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Linux/security/integrity/evm/evm_main.c

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  1 /*
  2  * Copyright (C) 2005-2010 IBM Corporation
  3  *
  4  * Author:
  5  * Mimi Zohar <zohar@us.ibm.com>
  6  * Kylene Hall <kjhall@us.ibm.com>
  7  *
  8  * This program is free software; you can redistribute it and/or modify
  9  * it under the terms of the GNU General Public License as published by
 10  * the Free Software Foundation, version 2 of the License.
 11  *
 12  * File: evm_main.c
 13  *      implements evm_inode_setxattr, evm_inode_post_setxattr,
 14  *      evm_inode_removexattr, and evm_verifyxattr
 15  */
 16 
 17 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
 18 
 19 #include <linux/module.h>
 20 #include <linux/crypto.h>
 21 #include <linux/audit.h>
 22 #include <linux/xattr.h>
 23 #include <linux/integrity.h>
 24 #include <linux/evm.h>
 25 #include <crypto/hash.h>
 26 #include <crypto/algapi.h>
 27 #include "evm.h"
 28 
 29 int evm_initialized;
 30 
 31 static char *integrity_status_msg[] = {
 32         "pass", "fail", "no_label", "no_xattrs", "unknown"
 33 };
 34 char *evm_hmac = "hmac(sha1)";
 35 char *evm_hash = "sha1";
 36 int evm_hmac_attrs;
 37 
 38 char *evm_config_xattrnames[] = {
 39 #ifdef CONFIG_SECURITY_SELINUX
 40         XATTR_NAME_SELINUX,
 41 #endif
 42 #ifdef CONFIG_SECURITY_SMACK
 43         XATTR_NAME_SMACK,
 44 #ifdef CONFIG_EVM_EXTRA_SMACK_XATTRS
 45         XATTR_NAME_SMACKEXEC,
 46         XATTR_NAME_SMACKTRANSMUTE,
 47         XATTR_NAME_SMACKMMAP,
 48 #endif
 49 #endif
 50 #ifdef CONFIG_IMA_APPRAISE
 51         XATTR_NAME_IMA,
 52 #endif
 53         XATTR_NAME_CAPS,
 54         NULL
 55 };
 56 
 57 static int evm_fixmode;
 58 static int __init evm_set_fixmode(char *str)
 59 {
 60         if (strncmp(str, "fix", 3) == 0)
 61                 evm_fixmode = 1;
 62         return 0;
 63 }
 64 __setup("evm=", evm_set_fixmode);
 65 
 66 static void __init evm_init_config(void)
 67 {
 68 #ifdef CONFIG_EVM_ATTR_FSUUID
 69         evm_hmac_attrs |= EVM_ATTR_FSUUID;
 70 #endif
 71         pr_info("HMAC attrs: 0x%x\n", evm_hmac_attrs);
 72 }
 73 
 74 static int evm_find_protected_xattrs(struct dentry *dentry)
 75 {
 76         struct inode *inode = d_backing_inode(dentry);
 77         char **xattr;
 78         int error;
 79         int count = 0;
 80 
 81         if (!inode->i_op->getxattr)
 82                 return -EOPNOTSUPP;
 83 
 84         for (xattr = evm_config_xattrnames; *xattr != NULL; xattr++) {
 85                 error = inode->i_op->getxattr(dentry, inode, *xattr, NULL, 0);
 86                 if (error < 0) {
 87                         if (error == -ENODATA)
 88                                 continue;
 89                         return error;
 90                 }
 91                 count++;
 92         }
 93 
 94         return count;
 95 }
 96 
 97 /*
 98  * evm_verify_hmac - calculate and compare the HMAC with the EVM xattr
 99  *
100  * Compute the HMAC on the dentry's protected set of extended attributes
101  * and compare it against the stored security.evm xattr.
102  *
103  * For performance:
104  * - use the previoulsy retrieved xattr value and length to calculate the
105  *   HMAC.)
106  * - cache the verification result in the iint, when available.
