
276 	return rc;
277 }
278 
279 /*
280  * ima_appraise_measurement - appraise file measurement
281  *
282  * Call evm_verifyxattr() to verify the integrity of 'security.ima'.
283  * Assuming success, compare the xattr hash with the collected measurement.
284  *
285  * Return 0 on success, error code otherwise
286  */
287 int ima_appraise_measurement(enum ima_hooks func,
288 			     struct integrity_iint_cache *iint,
289 			     struct file *file, const unsigned char *filename,
290 			     struct evm_ima_xattr_data *xattr_value,
291 			     int xattr_len)
292 {
293 	static const char op[] = "appraise_data";
294 	const char *cause = "unknown";
295 	struct dentry *dentry = file_dentry(file);
296 	struct inode *inode = d_backing_inode(dentry);
297 	enum integrity_status status = INTEGRITY_UNKNOWN;
298 	int rc = xattr_len;
299 
300 	if (!(inode->i_opflags & IOP_XATTR))
301 		return INTEGRITY_UNKNOWN;
302 
303 	if (rc <= 0) {
304 		if (rc && rc != -ENODATA)
305 			goto out;
306 
307 		cause = iint->flags & IMA_DIGSIG_REQUIRED ?
308 				"IMA-signature-required" : "missing-hash";
309 		status = INTEGRITY_NOLABEL;
310 		if (file->f_mode & FMODE_CREATED)
311 			iint->flags |= IMA_NEW_FILE;
312 		if ((iint->flags & IMA_NEW_FILE) &&
313 		    (!(iint->flags & IMA_DIGSIG_REQUIRED) ||
314 		     (inode->i_size == 0)))
315 			status = INTEGRITY_PASS;
316 		goto out;
317 	}
318 
319 	status = evm_verifyxattr(dentry, XATTR_NAME_IMA, xattr_value, rc, iint);
320 	switch (status) {
321 	case INTEGRITY_PASS:
322 	case INTEGRITY_PASS_IMMUTABLE:
323 	case INTEGRITY_UNKNOWN:
324 		break;
325 	case INTEGRITY_NOXATTRS:	/* No EVM protected xattrs. */
326 	case INTEGRITY_NOLABEL:		/* No security.evm xattr. */
327 		cause = "missing-HMAC";
328 		goto out;
329 	case INTEGRITY_FAIL:		/* Invalid HMAC/signature. */
330 		cause = "invalid-HMAC";
331 		goto out;
332 	default:
333 		WARN_ONCE(true, "Unexpected integrity status %d\n", status);
334 	}
335 
336 	if (xattr_value)
337 		rc = xattr_verify(func, iint, xattr_value, xattr_len, &status,
338 				  &cause);
339 
340 out:
341 	/*
342 	 * File signatures on some filesystems can not be properly verified.
343 	 * When such filesystems are mounted by an untrusted mounter or on a
344 	 * system not willing to accept such a risk, fail the file signature
345 	 * verification.
346 	 */
347 	if ((inode->i_sb->s_iflags & SB_I_IMA_UNVERIFIABLE_SIGNATURE) &&
348 	    ((inode->i_sb->s_iflags & SB_I_UNTRUSTED_MOUNTER) ||
349 	     (iint->flags & IMA_FAIL_UNVERIFIABLE_SIGS))) {
350 		status = INTEGRITY_FAIL;
351 		cause = "unverifiable-signature";
352 		integrity_audit_msg(AUDIT_INTEGRITY_DATA, inode, filename,
353 				    op, cause, rc, 0);
354 	} else if (status != INTEGRITY_PASS) {
355 		/* Fix mode, but don't replace file signatures. */
356 		if ((ima_appraise & IMA_APPRAISE_FIX) &&
357 		    (!xattr_value ||
358 		     xattr_value->type != EVM_IMA_XATTR_DIGSIG)) {
359 			if (!ima_fix_xattr(dentry, iint))
360 				status = INTEGRITY_PASS;
361 		}
362 
363 		/* Permit new files with file signatures, but without data. */
364 		if (inode->i_size == 0 && iint->flags & IMA_NEW_FILE &&
365 		    xattr_value && xattr_value->type == EVM_IMA_XATTR_DIGSIG) {
366 			status = INTEGRITY_PASS;
367 		}
368 
369 		integrity_audit_msg(AUDIT_INTEGRITY_DATA, inode, filename,
370 				    op, cause, rc, 0);
371 	} else {
372 		ima_cache_flags(iint, func);
373 	}
374 
375 	ima_set_cache_status(iint, func, status);
376 	return status;
377 }
378 
379 /*
380  * ima_update_xattr - update 'security.ima' hash value
381  */
382 void ima_update_xattr(struct integrity_iint_cache *iint, struct file *file)
383 {
384 	struct dentry *dentry = file_dentry(file);
385 	int rc = 0;
386 
387 	/* do not collect and update hash for digital signatures */
388 	if (test_bit(IMA_DIGSIG, &iint->atomic_flags))
389 		return;
390 
391 	if ((iint->ima_file_status != INTEGRITY_PASS) &&
392 	    !(iint->flags & IMA_HASH))
393 		return;
394 
395 	rc = ima_collect_measurement(iint, file, NULL, 0, ima_hash_algo);
396 	if (rc < 0)
397 		return;
398 
399 	inode_lock(file_inode(file));
400 	ima_fix_xattr(dentry, iint);
401 	inode_unlock(file_inode(file));
402 }
403 
404 /**
405  * ima_inode_post_setattr - reflect file metadata changes
406  * @dentry: pointer to the affected dentry
407  *
408  * Changes to a dentry's metadata might result in needing to appraise.
