xref: /linux/security/integrity/ima/ima_appraise.c (revision ca55b2fef3a9373fcfc30f82fd26bc7fccbda732) 
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 #include <crypto/hash_info.h>
19 
20 #include "ima.h"
21 
22 static int __init default_appraise_setup(char *str)
23 {
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 	return 1;
31 }
32 
33 __setup("ima_appraise=", default_appraise_setup);
34 
35 /*
36  * ima_must_appraise - set appraise flag
37  *
38  * Return 1 to appraise
39  */
40 int ima_must_appraise(struct inode *inode, int mask, enum ima_hooks func)
41 {
42 	if (!ima_appraise)
43 		return 0;
44 
45 	return ima_match_policy(inode, func, mask, IMA_APPRAISE);
46 }
47 
48 static int ima_fix_xattr(struct dentry *dentry,
49 			 struct integrity_iint_cache *iint)
50 {
51 	int rc, offset;
52 	u8 algo = iint->ima_hash->algo;
53 
54 	if (algo <= HASH_ALGO_SHA1) {
55 		offset = 1;
56 		iint->ima_hash->xattr.sha1.type = IMA_XATTR_DIGEST;
57 	} else {
58 		offset = 0;
59 		iint->ima_hash->xattr.ng.type = IMA_XATTR_DIGEST_NG;
60 		iint->ima_hash->xattr.ng.algo = algo;
61 	}
62 	rc = __vfs_setxattr_noperm(dentry, XATTR_NAME_IMA,
63 				   &iint->ima_hash->xattr.data[offset],
64 				   (sizeof(iint->ima_hash->xattr) - offset) +
65 				   iint->ima_hash->length, 0);
66 	return rc;
67 }
68 
69 /* Return specific func appraised cached result */
70 enum integrity_status ima_get_cache_status(struct integrity_iint_cache *iint,
71 					   int func)
72 {
73 	switch (func) {
74 	case MMAP_CHECK:
75 		return iint->ima_mmap_status;
76 	case BPRM_CHECK:
77 		return iint->ima_bprm_status;
78 	case MODULE_CHECK:
79 		return iint->ima_module_status;
80 	case FIRMWARE_CHECK:
81 		return iint->ima_firmware_status;
82 	case FILE_CHECK:
83 	default:
84 		return iint->ima_file_status;
85 	}
86 }
87 
88 static void ima_set_cache_status(struct integrity_iint_cache *iint,
89 				 int func, enum integrity_status status)
90 {
91 	switch (func) {
92 	case MMAP_CHECK:
93 		iint->ima_mmap_status = status;
94 		break;
95 	case BPRM_CHECK:
96 		iint->ima_bprm_status = status;
97 		break;
98 	case MODULE_CHECK:
99 		iint->ima_module_status = status;
100 		break;
101 	case FIRMWARE_CHECK:
102 		iint->ima_firmware_status = status;
103 		break;
104 	case FILE_CHECK:
105 	default:
106 		iint->ima_file_status = status;
107 		break;
108 	}
109 }
110 
111 static void ima_cache_flags(struct integrity_iint_cache *iint, int func)
112 {
113 	switch (func) {
114 	case MMAP_CHECK:
115 		iint->flags |= (IMA_MMAP_APPRAISED | IMA_APPRAISED);
116 		break;
117 	case BPRM_CHECK:
118 		iint->flags |= (IMA_BPRM_APPRAISED | IMA_APPRAISED);
119 		break;
120 	case MODULE_CHECK:
121 		iint->flags |= (IMA_MODULE_APPRAISED | IMA_APPRAISED);
122 		break;
123 	case FIRMWARE_CHECK:
124 		iint->flags |= (IMA_FIRMWARE_APPRAISED | IMA_APPRAISED);
125 		break;
126 	case FILE_CHECK:
127 	default:
128 		iint->flags |= (IMA_FILE_APPRAISED | IMA_APPRAISED);
129 		break;
130 	}
131 }
132 
133 void ima_get_hash_algo(struct evm_ima_xattr_data *xattr_value, int xattr_len,
134 		       struct ima_digest_data *hash)
135 {
136 	struct signature_v2_hdr *sig;
137 
138 	if (!xattr_value || xattr_len < 2)
139 		return;
140 
141 	switch (xattr_value->type) {
142 	case EVM_IMA_XATTR_DIGSIG:
143 		sig = (typeof(sig))xattr_value;
144 		if (sig->version != 2 || xattr_len <= sizeof(*sig))
145 			return;
146 		hash->algo = sig->hash_algo;
147 		break;
148 	case IMA_XATTR_DIGEST_NG:
149 		hash->algo = xattr_value->digest[0];
150 		break;
151 	case IMA_XATTR_DIGEST:
152 		/* this is for backward compatibility */
153 		if (xattr_len == 21) {
154 			unsigned int zero = 0;
155 			if (!memcmp(&xattr_value->digest[16], &zero, 4))
156 				hash->algo = HASH_ALGO_MD5;
157 			else
158 				hash->algo = HASH_ALGO_SHA1;
159 		} else if (xattr_len == 17)
160 			hash->algo = HASH_ALGO_MD5;
