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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/init.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;
 44 }
 45 
 46 /*
 47  * ima_must_appraise - set appraise flag
 48  *
 49  * Return 1 to appraise or hash
 50  */
 51 int ima_must_appraise(struct inode *inode, int mask, enum ima_hooks func)
 52 {
 53         u32 secid;
 54 
 55         if (!ima_appraise)
 56                 return 0;
 57 
 58         security_task_getsecid(current, &secid);
 59         return ima_match_policy(inode, current_cred(), secid, func, mask,
 60                                 IMA_APPRAISE | IMA_HASH, NULL);
 61 }
 62 
 63 static int ima_fix_xattr(struct dentry *dentry,
 64                          struct integrity_iint_cache *iint)
 65 {
 66         int rc, offset;
 67         u8 algo = iint->ima_hash->algo;
 68 
 69         if (algo <= HASH_ALGO_SHA1) {
 70                 offset = 1;
 71                 iint->ima_hash->xattr.sha1.type = IMA_XATTR_DIGEST;
 72         } else {
 73                 offset = 0;
 74                 iint->ima_hash->xattr.ng.type = IMA_XATTR_DIGEST_NG;
 75                 iint->ima_hash->xattr.ng.algo = algo;
 76         }
 77         rc = __vfs_setxattr_noperm(dentry, XATTR_NAME_IMA,
 78                                    &iint->ima_hash->xattr.data[offset],
 79                                    (sizeof(iint->ima_hash->xattr) - offset) +
 80                                    iint->ima_hash->length, 0);
 81         return rc;
 82 }
 83 
 84 /* Return specific func appraised cached result */
 85 enum integrity_status ima_get_cache_status(struct integrity_iint_cache *iint,
 86                                            enum ima_hooks func)
 87 {
 88         switch (func) {
 89         case MMAP_CHECK:
 90                 return iint->ima_mmap_status;
 91         case BPRM_CHECK:
 92                 return iint->ima_bprm_status;
 93         case CREDS_CHECK:
 94                 return iint->ima_creds_status;
 95         case FILE_CHECK:
 96         case POST_SETATTR:
 97                 return iint->ima_file_status;
 98         case MODULE_CHECK ... MAX_CHECK - 1:
 99         default:
100                 return iint->ima_read_status;
101         }
102 }
103 
104 static void ima_set_cache_status(struct integrity_iint_cache *iint,
105                                  enum ima_hooks func,
106                                  enum integrity_status status)
107 {
108         switch (func) {
109         case MMAP_CHECK:
110                 iint->ima_mmap_status = status;
111                 break;
112         case BPRM_CHECK:
113                 iint->ima_bprm_status = status;
114                 break;
115         case CREDS_CHECK:
116                 iint->ima_creds_status = status;
117         case FILE_CHECK:
118         case POST_SETATTR:
119                 iint->ima_file_status = status;
120                 break;
121         case MODULE_CHECK ... MAX_CHECK - 1:
122         default:
123                 iint->ima_read_status = status;
124                 break;
125         }
126 }
127 
128 static void ima_cache_flags(struct integrity_iint_cache *iint,
129                              enum ima_hooks func)
130 {
131         switch (func) {
132         case MMAP_CHECK:
133                 iint->flags |= (IMA_MMAP_APPRAISED | IMA_APPRAISED);
134                 break;
135         case BPRM_CHECK:
136                 iint->flags |= (IMA_BPRM_APPRAISED | IMA_APPRAISED);
137                 break;
138         case CREDS_CHECK:
139                 iint->flags |= (IMA_CREDS_APPRAISED | IMA_APPRAISED);
140                 break;
141         case FILE_CHECK:
142         case POST_SETATTR:
143                 iint->flags |= (IMA_FILE_APPRAISED | IMA_APPRAISED);
144                 break;
145         case MODULE_CHECK ... MAX_CHECK - 1:
146         default:
147                 iint->flags |= (IMA_READ_APPRAISED | IMA_APPRAISED);
148                 break;
149         }
150 }
151 
152 enum hash_algo ima_get_hash_algo(struct evm_ima_xattr_data *xattr_value,
153                                  int xattr_len)
154 {
155         struct signature_v2_hdr *sig;
156         enum hash_algo ret;
157 
158         if (!xattr_value || xattr_len < 2)
159                 /* return default hash algo */
160                 return ima_hash_algo;
161 
162         switch (xattr_value->type) {
163         case EVM_IMA_XATTR_DIGSIG:
164                 sig = (typeof(sig))xattr_value;
165                 if (sig->version != 2 || xattr_len <= sizeof(*sig))
166                         return ima_hash_algo;
167                 return sig->hash_algo;
168                 break;
169         case IMA_XATTR_DIGEST_NG:
