1 /*
2  * Copyright (C) 2005,2006,2007,2008 IBM Corporation
3  *
4  * Authors:
5  * Reiner Sailer <sailer@watson.ibm.com>
6  * Serge Hallyn <serue@us.ibm.com>
7  * Kylene Hall <kylene@us.ibm.com>
8  * Mimi Zohar <zohar@us.ibm.com>
9  *
10  * This program is free software; you can redistribute it and/or
11  * modify it under the terms of the GNU General Public License as
12  * published by the Free Software Foundation, version 2 of the
13  * License.
14  *
15  * File: ima_main.c
16  *	implements the IMA hooks: ima_bprm_check, ima_file_mmap,
17  *	and ima_file_check.
18  */
19 
20 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
21 
22 #include <linux/module.h>
23 #include <linux/file.h>
24 #include <linux/binfmts.h>
25 #include <linux/mount.h>
26 #include <linux/mman.h>
27 #include <linux/slab.h>
28 #include <linux/xattr.h>
29 #include <linux/ima.h>
30 #include <linux/iversion.h>
31 #include <linux/fs.h>
32 
33 #include "ima.h"
34 
35 #ifdef CONFIG_IMA_APPRAISE
36 int ima_appraise = IMA_APPRAISE_ENFORCE;
37 #else
38 int ima_appraise;
39 #endif
40 
41 int ima_hash_algo = HASH_ALGO_SHA1;
42 static int hash_setup_done;
43 
44 static int __init hash_setup(char *str)
45 {
46 	struct ima_template_desc *template_desc = ima_template_desc_current();
47 	int i;
48 
49 	if (hash_setup_done)
50 		return 1;
51 
52 	if (strcmp(template_desc->name, IMA_TEMPLATE_IMA_NAME) == 0) {
53 		if (strncmp(str, "sha1", 4) == 0)
54 			ima_hash_algo = HASH_ALGO_SHA1;
55 		else if (strncmp(str, "md5", 3) == 0)
56 			ima_hash_algo = HASH_ALGO_MD5;
57 		else
58 			return 1;
59 		goto out;
60 	}
61 
62 	i = match_string(hash_algo_name, HASH_ALGO__LAST, str);
63 	if (i < 0)
64 		return 1;
65 
66 	ima_hash_algo = i;
67 out:
68 	hash_setup_done = 1;
69 	return 1;
70 }
71 __setup("ima_hash=", hash_setup);
72 
73 /*
74  * ima_rdwr_violation_check
75  *
76  * Only invalidate the PCR for measured files:
77  *	- Opening a file for write when already open for read,
78  *	  results in a time of measure, time of use (ToMToU) error.
79  *	- Opening a file for read when already open for write,
80  *	  could result in a file measurement error.
81  *
82  */
83 static void ima_rdwr_violation_check(struct file *file,
84 				     struct integrity_iint_cache *iint,
85 				     int must_measure,
86 				     char **pathbuf,
87 				     const char **pathname,
88 				     char *filename)
89 {
90 	struct inode *inode = file_inode(file);
91 	fmode_t mode = file->f_mode;
92 	bool send_tomtou = false, send_writers = false;
93 
94 	if (mode & FMODE_WRITE) {
95 		if (atomic_read(&inode->i_readcount) && IS_IMA(inode)) {
96 			if (!iint)
97 				iint = integrity_iint_find(inode);
98 			/* IMA_MEASURE is set from reader side */
99 			if (iint && test_bit(IMA_MUST_MEASURE,
100 						&iint->atomic_flags))
101 				send_tomtou = true;
102 		}
103 	} else {
104 		if (must_measure)
105 			set_bit(IMA_MUST_MEASURE, &iint->atomic_flags);
106 		if ((atomic_read(&inode->i_writecount) > 0) && must_measure)
107 			send_writers = true;
108 	}
109 
110 	if (!send_tomtou && !send_writers)
111 		return;
112 
113 	*pathname = ima_d_path(&file->f_path, pathbuf, filename);
114 
115 	if (send_tomtou)
116 		ima_add_violation(file, *pathname, iint,
117 				  "invalid_pcr", "ToMToU");
118 	if (send_writers)
119 		ima_add_violation(file, *pathname, iint,
120 				  "invalid_pcr", "open_writers");
121 }
122 