107  *
108  * Returns integrity status
109  */
110 static enum integrity_status evm_verify_hmac(struct dentry *dentry,
111                                              const char *xattr_name,
112                                              char *xattr_value,
113                                              size_t xattr_value_len,
114                                              struct integrity_iint_cache *iint)
115 {
116         struct evm_ima_xattr_data *xattr_data = NULL;
117         struct evm_ima_xattr_data calc;
118         enum integrity_status evm_status = INTEGRITY_PASS;
119         int rc, xattr_len;
120 
121         if (iint && iint->evm_status == INTEGRITY_PASS)
122                 return iint->evm_status;
123 
124         /* if status is not PASS, try to check again - against -ENOMEM */
125 
126         /* first need to know the sig type */
127         rc = vfs_getxattr_alloc(dentry, XATTR_NAME_EVM, (char **)&xattr_data, 0,
128                                 GFP_NOFS);
129         if (rc <= 0) {
130                 evm_status = INTEGRITY_FAIL;
131                 if (rc == -ENODATA) {
132                         rc = evm_find_protected_xattrs(dentry);
133                         if (rc > 0)
134                                 evm_status = INTEGRITY_NOLABEL;
135                         else if (rc == 0)
136                                 evm_status = INTEGRITY_NOXATTRS; /* new file */
137                 } else if (rc == -EOPNOTSUPP) {
138                         evm_status = INTEGRITY_UNKNOWN;
139                 }
140                 goto out;
141         }
142 
143         xattr_len = rc;
144 
145         /* check value type */
146         switch (xattr_data->type) {
147         case EVM_XATTR_HMAC:
148                 rc = evm_calc_hmac(dentry, xattr_name, xattr_value,
149                                    xattr_value_len, calc.digest);
150                 if (rc)
151                         break;
152                 rc = crypto_memneq(xattr_data->digest, calc.digest,
153                             sizeof(calc.digest));
154                 if (rc)
155                         rc = -EINVAL;
156                 break;
157         case EVM_IMA_XATTR_DIGSIG:
158                 rc = evm_calc_hash(dentry, xattr_name, xattr_value,
159                                 xattr_value_len, calc.digest);
160                 if (rc)
161                         break;
162                 rc = integrity_digsig_verify(INTEGRITY_KEYRING_EVM,
163                                         (const char *)xattr_data, xattr_len,
164                                         calc.digest, sizeof(calc.digest));
165                 if (!rc) {
166                         /* Replace RSA with HMAC if not mounted readonly and
167                          * not immutable
168                          */
169                         if (!IS_RDONLY(d_backing_inode(dentry)) &&
170                             !IS_IMMUTABLE(d_backing_inode(dentry)))
171                                 evm_update_evmxattr(dentry, xattr_name,
172                                                     xattr_value,
173                                                     xattr_value_len);
174                 }
175                 break;
176         default:
177                 rc = -EINVAL;
178                 break;
179         }
180 
181         if (rc)
182                 evm_status = (rc == -ENODATA) ?
183                                 INTEGRITY_NOXATTRS : INTEGRITY_FAIL;
184 out:
185         if (iint)
186                 iint->evm_status = evm_status;
187         kfree(xattr_data);
188         return evm_status;
189 }
190 
191 static int evm_protected_xattr(const char *req_xattr_name)
192 {
193         char **xattrname;
194         int namelen;
195         int found = 0;
196 
197         namelen = strlen(req_xattr_name);
198         for (xattrname = evm_config_xattrnames; *xattrname != NULL; xattrname++) {
199                 if ((strlen(*xattrname) == namelen)
200                     && (strncmp(req_xattr_name, *xattrname, namelen) == 0)) {
201                         found = 1;
202                         break;
203                 }
204                 if (strncmp(req_xattr_name,
205                             *xattrname + XATTR_SECURITY_PREFIX_LEN,
206                             strlen(req_xattr_name)) == 0) {
207                         found = 1;
208                         break;
209                 }
210         }
211         return found;
212 }
213 
214 /**
215  * evm_verifyxattr - verify the integrity of the requested xattr
216  * @dentry: object of the verify xattr
217  * @xattr_name: requested xattr
218  * @xattr_value: requested xattr value
219  * @xattr_value_len: requested xattr value length
220  *
221  * Calculate the HMAC for the given dentry and verify it against the stored
222  * security.evm xattr. For performance, use the xattr value and length
223  * previously retrieved to calculate the HMAC.
