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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 #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 = dentry->d_inode;
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 = dentry->d_inode;
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 = dentry->d_inode;
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                 if (!xattr_value_len || (xvalue->type >= IMA_XATTR_LAST))
382                         return -EINVAL;
383                 ima_reset_appraise_flags(dentry->d_inode,
384                          (xvalue->type == EVM_IMA_XATTR_DIGSIG) ? 1 : 0);
385                 result = 0;
386         }
387         return result;
388 }
389 
390 int ima_inode_removexattr(struct dentry *dentry, const char *xattr_name)
391 {
392         int result;
393 
394         result = ima_protect_xattr(dentry, xattr_name, NULL, 0);
395         if (result == 1) {
396                 ima_reset_appraise_flags(dentry->d_inode, 0);
397                 result = 0;
398         }
399         return result;
400 }
401 

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