123 static void ima_check_last_writer(struct integrity_iint_cache *iint,
124 				  struct inode *inode, struct file *file)
125 {
126 	fmode_t mode = file->f_mode;
127 	bool update;
128 
129 	if (!(mode & FMODE_WRITE))
130 		return;
131 
132 	mutex_lock(&iint->mutex);
133 	if (atomic_read(&inode->i_writecount) == 1) {
134 		update = test_and_clear_bit(IMA_UPDATE_XATTR,
135 					    &iint->atomic_flags);
136 		if (!IS_I_VERSION(inode) ||
137 		    !inode_eq_iversion(inode, iint->version) ||
138 		    (iint->flags & IMA_NEW_FILE)) {
139 			iint->flags &= ~(IMA_DONE_MASK | IMA_NEW_FILE);
140 			iint->measured_pcrs = 0;
141 			if (update)
142 				ima_update_xattr(iint, file);
143 		}
144 	}
145 	mutex_unlock(&iint->mutex);
146 }
147 
148 /**
149  * ima_file_free - called on __fput()
150  * @file: pointer to file structure being freed
151  *
152  * Flag files that changed, based on i_version
153  */
154 void ima_file_free(struct file *file)
155 {
156 	struct inode *inode = file_inode(file);
157 	struct integrity_iint_cache *iint;
158 
159 	if (!ima_policy_flag || !S_ISREG(inode->i_mode))
160 		return;
161 
162 	iint = integrity_iint_find(inode);
163 	if (!iint)
164 		return;
165 
166 	ima_check_last_writer(iint, inode, file);
167 }
168 
169 static int process_measurement(struct file *file, const struct cred *cred,
170 			       u32 secid, char *buf, loff_t size, int mask,
171 			       enum ima_hooks func)
172 {
173 	struct inode *inode = file_inode(file);
174 	struct integrity_iint_cache *iint = NULL;
175 	struct ima_template_desc *template_desc;
176 	char *pathbuf = NULL;
177 	char filename[NAME_MAX];
178 	const char *pathname = NULL;
179 	int rc = 0, action, must_appraise = 0;
180 	int pcr = CONFIG_IMA_MEASURE_PCR_IDX;
181 	struct evm_ima_xattr_data *xattr_value = NULL;
182 	int xattr_len = 0;
183 	bool violation_check;
184 	enum hash_algo hash_algo;
185 
186 	if (!ima_policy_flag || !S_ISREG(inode->i_mode))
187 		return 0;
188 
189 	/* Return an IMA_MEASURE, IMA_APPRAISE, IMA_AUDIT action
190 	 * bitmask based on the appraise/audit/measurement policy.
191 	 * Included is the appraise submask.
192 	 */
193 	action = ima_get_action(inode, cred, secid, mask, func, &pcr);
194 	violation_check = ((func == FILE_CHECK || func == MMAP_CHECK) &&
195 			   (ima_policy_flag & IMA_MEASURE));
196 	if (!action && !violation_check)
197 		return 0;
198 
199 	must_appraise = action & IMA_APPRAISE;
200 
201 	/*  Is the appraise rule hook specific?  */
202 	if (action & IMA_FILE_APPRAISE)
203 		func = FILE_CHECK;
204 
205 	inode_lock(inode);
206 
207 	if (action) {
208 		iint = integrity_inode_get(inode);
209 		if (!iint)
210 			rc = -ENOMEM;
211 	}
212 
213 	if (!rc && violation_check)
214 		ima_rdwr_violation_check(file, iint, action & IMA_MEASURE,
215 					 &pathbuf, &pathname, filename);
216 
217 	inode_unlock(inode);
218 
219 	if (rc)
220 		goto out;
221 	if (!action)
222 		goto out;
223 
224 	mutex_lock(&iint->mutex);
225 
226 	if (test_and_clear_bit(IMA_CHANGE_ATTR, &iint->atomic_flags))
227 		/* reset appraisal flags if ima_inode_post_setattr was called */
228 		iint->flags &= ~(IMA_APPRAISE | IMA_APPRAISED |
229 				 IMA_APPRAISE_SUBMASK | IMA_APPRAISED_SUBMASK |
230 				 IMA_ACTION_FLAGS);
231 
232 	/*
233 	 * Re-evaulate the file if either the xattr has changed or the
234 	 * kernel has no way of detecting file change on the filesystem.
235 	 * (Limited to privileged mounted filesystems.)