170                 ret = xattr_value->digest[0];
171                 if (ret < HASH_ALGO__LAST)
172                         return ret;
173                 break;
174         case IMA_XATTR_DIGEST:
175                 /* this is for backward compatibility */
176                 if (xattr_len == 21) {
177                         unsigned int zero = 0;
178                         if (!memcmp(&xattr_value->digest[16], &zero, 4))
179                                 return HASH_ALGO_MD5;
180                         else
181                                 return HASH_ALGO_SHA1;
182                 } else if (xattr_len == 17)
183                         return HASH_ALGO_MD5;
184                 break;
185         }
186 
187         /* return default hash algo */
188         return ima_hash_algo;
189 }
190 
191 int ima_read_xattr(struct dentry *dentry,
192                    struct evm_ima_xattr_data **xattr_value)
193 {
194         ssize_t ret;
195 
196         ret = vfs_getxattr_alloc(dentry, XATTR_NAME_IMA, (char **)xattr_value,
197                                  0, GFP_NOFS);
198         if (ret == -EOPNOTSUPP)
199                 ret = 0;
200         return ret;
201 }
202 
203 /*
204  * ima_appraise_measurement - appraise file measurement
205  *
206  * Call evm_verifyxattr() to verify the integrity of 'security.ima'.
207  * Assuming success, compare the xattr hash with the collected measurement.
208  *
209  * Return 0 on success, error code otherwise
210  */
211 int ima_appraise_measurement(enum ima_hooks func,
212                              struct integrity_iint_cache *iint,
213                              struct file *file, const unsigned char *filename,
214                              struct evm_ima_xattr_data *xattr_value,
215                              int xattr_len)
216 {
217         static const char op[] = "appraise_data";
218         const char *cause = "unknown";
219         struct dentry *dentry = file_dentry(file);
220         struct inode *inode = d_backing_inode(dentry);
221         enum integrity_status status = INTEGRITY_UNKNOWN;
222         int rc = xattr_len, hash_start = 0;
223 
224         if (!(inode->i_opflags & IOP_XATTR))
225                 return INTEGRITY_UNKNOWN;
226 
227         if (rc <= 0) {
228                 if (rc && rc != -ENODATA)
229                         goto out;
230 
231                 cause = iint->flags & IMA_DIGSIG_REQUIRED ?
232                                 "IMA-signature-required" : "missing-hash";
233                 status = INTEGRITY_NOLABEL;
234                 if (file->f_mode & FMODE_CREATED)
235                         iint->flags |= IMA_NEW_FILE;
236                 if ((iint->flags & IMA_NEW_FILE) &&
237                     (!(iint->flags & IMA_DIGSIG_REQUIRED) ||
238                      (inode->i_size == 0)))
239                         status = INTEGRITY_PASS;
240                 goto out;
241         }
242 
243         status = evm_verifyxattr(dentry, XATTR_NAME_IMA, xattr_value, rc, iint);
244         switch (status) {
245         case INTEGRITY_PASS:
246         case INTEGRITY_PASS_IMMUTABLE:
247         case INTEGRITY_UNKNOWN:
248                 break;
249         case INTEGRITY_NOXATTRS:        /* No EVM protected xattrs. */
250         case INTEGRITY_NOLABEL:         /* No security.evm xattr. */
251                 cause = "missing-HMAC";
252                 goto out;
253         case INTEGRITY_FAIL:            /* Invalid HMAC/signature. */
254                 cause = "invalid-HMAC";
255                 goto out;
256         default:
257                 WARN_ONCE(true, "Unexpected integrity status %d\n", status);
258         }
259 
260         switch (xattr_value->type) {
261         case IMA_XATTR_DIGEST_NG:
262                 /* first byte contains algorithm id */
263                 hash_start = 1;
264                 /* fall through */
265         case IMA_XATTR_DIGEST:
266                 if (iint->flags & IMA_DIGSIG_REQUIRED) {
267                         cause = "IMA-signature-required";
268                         status = INTEGRITY_FAIL;
269                         break;
270                 }
271                 clear_bit(IMA_DIGSIG, &iint->atomic_flags);
272                 if (xattr_len - sizeof(xattr_value->type) - hash_start >=
273                                 iint->ima_hash->length)
274                         /* xattr length may be longer. md5 hash in previous
275                            version occupied 20 bytes in xattr, instead of 16
276                          */
277                         rc = memcmp(&xattr_value->digest[hash_start],
278                                     iint->ima_hash->digest,
279                                     iint->ima_hash->length);
280                 else
