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  * ima_appraise_measurement - appraise file measurement
204  *
205  * Call evm_verifyxattr() to verify the integrity of 'security.ima'.
206  * Assuming success, compare the xattr hash with the collected measurement.
207  *
208  * Return 0 on success, error code otherwise
209  */
210 int ima_appraise_measurement(enum ima_hooks func,
211 			     struct integrity_iint_cache *iint,
212 			     struct file *file, const unsigned char *filename,
213 			     struct evm_ima_xattr_data *xattr_value,
214 			     int xattr_len)
215 {
216 	static const char op[] = "appraise_data";
217 	const char *cause = "unknown";
218 	struct dentry *dentry = file_dentry(file);
219 	struct inode *inode = d_backing_inode(dentry);
220 	enum integrity_status status = INTEGRITY_UNKNOWN;
221 	int rc = xattr_len, hash_start = 0;
222 
223 	if (!(inode->i_opflags & IOP_XATTR))
224 		return INTEGRITY_UNKNOWN;
225 
226 	if (rc <= 0) {
227 		if (rc && rc != -ENODATA)
228 			goto out;
229 
230 		cause = iint->flags & IMA_DIGSIG_REQUIRED ?
231 				"IMA-signature-required" : "missing-hash";
232 		status = INTEGRITY_NOLABEL;
233 		if (file->f_mode & FMODE_CREATED)
234 			iint->flags |= IMA_NEW_FILE;
235 		if ((iint->flags & IMA_NEW_FILE) &&
236 		    (!(iint->flags & IMA_DIGSIG_REQUIRED) ||
237 		     (inode->i_size == 0)))
238 			status = INTEGRITY_PASS;
239 		goto out;
240 	}
241 
242 	status = evm_verifyxattr(dentry, XATTR_NAME_IMA, xattr_value, rc, iint);
243 	switch (status) {
244 	case INTEGRITY_PASS:
245 	case INTEGRITY_PASS_IMMUTABLE:
246 	case INTEGRITY_UNKNOWN:
247 		break;
248 	case INTEGRITY_NOXATTRS:	/* No EVM protected xattrs. */
249 	case INTEGRITY_NOLABEL:		/* No security.evm xattr. */
250 		cause = "missing-HMAC";
251 		goto out;
252 	case INTEGRITY_FAIL:		/* Invalid HMAC/signature. */
253 		cause = "invalid-HMAC";
254 		goto out;
255 	default:
256 		WARN_ONCE(true, "Unexpected integrity status %d\n", status);
257 	}
258 
259 	switch (xattr_value->type) {
260 	case IMA_XATTR_DIGEST_NG:
261 		/* first byte contains algorithm id */
262 		hash_start = 1;
263 		/* fall through */
264 	case IMA_XATTR_DIGEST:
265 		if (iint->flags & IMA_DIGSIG_REQUIRED) {
266 			cause = "IMA-signature-required";
267 			status = INTEGRITY_FAIL;
268 			break;
269 		}
270 		clear_bit(IMA_DIGSIG, &iint->atomic_flags);
271 		if (xattr_len - sizeof(xattr_value->type) - hash_start >=
272 				iint->ima_hash->length)
273 			/* xattr length may be longer. md5 hash in previous
274 			   version occupied 20 bytes in xattr, instead of 16
275 			 */
276 			rc = memcmp(&xattr_value->data[hash_start],
277 				    iint->ima_hash->digest,
278 				    iint->ima_hash->length);
279 		else
280 			rc = -EINVAL;
281 		if (rc) {
282 			cause = "invalid-hash";
283 			status = INTEGRITY_FAIL;
284 			break;
285 		}
286 		status = INTEGRITY_PASS;
287 		break;
288 	case EVM_IMA_XATTR_DIGSIG:
289 		set_bit(IMA_DIGSIG, &iint->atomic_flags);
290 		rc = integrity_digsig_verify(INTEGRITY_KEYRING_IMA,
291 					     (const char *)xattr_value,
292 					     xattr_len,
293 					     iint->ima_hash->digest,
294 					     iint->ima_hash->length);
295 		if (rc == -EOPNOTSUPP) {
296 			status = INTEGRITY_UNKNOWN;
297 			break;
298 		}
299 		if (IS_ENABLED(CONFIG_INTEGRITY_PLATFORM_KEYRING) && rc &&
300 		    func == KEXEC_KERNEL_CHECK)
301 			rc = integrity_digsig_verify(INTEGRITY_KEYRING_PLATFORM,
302 						     (const char *)xattr_value,
303 						     xattr_len,
304 						     iint->ima_hash->digest,
305 						     iint->ima_hash->length);
306 		if (rc) {
307 			cause = "invalid-signature";
308 			status = INTEGRITY_FAIL;
309 		} else {
310 			status = INTEGRITY_PASS;
311 		}
312 		break;
313 	default:
314 		status = INTEGRITY_UNKNOWN;
315 		cause = "unknown-ima-data";
316 		break;
317 	}
318 
319 out:
320 	/*
321 	 * File signatures on some filesystems can not be properly verified.
322 	 * When such filesystems are mounted by an untrusted mounter or on a
323 	 * system not willing to accept such a risk, fail the file signature
324 	 * verification.