224  *
225  * Returns the xattr integrity status.
226  *
227  * This function requires the caller to lock the inode's i_mutex before it
228  * is executed.
229  */
230 enum integrity_status evm_verifyxattr(struct dentry *dentry,
231                                       const char *xattr_name,
232                                       void *xattr_value, size_t xattr_value_len,
233                                       struct integrity_iint_cache *iint)
234 {
235         if (!evm_initialized || !evm_protected_xattr(xattr_name))
236                 return INTEGRITY_UNKNOWN;
237 
238         if (!iint) {
239                 iint = integrity_iint_find(d_backing_inode(dentry));
240                 if (!iint)
241                         return INTEGRITY_UNKNOWN;
242         }
243         return evm_verify_hmac(dentry, xattr_name, xattr_value,
244                                  xattr_value_len, iint);
245 }
246 EXPORT_SYMBOL_GPL(evm_verifyxattr);
247 
248 /*
249  * evm_verify_current_integrity - verify the dentry's metadata integrity
250  * @dentry: pointer to the affected dentry
251  *
252  * Verify and return the dentry's metadata integrity. The exceptions are
253  * before EVM is initialized or in 'fix' mode.
254  */
255 static enum integrity_status evm_verify_current_integrity(struct dentry *dentry)
256 {
257         struct inode *inode = d_backing_inode(dentry);
258 
259         if (!evm_initialized || !S_ISREG(inode->i_mode) || evm_fixmode)
260                 return 0;
261         return evm_verify_hmac(dentry, NULL, NULL, 0, NULL);
262 }
263 
264 /*
265  * evm_protect_xattr - protect the EVM extended attribute
266  *
267  * Prevent security.evm from being modified or removed without the
268  * necessary permissions or when the existing value is invalid.
269  *
270  * The posix xattr acls are 'system' prefixed, which normally would not
271  * affect security.evm.  An interesting side affect of writing posix xattr
272  * acls is their modifying of the i_mode, which is included in security.evm.
273  * For posix xattr acls only, permit security.evm, even if it currently
274  * doesn't exist, to be updated.
275  */
276 static int evm_protect_xattr(struct dentry *dentry, const char *xattr_name,
277                              const void *xattr_value, size_t xattr_value_len)
278 {
279         enum integrity_status evm_status;
280 
281         if (strcmp(xattr_name, XATTR_NAME_EVM) == 0) {
282                 if (!capable(CAP_SYS_ADMIN))
283                         return -EPERM;
284         } else if (!evm_protected_xattr(xattr_name)) {
285                 if (!posix_xattr_acl(xattr_name))
286                         return 0;
287                 evm_status = evm_verify_current_integrity(dentry);
288                 if ((evm_status == INTEGRITY_PASS) ||
289                     (evm_status == INTEGRITY_NOXATTRS))
290                         return 0;
291                 goto out;
292         }
293         evm_status = evm_verify_current_integrity(dentry);
294         if (evm_status == INTEGRITY_NOXATTRS) {
295                 struct integrity_iint_cache *iint;
296 
297                 iint = integrity_iint_find(d_backing_inode(dentry));
298                 if (iint && (iint->flags & IMA_NEW_FILE))
299                         return 0;
300 
301                 /* exception for pseudo filesystems */
302                 if (dentry->d_sb->s_magic == TMPFS_MAGIC
303                     || dentry->d_sb->s_magic == SYSFS_MAGIC)
304                         return 0;
305 
306                 integrity_audit_msg(AUDIT_INTEGRITY_METADATA,
307                                     dentry->d_inode, dentry->d_name.name,
308                                     "update_metadata",
309                                     integrity_status_msg[evm_status],
310                                     -EPERM, 0);
311         }
312 out:
313         if (evm_status != INTEGRITY_PASS)
314                 integrity_audit_msg(AUDIT_INTEGRITY_METADATA, d_backing_inode(dentry),
315                                     dentry->d_name.name, "appraise_metadata",
316                                     integrity_status_msg[evm_status],
317                                     -EPERM, 0);
318         return evm_status == INTEGRITY_PASS ? 0 : -EPERM;
319 }
320 
321 /**
322  * evm_inode_setxattr - protect the EVM extended attribute
323  * @dentry: pointer to the affected dentry
324  * @xattr_name: pointer to the affected extended attribute name
325  * @xattr_value: pointer to the new extended attribute value
326  * @xattr_value_len: pointer to the new extended attribute value length
327  *
328  * Before allowing the 'security.evm' protected xattr to be updated,
329  * verify the existing value is valid.  As only the kernel should have
330  * access to the EVM encrypted key needed to calculate the HMAC, prevent
331  * userspace from writing HMAC value.  Writing 'security.evm' requires
332  * requires CAP_SYS_ADMIN privileges.