161 		break;
162 	}
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(int func, struct integrity_iint_cache *iint,
186 			     struct file *file, const unsigned char *filename,
187 			     struct evm_ima_xattr_data *xattr_value,
188 			     int xattr_len, int opened)
189 {
190 	static const char op[] = "appraise_data";
191 	char *cause = "unknown";
192 	struct dentry *dentry = file->f_path.dentry;
193 	struct inode *inode = d_backing_inode(dentry);
194 	enum integrity_status status = INTEGRITY_UNKNOWN;
195 	int rc = xattr_len, hash_start = 0;
196 
197 	if (!inode->i_op->getxattr)
198 		return INTEGRITY_UNKNOWN;
199 
200 	if (rc <= 0) {
201 		if (rc && rc != -ENODATA)
202 			goto out;
203 
204 		cause = "missing-hash";
205 		status = INTEGRITY_NOLABEL;
206 		if (opened & FILE_CREATED) {
207 			iint->flags |= IMA_NEW_FILE;
208 			status = INTEGRITY_PASS;
209 		}
210 		goto out;
211 	}
212 
213 	status = evm_verifyxattr(dentry, XATTR_NAME_IMA, xattr_value, rc, iint);
214 	if ((status != INTEGRITY_PASS) && (status != INTEGRITY_UNKNOWN)) {
215 		if ((status == INTEGRITY_NOLABEL)
216 		    || (status == INTEGRITY_NOXATTRS))
217 			cause = "missing-HMAC";
218 		else if (status == INTEGRITY_FAIL)
219 			cause = "invalid-HMAC";
220 		goto out;
221 	}
222 	switch (xattr_value->type) {
223 	case IMA_XATTR_DIGEST_NG:
224 		/* first byte contains algorithm id */
225 		hash_start = 1;
226 	case IMA_XATTR_DIGEST:
227 		if (iint->flags & IMA_DIGSIG_REQUIRED) {
228 			cause = "IMA-signature-required";
229 			status = INTEGRITY_FAIL;
230 			break;
231 		}
232 		if (xattr_len - sizeof(xattr_value->type) - hash_start >=
233 				iint->ima_hash->length)
234 			/* xattr length may be longer. md5 hash in previous
235 			   version occupied 20 bytes in xattr, instead of 16
236 			 */
237 			rc = memcmp(&xattr_value->digest[hash_start],
238 				    iint->ima_hash->digest,
239 				    iint->ima_hash->length);
240 		else
241 			rc = -EINVAL;
242 		if (rc) {
243 			cause = "invalid-hash";
244 			status = INTEGRITY_FAIL;
245 			break;
246 		}
247 		status = INTEGRITY_PASS;
248 		break;
249 	case EVM_IMA_XATTR_DIGSIG:
250 		iint->flags |= IMA_DIGSIG;
251 		rc = integrity_digsig_verify(INTEGRITY_KEYRING_IMA,
252 					     (const char *)xattr_value, rc,
253 					     iint->ima_hash->digest,
254 					     iint->ima_hash->length);
255 		if (rc == -EOPNOTSUPP) {
256 			status = INTEGRITY_UNKNOWN;
257 		} else if (rc) {
258 			cause = "invalid-signature";
259 			status = INTEGRITY_FAIL;
260 		} else {
261 			status = INTEGRITY_PASS;
262 		}
263 		break;
264 	default:
265 		status = INTEGRITY_UNKNOWN;
266 		cause = "unknown-ima-data";
267 		break;
268 	}
269 
270 out:
271 	if (status != INTEGRITY_PASS) {
272 		if ((ima_appraise & IMA_APPRAISE_FIX) &&
273 		    (!xattr_value ||
274 		     xattr_value->type != EVM_IMA_XATTR_DIGSIG)) {
275 			if (!ima_fix_xattr(dentry, iint))
276 				status = INTEGRITY_PASS;
277 		}
278 		integrity_audit_msg(AUDIT_INTEGRITY_DATA, inode, filename,
279 				    op, cause, rc, 0);
280 	} else {
281 		ima_cache_flags(iint, func);
282 	}
283 	ima_set_cache_status(iint, func, status);
284 	return status;
285 }
286 
287 /*
288  * ima_update_xattr - update 'security.ima' hash value
289  */
290 void ima_update_xattr(struct integrity_iint_cache *iint, struct file *file)
291 {
292 	struct dentry *dentry = file->f_path.dentry;
293 	int rc = 0;
294 
295 	/* do not collect and update hash for digital signatures */
296 	if (iint->flags & IMA_DIGSIG)
297 		return;
298 
299 	rc = ima_collect_measurement(iint, file, NULL, NULL);
300 	if (rc < 0)
301 		return;
302 
303 	ima_fix_xattr(dentry, iint);
304 }
305 
306 /**
307  * ima_inode_post_setattr - reflect file metadata changes
308  * @dentry: pointer to the affected dentry
309  *
310  * Changes to a dentry's metadata might result in needing to appraise.
