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#include <linux/module.h>
 18#include <linux/crypto.h>
 19#include <linux/xattr.h>
 20#include <linux/integrity.h>
 21#include <linux/evm.h>
 22#include <crypto/hash.h>
 23#include "evm.h"
 24
 25int evm_initialized;
 26
 27char *evm_hmac = "hmac(sha1)";
 28char *evm_hash = "sha1";
 29
 30char *evm_config_xattrnames[] = {
 31#ifdef CONFIG_SECURITY_SELINUX
 32	XATTR_NAME_SELINUX,
 33#endif
 34#ifdef CONFIG_SECURITY_SMACK
 35	XATTR_NAME_SMACK,
 36#endif
 37	XATTR_NAME_CAPS,
 38	NULL
 39};
 40
 41static int evm_fixmode;
 42static int __init evm_set_fixmode(char *str)
 43{
 44	if (strncmp(str, "fix", 3) == 0)
 45		evm_fixmode = 1;
 46	return 0;
 47}
 48__setup("evm=", evm_set_fixmode);
 49
 50static int evm_find_protected_xattrs(struct dentry *dentry)
 51{
 52	struct inode *inode = dentry->d_inode;
 53	char **xattr;
 54	int error;
 55	int count = 0;
 56
 57	if (!inode->i_op || !inode->i_op->getxattr)
 58		return -EOPNOTSUPP;
 59
 60	for (xattr = evm_config_xattrnames; *xattr != NULL; xattr++) {
 61		error = inode->i_op->getxattr(dentry, *xattr, NULL, 0);
 62		if (error < 0) {
 63			if (error == -ENODATA)
 64				continue;
 65			return error;
 66		}
 67		count++;
 68	}
 69
 70	return count;
 71}
 72
 73/*
 74 * evm_verify_hmac - calculate and compare the HMAC with the EVM xattr
 75 *
 76 * Compute the HMAC on the dentry's protected set of extended attributes
 77 * and compare it against the stored security.evm xattr.
 78 *
 79 * For performance:
 80 * - use the previoulsy retrieved xattr value and length to calculate the
 81 *   HMAC.)
 82 * - cache the verification result in the iint, when available.
 83 *
 84 * Returns integrity status
 85 */
 86static enum integrity_status evm_verify_hmac(struct dentry *dentry,
 87					     const char *xattr_name,
 88					     char *xattr_value,
 89					     size_t xattr_value_len,
 90					     struct integrity_iint_cache *iint)
 91{
 92	struct evm_ima_xattr_data *xattr_data = NULL;
 93	struct evm_ima_xattr_data calc;
 94	enum integrity_status evm_status = INTEGRITY_PASS;
 95	int rc, xattr_len;
 96
 97	if (iint && iint->evm_status == INTEGRITY_PASS)
 98		return iint->evm_status;
 99
100	/* if status is not PASS, try to check again - against -ENOMEM */
101
102	/* first need to know the sig type */
103	rc = vfs_getxattr_alloc(dentry, XATTR_NAME_EVM, (char **)&xattr_data, 0,
104				GFP_NOFS);
105	if (rc <= 0) {
106		if (rc == 0)
107			evm_status = INTEGRITY_FAIL; /* empty */
108		else if (rc == -ENODATA) {
109			rc = evm_find_protected_xattrs(dentry);
110			if (rc > 0)
111				evm_status = INTEGRITY_NOLABEL;
112			else if (rc == 0)
113				evm_status = INTEGRITY_NOXATTRS; /* new file */
114		}
115		goto out;
116	}
117
118	xattr_len = rc - 1;
119
120	/* check value type */
121	switch (xattr_data->type) {
122	case EVM_XATTR_HMAC:
123		rc = evm_calc_hmac(dentry, xattr_name, xattr_value,
124				   xattr_value_len, calc.digest);
125		if (rc)
126			break;
127		rc = memcmp(xattr_data->digest, calc.digest,
128			    sizeof(calc.digest));
129		if (rc)
130			rc = -EINVAL;
131		break;
132	case EVM_IMA_XATTR_DIGSIG:
133		rc = evm_calc_hash(dentry, xattr_name, xattr_value,
134				xattr_value_len, calc.digest);
135		if (rc)
136			break;
137		rc = integrity_digsig_verify(INTEGRITY_KEYRING_EVM,
138					xattr_data->digest, xattr_len,
139					calc.digest, sizeof(calc.digest));
140		if (!rc) {
141			/* we probably want to replace rsa with hmac here */
142			evm_update_evmxattr(dentry, xattr_name, xattr_value,
143				   xattr_value_len);
144		}
145		break;
146	default:
147		rc = -EINVAL;
148		break;
149	}
150
151	if (rc)
152		evm_status = (rc == -ENODATA) ?
