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 	if (!ima_appraise)
54 		return 0;
55 
56 	return ima_match_policy(inode, func, mask, IMA_APPRAISE | IMA_HASH,
57 				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 FILE_CHECK:
91 	case POST_SETATTR:
92 		return iint->ima_file_status;
93 	case MODULE_CHECK ... MAX_CHECK - 1:
94 	default:
95 		return iint->ima_read_status;
96 	}
97 }
98 
99 static void ima_set_cache_status(struct integrity_iint_cache *iint,
100 				 enum ima_hooks func,
101 				 enum integrity_status status)
102 {
103 	switch (func) {
104 	case MMAP_CHECK:
105 		iint->ima_mmap_status = status;
106 		break;
107 	case BPRM_CHECK:
108 		iint->ima_bprm_status = status;
109 		break;
110 	case FILE_CHECK:
111 	case POST_SETATTR:
112 		iint->ima_file_status = status;
113 		break;
114 	case MODULE_CHECK ... MAX_CHECK - 1:
115 	default:
116 		iint->ima_read_status = status;
117 		break;
118 	}
119 }
120 
121 static void ima_cache_flags(struct integrity_iint_cache *iint,
122 			     enum ima_hooks func)
123 {
124 	switch (func) {
125 	case MMAP_CHECK:
126 		iint->flags |= (IMA_MMAP_APPRAISED | IMA_APPRAISED);
127 		break;
128 	case BPRM_CHECK:
129 		iint->flags |= (IMA_BPRM_APPRAISED | IMA_APPRAISED);
130 		break;
131 	case FILE_CHECK:
132 	case POST_SETATTR:
133 		iint->flags |= (IMA_FILE_APPRAISED | IMA_APPRAISED);
134 		break;
135 	case MODULE_CHECK ... MAX_CHECK - 1:
136 	default:
137 		iint->flags |= (IMA_READ_APPRAISED | IMA_APPRAISED);
138 		break;
139 	}
140 }
141 
142 enum hash_algo ima_get_hash_algo(struct evm_ima_xattr_data *xattr_value,
143 				 int xattr_len)
144 {
145 	struct signature_v2_hdr *sig;
146 	enum hash_algo ret;
147 
148 	if (!xattr_value || xattr_len < 2)
149 		/* return default hash algo */
150 		return ima_hash_algo;
151 
152 	switch (xattr_value->type) {
153 	case EVM_IMA_XATTR_DIGSIG:
154 		sig = (typeof(sig))xattr_value;
155 		if (sig->version != 2 || xattr_len <= sizeof(*sig))
156 			return ima_hash_algo;
157 		return sig->hash_algo;
158 		break;
159 	case IMA_XATTR_DIGEST_NG:
160 		ret = xattr_value->digest[0];
161 		if (ret < HASH_ALGO__LAST)
162 			return ret;
163 		break;
164 	case IMA_XATTR_DIGEST:
165 		/* this is for backward compatibility */
166 		if (xattr_len == 21) {
167 			unsigned int zero = 0;
168 			if (!memcmp(&xattr_value->digest[16], &zero, 4))
169 				return HASH_ALGO_MD5;
170 			else
171 				return HASH_ALGO_SHA1;
172 		} else if (xattr_len == 17)
173 			return HASH_ALGO_MD5;
174 		break;
175 	}
176 
177 	/* return default hash algo */
178 	return ima_hash_algo;
179 }
180 
181 int ima_read_xattr(struct dentry *dentry,
182 		   struct evm_ima_xattr_data **xattr_value)
183 {
184 	ssize_t ret;
185 
186 	ret = vfs_getxattr_alloc(dentry, XATTR_NAME_IMA, (char **)xattr_value,
187 				 0, GFP_NOFS);
188 	if (ret == -EOPNOTSUPP)
189 		ret = 0;
190 	return ret;
191 }
192 
193 /*
194  * ima_appraise_measurement - appraise file measurement
195  *
196  * Call evm_verifyxattr() to verify the integrity of 'security.ima'.
197  * Assuming success, compare the xattr hash with the collected measurement.