409  *
410  * This function is called from notify_change(), which expects the caller
411  * to lock the inode's i_mutex.
412  */
413 void ima_inode_post_setattr(struct dentry *dentry)
414 {
415 	struct inode *inode = d_backing_inode(dentry);
416 	struct integrity_iint_cache *iint;
417 	int action;
418 
419 	if (!(ima_policy_flag & IMA_APPRAISE) || !S_ISREG(inode->i_mode)
420 	    || !(inode->i_opflags & IOP_XATTR))
421 		return;
422 
423 	action = ima_must_appraise(inode, MAY_ACCESS, POST_SETATTR);
424 	if (!action)
425 		__vfs_removexattr(dentry, XATTR_NAME_IMA);
426 	iint = integrity_iint_find(inode);
427 	if (iint) {
428 		set_bit(IMA_CHANGE_ATTR, &iint->atomic_flags);
429 		if (!action)
430 			clear_bit(IMA_UPDATE_XATTR, &iint->atomic_flags);
431 	}
432 }
433 
434 /*
435  * ima_protect_xattr - protect 'security.ima'
436  *
437  * Ensure that not just anyone can modify or remove 'security.ima'.
438  */
439 static int ima_protect_xattr(struct dentry *dentry, const char *xattr_name,
440 			     const void *xattr_value, size_t xattr_value_len)
441 {
442 	if (strcmp(xattr_name, XATTR_NAME_IMA) == 0) {
443 		if (!capable(CAP_SYS_ADMIN))
444 			return -EPERM;
445 		return 1;
446 	}
447 	return 0;
448 }
449 
450 static void ima_reset_appraise_flags(struct inode *inode, int digsig)
451 {
452 	struct integrity_iint_cache *iint;
453 
454 	if (!(ima_policy_flag & IMA_APPRAISE) || !S_ISREG(inode->i_mode))
455 		return;
456 
457 	iint = integrity_iint_find(inode);
458 	if (!iint)
459 		return;
460 	iint->measured_pcrs = 0;
461 	set_bit(IMA_CHANGE_XATTR, &iint->atomic_flags);
462 	if (digsig)
463 		set_bit(IMA_DIGSIG, &iint->atomic_flags);
464 	else
465 		clear_bit(IMA_DIGSIG, &iint->atomic_flags);
466 }
467 
468 int ima_inode_setxattr(struct dentry *dentry, const char *xattr_name,
469 		       const void *xattr_value, size_t xattr_value_len)
470 {
471 	const struct evm_ima_xattr_data *xvalue = xattr_value;
472 	int result;
473 
474 	result = ima_protect_xattr(dentry, xattr_name, xattr_value,
475 				   xattr_value_len);
476 	if (result == 1) {
477 		if (!xattr_value_len || (xvalue->type >= IMA_XATTR_LAST))
478 			return -EINVAL;
479 		ima_reset_appraise_flags(d_backing_inode(dentry),
480 			xvalue->type == EVM_IMA_XATTR_DIGSIG);
481 		result = 0;
482 	}
483 	return result;
484 }
485 
486 int ima_inode_removexattr(struct dentry *dentry, const char *xattr_name)
487 {
488 	int result;
489 
490 	result = ima_protect_xattr(dentry, xattr_name, NULL, 0);
491 	if (result == 1) {
492 		ima_reset_appraise_flags(d_backing_inode(dentry), 0);
493 		result = 0;
494 	}
495 	return result;
496 }
497