153				INTEGRITY_NOXATTRS : INTEGRITY_FAIL;
154out:
155	if (iint)
156		iint->evm_status = evm_status;
157	kfree(xattr_data);
158	return evm_status;
159}
160
161static int evm_protected_xattr(const char *req_xattr_name)
162{
163	char **xattrname;
164	int namelen;
165	int found = 0;
166
167	namelen = strlen(req_xattr_name);
168	for (xattrname = evm_config_xattrnames; *xattrname != NULL; xattrname++) {
169		if ((strlen(*xattrname) == namelen)
170		    && (strncmp(req_xattr_name, *xattrname, namelen) == 0)) {
171			found = 1;
172			break;
173		}
174		if (strncmp(req_xattr_name,
175			    *xattrname + XATTR_SECURITY_PREFIX_LEN,
176			    strlen(req_xattr_name)) == 0) {
177			found = 1;
178			break;
179		}
180	}
181	return found;
182}
183
184/**
185 * evm_verifyxattr - verify the integrity of the requested xattr
186 * @dentry: object of the verify xattr
187 * @xattr_name: requested xattr
188 * @xattr_value: requested xattr value
189 * @xattr_value_len: requested xattr value length
190 *
191 * Calculate the HMAC for the given dentry and verify it against the stored
192 * security.evm xattr. For performance, use the xattr value and length
193 * previously retrieved to calculate the HMAC.
194 *
195 * Returns the xattr integrity status.
196 *
197 * This function requires the caller to lock the inode's i_mutex before it
198 * is executed.
199 */
200enum integrity_status evm_verifyxattr(struct dentry *dentry,
201				      const char *xattr_name,
202				      void *xattr_value, size_t xattr_value_len,
203				      struct integrity_iint_cache *iint)
204{
205	if (!evm_initialized || !evm_protected_xattr(xattr_name))
206		return INTEGRITY_UNKNOWN;
207
208	if (!iint) {
209		iint = integrity_iint_find(dentry->d_inode);
210		if (!iint)
211			return INTEGRITY_UNKNOWN;
212	}
213	return evm_verify_hmac(dentry, xattr_name, xattr_value,
214				 xattr_value_len, iint);
215}
216EXPORT_SYMBOL_GPL(evm_verifyxattr);
217
218/*
219 * evm_verify_current_integrity - verify the dentry's metadata integrity
220 * @dentry: pointer to the affected dentry
221 *
222 * Verify and return the dentry's metadata integrity. The exceptions are
223 * before EVM is initialized or in 'fix' mode.
224 */
225static enum integrity_status evm_verify_current_integrity(struct dentry *dentry)
226{
227	struct inode *inode = dentry->d_inode;
228
229	if (!evm_initialized || !S_ISREG(inode->i_mode) || evm_fixmode)
230		return 0;
231	return evm_verify_hmac(dentry, NULL, NULL, 0, NULL);
232}
233
234/*
235 * evm_protect_xattr - protect the EVM extended attribute
236 *
237 * Prevent security.evm from being modified or removed without the
238 * necessary permissions or when the existing value is invalid.
239 *
240 * The posix xattr acls are 'system' prefixed, which normally would not
241 * affect security.evm.  An interesting side affect of writing posix xattr
242 * acls is their modifying of the i_mode, which is included in security.evm.
243 * For posix xattr acls only, permit security.evm, even if it currently
244 * doesn't exist, to be updated.
245 */
246static int evm_protect_xattr(struct dentry *dentry, const char *xattr_name,
247			     const void *xattr_value, size_t xattr_value_len)
248{
249	enum integrity_status evm_status;
250
251	if (strcmp(xattr_name, XATTR_NAME_EVM) == 0) {
252		if (!capable(CAP_SYS_ADMIN))
253			return -EPERM;
254	} else if (!evm_protected_xattr(xattr_name)) {
255		if (!posix_xattr_acl(xattr_name))
256			return 0;
257		evm_status = evm_verify_current_integrity(dentry);
258		if ((evm_status == INTEGRITY_PASS) ||
259		    (evm_status == INTEGRITY_NOXATTRS))
260			return 0;
261		return -EPERM;
262	}
263	evm_status = evm_verify_current_integrity(dentry);
264	return evm_status == INTEGRITY_PASS ? 0 : -EPERM;
265}
266
267/**
268 * evm_inode_setxattr - protect the EVM extended attribute
269 * @dentry: pointer to the affected dentry
270 * @xattr_name: pointer to the affected extended attribute name
271 * @xattr_value: pointer to the new extended attribute value
272 * @xattr_value_len: pointer to the new extended attribute value length
273 *
274 * Updating 'security.evm' requires CAP_SYS_ADMIN privileges and that
275 * the current value is valid.