333  */
334 int evm_inode_setxattr(struct dentry *dentry, const char *xattr_name,
335                        const void *xattr_value, size_t xattr_value_len)
336 {
337         const struct evm_ima_xattr_data *xattr_data = xattr_value;
338 
339         if (strcmp(xattr_name, XATTR_NAME_EVM) == 0) {
340                 if (!xattr_value_len)
341                         return -EINVAL;
342                 if (xattr_data->type != EVM_IMA_XATTR_DIGSIG)
343                         return -EPERM;
344         }
345         return evm_protect_xattr(dentry, xattr_name, xattr_value,
346                                  xattr_value_len);
347 }
348 
349 /**
350  * evm_inode_removexattr - protect the EVM extended attribute
351  * @dentry: pointer to the affected dentry
352  * @xattr_name: pointer to the affected extended attribute name
353  *
354  * Removing 'security.evm' requires CAP_SYS_ADMIN privileges and that
355  * the current value is valid.
356  */
357 int evm_inode_removexattr(struct dentry *dentry, const char *xattr_name)
358 {
359         return evm_protect_xattr(dentry, xattr_name, NULL, 0);
360 }
361 
362 static void evm_reset_status(struct inode *inode)
363 {
364         struct integrity_iint_cache *iint;
365 
366         iint = integrity_iint_find(inode);
367         if (iint)
368                 iint->evm_status = INTEGRITY_UNKNOWN;
369 }
370 
371 /**
372  * evm_inode_post_setxattr - update 'security.evm' to reflect the changes
373  * @dentry: pointer to the affected dentry
374  * @xattr_name: pointer to the affected extended attribute name
375  * @xattr_value: pointer to the new extended attribute value
376  * @xattr_value_len: pointer to the new extended attribute value length
377  *
378  * Update the HMAC stored in 'security.evm' to reflect the change.
379  *
380  * No need to take the i_mutex lock here, as this function is called from
381  * __vfs_setxattr_noperm().  The caller of which has taken the inode's
382  * i_mutex lock.
383  */
384 void evm_inode_post_setxattr(struct dentry *dentry, const char *xattr_name,
385                              const void *xattr_value, size_t xattr_value_len)
386 {
387         if (!evm_initialized || (!evm_protected_xattr(xattr_name)
388                                  && !posix_xattr_acl(xattr_name)))
389                 return;
390 
391         evm_reset_status(dentry->d_inode);
392 
393         evm_update_evmxattr(dentry, xattr_name, xattr_value, xattr_value_len);
394 }
395 
396 /**
397  * evm_inode_post_removexattr - update 'security.evm' after removing the xattr
398  * @dentry: pointer to the affected dentry
399  * @xattr_name: pointer to the affected extended attribute name
400  *
401  * Update the HMAC stored in 'security.evm' to reflect removal of the xattr.
402  *
403  * No need to take the i_mutex lock here, as this function is called from
404  * vfs_removexattr() which takes the i_mutex.
