xref: /linux/security/integrity/ima/ima_appraise.c (revision 0883c2c06fb5bcf5b9e008270827e63c09a88c1e) 
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 	if (strncmp(str, "off", 3) == 0)
24 		ima_appraise = 0;
25 	else if (strncmp(str, "log", 3) == 0)
26 		ima_appraise = IMA_APPRAISE_LOG;
27 	else if (strncmp(str, "fix", 3) == 0)
28 		ima_appraise = IMA_APPRAISE_FIX;
29 	return 1;
30 }
31 
32 __setup("ima_appraise=", default_appraise_setup);
33 
34 /*
35  * ima_must_appraise - set appraise flag
36  *
37  * Return 1 to appraise
38  */
39 int ima_must_appraise(struct inode *inode, int mask, enum ima_hooks func)
40 {
41 	if (!ima_appraise)
42 		return 0;
43 
44 	return ima_match_policy(inode, func, mask, IMA_APPRAISE);
45 }
46 
47 static int ima_fix_xattr(struct dentry *dentry,
48 			 struct integrity_iint_cache *iint)
49 {
50 	int rc, offset;
51 	u8 algo = iint->ima_hash->algo;
52 
53 	if (algo <= HASH_ALGO_SHA1) {
54 		offset = 1;
55 		iint->ima_hash->xattr.sha1.type = IMA_XATTR_DIGEST;
56 	} else {
57 		offset = 0;
58 		iint->ima_hash->xattr.ng.type = IMA_XATTR_DIGEST_NG;
59 		iint->ima_hash->xattr.ng.algo = algo;
60 	}
61 	rc = __vfs_setxattr_noperm(dentry, XATTR_NAME_IMA,
62 				   &iint->ima_hash->xattr.data[offset],
63 				   (sizeof(iint->ima_hash->xattr) - offset) +
64 				   iint->ima_hash->length, 0);
65 	return rc;
66 }
67 
68 /* Return specific func appraised cached result */
69 enum integrity_status ima_get_cache_status(struct integrity_iint_cache *iint,
70 					   enum ima_hooks func)
71 {
72 	switch (func) {
73 	case MMAP_CHECK:
74 		return iint->ima_mmap_status;
75 	case BPRM_CHECK:
76 		return iint->ima_bprm_status;
77 	case FILE_CHECK:
78 	case POST_SETATTR:
79 		return iint->ima_file_status;
80 	case MODULE_CHECK ... MAX_CHECK - 1:
81 	default:
82 		return iint->ima_read_status;
83 	}
84 }
85 
86 static void ima_set_cache_status(struct integrity_iint_cache *iint,
87 				 enum ima_hooks func,
88 				 enum integrity_status status)
89 {
90 	switch (func) {
91 	case MMAP_CHECK:
92 		iint->ima_mmap_status = status;
93 		break;
94 	case BPRM_CHECK:
95 		iint->ima_bprm_status = status;
96 		break;
97 	case FILE_CHECK:
98 	case POST_SETATTR:
99 		iint->ima_file_status = status;
100 		break;
101 	case MODULE_CHECK ... MAX_CHECK - 1:
102 	default:
103 		iint->ima_read_status = status;
104 		break;
105 	}
106 }
107 
108 static void ima_cache_flags(struct integrity_iint_cache *iint,
109 			     enum ima_hooks func)
110 {
111 	switch (func) {
112 	case MMAP_CHECK:
113 		iint->flags |= (IMA_MMAP_APPRAISED | IMA_APPRAISED);
114 		break;
115 	case BPRM_CHECK:
116 		iint->flags |= (IMA_BPRM_APPRAISED | IMA_APPRAISED);
117 		break;
118 	case FILE_CHECK:
119 	case POST_SETATTR:
120 		iint->flags |= (IMA_FILE_APPRAISED | IMA_APPRAISED);
121 		break;
122 	case MODULE_CHECK ... MAX_CHECK - 1:
123 	default:
124 		iint->flags |= (IMA_READ_APPRAISED | IMA_APPRAISED);
125 		break;
126 	}
127 }
128 
129 enum hash_algo ima_get_hash_algo(struct evm_ima_xattr_data *xattr_value,
130 				 int xattr_len)
131 {
132 	struct signature_v2_hdr *sig;
133 
134 	if (!xattr_value || xattr_len < 2)
135 		/* return default hash algo */
136 		return ima_hash_algo;
137 
138 	switch (xattr_value->type) {
139 	case EVM_IMA_XATTR_DIGSIG:
140 		sig = (typeof(sig))xattr_value;
141 		if (sig->version != 2 || xattr_len <= sizeof(*sig))
142 			return ima_hash_algo;
143 		return sig->hash_algo;
144 		break;
145 	case IMA_XATTR_DIGEST_NG:
146 		return xattr_value->digest[0];
147 		break;
148 	case IMA_XATTR_DIGEST:
149 		/* this is for backward compatibility */
150 		if (xattr_len == 21) {
151 			unsigned int zero = 0;
152 			if (!memcmp(&xattr_value->digest[16], &zero, 4))
153 				return HASH_ALGO_MD5;
154 			else
155 				return HASH_ALGO_SHA1;
156 		} else if (xattr_len == 17)
157 			return HASH_ALGO_MD5;
158 		break;
159 	}
160 
161 	/* return default hash algo */
162 	return ima_hash_algo;
163 }
164 
165 int ima_read_xattr(struct dentry *dentry,
166 		   struct evm_ima_xattr_data **xattr_value)
167 {
168 	struct inode *inode = d_backing_inode(dentry);
169 
170 	if (!inode->i_op->getxattr)
171 		return 0;
172 
173 	return vfs_getxattr_alloc(dentry, XATTR_NAME_IMA, (char **)xattr_value,
174 				  0, GFP_NOFS);
175 }
176 
177 /*
178  * ima_appraise_measurement - appraise file measurement
179  *
180  * Call evm_verifyxattr() to verify the integrity of 'security.ima'.