281                         rc = -EINVAL;
282                 if (rc) {
283                         cause = "invalid-hash";
284                         status = INTEGRITY_FAIL;
285                         break;
286                 }
287                 status = INTEGRITY_PASS;
288                 break;
289         case EVM_IMA_XATTR_DIGSIG:
290                 set_bit(IMA_DIGSIG, &iint->atomic_flags);
291                 rc = integrity_digsig_verify(INTEGRITY_KEYRING_IMA,
292                                              (const char *)xattr_value,
293                                              xattr_len,
294                                              iint->ima_hash->digest,
295                                              iint->ima_hash->length);
296                 if (rc == -EOPNOTSUPP) {
297                         status = INTEGRITY_UNKNOWN;
298                         break;
299                 }
300                 if (IS_ENABLED(CONFIG_INTEGRITY_PLATFORM_KEYRING) && rc &&
301                     func == KEXEC_KERNEL_CHECK)
302                         rc = integrity_digsig_verify(INTEGRITY_KEYRING_PLATFORM,
303                                                      (const char *)xattr_value,
304                                                      xattr_len,
305                                                      iint->ima_hash->digest,
306                                                      iint->ima_hash->length);
307                 if (rc) {
308                         cause = "invalid-signature";
309                         status = INTEGRITY_FAIL;
310                 } else {
311                         status = INTEGRITY_PASS;
312                 }
313                 break;
314         default:
315                 status = INTEGRITY_UNKNOWN;
316                 cause = "unknown-ima-data";
317                 break;
318         }
319 
320 out:
321         /*
322          * File signatures on some filesystems can not be properly verified.
323          * When such filesystems are mounted by an untrusted mounter or on a
324          * system not willing to accept such a risk, fail the file signature
325          * verification.
326          */
327         if ((inode->i_sb->s_iflags & SB_I_IMA_UNVERIFIABLE_SIGNATURE) &&
328             ((inode->i_sb->s_iflags & SB_I_UNTRUSTED_MOUNTER) ||
329              (iint->flags & IMA_FAIL_UNVERIFIABLE_SIGS))) {
330                 status = INTEGRITY_FAIL;
331                 cause = "unverifiable-signature";
332                 integrity_audit_msg(AUDIT_INTEGRITY_DATA, inode, filename,
333                                     op, cause, rc, 0);
334         } else if (status != INTEGRITY_PASS) {
335                 /* Fix mode, but don't replace file signatures. */
336                 if ((ima_appraise & IMA_APPRAISE_FIX) &&
337                     (!xattr_value ||
338                      xattr_value->type != EVM_IMA_XATTR_DIGSIG)) {
339                         if (!ima_fix_xattr(dentry, iint))
340                                 status = INTEGRITY_PASS;
341                 }
342 
343                 /* Permit new files with file signatures, but without data. */
344                 if (inode->i_size == 0 && iint->flags & IMA_NEW_FILE &&
345                     xattr_value && xattr_value->type == EVM_IMA_XATTR_DIGSIG) {
346                         status = INTEGRITY_PASS;
347                 }
348 
349                 integrity_audit_msg(AUDIT_INTEGRITY_DATA, inode, filename,
350                                     op, cause, rc, 0);
351         } else {
352                 ima_cache_flags(iint, func);
353         }
354 
355         ima_set_cache_status(iint, func, status);
356         return status;
357 }
358 
359 /*
360  * ima_update_xattr - update 'security.ima' hash value
361  */
362 void ima_update_xattr(struct integrity_iint_cache *iint, struct file *file)
363 {
364         struct dentry *dentry = file_dentry(file);
365         int rc = 0;
366 
367         /* do not collect and update hash for digital signatures */
368         if (test_bit(IMA_DIGSIG, &iint->atomic_flags))
369                 return;
370 
371         if ((iint->ima_file_status != INTEGRITY_PASS) &&
372             !(iint->flags & IMA_HASH))
373                 return;
374 
375         rc = ima_collect_measurement(iint, file, NULL, 0, ima_hash_algo);
376         if (rc < 0)
377                 return;
378 
379         inode_lock(file_inode(file));
380         ima_fix_xattr(dentry, iint);
381         inode_unlock(file_inode(file));
382 }
383 
384 /**
385  * ima_inode_post_setattr - reflect file metadata changes
386  * @dentry: pointer to the affected dentry
387  *
388  * Changes to a dentry's metadata might result in needing to appraise.
