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) ? 1 : 0;
44 }
45 
46 /*
47  * ima_must_appraise - set appraise flag
48  *
49  * Return 1 to appraise
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, NULL);
57 }
58 
59 static int ima_fix_xattr(struct dentry *dentry,
60 			 struct integrity_iint_cache *iint)
61 {
62 	int rc, offset;
63 	u8 algo = iint->ima_hash->algo;
64 
65 	if (algo <= HASH_ALGO_SHA1) {
66 		offset = 1;
67 		iint->ima_hash->xattr.sha1.type = IMA_XATTR_DIGEST;
68 	} else {
69 		offset = 0;
70 		iint->ima_hash->xattr.ng.type = IMA_XATTR_DIGEST_NG;
71 		iint->ima_hash->xattr.ng.algo = algo;
72 	}
73 	rc = __vfs_setxattr_noperm(dentry, XATTR_NAME_IMA,
74 				   &iint->ima_hash->xattr.data[offset],
75 				   (sizeof(iint->ima_hash->xattr) - offset) +
76 				   iint->ima_hash->length, 0);
77 	return rc;
78 }
79 
80 /* Return specific func appraised cached result */
81 enum integrity_status ima_get_cache_status(struct integrity_iint_cache *iint,
82 					   enum ima_hooks func)
83 {
84 	switch (func) {
85 	case MMAP_CHECK:
86 		return iint->ima_mmap_status;
87 	case BPRM_CHECK:
88 		return iint->ima_bprm_status;
89 	case FILE_CHECK:
90 	case POST_SETATTR:
91 		return iint->ima_file_status;
92 	case MODULE_CHECK ... MAX_CHECK - 1:
93 	default:
94 		return iint->ima_read_status;
95 	}
96 }
97 
98 static void ima_set_cache_status(struct integrity_iint_cache *iint,
99 				 enum ima_hooks func,
100 				 enum integrity_status status)
101 {
102 	switch (func) {
103 	case MMAP_CHECK:
104 		iint->ima_mmap_status = status;
105 		break;
106 	case BPRM_CHECK:
107 		iint->ima_bprm_status = status;
108 		break;
109 	case FILE_CHECK:
110 	case POST_SETATTR:
111 		iint->ima_file_status = status;
112 		break;
113 	case MODULE_CHECK ... MAX_CHECK - 1:
114 	default:
115 		iint->ima_read_status = status;
116 		break;
117 	}
118 }
119 
120 static void ima_cache_flags(struct integrity_iint_cache *iint,
121 			     enum ima_hooks func)
122 {
123 	switch (func) {
124 	case MMAP_CHECK:
125 		iint->flags |= (IMA_MMAP_APPRAISED | IMA_APPRAISED);
126 		break;
127 	case BPRM_CHECK:
128 		iint->flags |= (IMA_BPRM_APPRAISED | IMA_APPRAISED);
129 		break;
130 	case FILE_CHECK:
131 	case POST_SETATTR:
132 		iint->flags |= (IMA_FILE_APPRAISED | IMA_APPRAISED);
133 		break;
134 	case MODULE_CHECK ... MAX_CHECK - 1:
135 	default:
136 		iint->flags |= (IMA_READ_APPRAISED | IMA_APPRAISED);
137 		break;
138 	}
139 }
140 
141 enum hash_algo ima_get_hash_algo(struct evm_ima_xattr_data *xattr_value,
142 				 int xattr_len)
143 {
144 	struct signature_v2_hdr *sig;
145 	enum hash_algo ret;
146 
147 	if (!xattr_value || xattr_len < 2)
148 		/* return default hash algo */
149 		return ima_hash_algo;
150 
151 	switch (xattr_value->type) {
152 	case EVM_IMA_XATTR_DIGSIG:
153 		sig = (typeof(sig))xattr_value;
154 		if (sig->version != 2 || xattr_len <= sizeof(*sig))
155 			return ima_hash_algo;
156 		return sig->hash_algo;
157 		break;
158 	case IMA_XATTR_DIGEST_NG:
159 		ret = xattr_value->digest[0];
160 		if (ret < HASH_ALGO__LAST)
161 			return ret;
162 		break;
163 	case IMA_XATTR_DIGEST:
164 		/* this is for backward compatibility */
165 		if (xattr_len == 21) {
166 			unsigned int zero = 0;
167 			if (!memcmp(&xattr_value->digest[16], &zero, 4))
168 				return HASH_ALGO_MD5;
169 			else
170 				return HASH_ALGO_SHA1;
171 		} else if (xattr_len == 17)
172 			return HASH_ALGO_MD5;
173 		break;
174 	}
175 
176 	/* return default hash algo */
177 	return ima_hash_algo;
178 }
179 
180 int ima_read_xattr(struct dentry *dentry,
181 		   struct evm_ima_xattr_data **xattr_value)
182 {
183 	ssize_t ret;
184 
185 	ret = vfs_getxattr_alloc(dentry, XATTR_NAME_IMA, (char **)xattr_value,
186 				 0, GFP_NOFS);
187 	if (ret == -EOPNOTSUPP)
188 		ret = 0;
189 	return ret;
190 }
191 
192 /*
193  * ima_appraise_measurement - appraise file measurement
194  *
195  * Call evm_verifyxattr() to verify the integrity of 'security.ima'.
