Merge tag 'for-linus-5.8b-rc5-tag' of git://git.kernel.org/pub/scm/linux/kernel/git...
[linux-2.6-microblaze.git] / security / integrity / evm / evm_main.c
1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3  * Copyright (C) 2005-2010 IBM Corporation
4  *
5  * Author:
6  * Mimi Zohar <zohar@us.ibm.com>
7  * Kylene Hall <kjhall@us.ibm.com>
8  *
9  * File: evm_main.c
10  *      implements evm_inode_setxattr, evm_inode_post_setxattr,
11  *      evm_inode_removexattr, and evm_verifyxattr
12  */
13
14 #include <linux/init.h>
15 #include <linux/crypto.h>
16 #include <linux/audit.h>
17 #include <linux/xattr.h>
18 #include <linux/integrity.h>
19 #include <linux/evm.h>
20 #include <linux/magic.h>
21
22 #include <crypto/hash.h>
23 #include <crypto/hash_info.h>
24 #include <crypto/algapi.h>
25 #include "evm.h"
26
27 int evm_initialized;
28
29 static const char * const integrity_status_msg[] = {
30         "pass", "pass_immutable", "fail", "no_label", "no_xattrs", "unknown"
31 };
32 int evm_hmac_attrs;
33
34 static struct xattr_list evm_config_default_xattrnames[] = {
35 #ifdef CONFIG_SECURITY_SELINUX
36         {.name = XATTR_NAME_SELINUX},
37 #endif
38 #ifdef CONFIG_SECURITY_SMACK
39         {.name = XATTR_NAME_SMACK},
40 #ifdef CONFIG_EVM_EXTRA_SMACK_XATTRS
41         {.name = XATTR_NAME_SMACKEXEC},
42         {.name = XATTR_NAME_SMACKTRANSMUTE},
43         {.name = XATTR_NAME_SMACKMMAP},
44 #endif
45 #endif
46 #ifdef CONFIG_SECURITY_APPARMOR
47         {.name = XATTR_NAME_APPARMOR},
48 #endif
49 #ifdef CONFIG_IMA_APPRAISE
50         {.name = XATTR_NAME_IMA},
51 #endif
52         {.name = XATTR_NAME_CAPS},
53 };
54
55 LIST_HEAD(evm_config_xattrnames);
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         int i, xattrs;
69
70         xattrs = ARRAY_SIZE(evm_config_default_xattrnames);
71
72         pr_info("Initialising EVM extended attributes:\n");
73         for (i = 0; i < xattrs; i++) {
74                 pr_info("%s\n", evm_config_default_xattrnames[i].name);
75                 list_add_tail(&evm_config_default_xattrnames[i].list,
76                               &evm_config_xattrnames);
77         }
78
79 #ifdef CONFIG_EVM_ATTR_FSUUID
80         evm_hmac_attrs |= EVM_ATTR_FSUUID;
81 #endif
82         pr_info("HMAC attrs: 0x%x\n", evm_hmac_attrs);
83 }
84
85 static bool evm_key_loaded(void)
86 {
87         return (bool)(evm_initialized & EVM_KEY_MASK);
88 }
89
90 static int evm_find_protected_xattrs(struct dentry *dentry)
91 {
92         struct inode *inode = d_backing_inode(dentry);
93         struct xattr_list *xattr;
94         int error;
95         int count = 0;
96
97         if (!(inode->i_opflags & IOP_XATTR))
98                 return -EOPNOTSUPP;
99
100         list_for_each_entry_lockless(xattr, &evm_config_xattrnames, list) {
101                 error = __vfs_getxattr(dentry, inode, xattr->name, NULL, 0);
102                 if (error < 0) {
103                         if (error == -ENODATA)
104                                 continue;
105                         return error;
106                 }
107                 count++;
108         }
109
110         return count;
111 }
112
113 /*
114  * evm_verify_hmac - calculate and compare the HMAC with the EVM xattr
115  *
116  * Compute the HMAC on the dentry's protected set of extended attributes
117  * and compare it against the stored security.evm xattr.
118  *
119  * For performance:
120  * - use the previoulsy retrieved xattr value and length to calculate the
121  *   HMAC.)
122  * - cache the verification result in the iint, when available.
