xref: /linux/security/integrity/ima/ima_appraise.c (revision e9f0878c4b2004ac19581274c1ae4c61ae3ca70e) 
1 /*
2  * Copyright (C) 2011 IBM Corporation
3  *
4  * Author:
5  * Mimi Zohar <zohar@us.ibm.com>
6  *
7  * This program is free software; you can redistribute it and/or modify
8  * it under the terms of the GNU General Public License as published by
9  * the Free Software Foundation, version 2 of the License.
10  */
11 #include <linux/module.h>
12 #include <linux/file.h>
13 #include <linux/fs.h>
14 #include <linux/xattr.h>
15 #include <linux/magic.h>
16 #include <linux/ima.h>
17 #include <linux/evm.h>
18 
19 #include "ima.h"
20 
21 static int __init default_appraise_setup(char *str)
22 {
23 #ifdef CONFIG_IMA_APPRAISE_BOOTPARAM
24 	if (strncmp(str, "off", 3) == 0)
25 		ima_appraise = 0;
26 	else if (strncmp(str, "log", 3) == 0)
27 		ima_appraise = IMA_APPRAISE_LOG;
28 	else if (strncmp(str, "fix", 3) == 0)
29 		ima_appraise = IMA_APPRAISE_FIX;
30 #endif
31 	return 1;
32 }
33 
34 __setup("ima_appraise=", default_appraise_setup);
35 
36 /*
37  * is_ima_appraise_enabled - return appraise status
38  *
39  * Only return enabled, if not in ima_appraise="fix" or "log" modes.
40  */
41 bool is_ima_appraise_enabled(void)
42 {
43 	return ima_appraise & IMA_APPRAISE_ENFORCE;
44 }
45 
46 /*
47  * ima_must_appraise - set appraise flag
48  *
49  * Return 1 to appraise or hash
50  */
51 int ima_must_appraise(struct inode *inode, int mask, enum ima_hooks func)
52 {
53 	u32 secid;
54 
55 	if (!ima_appraise)
56 		return 0;
57 
58 	security_task_getsecid(current, &secid);
59 	return ima_match_policy(inode, current_cred(), secid, func, mask,
60 				IMA_APPRAISE | IMA_HASH, NULL);
61 }
62 
63 static int ima_fix_xattr(struct dentry *dentry,
64 			 struct integrity_iint_cache *iint)
65 {
66 	int rc, offset;
67 	u8 algo = iint->ima_hash->algo;
68 
69 	if (algo <= HASH_ALGO_SHA1) {
70 		offset = 1;
71 		iint->ima_hash->xattr.sha1.type = IMA_XATTR_DIGEST;
72 	} else {
73 		offset = 0;
74 		iint->ima_hash->xattr.ng.type = IMA_XATTR_DIGEST_NG;
75 		iint->ima_hash->xattr.ng.algo = algo;
76 	}
77 	rc = __vfs_setxattr_noperm(dentry, XATTR_NAME_IMA,
78 				   &iint->ima_hash->xattr.data[offset],
79 				   (sizeof(iint->ima_hash->xattr) - offset) +
80 				   iint->ima_hash->length, 0);
81 	return rc;
82 }
83 
84 /* Return specific func appraised cached result */
85 enum integrity_status ima_get_cache_status(struct integrity_iint_cache *iint,
86 					   enum ima_hooks func)
87 {
88 	switch (func) {
89 	case MMAP_CHECK:
90 		return iint->ima_mmap_status;
91 	case BPRM_CHECK:
92 		return iint->ima_bprm_status;
93 	case CREDS_CHECK:
94 		return iint->ima_creds_status;
95 	case FILE_CHECK:
96 	case POST_SETATTR:
97 		return iint->ima_file_status;
98 	case MODULE_CHECK ... MAX_CHECK - 1:
99 	default:
100 		return iint->ima_read_status;
101 	}
102 }
103 
104 static void ima_set_cache_status(struct integrity_iint_cache *iint,
105 				 enum ima_hooks func,
106 				 enum integrity_status status)
107 {
108 	switch (func) {
109 	case MMAP_CHECK:
110 		iint->ima_mmap_status = status;
111 		break;
112 	case BPRM_CHECK:
113 		iint->ima_bprm_status = status;
114 		break;
115 	case CREDS_CHECK:
116 		iint->ima_creds_status = status;
117 	case FILE_CHECK:
