xref: /linux/security/integrity/ima/ima_appraise.c (revision 44f57d78) 
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);
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 		ret = xattr_value->digest[0];
169 		if (ret < HASH_ALGO__LAST)
170 			return ret;
171 		break;
172 	case IMA_XATTR_DIGEST:
173 		/* this is for backward compatibility */
174 		if (xattr_len == 21) {
175 			unsigned int zero = 0;
176 			if (!memcmp(&xattr_value->digest[16], &zero, 4))
177 				return HASH_ALGO_MD5;
178 			else
179 				return HASH_ALGO_SHA1;
180 		} else if (xattr_len == 17)
181 			return HASH_ALGO_MD5;
182 		break;
183 	}
184 
185 	/* return default hash algo */
186 	return ima_hash_algo;
187 }
188 
189 int ima_read_xattr(struct dentry *dentry,
190 		   struct evm_ima_xattr_data **xattr_value)
191 {
192 	ssize_t ret;
193 
194 	ret = vfs_getxattr_alloc(dentry, XATTR_NAME_IMA, (char **)xattr_value,
195 				 0, GFP_NOFS);
196 	if (ret == -EOPNOTSUPP)
197 		ret = 0;
198 	return ret;
199 }
200 
201 /*
202  * ima_appraise_measurement - appraise file measurement
203  *
204  * Call evm_verifyxattr() to verify the integrity of 'security.ima'.
205  * Assuming success, compare the xattr hash with the collected measurement.
206  *
207  * Return 0 on success, error code otherwise
208  */
209 int ima_appraise_measurement(enum ima_hooks func,
210 			     struct integrity_iint_cache *iint,
211 			     struct file *file, const unsigned char *filename,
212 			     struct evm_ima_xattr_data *xattr_value,
213 			     int xattr_len)
214 {
215 	static const char op[] = "appraise_data";
216 	const char *cause = "unknown";
217 	struct dentry *dentry = file_dentry(file);
218 	struct inode *inode = d_backing_inode(dentry);
219 	enum integrity_status status = INTEGRITY_UNKNOWN;
220 	int rc = xattr_len, hash_start = 0;
221 
222 	if (!(inode->i_opflags & IOP_XATTR))
223 		return INTEGRITY_UNKNOWN;
224 
225 	if (rc <= 0) {
226 		if (rc && rc != -ENODATA)
227 			goto out;
228 
229 		cause = iint->flags & IMA_DIGSIG_REQUIRED ?
230 				"IMA-signature-required" : "missing-hash";
231 		status = INTEGRITY_NOLABEL;
232 		if (file->f_mode & FMODE_CREATED)
233 			iint->flags |= IMA_NEW_FILE;
234 		if ((iint->flags & IMA_NEW_FILE) &&
235 		    (!(iint->flags & IMA_DIGSIG_REQUIRED) ||
236 		     (inode->i_size == 0)))
237 			status = INTEGRITY_PASS;
238 		goto out;
239 	}
240 
241 	status = evm_verifyxattr(dentry, XATTR_NAME_IMA, xattr_value, rc, iint);
242 	switch (status) {
243 	case INTEGRITY_PASS:
244 	case INTEGRITY_PASS_IMMUTABLE:
245 	case INTEGRITY_UNKNOWN:
246 		break;
247 	case INTEGRITY_NOXATTRS:	/* No EVM protected xattrs. */
248 	case INTEGRITY_NOLABEL:		/* No security.evm xattr. */
249 		cause = "missing-HMAC";
250 		goto out;
251 	case INTEGRITY_FAIL:		/* Invalid HMAC/signature. */
252 		cause = "invalid-HMAC";
253 		goto out;
254 	default:
255 		WARN_ONCE(true, "Unexpected integrity status %d\n", status);
256 	}
257 
258 	switch (xattr_value->type) {
259 	case IMA_XATTR_DIGEST_NG:
260 		/* first byte contains algorithm id */
261 		hash_start = 1;
262 		/* fall through */
263 	case IMA_XATTR_DIGEST:
264 		if (iint->flags & IMA_DIGSIG_REQUIRED) {
265 			cause = "IMA-signature-required";
266 			status = INTEGRITY_FAIL;
267 			break;
268 		}
269 		clear_bit(IMA_DIGSIG, &iint->atomic_flags);
270 		if (xattr_len - sizeof(xattr_value->type) - hash_start >=
271 				iint->ima_hash->length)
272 			/* xattr length may be longer. md5 hash in previous
273 			   version occupied 20 bytes in xattr, instead of 16
274 			 */