236 	 */
237 	if (test_and_clear_bit(IMA_CHANGE_XATTR, &iint->atomic_flags) ||
238 	    ((inode->i_sb->s_iflags & SB_I_IMA_UNVERIFIABLE_SIGNATURE) &&
239 	     !(inode->i_sb->s_iflags & SB_I_UNTRUSTED_MOUNTER) &&
240 	     !(action & IMA_FAIL_UNVERIFIABLE_SIGS))) {
241 		iint->flags &= ~IMA_DONE_MASK;
242 		iint->measured_pcrs = 0;
243 	}
244 
245 	/* Determine if already appraised/measured based on bitmask
246 	 * (IMA_MEASURE, IMA_MEASURED, IMA_XXXX_APPRAISE, IMA_XXXX_APPRAISED,
247 	 *  IMA_AUDIT, IMA_AUDITED)
248 	 */
249 	iint->flags |= action;
250 	action &= IMA_DO_MASK;
251 	action &= ~((iint->flags & (IMA_DONE_MASK ^ IMA_MEASURED)) >> 1);
252 
253 	/* If target pcr is already measured, unset IMA_MEASURE action */
254 	if ((action & IMA_MEASURE) && (iint->measured_pcrs & (0x1 << pcr)))
255 		action ^= IMA_MEASURE;
256 
257 	/* HASH sets the digital signature and update flags, nothing else */
258 	if ((action & IMA_HASH) &&
259 	    !(test_bit(IMA_DIGSIG, &iint->atomic_flags))) {
260 		xattr_len = ima_read_xattr(file_dentry(file), &xattr_value);
261 		if ((xattr_value && xattr_len > 2) &&
262 		    (xattr_value->type == EVM_IMA_XATTR_DIGSIG))
263 			set_bit(IMA_DIGSIG, &iint->atomic_flags);
264 		iint->flags |= IMA_HASHED;
265 		action ^= IMA_HASH;
266 		set_bit(IMA_UPDATE_XATTR, &iint->atomic_flags);
267 	}
268 
269 	/* Nothing to do, just return existing appraised status */
270 	if (!action) {
271 		if (must_appraise)
272 			rc = ima_get_cache_status(iint, func);
273 		goto out_locked;
274 	}
275 
276 	template_desc = ima_template_desc_current();
277 	if ((action & IMA_APPRAISE_SUBMASK) ||
278 		    strcmp(template_desc->name, IMA_TEMPLATE_IMA_NAME) != 0)
279 		/* read 'security.ima' */
280 		xattr_len = ima_read_xattr(file_dentry(file), &xattr_value);
281 
282 	hash_algo = ima_get_hash_algo(xattr_value, xattr_len);
283 
284 	rc = ima_collect_measurement(iint, file, buf, size, hash_algo);
285 	if (rc != 0 && rc != -EBADF && rc != -EINVAL)
286 		goto out_locked;
287 
288 	if (!pathbuf)	/* ima_rdwr_violation possibly pre-fetched */
289 		pathname = ima_d_path(&file->f_path, &pathbuf, filename);
290 
291 	if (action & IMA_MEASURE)
292 		ima_store_measurement(iint, file, pathname,
293 				      xattr_value, xattr_len, pcr);
294 	if (rc == 0 && (action & IMA_APPRAISE_SUBMASK)) {
295 		inode_lock(inode);
296 		rc = ima_appraise_measurement(func, iint, file, pathname,
297 					      xattr_value, xattr_len);
298 		inode_unlock(inode);
299 	}
300 	if (action & IMA_AUDIT)
301 		ima_audit_measurement(iint, pathname);
302 
303 	if ((file->f_flags & O_DIRECT) && (iint->flags & IMA_PERMIT_DIRECTIO))
304 		rc = 0;
305 out_locked:
306 	if ((mask & MAY_WRITE) && test_bit(IMA_DIGSIG, &iint->atomic_flags) &&
307 	     !(iint->flags & IMA_NEW_FILE))
308 		rc = -EACCES;
309 	mutex_unlock(&iint->mutex);
310 	kfree(xattr_value);
311 out:
312 	if (pathbuf)
313 		__putname(pathbuf);
314 	if (must_appraise) {
315 		if (rc && (ima_appraise & IMA_APPRAISE_ENFORCE))
316 			return -EACCES;
317 		if (file->f_mode & FMODE_WRITE)
318 			set_bit(IMA_UPDATE_XATTR, &iint->atomic_flags);
319 	}
320 	return 0;
321 }
322 
323 /**
324  * ima_file_mmap - based on policy, collect/store measurement.
325  * @file: pointer to the file to be measured (May be NULL)
326  * @prot: contains the protection that will be applied by the kernel.
327  *
328  * Measure files being mmapped executable based on the ima_must_measure()
329  * policy decision.
330  *
331  * On success return 0.  On integrity appraisal error, assuming the file
332  * is in policy and IMA-appraisal is in enforcing mode, return -EACCES.
