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TOMOYO Linux Cross Reference
Linux/security/integrity/ima/ima_appraise.c

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  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 

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