196  * Assuming success, compare the xattr hash with the collected measurement.
197  *
198  * Return 0 on success, error code otherwise
199  */
200 int ima_appraise_measurement(enum ima_hooks func,
201 			     struct integrity_iint_cache *iint,
202 			     struct file *file, const unsigned char *filename,
203 			     struct evm_ima_xattr_data *xattr_value,
204 			     int xattr_len, int opened)
205 {
206 	static const char op[] = "appraise_data";
207 	char *cause = "unknown";
208 	struct dentry *dentry = file_dentry(file);
209 	struct inode *inode = d_backing_inode(dentry);
210 	enum integrity_status status = INTEGRITY_UNKNOWN;
211 	int rc = xattr_len, hash_start = 0;
212 
213 	if (!(inode->i_opflags & IOP_XATTR))
214 		return INTEGRITY_UNKNOWN;
215 
216 	if (rc <= 0) {
217 		if (rc && rc != -ENODATA)
218 			goto out;
219 
220 		cause = iint->flags & IMA_DIGSIG_REQUIRED ?
221 				"IMA-signature-required" : "missing-hash";
222 		status = INTEGRITY_NOLABEL;
223 		if (opened & FILE_CREATED)
224 			iint->flags |= IMA_NEW_FILE;
225 		if ((iint->flags & IMA_NEW_FILE) &&
226 		    !(iint->flags & IMA_DIGSIG_REQUIRED))
227 			status = INTEGRITY_PASS;
228 		goto out;
229 	}
230 
231 	status = evm_verifyxattr(dentry, XATTR_NAME_IMA, xattr_value, rc, iint);
232 	if ((status != INTEGRITY_PASS) && (status != INTEGRITY_UNKNOWN)) {
233 		if ((status == INTEGRITY_NOLABEL)
234 		    || (status == INTEGRITY_NOXATTRS))
235 			cause = "missing-HMAC";
236 		else if (status == INTEGRITY_FAIL)
237 			cause = "invalid-HMAC";
238 		goto out;
239 	}
240 	switch (xattr_value->type) {
241 	case IMA_XATTR_DIGEST_NG:
242 		/* first byte contains algorithm id */
243 		hash_start = 1;
244 		/* fall through */
245 	case IMA_XATTR_DIGEST:
246 		if (iint->flags & IMA_DIGSIG_REQUIRED) {
247 			cause = "IMA-signature-required";
248 			status = INTEGRITY_FAIL;
249 			break;
250 		}
251 		if (xattr_len - sizeof(xattr_value->type) - hash_start >=
252 				iint->ima_hash->length)
253 			/* xattr length may be longer. md5 hash in previous
254 			   version occupied 20 bytes in xattr, instead of 16
255 			 */
256 			rc = memcmp(&xattr_value->digest[hash_start],
257 				    iint->ima_hash->digest,
258 				    iint->ima_hash->length);
259 		else
260 			rc = -EINVAL;
261 		if (rc) {
262 			cause = "invalid-hash";
263 			status = INTEGRITY_FAIL;
264 			break;
265 		}
266 		status = INTEGRITY_PASS;
267 		break;
268 	case EVM_IMA_XATTR_DIGSIG:
269 		iint->flags |= IMA_DIGSIG;
270 		rc = integrity_digsig_verify(INTEGRITY_KEYRING_IMA,
271 					     (const char *)xattr_value, rc,
272 					     iint->ima_hash->digest,
273 					     iint->ima_hash->length);
274 		if (rc == -EOPNOTSUPP) {
275 			status = INTEGRITY_UNKNOWN;
276 		} else if (rc) {
277 			cause = "invalid-signature";
278 			status = INTEGRITY_FAIL;
279 		} else {
280 			status = INTEGRITY_PASS;
281 		}
282 		break;
283 	default:
284 		status = INTEGRITY_UNKNOWN;
285 		cause = "unknown-ima-data";
286 		break;
287 	}
288 
289 out:
290 	if (status != INTEGRITY_PASS) {
291 		if ((ima_appraise & IMA_APPRAISE_FIX) &&
292 		    (!xattr_value ||
293 		     xattr_value->type != EVM_IMA_XATTR_DIGSIG)) {
294 			if (!ima_fix_xattr(dentry, iint))
295 				status = INTEGRITY_PASS;
296 		} else if ((inode->i_size == 0) &&
297 			   (iint->flags & IMA_NEW_FILE) &&
298 			   (xattr_value &&
299 			    xattr_value->type == EVM_IMA_XATTR_DIGSIG)) {
300 			status = INTEGRITY_PASS;
301 		}
302 		integrity_audit_msg(AUDIT_INTEGRITY_DATA, inode, filename,
303 				    op, cause, rc, 0);
304 	} else {
305 		ima_cache_flags(iint, func);
306 	}
307 	ima_set_cache_status(iint, func, status);
308 	return status;
309 }
310 
311 /*
312  * ima_update_xattr - update 'security.ima' hash value
313  */
314 void ima_update_xattr(struct integrity_iint_cache *iint, struct file *file)
315 {
316 	struct dentry *dentry = file_dentry(file);
317 	int rc = 0;
318 
319 	/* do not collect and update hash for digital signatures */
320 	if (iint->flags & IMA_DIGSIG)
321 		return;
322 
323 	rc = ima_collect_measurement(iint, file, NULL, 0, ima_hash_algo);
324 	if (rc < 0)
325 		return;
326 
327 	ima_fix_xattr(dentry, iint);
328 }
329 
330 /**
331  * ima_inode_post_setattr - reflect file metadata changes
332  * @dentry: pointer to the affected dentry
333  *
334  * Changes to a dentry's metadata might result in needing to appraise.