325 	 */
326 	if ((inode->i_sb->s_iflags & SB_I_IMA_UNVERIFIABLE_SIGNATURE) &&
327 	    ((inode->i_sb->s_iflags & SB_I_UNTRUSTED_MOUNTER) ||
328 	     (iint->flags & IMA_FAIL_UNVERIFIABLE_SIGS))) {
329 		status = INTEGRITY_FAIL;
330 		cause = "unverifiable-signature";
331 		integrity_audit_msg(AUDIT_INTEGRITY_DATA, inode, filename,
332 				    op, cause, rc, 0);
333 	} else if (status != INTEGRITY_PASS) {
334 		/* Fix mode, but don't replace file signatures. */
335 		if ((ima_appraise & IMA_APPRAISE_FIX) &&
336 		    (!xattr_value ||
337 		     xattr_value->type != EVM_IMA_XATTR_DIGSIG)) {
338 			if (!ima_fix_xattr(dentry, iint))
339 				status = INTEGRITY_PASS;
340 		}
341 
342 		/* Permit new files with file signatures, but without data. */
343 		if (inode->i_size == 0 && iint->flags & IMA_NEW_FILE &&
344 		    xattr_value && xattr_value->type == EVM_IMA_XATTR_DIGSIG) {
345 			status = INTEGRITY_PASS;
346 		}
347 
348 		integrity_audit_msg(AUDIT_INTEGRITY_DATA, inode, filename,
349 				    op, cause, rc, 0);
350 	} else {
351 		ima_cache_flags(iint, func);
352 	}
353 
354 	ima_set_cache_status(iint, func, status);
355 	return status;
356 }
357 
358 /*
359  * ima_update_xattr - update 'security.ima' hash value
360  */
361 void ima_update_xattr(struct integrity_iint_cache *iint, struct file *file)
362 {
363 	struct dentry *dentry = file_dentry(file);
364 	int rc = 0;
365 
366 	/* do not collect and update hash for digital signatures */
367 	if (test_bit(IMA_DIGSIG, &iint->atomic_flags))
368 		return;
369 
370 	if ((iint->ima_file_status != INTEGRITY_PASS) &&
371 	    !(iint->flags & IMA_HASH))
372 		return;
373 
374 	rc = ima_collect_measurement(iint, file, NULL, 0, ima_hash_algo);
375 	if (rc < 0)
376 		return;
377 
378 	inode_lock(file_inode(file));
379 	ima_fix_xattr(dentry, iint);
380 	inode_unlock(file_inode(file));
381 }
382 
383 /**
384  * ima_inode_post_setattr - reflect file metadata changes
385  * @dentry: pointer to the affected dentry
386  *
387  * Changes to a dentry's metadata might result in needing to appraise.
388  *
389  * This function is called from notify_change(), which expects the caller
390  * to lock the inode's i_mutex.
391  */
392 void ima_inode_post_setattr(struct dentry *dentry)
393 {
394 	struct inode *inode = d_backing_inode(dentry);
395 	struct integrity_iint_cache *iint;
396 	int action;
397 
398 	if (!(ima_policy_flag & IMA_APPRAISE) || !S_ISREG(inode->i_mode)
399 	    || !(inode->i_opflags & IOP_XATTR))
400 		return;
401 
402 	action = ima_must_appraise(inode, MAY_ACCESS, POST_SETATTR);
403 	if (!action)
404 		__vfs_removexattr(dentry, XATTR_NAME_IMA);
405 	iint = integrity_iint_find(inode);
406 	if (iint) {
407 		set_bit(IMA_CHANGE_ATTR, &iint->atomic_flags);
408 		if (!action)
409 			clear_bit(IMA_UPDATE_XATTR, &iint->atomic_flags);
410 	}
411 }
412 
413 /*
414  * ima_protect_xattr - protect 'security.ima'
415  *
416  * Ensure that not just anyone can modify or remove 'security.ima'.
417  */
418 static int ima_protect_xattr(struct dentry *dentry, const char *xattr_name,
419 			     const void *xattr_value, size_t xattr_value_len)
420 {
421 	if (strcmp(xattr_name, XATTR_NAME_IMA) == 0) {
422 		if (!capable(CAP_SYS_ADMIN))
423 			return -EPERM;
424 		return 1;
425 	}
426 	return 0;
427 }
428 
429 static void ima_reset_appraise_flags(struct inode *inode, int digsig)
430 {
431 	struct integrity_iint_cache *iint;
432 
433 	if (!(ima_policy_flag & IMA_APPRAISE) || !S_ISREG(inode->i_mode))
434 		return;
435 
436 	iint = integrity_iint_find(inode);
437 	if (!iint)
438 		return;
439 	iint->measured_pcrs = 0;
440 	set_bit(IMA_CHANGE_XATTR, &iint->atomic_flags);
441 	if (digsig)
442 		set_bit(IMA_DIGSIG, &iint->atomic_flags);
443 	else
444 		clear_bit(IMA_DIGSIG, &iint->atomic_flags);
445 }
446 
447 int ima_inode_setxattr(struct dentry *dentry, const char *xattr_name,
448 		       const void *xattr_value, size_t xattr_value_len)
449 {
450 	const struct evm_ima_xattr_data *xvalue = xattr_value;
451 	int result;
452 
453 	result = ima_protect_xattr(dentry, xattr_name, xattr_value,
454 				   xattr_value_len);
455 	if (result == 1) {
456 		if (!xattr_value_len || (xvalue->type >= IMA_XATTR_LAST))
457 			return -EINVAL;
458 		ima_reset_appraise_flags(d_backing_inode(dentry),
459 			xvalue->type == EVM_IMA_XATTR_DIGSIG);
460 		result = 0;
461 	}
462 	return result;
463 }
464 
465 int ima_inode_removexattr(struct dentry *dentry, const char *xattr_name)
466 {
467 	int result;
468 
469 	result = ima_protect_xattr(dentry, xattr_name, NULL, 0);
470 	if (result == 1) {
471 		ima_reset_appraise_flags(d_backing_inode(dentry), 0);
472 		result = 0;
473 	}
474 	return result;
475 }
476