118 	case POST_SETATTR:
119 		iint->ima_file_status = status;
120 		break;
121 	case MODULE_CHECK ... MAX_CHECK - 1:
122 	default:
123 		iint->ima_read_status = status;
124 		break;
125 	}
126 }
127 
128 static void ima_cache_flags(struct integrity_iint_cache *iint,
129 			     enum ima_hooks func)
130 {
131 	switch (func) {
132 	case MMAP_CHECK:
133 		iint->flags |= (IMA_MMAP_APPRAISED | IMA_APPRAISED);
134 		break;
135 	case BPRM_CHECK:
136 		iint->flags |= (IMA_BPRM_APPRAISED | IMA_APPRAISED);
137 		break;
138 	case CREDS_CHECK:
139 		iint->flags |= (IMA_CREDS_APPRAISED | IMA_APPRAISED);
140 		break;
141 	case FILE_CHECK:
142 	case POST_SETATTR:
143 		iint->flags |= (IMA_FILE_APPRAISED | IMA_APPRAISED);
144 		break;
145 	case MODULE_CHECK ... MAX_CHECK - 1:
146 	default:
147 		iint->flags |= (IMA_READ_APPRAISED | IMA_APPRAISED);
148 		break;
149 	}
150 }
151 
152 enum hash_algo ima_get_hash_algo(struct evm_ima_xattr_data *xattr_value,
153 				 int xattr_len)
154 {
155 	struct signature_v2_hdr *sig;
156 	enum hash_algo ret;
157 
158 	if (!xattr_value || xattr_len < 2)
159 		/* return default hash algo */
160 		return ima_hash_algo;
161 
162 	switch (xattr_value->type) {
163 	case EVM_IMA_XATTR_DIGSIG:
164 		sig = (typeof(sig))xattr_value;
165 		if (sig->version != 2 || xattr_len <= sizeof(*sig))
166 			return ima_hash_algo;
167 		return sig->hash_algo;
168 		break;
169 	case IMA_XATTR_DIGEST_NG:
170 		ret = xattr_value->digest[0];
171 		if (ret < HASH_ALGO__LAST)
172 			return ret;
173 		break;
174 	case IMA_XATTR_DIGEST:
175 		/* this is for backward compatibility */
176 		if (xattr_len == 21) {
177 			unsigned int zero = 0;
178 			if (!memcmp(&xattr_value->digest[16], &zero, 4))
179 				return HASH_ALGO_MD5;
180 			else
181 				return HASH_ALGO_SHA1;
182 		} else if (xattr_len == 17)
183 			return HASH_ALGO_MD5;
184 		break;
185 	}
186 
187 	/* return default hash algo */
188 	return ima_hash_algo;
189 }
190 
191 int ima_read_xattr(struct dentry *dentry,
192 		   struct evm_ima_xattr_data **xattr_value)
193 {
194 	ssize_t ret;
195 
196 	ret = vfs_getxattr_alloc(dentry, XATTR_NAME_IMA, (char **)xattr_value,
197 				 0, GFP_NOFS);
198 	if (ret == -EOPNOTSUPP)
199 		ret = 0;
200 	return ret;
201 }
202 
203 /*
204  * ima_appraise_measurement - appraise file measurement
205  *
206  * Call evm_verifyxattr() to verify the integrity of 'security.ima'.
207  * Assuming success, compare the xattr hash with the collected measurement.
208  *
209  * Return 0 on success, error code otherwise
210  */
211 int ima_appraise_measurement(enum ima_hooks func,
212 			     struct integrity_iint_cache *iint,
213 			     struct file *file, const unsigned char *filename,
214 			     struct evm_ima_xattr_data *xattr_value,
215 			     int xattr_len)
216 {
217 	static const char op[] = "appraise_data";
218 	const char *cause = "unknown";
219 	struct dentry *dentry = file_dentry(file);
220 	struct inode *inode = d_backing_inode(dentry);
221 	enum integrity_status status = INTEGRITY_UNKNOWN;
222 	int rc = xattr_len, hash_start = 0;
223 
224 	if (!(inode->i_opflags & IOP_XATTR))
225 		return INTEGRITY_UNKNOWN;
226 
227 	if (rc <= 0) {
228 		if (rc && rc != -ENODATA)
229 			goto out;
230 
231 		cause = iint->flags & IMA_DIGSIG_REQUIRED ?