275 			rc = memcmp(&xattr_value->digest[hash_start],
276 				    iint->ima_hash->digest,
277 				    iint->ima_hash->length);
278 		else
279 			rc = -EINVAL;
280 		if (rc) {
281 			cause = "invalid-hash";
282 			status = INTEGRITY_FAIL;
283 			break;
284 		}
285 		status = INTEGRITY_PASS;
286 		break;
287 	case EVM_IMA_XATTR_DIGSIG:
288 		set_bit(IMA_DIGSIG, &iint->atomic_flags);
289 		rc = integrity_digsig_verify(INTEGRITY_KEYRING_IMA,
290 					     (const char *)xattr_value,
291 					     xattr_len,
292 					     iint->ima_hash->digest,
293 					     iint->ima_hash->length);
294 		if (rc == -EOPNOTSUPP) {
295 			status = INTEGRITY_UNKNOWN;
296 			break;
297 		}
298 		if (IS_ENABLED(CONFIG_INTEGRITY_PLATFORM_KEYRING) && rc &&
299 		    func == KEXEC_KERNEL_CHECK)
300 			rc = integrity_digsig_verify(INTEGRITY_KEYRING_PLATFORM,
301 						     (const char *)xattr_value,
302 						     xattr_len,
303 						     iint->ima_hash->digest,
304 						     iint->ima_hash->length);
305 		if (rc) {
306 			cause = "invalid-signature";
307 			status = INTEGRITY_FAIL;
308 		} else {
309 			status = INTEGRITY_PASS;
310 		}
311 		break;
312 	default:
313 		status = INTEGRITY_UNKNOWN;
314 		cause = "unknown-ima-data";
315 		break;
316 	}
317 
318 out:
319 	/*
320 	 * File signatures on some filesystems can not be properly verified.
321 	 * When such filesystems are mounted by an untrusted mounter or on a
322 	 * system not willing to accept such a risk, fail the file signature
323 	 * verification.
324 	 */
325 	if ((inode->i_sb->s_iflags & SB_I_IMA_UNVERIFIABLE_SIGNATURE) &&
326 	    ((inode->i_sb->s_iflags & SB_I_UNTRUSTED_MOUNTER) ||
327 	     (iint->flags & IMA_FAIL_UNVERIFIABLE_SIGS))) {
328 		status = INTEGRITY_FAIL;
329 		cause = "unverifiable-signature";
330 		integrity_audit_msg(AUDIT_INTEGRITY_DATA, inode, filename,
331 				    op, cause, rc, 0);
332 	} else if (status != INTEGRITY_PASS) {
333 		/* Fix mode, but don't replace file signatures. */
334 		if ((ima_appraise & IMA_APPRAISE_FIX) &&
335 		    (!xattr_value ||
336 		     xattr_value->type != EVM_IMA_XATTR_DIGSIG)) {
337 			if (!ima_fix_xattr(dentry, iint))
338 				status = INTEGRITY_PASS;
339 		}
340 
341 		/* Permit new files with file signatures, but without data. */
342 		if (inode->i_size == 0 && iint->flags & IMA_NEW_FILE &&
343 		    xattr_value && xattr_value->type == EVM_IMA_XATTR_DIGSIG) {
344 			status = INTEGRITY_PASS;
345 		}
346 
347 		integrity_audit_msg(AUDIT_INTEGRITY_DATA, inode, filename,
348 				    op, cause, rc, 0);
349 	} else {
350 		ima_cache_flags(iint, func);
351 	}
352 
353 	ima_set_cache_status(iint, func, status);
354 	return status;
355 }
356 
357 /*
358  * ima_update_xattr - update 'security.ima' hash value
359  */
360 void ima_update_xattr(struct integrity_iint_cache *iint, struct file *file)
361 {
362 	struct dentry *dentry = file_dentry(file);
363 	int rc = 0;
364 
365 	/* do not collect and update hash for digital signatures */
366 	if (test_bit(IMA_DIGSIG, &iint->atomic_flags))
367 		return;
368 
369 	if ((iint->ima_file_status != INTEGRITY_PASS) &&
370 	    !(iint->flags & IMA_HASH))
371 		return;
372 
373 	rc = ima_collect_measurement(iint, file, NULL, 0, ima_hash_algo);
374 	if (rc < 0)
375 		return;
376 
377 	inode_lock(file_inode(file));
378 	ima_fix_xattr(dentry, iint);
379 	inode_unlock(file_inode(file));
380 }
381 
382 /**
383  * ima_inode_post_setattr - reflect file metadata changes
384  * @dentry: pointer to the affected dentry
385  *
386  * Changes to a dentry's metadata might result in needing to appraise.