181  * Assuming success, compare the xattr hash with the collected measurement.
182  *
183  * Return 0 on success, error code otherwise
184  */
185 int ima_appraise_measurement(enum ima_hooks func,
186 			     struct integrity_iint_cache *iint,
187 			     struct file *file, const unsigned char *filename,
188 			     struct evm_ima_xattr_data *xattr_value,
189 			     int xattr_len, int opened)
190 {
191 	static const char op[] = "appraise_data";
192 	char *cause = "unknown";
193 	struct dentry *dentry = file->f_path.dentry;
194 	struct inode *inode = d_backing_inode(dentry);
195 	enum integrity_status status = INTEGRITY_UNKNOWN;
196 	int rc = xattr_len, hash_start = 0;
197 
198 	if (!inode->i_op->getxattr)
199 		return INTEGRITY_UNKNOWN;
200 
201 	if (rc <= 0) {
202 		if (rc && rc != -ENODATA)
203 			goto out;
204 
205 		cause = "missing-hash";
206 		status = INTEGRITY_NOLABEL;
207 		if (opened & FILE_CREATED) {
208 			iint->flags |= IMA_NEW_FILE;
209 			status = INTEGRITY_PASS;
210 		}
211 		goto out;
212 	}
213 
214 	status = evm_verifyxattr(dentry, XATTR_NAME_IMA, xattr_value, rc, iint);
215 	if ((status != INTEGRITY_PASS) && (status != INTEGRITY_UNKNOWN)) {
216 		if ((status == INTEGRITY_NOLABEL)
217 		    || (status == INTEGRITY_NOXATTRS))
218 			cause = "missing-HMAC";
219 		else if (status == INTEGRITY_FAIL)
220 			cause = "invalid-HMAC";
221 		goto out;
222 	}
223 	switch (xattr_value->type) {
224 	case IMA_XATTR_DIGEST_NG:
225 		/* first byte contains algorithm id */
226 		hash_start = 1;
227 	case IMA_XATTR_DIGEST:
228 		if (iint->flags & IMA_DIGSIG_REQUIRED) {
229 			cause = "IMA-signature-required";
230 			status = INTEGRITY_FAIL;
231 			break;
232 		}
233 		if (xattr_len - sizeof(xattr_value->type) - hash_start >=
234 				iint->ima_hash->length)
235 			/* xattr length may be longer. md5 hash in previous
236 			   version occupied 20 bytes in xattr, instead of 16
237 			 */
238 			rc = memcmp(&xattr_value->digest[hash_start],
239 				    iint->ima_hash->digest,
240 				    iint->ima_hash->length);
241 		else
242 			rc = -EINVAL;
243 		if (rc) {
244 			cause = "invalid-hash";
245 			status = INTEGRITY_FAIL;
246 			break;
247 		}
248 		status = INTEGRITY_PASS;
249 		break;
250 	case EVM_IMA_XATTR_DIGSIG:
251 		iint->flags |= IMA_DIGSIG;
252 		rc = integrity_digsig_verify(INTEGRITY_KEYRING_IMA,
253 					     (const char *)xattr_value, rc,
254 					     iint->ima_hash->digest,
255 					     iint->ima_hash->length);
256 		if (rc == -EOPNOTSUPP) {
257 			status = INTEGRITY_UNKNOWN;
258 		} else if (rc) {
259 			cause = "invalid-signature";
260 			status = INTEGRITY_FAIL;
261 		} else {
262 			status = INTEGRITY_PASS;
263 		}
264 		break;
265 	default:
266 		status = INTEGRITY_UNKNOWN;
267 		cause = "unknown-ima-data";
268 		break;
269 	}
270 
271 out:
272 	if (status != INTEGRITY_PASS) {
273 		if ((ima_appraise & IMA_APPRAISE_FIX) &&
274 		    (!xattr_value ||
275 		     xattr_value->type != EVM_IMA_XATTR_DIGSIG)) {
276 			if (!ima_fix_xattr(dentry, iint))
277 				status = INTEGRITY_PASS;
278 		} else if ((inode->i_size == 0) &&
279 			   (iint->flags & IMA_NEW_FILE) &&
280 			   (xattr_value &&
281 			    xattr_value->type == EVM_IMA_XATTR_DIGSIG)) {
282 			status = INTEGRITY_PASS;
283 		}
284 		integrity_audit_msg(AUDIT_INTEGRITY_DATA, inode, filename,
285 				    op, cause, rc, 0);
286 	} else {
287 		ima_cache_flags(iint, func);
288 	}
289 	ima_set_cache_status(iint, func, status);
290 	return status;
291 }
292 
293 /*
294  * ima_update_xattr - update 'security.ima' hash value
295  */
296 void ima_update_xattr(struct integrity_iint_cache *iint, struct file *file)
297 {
298 	struct dentry *dentry = file->f_path.dentry;
299 	int rc = 0;
300 
301 	/* do not collect and update hash for digital signatures */
302 	if (iint->flags & IMA_DIGSIG)
303 		return;
304 
305 	rc = ima_collect_measurement(iint, file, NULL, 0, ima_hash_algo);
306 	if (rc < 0)
307 		return;
308 
309 	ima_fix_xattr(dentry, iint);
310 }
311 
312 /**
313  * ima_inode_post_setattr - reflect file metadata changes
314  * @dentry: pointer to the affected dentry
315  *
316  * Changes to a dentry's metadata might result in needing to appraise.