232 				"IMA-signature-required" : "missing-hash";
233 		status = INTEGRITY_NOLABEL;
234 		if (file->f_mode & FMODE_CREATED)
235 			iint->flags |= IMA_NEW_FILE;
236 		if ((iint->flags & IMA_NEW_FILE) &&
237 		    (!(iint->flags & IMA_DIGSIG_REQUIRED) ||
238 		     (inode->i_size == 0)))
239 			status = INTEGRITY_PASS;
240 		goto out;
241 	}
242 
243 	status = evm_verifyxattr(dentry, XATTR_NAME_IMA, xattr_value, rc, iint);
244 	switch (status) {
245 	case INTEGRITY_PASS:
246 	case INTEGRITY_PASS_IMMUTABLE:
247 	case INTEGRITY_UNKNOWN:
248 		break;
249 	case INTEGRITY_NOXATTRS:	/* No EVM protected xattrs. */
250 	case INTEGRITY_NOLABEL:		/* No security.evm xattr. */
251 		cause = "missing-HMAC";
252 		goto out;
253 	case INTEGRITY_FAIL:		/* Invalid HMAC/signature. */
254 		cause = "invalid-HMAC";
255 		goto out;
256 	default:
257 		WARN_ONCE(true, "Unexpected integrity status %d\n", status);
258 	}
259 
260 	switch (xattr_value->type) {
261 	case IMA_XATTR_DIGEST_NG:
262 		/* first byte contains algorithm id */
263 		hash_start = 1;
264 		/* fall through */
265 	case IMA_XATTR_DIGEST:
266 		if (iint->flags & IMA_DIGSIG_REQUIRED) {
267 			cause = "IMA-signature-required";
268 			status = INTEGRITY_FAIL;
269 			break;
270 		}
271 		clear_bit(IMA_DIGSIG, &iint->atomic_flags);
272 		if (xattr_len - sizeof(xattr_value->type) - hash_start >=
273 				iint->ima_hash->length)
274 			/* xattr length may be longer. md5 hash in previous
275 			   version occupied 20 bytes in xattr, instead of 16
276 			 */
277 			rc = memcmp(&xattr_value->digest[hash_start],
278 				    iint->ima_hash->digest,
279 				    iint->ima_hash->length);
280 		else
281 			rc = -EINVAL;
282 		if (rc) {
283 			cause = "invalid-hash";
284 			status = INTEGRITY_FAIL;
285 			break;
286 		}
287 		status = INTEGRITY_PASS;
288 		break;
289 	case EVM_IMA_XATTR_DIGSIG:
290 		set_bit(IMA_DIGSIG, &iint->atomic_flags);
291 		rc = integrity_digsig_verify(INTEGRITY_KEYRING_IMA,
292 					     (const char *)xattr_value, rc,
293 					     iint->ima_hash->digest,
294 					     iint->ima_hash->length);
295 		if (rc == -EOPNOTSUPP) {
296 			status = INTEGRITY_UNKNOWN;
297 		} else if (rc) {
298 			cause = "invalid-signature";
299 			status = INTEGRITY_FAIL;
300 		} else {
301 			status = INTEGRITY_PASS;
302 		}
303 		break;
304 	default:
305 		status = INTEGRITY_UNKNOWN;
306 		cause = "unknown-ima-data";
307 		break;
308 	}
309 
310 out:
311 	/*
312 	 * File signatures on some filesystems can not be properly verified.
313 	 * When such filesystems are mounted by an untrusted mounter or on a
314 	 * system not willing to accept such a risk, fail the file signature
315 	 * verification.
316 	 */
317 	if ((inode->i_sb->s_iflags & SB_I_IMA_UNVERIFIABLE_SIGNATURE) &&
318 	    ((inode->i_sb->s_iflags & SB_I_UNTRUSTED_MOUNTER) ||
319 	     (iint->flags & IMA_FAIL_UNVERIFIABLE_SIGS))) {
320 		status = INTEGRITY_FAIL;
321 		cause = "unverifiable-signature";
322 		integrity_audit_msg(AUDIT_INTEGRITY_DATA, inode, filename,
323 				    op, cause, rc, 0);
324 	} else if (status != INTEGRITY_PASS) {
325 		/* Fix mode, but don't replace file signatures. */
326 		if ((ima_appraise & IMA_APPRAISE_FIX) &&
327 		    (!xattr_value ||
328 		     xattr_value->type != EVM_IMA_XATTR_DIGSIG)) {
329 			if (!ima_fix_xattr(dentry, iint))
330 				status = INTEGRITY_PASS;
331 		}
332 
333 		/* Permit new files with file signatures, but without data. */
334 		if (inode->i_size == 0 && iint->flags & IMA_NEW_FILE &&
335 		    xattr_value && xattr_value->type == EVM_IMA_XATTR_DIGSIG) {
336 			status = INTEGRITY_PASS;
337 		}
338 
339 		integrity_audit_msg(AUDIT_INTEGRITY_DATA, inode, filename,
340 				    op, cause, rc, 0);
341 	} else {
342 		ima_cache_flags(iint, func);
343 	}
344 
345 	ima_set_cache_status(iint, func, status);
346 	return status;
347 }
348 
349 /*
350  * ima_update_xattr - update 'security.ima' hash value
351  */
352 void ima_update_xattr(struct integrity_iint_cache *iint, struct file *file)
353 {
354 	struct dentry *dentry = file_dentry(file);
355 	int rc = 0;
356 
357 	/* do not collect and update hash for digital signatures */
358 	if (test_bit(IMA_DIGSIG, &iint->atomic_flags))
359 		return;
360 
361 	if ((iint->ima_file_status != INTEGRITY_PASS) &&
362 	    !(iint->flags & IMA_HASH))
363 		return;
364 
365 	rc = ima_collect_measurement(iint, file, NULL, 0, ima_hash_algo);
366 	if (rc < 0)
367 		return;
368 
369 	inode_lock(file_inode(file));
370 	ima_fix_xattr(dentry, iint);
371 	inode_unlock(file_inode(file));
372 }
373 
374 /**
375  * ima_inode_post_setattr - reflect file metadata changes
376  * @dentry: pointer to the affected dentry
377  *
378  * Changes to a dentry's metadata might result in needing to appraise.