389  *
390  * This function is called from notify_change(), which expects the caller
391  * to lock the inode's i_mutex.
392  */
393 void ima_inode_post_setattr(struct dentry *dentry)
394 {
395         struct inode *inode = d_backing_inode(dentry);
396         struct integrity_iint_cache *iint;
397         int action;
398 
399         if (!(ima_policy_flag & IMA_APPRAISE) || !S_ISREG(inode->i_mode)
400             || !(inode->i_opflags & IOP_XATTR))
401                 return;
402 
403         action = ima_must_appraise(inode, MAY_ACCESS, POST_SETATTR);
404         if (!action)
405                 __vfs_removexattr(dentry, XATTR_NAME_IMA);
406         iint = integrity_iint_find(inode);
407         if (iint) {
408                 set_bit(IMA_CHANGE_ATTR, &iint->atomic_flags);
409                 if (!action)
410                         clear_bit(IMA_UPDATE_XATTR, &iint->atomic_flags);
411         }
412 }
413 
414 /*
415  * ima_protect_xattr - protect 'security.ima'
416  *
417  * Ensure that not just anyone can modify or remove 'security.ima'.
418  */
419 static int ima_protect_xattr(struct dentry *dentry, const char *xattr_name,
420                              const void *xattr_value, size_t xattr_value_len)
421 {
422         if (strcmp(xattr_name, XATTR_NAME_IMA) == 0) {
423                 if (!capable(CAP_SYS_ADMIN))
424                         return -EPERM;
425                 return 1;
426         }
427         return 0;
428 }
429 
430 static void ima_reset_appraise_flags(struct inode *inode, int digsig)
431 {
432         struct integrity_iint_cache *iint;
433 
434         if (!(ima_policy_flag & IMA_APPRAISE) || !S_ISREG(inode->i_mode))
435                 return;
436 
437         iint = integrity_iint_find(inode);
438         if (!iint)
439                 return;
440         iint->measured_pcrs = 0;
441         set_bit(IMA_CHANGE_XATTR, &iint->atomic_flags);
442         if (digsig)
443                 set_bit(IMA_DIGSIG, &iint->atomic_flags);
444         else
445                 clear_bit(IMA_DIGSIG, &iint->atomic_flags);
446 }
447 
448 int ima_inode_setxattr(struct dentry *dentry, const char *xattr_name,
449                        const void *xattr_value, size_t xattr_value_len)
450 {
451         const struct evm_ima_xattr_data *xvalue = xattr_value;
452         int result;
453 
454         result = ima_protect_xattr(dentry, xattr_name, xattr_value,
455                                    xattr_value_len);
456         if (result == 1) {
457                 if (!xattr_value_len || (xvalue->type >= IMA_XATTR_LAST))
458                         return -EINVAL;
459                 ima_reset_appraise_flags(d_backing_inode(dentry),
460                         xvalue->type == EVM_IMA_XATTR_DIGSIG);
461                 result = 0;
462         }
463         return result;
464 }
465 
466 int ima_inode_removexattr(struct dentry *dentry, const char *xattr_name)
467 {
468         int result;
469 
470         result = ima_protect_xattr(dentry, xattr_name, NULL, 0);
471         if (result == 1) {
472                 ima_reset_appraise_flags(d_backing_inode(dentry), 0);
473                 result = 0;
474         }
475         return result;
476 }
477 

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