311  *
312  * This function is called from notify_change(), which expects the caller
313  * to lock the inode's i_mutex.
314  */
315 void ima_inode_post_setattr(struct dentry *dentry)
316 {
317 	struct inode *inode = d_backing_inode(dentry);
318 	struct integrity_iint_cache *iint;
319 	int must_appraise, rc;
320 
321 	if (!(ima_policy_flag & IMA_APPRAISE) || !S_ISREG(inode->i_mode)
322 	    || !inode->i_op->removexattr)
323 		return;
324 
325 	must_appraise = ima_must_appraise(inode, MAY_ACCESS, POST_SETATTR);
326 	iint = integrity_iint_find(inode);
327 	if (iint) {
328 		iint->flags &= ~(IMA_APPRAISE | IMA_APPRAISED |
329 				 IMA_APPRAISE_SUBMASK | IMA_APPRAISED_SUBMASK |
330 				 IMA_ACTION_FLAGS);
331 		if (must_appraise)
332 			iint->flags |= IMA_APPRAISE;
333 	}
334 	if (!must_appraise)
335 		rc = inode->i_op->removexattr(dentry, XATTR_NAME_IMA);
336 	return;
337 }
338 
339 /*
340  * ima_protect_xattr - protect 'security.ima'
341  *
342  * Ensure that not just anyone can modify or remove 'security.ima'.
343  */
344 static int ima_protect_xattr(struct dentry *dentry, const char *xattr_name,
345 			     const void *xattr_value, size_t xattr_value_len)
346 {
347 	if (strcmp(xattr_name, XATTR_NAME_IMA) == 0) {
348 		if (!capable(CAP_SYS_ADMIN))
349 			return -EPERM;
350 		return 1;
351 	}
352 	return 0;
353 }
354 
355 static void ima_reset_appraise_flags(struct inode *inode, int digsig)
356 {
357 	struct integrity_iint_cache *iint;
358 
359 	if (!(ima_policy_flag & IMA_APPRAISE) || !S_ISREG(inode->i_mode))
360 		return;
361 
362 	iint = integrity_iint_find(inode);
363 	if (!iint)
364 		return;
365 
366 	iint->flags &= ~IMA_DONE_MASK;
367 	if (digsig)
368 		iint->flags |= IMA_DIGSIG;
369 	return;
370 }
371 
372 int ima_inode_setxattr(struct dentry *dentry, const char *xattr_name,
373 		       const void *xattr_value, size_t xattr_value_len)
374 {
375 	const struct evm_ima_xattr_data *xvalue = xattr_value;
376 	int result;
377 
378 	result = ima_protect_xattr(dentry, xattr_name, xattr_value,
379 				   xattr_value_len);
380 	if (result == 1) {
381 		bool digsig;
382 
383 		if (!xattr_value_len || (xvalue->type >= IMA_XATTR_LAST))
384 			return -EINVAL;
385 		digsig = (xvalue->type == EVM_IMA_XATTR_DIGSIG);
386 		if (!digsig && (ima_appraise & IMA_APPRAISE_ENFORCE))
387 			return -EPERM;
388 		ima_reset_appraise_flags(d_backing_inode(dentry), digsig);
389 		result = 0;
390 	}
391 	return result;
392 }
393 
394 int ima_inode_removexattr(struct dentry *dentry, const char *xattr_name)
395 {
396 	int result;
397 
398 	result = ima_protect_xattr(dentry, xattr_name, NULL, 0);
399 	if (result == 1) {
400 		ima_reset_appraise_flags(d_backing_inode(dentry), 0);
401 		result = 0;
402 	}
403 	return result;
404 }
405