387  *
388  * This function is called from notify_change(), which expects the caller
389  * to lock the inode's i_mutex.
390  */
391 void ima_inode_post_setattr(struct dentry *dentry)
392 {
393 	struct inode *inode = d_backing_inode(dentry);
394 	struct integrity_iint_cache *iint;
395 	int action;
396 
397 	if (!(ima_policy_flag & IMA_APPRAISE) || !S_ISREG(inode->i_mode)
398 	    || !(inode->i_opflags & IOP_XATTR))
399 		return;
400 
401 	action = ima_must_appraise(inode, MAY_ACCESS, POST_SETATTR);
402 	if (!action)
403 		__vfs_removexattr(dentry, XATTR_NAME_IMA);
404 	iint = integrity_iint_find(inode);
405 	if (iint) {
406 		set_bit(IMA_CHANGE_ATTR, &iint->atomic_flags);
407 		if (!action)
408 			clear_bit(IMA_UPDATE_XATTR, &iint->atomic_flags);
409 	}
410 }
411 
412 /*
413  * ima_protect_xattr - protect 'security.ima'
414  *
415  * Ensure that not just anyone can modify or remove 'security.ima'.
416  */
417 static int ima_protect_xattr(struct dentry *dentry, const char *xattr_name,
418 			     const void *xattr_value, size_t xattr_value_len)
419 {
420 	if (strcmp(xattr_name, XATTR_NAME_IMA) == 0) {
421 		if (!capable(CAP_SYS_ADMIN))
422 			return -EPERM;
423 		return 1;
424 	}
425 	return 0;
426 }
427 
428 static void ima_reset_appraise_flags(struct inode *inode, int digsig)
429 {
430 	struct integrity_iint_cache *iint;
431 
432 	if (!(ima_policy_flag & IMA_APPRAISE) || !S_ISREG(inode->i_mode))
433 		return;
434 
435 	iint = integrity_iint_find(inode);
436 	if (!iint)
437 		return;
438 	iint->measured_pcrs = 0;
439 	set_bit(IMA_CHANGE_XATTR, &iint->atomic_flags);
440 	if (digsig)
441 		set_bit(IMA_DIGSIG, &iint->atomic_flags);
442 	else
443 		clear_bit(IMA_DIGSIG, &iint->atomic_flags);
444 }
445 
446 int ima_inode_setxattr(struct dentry *dentry, const char *xattr_name,
447 		       const void *xattr_value, size_t xattr_value_len)
448 {
449 	const struct evm_ima_xattr_data *xvalue = xattr_value;
450 	int result;
451 
452 	result = ima_protect_xattr(dentry, xattr_name, xattr_value,
453 				   xattr_value_len);
454 	if (result == 1) {
455 		if (!xattr_value_len || (xvalue->type >= IMA_XATTR_LAST))
456 			return -EINVAL;
457 		ima_reset_appraise_flags(d_backing_inode(dentry),
458 			xvalue->type == EVM_IMA_XATTR_DIGSIG);
459 		result = 0;
460 	}
461 	return result;
462 }
463 
464 int ima_inode_removexattr(struct dentry *dentry, const char *xattr_name)
465 {
466 	int result;
467 
468 	result = ima_protect_xattr(dentry, xattr_name, NULL, 0);
469 	if (result == 1) {
470 		ima_reset_appraise_flags(d_backing_inode(dentry), 0);
471 		result = 0;
472 	}
473 	return result;
474 }
475