317  *
318  * This function is called from notify_change(), which expects the caller
319  * to lock the inode's i_mutex.
320  */
321 void ima_inode_post_setattr(struct dentry *dentry)
322 {
323 	struct inode *inode = d_backing_inode(dentry);
324 	struct integrity_iint_cache *iint;
325 	int must_appraise, rc;
326 
327 	if (!(ima_policy_flag & IMA_APPRAISE) || !S_ISREG(inode->i_mode)
328 	    || !inode->i_op->removexattr)
329 		return;
330 
331 	must_appraise = ima_must_appraise(inode, MAY_ACCESS, POST_SETATTR);
332 	iint = integrity_iint_find(inode);
333 	if (iint) {
334 		iint->flags &= ~(IMA_APPRAISE | IMA_APPRAISED |
335 				 IMA_APPRAISE_SUBMASK | IMA_APPRAISED_SUBMASK |
336 				 IMA_ACTION_RULE_FLAGS);
337 		if (must_appraise)
338 			iint->flags |= IMA_APPRAISE;
339 	}
340 	if (!must_appraise)
341 		rc = inode->i_op->removexattr(dentry, XATTR_NAME_IMA);
342 	return;
343 }
344 
345 /*
346  * ima_protect_xattr - protect 'security.ima'
347  *
348  * Ensure that not just anyone can modify or remove 'security.ima'.
349  */
350 static int ima_protect_xattr(struct dentry *dentry, const char *xattr_name,
351 			     const void *xattr_value, size_t xattr_value_len)
352 {
353 	if (strcmp(xattr_name, XATTR_NAME_IMA) == 0) {
354 		if (!capable(CAP_SYS_ADMIN))
355 			return -EPERM;
356 		return 1;
357 	}
358 	return 0;
359 }
360 
361 static void ima_reset_appraise_flags(struct inode *inode, int digsig)
362 {
363 	struct integrity_iint_cache *iint;
364 
365 	if (!(ima_policy_flag & IMA_APPRAISE) || !S_ISREG(inode->i_mode))
366 		return;
367 
368 	iint = integrity_iint_find(inode);
369 	if (!iint)
370 		return;
371 
372 	iint->flags &= ~IMA_DONE_MASK;
373 	if (digsig)
374 		iint->flags |= IMA_DIGSIG;
375 	return;
376 }
377 
378 int ima_inode_setxattr(struct dentry *dentry, const char *xattr_name,
379 		       const void *xattr_value, size_t xattr_value_len)
380 {
381 	const struct evm_ima_xattr_data *xvalue = xattr_value;
382 	int result;
383 
384 	result = ima_protect_xattr(dentry, xattr_name, xattr_value,
385 				   xattr_value_len);
386 	if (result == 1) {
387 		bool digsig;
388 
389 		if (!xattr_value_len || (xvalue->type >= IMA_XATTR_LAST))
390 			return -EINVAL;
391 		digsig = (xvalue->type == EVM_IMA_XATTR_DIGSIG);
392 		if (!digsig && (ima_appraise & IMA_APPRAISE_ENFORCE))
393 			return -EPERM;
394 		ima_reset_appraise_flags(d_backing_inode(dentry), digsig);
395 		result = 0;
396 	}
397 	return result;
398 }
399 
400 int ima_inode_removexattr(struct dentry *dentry, const char *xattr_name)
401 {
402 	int result;
403 
404 	result = ima_protect_xattr(dentry, xattr_name, NULL, 0);
405 	if (result == 1) {
406 		ima_reset_appraise_flags(d_backing_inode(dentry), 0);
407 		result = 0;
408 	}
409 	return result;
410 }
411