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Linux/security/integrity/ima/ima_main.c

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

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