333  */
334 int ima_file_mmap(struct file *file, unsigned long prot)
335 {
336 	u32 secid;
337 
338 	if (file && (prot & PROT_EXEC)) {
339 		security_task_getsecid(current, &secid);
340 		return process_measurement(file, current_cred(), secid, NULL,
341 					   0, MAY_EXEC, MMAP_CHECK);
342 	}
343 
344 	return 0;
345 }
346 
347 /**
348  * ima_bprm_check - based on policy, collect/store measurement.
349  * @bprm: contains the linux_binprm structure
350  *
351  * The OS protects against an executable file, already open for write,
352  * from being executed in deny_write_access() and an executable file,
353  * already open for execute, from being modified in get_write_access().
354  * So we can be certain that what we verify and measure here is actually
355  * what is being executed.
356  *
357  * On success return 0.  On integrity appraisal error, assuming the file
358  * is in policy and IMA-appraisal is in enforcing mode, return -EACCES.
359  */
360 int ima_bprm_check(struct linux_binprm *bprm)
361 {
362 	int ret;
363 	u32 secid;
364 
365 	security_task_getsecid(current, &secid);
366 	ret = process_measurement(bprm->file, current_cred(), secid, NULL, 0,
367 				  MAY_EXEC, BPRM_CHECK);
368 	if (ret)
369 		return ret;
370 
371 	security_cred_getsecid(bprm->cred, &secid);
372 	return process_measurement(bprm->file, bprm->cred, secid, NULL, 0,
373 				   MAY_EXEC, CREDS_CHECK);
374 }
375 
376 /**
377  * ima_path_check - based on policy, collect/store measurement.
378  * @file: pointer to the file to be measured
379  * @mask: contains MAY_READ, MAY_WRITE, MAY_EXEC or MAY_APPEND
380  *
381  * Measure files based on the ima_must_measure() policy decision.
382  *
383  * On success return 0.  On integrity appraisal error, assuming the file
384  * is in policy and IMA-appraisal is in enforcing mode, return -EACCES.
385  */
386 int ima_file_check(struct file *file, int mask)
387 {
388 	u32 secid;
389 
390 	security_task_getsecid(current, &secid);
391 	return process_measurement(file, current_cred(), secid, NULL, 0,
392 				   mask & (MAY_READ | MAY_WRITE | MAY_EXEC |
393 					   MAY_APPEND), FILE_CHECK);
394 }
395 EXPORT_SYMBOL_GPL(ima_file_check);
396 
397 /**
398  * ima_post_path_mknod - mark as a new inode
399  * @dentry: newly created dentry
400  *
401  * Mark files created via the mknodat syscall as new, so that the
402  * file data can be written later.
403  */
404 void ima_post_path_mknod(struct dentry *dentry)
405 {
406 	struct integrity_iint_cache *iint;
407 	struct inode *inode = dentry->d_inode;
408 	int must_appraise;
409 
410 	must_appraise = ima_must_appraise(inode, MAY_ACCESS, FILE_CHECK);
411 	if (!must_appraise)
412 		return;
413 
414 	iint = integrity_inode_get(inode);
415 	if (iint)
416 		iint->flags |= IMA_NEW_FILE;
417 }
418 
419 /**
420  * ima_read_file - pre-measure/appraise hook decision based on policy
421  * @file: pointer to the file to be measured/appraised/audit
422  * @read_id: caller identifier
423  *
424  * Permit reading a file based on policy. The policy rules are written
425  * in terms of the policy identifier.  Appraising the integrity of
426  * a file requires a file descriptor.
427  *
428  * For permission return 0, otherwise return -EACCES.
429  */
430 int ima_read_file(struct file *file, enum kernel_read_file_id read_id)
431 {
432 	/*
433 	 * READING_FIRMWARE_PREALLOC_BUFFER
434 	 *
435 	 * Do devices using pre-allocated memory run the risk of the
436 	 * firmware being accessible to the device prior to the completion
437 	 * of IMA's signature verification any more than when using two
438 	 * buffers?
439 	 */
440 	return 0;
441 }
442 
443 static int read_idmap[READING_MAX_ID] = {
444 	[READING_FIRMWARE] = FIRMWARE_CHECK,
445 	[READING_FIRMWARE_PREALLOC_BUFFER] = FIRMWARE_CHECK,
446 	[READING_MODULE] = MODULE_CHECK,
447 	[READING_KEXEC_IMAGE] = KEXEC_KERNEL_CHECK,
448 	[READING_KEXEC_INITRAMFS] = KEXEC_INITRAMFS_CHECK,
449 	[READING_POLICY] = POLICY_CHECK
450 };
451 
452 /**
453  * ima_post_read_file - in memory collect/appraise/audit measurement
454  * @file: pointer to the file to be measured/appraised/audit
455  * @buf: pointer to in memory file contents
456  * @size: size of in memory file contents
457  * @read_id: caller identifier
458  *
459  * Measure/appraise/audit in memory file based on policy.  Policy rules
460  * are written in terms of a policy identifier.