123  *
124  * Returns integrity status
125  */
126 static enum integrity_status evm_verify_hmac(struct dentry *dentry,
127                                              const char *xattr_name,
128                                              char *xattr_value,
129                                              size_t xattr_value_len,
130                                              struct integrity_iint_cache *iint)
131 {
132         struct evm_ima_xattr_data *xattr_data = NULL;
133         struct signature_v2_hdr *hdr;
134         enum integrity_status evm_status = INTEGRITY_PASS;
135         struct evm_digest digest;
136         struct inode *inode;
137         int rc, xattr_len;
138
139         if (iint && (iint->evm_status == INTEGRITY_PASS ||
140                      iint->evm_status == INTEGRITY_PASS_IMMUTABLE))
141                 return iint->evm_status;
142
143         /* if status is not PASS, try to check again - against -ENOMEM */
144
145         /* first need to know the sig type */
146         rc = vfs_getxattr_alloc(dentry, XATTR_NAME_EVM, (char **)&xattr_data, 0,
147                                 GFP_NOFS);
148         if (rc <= 0) {
149                 evm_status = INTEGRITY_FAIL;
150                 if (rc == -ENODATA) {
151                         rc = evm_find_protected_xattrs(dentry);
152                         if (rc > 0)
153                                 evm_status = INTEGRITY_NOLABEL;
154                         else if (rc == 0)
155                                 evm_status = INTEGRITY_NOXATTRS; /* new file */
156                 } else if (rc == -EOPNOTSUPP) {
157                         evm_status = INTEGRITY_UNKNOWN;
158                 }
159                 goto out;
160         }
161
162         xattr_len = rc;
163
164         /* check value type */
165         switch (xattr_data->type) {
166         case EVM_XATTR_HMAC:
167                 if (xattr_len != sizeof(struct evm_xattr)) {
168                         evm_status = INTEGRITY_FAIL;
169                         goto out;
170                 }
171
172                 digest.hdr.algo = HASH_ALGO_SHA1;
173                 rc = evm_calc_hmac(dentry, xattr_name, xattr_value,
174                                    xattr_value_len, &digest);
175                 if (rc)
176                         break;
177                 rc = crypto_memneq(xattr_data->data, digest.digest,
178                                    SHA1_DIGEST_SIZE);
179                 if (rc)
180                         rc = -EINVAL;
181                 break;
182         case EVM_IMA_XATTR_DIGSIG:
183         case EVM_XATTR_PORTABLE_DIGSIG:
184                 hdr = (struct signature_v2_hdr *)xattr_data;
185                 digest.hdr.algo = hdr->hash_algo;
186                 rc = evm_calc_hash(dentry, xattr_name, xattr_value,
187                                    xattr_value_len, xattr_data->type, &digest);
188                 if (rc)
189                         break;
190                 rc = integrity_digsig_verify(INTEGRITY_KEYRING_EVM,
191                                         (const char *)xattr_data, xattr_len,
192                                         digest.digest, digest.hdr.length);
193                 if (!rc) {
194                         inode = d_backing_inode(dentry);
195
196                         if (xattr_data->type == EVM_XATTR_PORTABLE_DIGSIG) {
197                                 if (iint)
198                                         iint->flags |= EVM_IMMUTABLE_DIGSIG;
199                                 evm_status = INTEGRITY_PASS_IMMUTABLE;
200                         } else if (!IS_RDONLY(inode) &&
201                                    !(inode->i_sb->s_readonly_remount) &&
202                                    !IS_IMMUTABLE(inode)) {
203                                 evm_update_evmxattr(dentry, xattr_name,
204                                                     xattr_value,
205                                                     xattr_value_len);
206                         }
207                 }
208                 break;
209         default:
210                 rc = -EINVAL;
211                 break;
212         }
213
214         if (rc)
215                 evm_status = (rc == -ENODATA) ?
216                                 INTEGRITY_NOXATTRS : INTEGRITY_FAIL;
217 out:
218         if (iint)
219                 iint->evm_status = evm_status;
220         kfree(xattr_data);
221         return evm_status;
222 }
223
224 static int evm_protected_xattr(const char *req_xattr_name)
225 {
226         int namelen;
227         int found = 0;
228         struct xattr_list *xattr;
229
230         namelen = strlen(req_xattr_name);
231         list_for_each_entry_lockless(xattr, &evm_config_xattrnames, list) {
232                 if ((strlen(xattr->name) == namelen)
233                     && (strncmp(req_xattr_name, xattr->name, namelen) == 0)) {
234                         found = 1;
235                         break;
236                 }
237                 if (strncmp(req_xattr_name,
238                             xattr->name + XATTR_SECURITY_PREFIX_LEN,
239                             strlen(req_xattr_name)) == 0) {
240                         found = 1;
241                         break;
242                 }
243         }
244
245         return found;
246 }
247
248 /**
249  * evm_verifyxattr - verify the integrity of the requested xattr
250  * @dentry: object of the verify xattr
251  * @xattr_name: requested xattr
252  * @xattr_value: requested xattr value
253  * @xattr_value_len: requested xattr value length
254  *
255  * Calculate the HMAC for the given dentry and verify it against the stored
256  * security.evm xattr. For performance, use the xattr value and length
257  * previously retrieved to calculate the HMAC.