198  *
199  * Return 0 on success, error code otherwise
200  */
201 int ima_appraise_measurement(enum ima_hooks func,
202 			     struct integrity_iint_cache *iint,
203 			     struct file *file, const unsigned char *filename,
204 			     struct evm_ima_xattr_data *xattr_value,
205 			     int xattr_len, int opened)
206 {
207 	static const char op[] = "appraise_data";
208 	char *cause = "unknown";
209 	struct dentry *dentry = file_dentry(file);
210 	struct inode *inode = d_backing_inode(dentry);
211 	enum integrity_status status = INTEGRITY_UNKNOWN;
212 	int rc = xattr_len, hash_start = 0;
213 
214 	if (!(inode->i_opflags & IOP_XATTR))
215 		return INTEGRITY_UNKNOWN;
216 
217 	if (rc <= 0) {
218 		if (rc && rc != -ENODATA)
219 			goto out;
220 
221 		cause = iint->flags & IMA_DIGSIG_REQUIRED ?
222 				"IMA-signature-required" : "missing-hash";
223 		status = INTEGRITY_NOLABEL;
224 		if (opened & FILE_CREATED)
225 			iint->flags |= IMA_NEW_FILE;
226 		if ((iint->flags & IMA_NEW_FILE) &&
227 		    (!(iint->flags & IMA_DIGSIG_REQUIRED) ||
228 		     (inode->i_size == 0)))
229 			status = INTEGRITY_PASS;
230 		goto out;
231 	}
232 
233 	status = evm_verifyxattr(dentry, XATTR_NAME_IMA, xattr_value, rc, iint);
234 	if ((status != INTEGRITY_PASS) &&
235 	    (status != INTEGRITY_PASS_IMMUTABLE) &&
236 	    (status != INTEGRITY_UNKNOWN)) {
237 		if ((status == INTEGRITY_NOLABEL)
238 		    || (status == INTEGRITY_NOXATTRS))
239 			cause = "missing-HMAC";
240 		else if (status == INTEGRITY_FAIL)
241 			cause = "invalid-HMAC";
242 		goto out;
243 	}
244 	switch (xattr_value->type) {
245 	case IMA_XATTR_DIGEST_NG:
246 		/* first byte contains algorithm id */
247 		hash_start = 1;
248 		/* fall through */
249 	case IMA_XATTR_DIGEST:
250 		if (iint->flags & IMA_DIGSIG_REQUIRED) {
251 			cause = "IMA-signature-required";
252 			status = INTEGRITY_FAIL;
253 			break;
254 		}
255 		clear_bit(IMA_DIGSIG, &iint->atomic_flags);
256 		if (xattr_len - sizeof(xattr_value->type) - hash_start >=
257 				iint->ima_hash->length)
258 			/* xattr length may be longer. md5 hash in previous
259 			   version occupied 20 bytes in xattr, instead of 16
260 			 */
261 			rc = memcmp(&xattr_value->digest[hash_start],
262 				    iint->ima_hash->digest,
263 				    iint->ima_hash->length);
264 		else
265 			rc = -EINVAL;
266 		if (rc) {
267 			cause = "invalid-hash";
268 			status = INTEGRITY_FAIL;
269 			break;
270 		}
271 		status = INTEGRITY_PASS;
272 		break;
273 	case EVM_IMA_XATTR_DIGSIG:
274 		set_bit(IMA_DIGSIG, &iint->atomic_flags);
275 		rc = integrity_digsig_verify(INTEGRITY_KEYRING_IMA,
276 					     (const char *)xattr_value, rc,
277 					     iint->ima_hash->digest,
278 					     iint->ima_hash->length);
279 		if (rc == -EOPNOTSUPP) {
280 			status = INTEGRITY_UNKNOWN;
281 		} else if (rc) {
282 			cause = "invalid-signature";
283 			status = INTEGRITY_FAIL;
284 		} else {
285 			status = INTEGRITY_PASS;
286 		}
287 		break;
288 	default:
289 		status = INTEGRITY_UNKNOWN;
290 		cause = "unknown-ima-data";
291 		break;
292 	}
293 
294 out:
295 	if (status != INTEGRITY_PASS) {
296 		if ((ima_appraise & IMA_APPRAISE_FIX) &&
297 		    (!xattr_value ||
298 		     xattr_value->type != EVM_IMA_XATTR_DIGSIG)) {
299 			if (!ima_fix_xattr(dentry, iint))
300 				status = INTEGRITY_PASS;
301 		} else if ((inode->i_size == 0) &&
302 			   (iint->flags & IMA_NEW_FILE) &&
303 			   (xattr_value &&
304 			    xattr_value->type == EVM_IMA_XATTR_DIGSIG)) {
305 			status = INTEGRITY_PASS;
306 		}
307 		integrity_audit_msg(AUDIT_INTEGRITY_DATA, inode, filename,
308 				    op, cause, rc, 0);
309 	} else {
310 		ima_cache_flags(iint, func);
311 	}
312 	ima_set_cache_status(iint, func, status);
313 	return status;
314 }
315 
316 /*
317  * ima_update_xattr - update 'security.ima' hash value
318  */
319 void ima_update_xattr(struct integrity_iint_cache *iint, struct file *file)
320 {
321 	struct dentry *dentry = file_dentry(file);
322 	int rc = 0;
323 
324 	/* do not collect and update hash for digital signatures */
325 	if (test_bit(IMA_DIGSIG, &iint->atomic_flags))
326 		return;
327 
328 	if ((iint->ima_file_status != INTEGRITY_PASS) &&
329 	    !(iint->flags & IMA_HASH))
330 		return;
331 
332 	rc = ima_collect_measurement(iint, file, NULL, 0, ima_hash_algo);
333 	if (rc < 0)
334 		return;
335 
336 	inode_lock(file_inode(file));
337 	ima_fix_xattr(dentry, iint);
338 	inode_unlock(file_inode(file));
339 }
340 
341 /**
342  * ima_inode_post_setattr - reflect file metadata changes
343  * @dentry: pointer to the affected dentry
344  *
345  * Changes to a dentry's metadata might result in needing to appraise.