461  *
462  * On success return 0.  On integrity appraisal error, assuming the file
463  * is in policy and IMA-appraisal is in enforcing mode, return -EACCES.
464  */
465 int ima_post_read_file(struct file *file, void *buf, loff_t size,
466 		       enum kernel_read_file_id read_id)
467 {
468 	enum ima_hooks func;
469 	u32 secid;
470 
471 	if (!file && read_id == READING_FIRMWARE) {
472 		if ((ima_appraise & IMA_APPRAISE_FIRMWARE) &&
473 		    (ima_appraise & IMA_APPRAISE_ENFORCE)) {
474 			pr_err("Prevent firmware loading_store.\n");
475 			return -EACCES;	/* INTEGRITY_UNKNOWN */
476 		}
477 		return 0;
478 	}
479 
480 	/* permit signed certs */
481 	if (!file && read_id == READING_X509_CERTIFICATE)
482 		return 0;
483 
484 	if (!file || !buf || size == 0) { /* should never happen */
485 		if (ima_appraise & IMA_APPRAISE_ENFORCE)
486 			return -EACCES;
487 		return 0;
488 	}
489 
490 	func = read_idmap[read_id] ?: FILE_CHECK;
491 	security_task_getsecid(current, &secid);
492 	return process_measurement(file, current_cred(), secid, buf, size,
493 				   MAY_READ, func);
494 }
495 
496 /**
497  * ima_load_data - appraise decision based on policy
498  * @id: kernel load data caller identifier
499  *
500  * Callers of this LSM hook can not measure, appraise, or audit the
501  * data provided by userspace.  Enforce policy rules requring a file
502  * signature (eg. kexec'ed kernel image).
503  *
504  * For permission return 0, otherwise return -EACCES.
505  */
506 int ima_load_data(enum kernel_load_data_id id)
507 {
508 	bool sig_enforce;
509 
510 	if ((ima_appraise & IMA_APPRAISE_ENFORCE) != IMA_APPRAISE_ENFORCE)
511 		return 0;
512 
513 	switch (id) {
514 	case LOADING_KEXEC_IMAGE:
515 		if (ima_appraise & IMA_APPRAISE_KEXEC) {
516 			pr_err("impossible to appraise a kernel image without a file descriptor; try using kexec_file_load syscall.\n");
517 			return -EACCES;	/* INTEGRITY_UNKNOWN */
518 		}
519 		break;
520 	case LOADING_FIRMWARE:
521 		if (ima_appraise & IMA_APPRAISE_FIRMWARE) {
522 			pr_err("Prevent firmware sysfs fallback loading.\n");
523 			return -EACCES;	/* INTEGRITY_UNKNOWN */
524 		}
525 		break;
526 	case LOADING_MODULE:
527 		sig_enforce = is_module_sig_enforced();
528 
529 		if (!sig_enforce && (ima_appraise & IMA_APPRAISE_MODULES)) {
530 			pr_err("impossible to appraise a module without a file descriptor. sig_enforce kernel parameter might help\n");
531 			return -EACCES;	/* INTEGRITY_UNKNOWN */
532 		}
533 	default:
534 		break;
535 	}
536 	return 0;
537 }
538 
539 static int __init init_ima(void)
540 {
541 	int error;
542 
543 	ima_init_template_list();
544 	hash_setup(CONFIG_IMA_DEFAULT_HASH);
545 	error = ima_init();
546 
547 	if (error && strcmp(hash_algo_name[ima_hash_algo],
548 			    CONFIG_IMA_DEFAULT_HASH) != 0) {
549 		pr_info("Allocating %s failed, going to use default hash algorithm %s\n",
550 			hash_algo_name[ima_hash_algo], CONFIG_IMA_DEFAULT_HASH);
551 		hash_setup_done = 0;
552 		hash_setup(CONFIG_IMA_DEFAULT_HASH);
553 		error = ima_init();
554 	}
555 
556 	if (!error)
557 		ima_update_policy_flag();
558 
559 	return error;
560 }
561 
562 late_initcall(init_ima);	/* Start IMA after the TPM is available */
563 
564 MODULE_DESCRIPTION("Integrity Measurement Architecture");
565 MODULE_LICENSE("GPL");
566