258  *
259  * Returns the xattr integrity status.
260  *
261  * This function requires the caller to lock the inode's i_mutex before it
262  * is executed.
263  */
264 enum integrity_status evm_verifyxattr(struct dentry *dentry,
265                                       const char *xattr_name,
266                                       void *xattr_value, size_t xattr_value_len,
267                                       struct integrity_iint_cache *iint)
268 {
269         if (!evm_key_loaded() || !evm_protected_xattr(xattr_name))
270                 return INTEGRITY_UNKNOWN;
271
272         if (!iint) {
273                 iint = integrity_iint_find(d_backing_inode(dentry));
274                 if (!iint)
275                         return INTEGRITY_UNKNOWN;
276         }
277         return evm_verify_hmac(dentry, xattr_name, xattr_value,
278                                  xattr_value_len, iint);
279 }
280 EXPORT_SYMBOL_GPL(evm_verifyxattr);
281
282 /*
283  * evm_verify_current_integrity - verify the dentry's metadata integrity
284  * @dentry: pointer to the affected dentry
285  *
286  * Verify and return the dentry's metadata integrity. The exceptions are
287  * before EVM is initialized or in 'fix' mode.
288  */
289 static enum integrity_status evm_verify_current_integrity(struct dentry *dentry)
290 {
291         struct inode *inode = d_backing_inode(dentry);
292
293         if (!evm_key_loaded() || !S_ISREG(inode->i_mode) || evm_fixmode)
294                 return 0;
295         return evm_verify_hmac(dentry, NULL, NULL, 0, NULL);
296 }
297
298 /*
299  * evm_protect_xattr - protect the EVM extended attribute
300  *
301  * Prevent security.evm from being modified or removed without the
302  * necessary permissions or when the existing value is invalid.
303  *
304  * The posix xattr acls are 'system' prefixed, which normally would not
305  * affect security.evm.  An interesting side affect of writing posix xattr
306  * acls is their modifying of the i_mode, which is included in security.evm.
307  * For posix xattr acls only, permit security.evm, even if it currently
308  * doesn't exist, to be updated unless the EVM signature is immutable.
309  */
310 static int evm_protect_xattr(struct dentry *dentry, const char *xattr_name,
311                              const void *xattr_value, size_t xattr_value_len)
312 {
313         enum integrity_status evm_status;
314
315         if (strcmp(xattr_name, XATTR_NAME_EVM) == 0) {
316                 if (!capable(CAP_SYS_ADMIN))
317                         return -EPERM;
318         } else if (!evm_protected_xattr(xattr_name)) {
319                 if (!posix_xattr_acl(xattr_name))
320                         return 0;
321                 evm_status = evm_verify_current_integrity(dentry);
322                 if ((evm_status == INTEGRITY_PASS) ||
323                     (evm_status == INTEGRITY_NOXATTRS))
324                         return 0;
325                 goto out;
326         }
327
328         evm_status = evm_verify_current_integrity(dentry);
329         if (evm_status == INTEGRITY_NOXATTRS) {
330                 struct integrity_iint_cache *iint;
331
332                 iint = integrity_iint_find(d_backing_inode(dentry));
333                 if (iint && (iint->flags & IMA_NEW_FILE))
334                         return 0;
335
336                 /* exception for pseudo filesystems */
337                 if (dentry->d_sb->s_magic == TMPFS_MAGIC
338                     || dentry->d_sb->s_magic == SYSFS_MAGIC)
339                         return 0;
340
341                 integrity_audit_msg(AUDIT_INTEGRITY_METADATA,
342                                     dentry->d_inode, dentry->d_name.name,
343                                     "update_metadata",
344                                     integrity_status_msg[evm_status],
345                                     -EPERM, 0);
346         }
347 out:
348         if (evm_status != INTEGRITY_PASS)
349                 integrity_audit_msg(AUDIT_INTEGRITY_METADATA, d_backing_inode(dentry),
350                                     dentry->d_name.name, "appraise_metadata",
351                                     integrity_status_msg[evm_status],
352                                     -EPERM, 0);
353         return evm_status == INTEGRITY_PASS ? 0 : -EPERM;
354 }
355
356 /**
357  * evm_inode_setxattr - protect the EVM extended attribute
358  * @dentry: pointer to the affected dentry
359  * @xattr_name: pointer to the affected extended attribute name
360  * @xattr_value: pointer to the new extended attribute value
361  * @xattr_value_len: pointer to the new extended attribute value length
362  *
363  * Before allowing the 'security.evm' protected xattr to be updated,
364  * verify the existing value is valid.  As only the kernel should have
365  * access to the EVM encrypted key needed to calculate the HMAC, prevent
366  * userspace from writing HMAC value.  Writing 'security.evm' requires
367  * requires CAP_SYS_ADMIN privileges.