405  */
406 void evm_inode_post_removexattr(struct dentry *dentry, const char *xattr_name)
407 {
408         if (!evm_initialized || !evm_protected_xattr(xattr_name))
409                 return;
410 
411         evm_reset_status(dentry->d_inode);
412 
413         evm_update_evmxattr(dentry, xattr_name, NULL, 0);
414 }
415 
416 /**
417  * evm_inode_setattr - prevent updating an invalid EVM extended attribute
418  * @dentry: pointer to the affected dentry
419  */
420 int evm_inode_setattr(struct dentry *dentry, struct iattr *attr)
421 {
422         unsigned int ia_valid = attr->ia_valid;
423         enum integrity_status evm_status;
424 
425         if (!(ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID)))
426                 return 0;
427         evm_status = evm_verify_current_integrity(dentry);
428         if ((evm_status == INTEGRITY_PASS) ||
429             (evm_status == INTEGRITY_NOXATTRS))
430                 return 0;
431         integrity_audit_msg(AUDIT_INTEGRITY_METADATA, d_backing_inode(dentry),
432                             dentry->d_name.name, "appraise_metadata",
433                             integrity_status_msg[evm_status], -EPERM, 0);
434         return -EPERM;
435 }
436 
437 /**
438  * evm_inode_post_setattr - update 'security.evm' after modifying metadata
439  * @dentry: pointer to the affected dentry
440  * @ia_valid: for the UID and GID status
441  *
442  * For now, update the HMAC stored in 'security.evm' to reflect UID/GID
443  * changes.
444  *
445  * This function is called from notify_change(), which expects the caller
446  * to lock the inode's i_mutex.
447  */
448 void evm_inode_post_setattr(struct dentry *dentry, int ia_valid)
449 {
450         if (!evm_initialized)
451                 return;
452 
453         if (ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID))
454                 evm_update_evmxattr(dentry, NULL, NULL, 0);
455 }
456 
457 /*
458  * evm_inode_init_security - initializes security.evm
459  */
460 int evm_inode_init_security(struct inode *inode,
461                                  const struct xattr *lsm_xattr,
462                                  struct xattr *evm_xattr)
463 {
464         struct evm_ima_xattr_data *xattr_data;
465         int rc;
466 
467         if (!evm_initialized || !evm_protected_xattr(lsm_xattr->name))
468                 return 0;
469 
470         xattr_data = kzalloc(sizeof(*xattr_data), GFP_NOFS);
471         if (!xattr_data)
472                 return -ENOMEM;
473 
474         xattr_data->type = EVM_XATTR_HMAC;
475         rc = evm_init_hmac(inode, lsm_xattr, xattr_data->digest);
476         if (rc < 0)
477                 goto out;
478 
479         evm_xattr->value = xattr_data;
480         evm_xattr->value_len = sizeof(*xattr_data);
481         evm_xattr->name = XATTR_EVM_SUFFIX;
482         return 0;
483 out:
484         kfree(xattr_data);
485         return rc;
486 }
487 EXPORT_SYMBOL_GPL(evm_inode_init_security);
488 
489 #ifdef CONFIG_EVM_LOAD_X509
490 void __init evm_load_x509(void)
491 {
492         int rc;
493 
494         rc = integrity_load_x509(INTEGRITY_KEYRING_EVM, CONFIG_EVM_X509_PATH);
495         if (!rc)
496                 evm_initialized |= EVM_INIT_X509;
497 }
498 #endif
499 
500 static int __init init_evm(void)
501 {
502         int error;
503 
504         evm_init_config();
505 
506         error = integrity_init_keyring(INTEGRITY_KEYRING_EVM);
507         if (error)
508                 return error;
509 
510         error = evm_init_secfs();
511         if (error < 0) {
512                 pr_info("Error registering secfs\n");
513                 return error;
514         }
515 
516         return 0;
517 }
518 
519 /*
520  * evm_display_config - list the EVM protected security extended attributes
521  */
522 static int __init evm_display_config(void)
523 {
524         char **xattrname;
525 
526         for (xattrname = evm_config_xattrnames; *xattrname != NULL; xattrname++)
527                 pr_info("%s\n", *xattrname);
528         return 0;
529 }
530 
531 pure_initcall(evm_display_config);
532 late_initcall(init_evm);
533 
534 MODULE_DESCRIPTION("Extended Verification Module");
535 MODULE_LICENSE("GPL");
536 

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