379  *
380  * This function is called from notify_change(), which expects the caller
381  * to lock the inode's i_mutex.
382  */
383 void ima_inode_post_setattr(struct dentry *dentry)
384 {
385 	struct inode *inode = d_backing_inode(dentry);
386 	struct integrity_iint_cache *iint;
387 	int action;
388 
389 	if (!(ima_policy_flag & IMA_APPRAISE) || !S_ISREG(inode->i_mode)
390 	    || !(inode->i_opflags & IOP_XATTR))
391 		return;
392 
393 	action = ima_must_appraise(inode, MAY_ACCESS, POST_SETATTR);
394 	if (!action)
395 		__vfs_removexattr(dentry, XATTR_NAME_IMA);
396 	iint = integrity_iint_find(inode);
397 	if (iint) {
398 		set_bit(IMA_CHANGE_ATTR, &iint->atomic_flags);
399 		if (!action)
400 			clear_bit(IMA_UPDATE_XATTR, &iint->atomic_flags);
401 	}
402 }
403 
404 /*
405  * ima_protect_xattr - protect 'security.ima'
406  *
407  * Ensure that not just anyone can modify or remove 'security.ima'.
408  */
409 static int ima_protect_xattr(struct dentry *dentry, const char *xattr_name,
410 			     const void *xattr_value, size_t xattr_value_len)
411 {
412 	if (strcmp(xattr_name, XATTR_NAME_IMA) == 0) {
413 		if (!capable(CAP_SYS_ADMIN))
414 			return -EPERM;
415 		return 1;
416 	}
417 	return 0;
418 }
419 
420 static void ima_reset_appraise_flags(struct inode *inode, int digsig)
421 {
422 	struct integrity_iint_cache *iint;
423 
424 	if (!(ima_policy_flag & IMA_APPRAISE) || !S_ISREG(inode->i_mode))
425 		return;
426 
427 	iint = integrity_iint_find(inode);
428 	if (!iint)
429 		return;
430 	iint->measured_pcrs = 0;
431 	set_bit(IMA_CHANGE_XATTR, &iint->atomic_flags);
432 	if (digsig)
433 		set_bit(IMA_DIGSIG, &iint->atomic_flags);
434 	else
435 		clear_bit(IMA_DIGSIG, &iint->atomic_flags);
436 }
437 
438 int ima_inode_setxattr(struct dentry *dentry, const char *xattr_name,
439 		       const void *xattr_value, size_t xattr_value_len)
440 {
441 	const struct evm_ima_xattr_data *xvalue = xattr_value;
442 	int result;
443 
444 	result = ima_protect_xattr(dentry, xattr_name, xattr_value,
445 				   xattr_value_len);
446 	if (result == 1) {
447 		if (!xattr_value_len || (xvalue->type >= IMA_XATTR_LAST))
448 			return -EINVAL;
449 		ima_reset_appraise_flags(d_backing_inode(dentry),
450 			xvalue->type == EVM_IMA_XATTR_DIGSIG);
451 		result = 0;
452 	}
453 	return result;
454 }
455 
456 int ima_inode_removexattr(struct dentry *dentry, const char *xattr_name)
457 {
458 	int result;
459 
460 	result = ima_protect_xattr(dentry, xattr_name, NULL, 0);
461 	if (result == 1) {
462 		ima_reset_appraise_flags(d_backing_inode(dentry), 0);
463 		result = 0;
464 	}
465 	return result;
466 }
467