368  */
369 int evm_inode_setxattr(struct dentry *dentry, const char *xattr_name,
370                        const void *xattr_value, size_t xattr_value_len)
371 {
372         const struct evm_ima_xattr_data *xattr_data = xattr_value;
373
374         /* Policy permits modification of the protected xattrs even though
375          * there's no HMAC key loaded
376          */
377         if (evm_initialized & EVM_ALLOW_METADATA_WRITES)
378                 return 0;
379
380         if (strcmp(xattr_name, XATTR_NAME_EVM) == 0) {
381                 if (!xattr_value_len)
382                         return -EINVAL;
383                 if (xattr_data->type != EVM_IMA_XATTR_DIGSIG &&
384                     xattr_data->type != EVM_XATTR_PORTABLE_DIGSIG)
385                         return -EPERM;
386         }
387         return evm_protect_xattr(dentry, xattr_name, xattr_value,
388                                  xattr_value_len);
389 }
390
391 /**
392  * evm_inode_removexattr - protect the EVM extended attribute
393  * @dentry: pointer to the affected dentry
394  * @xattr_name: pointer to the affected extended attribute name
395  *
396  * Removing 'security.evm' requires CAP_SYS_ADMIN privileges and that
397  * the current value is valid.
398  */
399 int evm_inode_removexattr(struct dentry *dentry, const char *xattr_name)
400 {
401         /* Policy permits modification of the protected xattrs even though
402          * there's no HMAC key loaded
403          */
404         if (evm_initialized & EVM_ALLOW_METADATA_WRITES)
405                 return 0;
406
407         return evm_protect_xattr(dentry, xattr_name, NULL, 0);
408 }
409
410 static void evm_reset_status(struct inode *inode)
411 {
412         struct integrity_iint_cache *iint;
413
414         iint = integrity_iint_find(inode);
415         if (iint)
416                 iint->evm_status = INTEGRITY_UNKNOWN;
417 }
418
419 /**
420  * evm_inode_post_setxattr - update 'security.evm' to reflect the changes
421  * @dentry: pointer to the affected dentry
422  * @xattr_name: pointer to the affected extended attribute name
423  * @xattr_value: pointer to the new extended attribute value
424  * @xattr_value_len: pointer to the new extended attribute value length
425  *
426  * Update the HMAC stored in 'security.evm' to reflect the change.
427  *
428  * No need to take the i_mutex lock here, as this function is called from
429  * __vfs_setxattr_noperm().  The caller of which has taken the inode's
430  * i_mutex lock.
431  */
432 void evm_inode_post_setxattr(struct dentry *dentry, const char *xattr_name,
433                              const void *xattr_value, size_t xattr_value_len)
434 {
435         if (!evm_key_loaded() || (!evm_protected_xattr(xattr_name)
436                                   && !posix_xattr_acl(xattr_name)))
437                 return;
438
439         evm_reset_status(dentry->d_inode);
440
441         evm_update_evmxattr(dentry, xattr_name, xattr_value, xattr_value_len);
442 }
443
444 /**
445  * evm_inode_post_removexattr - update 'security.evm' after removing the xattr
446  * @dentry: pointer to the affected dentry
447  * @xattr_name: pointer to the affected extended attribute name
448  *
449  * Update the HMAC stored in 'security.evm' to reflect removal of the xattr.
450  *
451  * No need to take the i_mutex lock here, as this function is called from
452  * vfs_removexattr() which takes the i_mutex.