335  *
336  * This function is called from notify_change(), which expects the caller
337  * to lock the inode's i_mutex.
338  */
339 void ima_inode_post_setattr(struct dentry *dentry)
340 {
341 	struct inode *inode = d_backing_inode(dentry);
342 	struct integrity_iint_cache *iint;
343 	int must_appraise;
344 
345 	if (!(ima_policy_flag & IMA_APPRAISE) || !S_ISREG(inode->i_mode)
346 	    || !(inode->i_opflags & IOP_XATTR))
347 		return;
348 
349 	must_appraise = ima_must_appraise(inode, MAY_ACCESS, POST_SETATTR);
350 	iint = integrity_iint_find(inode);
351 	if (iint) {
352 		iint->flags &= ~(IMA_APPRAISE | IMA_APPRAISED |
353 				 IMA_APPRAISE_SUBMASK | IMA_APPRAISED_SUBMASK |
354 				 IMA_ACTION_RULE_FLAGS);
355 		if (must_appraise)
356 			iint->flags |= IMA_APPRAISE;
357 	}
358 	if (!must_appraise)
359 		__vfs_removexattr(dentry, XATTR_NAME_IMA);
360 }
361 
362 /*
363  * ima_protect_xattr - protect 'security.ima'
364  *
365  * Ensure that not just anyone can modify or remove 'security.ima'.
366  */
367 static int ima_protect_xattr(struct dentry *dentry, const char *xattr_name,
368 			     const void *xattr_value, size_t xattr_value_len)
369 {
370 	if (strcmp(xattr_name, XATTR_NAME_IMA) == 0) {
371 		if (!capable(CAP_SYS_ADMIN))
372 			return -EPERM;
373 		return 1;
374 	}
375 	return 0;
376 }
377 
378 static void ima_reset_appraise_flags(struct inode *inode, int digsig)
379 {
380 	struct integrity_iint_cache *iint;
381 
382 	if (!(ima_policy_flag & IMA_APPRAISE) || !S_ISREG(inode->i_mode))
383 		return;
384 
385 	iint = integrity_iint_find(inode);
386 	if (!iint)
387 		return;
388 
389 	iint->flags &= ~IMA_DONE_MASK;
390 	iint->measured_pcrs = 0;
391 	if (digsig)
392 		iint->flags |= IMA_DIGSIG;
393 	return;
394 }
395 
396 int ima_inode_setxattr(struct dentry *dentry, const char *xattr_name,
397 		       const void *xattr_value, size_t xattr_value_len)
398 {
399 	const struct evm_ima_xattr_data *xvalue = xattr_value;
400 	int result;
401 
402 	result = ima_protect_xattr(dentry, xattr_name, xattr_value,
403 				   xattr_value_len);
404 	if (result == 1) {
405 		if (!xattr_value_len || (xvalue->type >= IMA_XATTR_LAST))
406 			return -EINVAL;
407 		ima_reset_appraise_flags(d_backing_inode(dentry),
408 			 (xvalue->type == EVM_IMA_XATTR_DIGSIG) ? 1 : 0);
409 		result = 0;
410 	}
411 	return result;
412 }
413 
414 int ima_inode_removexattr(struct dentry *dentry, const char *xattr_name)
415 {
416 	int result;
417 
418 	result = ima_protect_xattr(dentry, xattr_name, NULL, 0);
419 	if (result == 1) {
420 		ima_reset_appraise_flags(d_backing_inode(dentry), 0);
421 		result = 0;
422 	}
423 	return result;
424 }
425