346  *
347  * This function is called from notify_change(), which expects the caller
348  * to lock the inode's i_mutex.
349  */
350 void ima_inode_post_setattr(struct dentry *dentry)
351 {
352 	struct inode *inode = d_backing_inode(dentry);
353 	struct integrity_iint_cache *iint;
354 	int action;
355 
356 	if (!(ima_policy_flag & IMA_APPRAISE) || !S_ISREG(inode->i_mode)
357 	    || !(inode->i_opflags & IOP_XATTR))
358 		return;
359 
360 	action = ima_must_appraise(inode, MAY_ACCESS, POST_SETATTR);
361 	if (!action)
362 		__vfs_removexattr(dentry, XATTR_NAME_IMA);
363 	iint = integrity_iint_find(inode);
364 	if (iint) {
365 		set_bit(IMA_CHANGE_ATTR, &iint->atomic_flags);
366 		if (!action)
367 			clear_bit(IMA_UPDATE_XATTR, &iint->atomic_flags);
368 	}
369 }
370 
371 /*
372  * ima_protect_xattr - protect 'security.ima'
373  *
374  * Ensure that not just anyone can modify or remove 'security.ima'.
375  */
376 static int ima_protect_xattr(struct dentry *dentry, const char *xattr_name,
377 			     const void *xattr_value, size_t xattr_value_len)
378 {
379 	if (strcmp(xattr_name, XATTR_NAME_IMA) == 0) {
380 		if (!capable(CAP_SYS_ADMIN))
381 			return -EPERM;
382 		return 1;
383 	}
384 	return 0;
385 }
386 
387 static void ima_reset_appraise_flags(struct inode *inode, int digsig)
388 {
389 	struct integrity_iint_cache *iint;
390 
391 	if (!(ima_policy_flag & IMA_APPRAISE) || !S_ISREG(inode->i_mode))
392 		return;
393 
394 	iint = integrity_iint_find(inode);
395 	if (!iint)
396 		return;
397 	iint->measured_pcrs = 0;
398 	set_bit(IMA_CHANGE_XATTR, &iint->atomic_flags);
399 	if (digsig)
400 		set_bit(IMA_DIGSIG, &iint->atomic_flags);
401 	else
402 		clear_bit(IMA_DIGSIG, &iint->atomic_flags);
403 }
404 
405 int ima_inode_setxattr(struct dentry *dentry, const char *xattr_name,
406 		       const void *xattr_value, size_t xattr_value_len)
407 {
408 	const struct evm_ima_xattr_data *xvalue = xattr_value;
409 	int result;
410 
411 	result = ima_protect_xattr(dentry, xattr_name, xattr_value,
412 				   xattr_value_len);
413 	if (result == 1) {
414 		if (!xattr_value_len || (xvalue->type >= IMA_XATTR_LAST))
415 			return -EINVAL;
416 		ima_reset_appraise_flags(d_backing_inode(dentry),
417 			xvalue->type == EVM_IMA_XATTR_DIGSIG);
418 		result = 0;
419 	}
420 	return result;
421 }
422 
423 int ima_inode_removexattr(struct dentry *dentry, const char *xattr_name)
424 {
425 	int result;
426 
427 	result = ima_protect_xattr(dentry, xattr_name, NULL, 0);
428 	if (result == 1) {
429 		ima_reset_appraise_flags(d_backing_inode(dentry), 0);
430 		result = 0;
431 	}
432 	return result;
433 }
434