453  */
454 void evm_inode_post_removexattr(struct dentry *dentry, const char *xattr_name)
455 {
456         if (!evm_key_loaded() || !evm_protected_xattr(xattr_name))
457                 return;
458
459         evm_reset_status(dentry->d_inode);
460
461         evm_update_evmxattr(dentry, xattr_name, NULL, 0);
462 }
463
464 /**
465  * evm_inode_setattr - prevent updating an invalid EVM extended attribute
466  * @dentry: pointer to the affected dentry
467  *
468  * Permit update of file attributes when files have a valid EVM signature,
469  * except in the case of them having an immutable portable signature.
470  */
471 int evm_inode_setattr(struct dentry *dentry, struct iattr *attr)
472 {
473         unsigned int ia_valid = attr->ia_valid;
474         enum integrity_status evm_status;
475
476         /* Policy permits modification of the protected attrs even though
477          * there's no HMAC key loaded
478          */
479         if (evm_initialized & EVM_ALLOW_METADATA_WRITES)
480                 return 0;
481
482         if (!(ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID)))
483                 return 0;
484         evm_status = evm_verify_current_integrity(dentry);
485         if ((evm_status == INTEGRITY_PASS) ||
486             (evm_status == INTEGRITY_NOXATTRS))
487                 return 0;
488         integrity_audit_msg(AUDIT_INTEGRITY_METADATA, d_backing_inode(dentry),
489                             dentry->d_name.name, "appraise_metadata",
490                             integrity_status_msg[evm_status], -EPERM, 0);
491         return -EPERM;
492 }
493
494 /**
495  * evm_inode_post_setattr - update 'security.evm' after modifying metadata
496  * @dentry: pointer to the affected dentry
497  * @ia_valid: for the UID and GID status
498  *
499  * For now, update the HMAC stored in 'security.evm' to reflect UID/GID
500  * changes.
501  *
502  * This function is called from notify_change(), which expects the caller
503  * to lock the inode's i_mutex.
504  */
505 void evm_inode_post_setattr(struct dentry *dentry, int ia_valid)
506 {
507         if (!evm_key_loaded())
508                 return;
509
510         if (ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID))
511                 evm_update_evmxattr(dentry, NULL, NULL, 0);
512 }
513
514 /*
515  * evm_inode_init_security - initializes security.evm
516  */
517 int evm_inode_init_security(struct inode *inode,
518                                  const struct xattr *lsm_xattr,
519                                  struct xattr *evm_xattr)
520 {
521         struct evm_xattr *xattr_data;
522         int rc;
523
524         if (!evm_key_loaded() || !evm_protected_xattr(lsm_xattr->name))
525                 return 0;
526
527         xattr_data = kzalloc(sizeof(*xattr_data), GFP_NOFS);
528         if (!xattr_data)
529                 return -ENOMEM;
530
531         xattr_data->data.type = EVM_XATTR_HMAC;
532         rc = evm_init_hmac(inode, lsm_xattr, xattr_data->digest);
533         if (rc < 0)
534                 goto out;
535
536         evm_xattr->value = xattr_data;
537         evm_xattr->value_len = sizeof(*xattr_data);
538         evm_xattr->name = XATTR_EVM_SUFFIX;
539         return 0;
540 out:
541         kfree(xattr_data);
542         return rc;
543 }
544 EXPORT_SYMBOL_GPL(evm_inode_init_security);
545
546 #ifdef CONFIG_EVM_LOAD_X509
547 void __init evm_load_x509(void)
548 {
549         int rc;
550
551         rc = integrity_load_x509(INTEGRITY_KEYRING_EVM, CONFIG_EVM_X509_PATH);
552         if (!rc)
553                 evm_initialized |= EVM_INIT_X509;
554 }
555 #endif
556
557 static int __init init_evm(void)
558 {
559         int error;
560         struct list_head *pos, *q;
561
562         evm_init_config();
563
564         error = integrity_init_keyring(INTEGRITY_KEYRING_EVM);
565         if (error)
566                 goto error;
567
568         error = evm_init_secfs();
569         if (error < 0) {
570                 pr_info("Error registering secfs\n");
571                 goto error;
572         }
573
574 error:
575         if (error != 0) {
576                 if (!list_empty(&evm_config_xattrnames)) {
577                         list_for_each_safe(pos, q, &evm_config_xattrnames)
578                                 list_del(pos);
579                 }
580         }
581
582         return error;
583 }
584
585 late_initcall(init_evm);