276 */
277int evm_inode_setxattr(struct dentry *dentry, const char *xattr_name,
278		       const void *xattr_value, size_t xattr_value_len)
279{
280	return evm_protect_xattr(dentry, xattr_name, xattr_value,
281				 xattr_value_len);
282}
283
284/**
285 * evm_inode_removexattr - protect the EVM extended attribute
286 * @dentry: pointer to the affected dentry
287 * @xattr_name: pointer to the affected extended attribute name
288 *
289 * Removing 'security.evm' requires CAP_SYS_ADMIN privileges and that
290 * the current value is valid.
291 */
292int evm_inode_removexattr(struct dentry *dentry, const char *xattr_name)
293{
294	return evm_protect_xattr(dentry, xattr_name, NULL, 0);
295}
296
297/**
298 * evm_inode_post_setxattr - update 'security.evm' to reflect the changes
299 * @dentry: pointer to the affected dentry
300 * @xattr_name: pointer to the affected extended attribute name
301 * @xattr_value: pointer to the new extended attribute value
302 * @xattr_value_len: pointer to the new extended attribute value length
303 *
304 * Update the HMAC stored in 'security.evm' to reflect the change.
305 *
306 * No need to take the i_mutex lock here, as this function is called from
307 * __vfs_setxattr_noperm().  The caller of which has taken the inode's
308 * i_mutex lock.
309 */
310void evm_inode_post_setxattr(struct dentry *dentry, const char *xattr_name,
311			     const void *xattr_value, size_t xattr_value_len)
312{
313	if (!evm_initialized || (!evm_protected_xattr(xattr_name)
314				 && !posix_xattr_acl(xattr_name)))
315		return;
316
317	evm_update_evmxattr(dentry, xattr_name, xattr_value, xattr_value_len);
318	return;
319}
320
321/**
322 * evm_inode_post_removexattr - update 'security.evm' after removing the xattr
323 * @dentry: pointer to the affected dentry
324 * @xattr_name: pointer to the affected extended attribute name
325 *
326 * Update the HMAC stored in 'security.evm' to reflect removal of the xattr.
327 */
328void evm_inode_post_removexattr(struct dentry *dentry, const char *xattr_name)
329{
330	struct inode *inode = dentry->d_inode;
331
332	if (!evm_initialized || !evm_protected_xattr(xattr_name))
333		return;
334
335	mutex_lock(&inode->i_mutex);
336	evm_update_evmxattr(dentry, xattr_name, NULL, 0);
337	mutex_unlock(&inode->i_mutex);
338	return;
339}
340
341/**
342 * evm_inode_setattr - prevent updating an invalid EVM extended attribute
343 * @dentry: pointer to the affected dentry
344 */
345int evm_inode_setattr(struct dentry *dentry, struct iattr *attr)
346{
347	unsigned int ia_valid = attr->ia_valid;
348	enum integrity_status evm_status;
349
350	if (!(ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID)))
351		return 0;
352	evm_status = evm_verify_current_integrity(dentry);
353	if ((evm_status == INTEGRITY_PASS) ||
354	    (evm_status == INTEGRITY_NOXATTRS))
355		return 0;
356	return -EPERM;
357}
358
359/**
360 * evm_inode_post_setattr - update 'security.evm' after modifying metadata
361 * @dentry: pointer to the affected dentry
362 * @ia_valid: for the UID and GID status
363 *
364 * For now, update the HMAC stored in 'security.evm' to reflect UID/GID
365 * changes.
366 *
367 * This function is called from notify_change(), which expects the caller
368 * to lock the inode's i_mutex.
369 */
370void evm_inode_post_setattr(struct dentry *dentry, int ia_valid)
371{
372	if (!evm_initialized)
373		return;
374
375	if (ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID))
376		evm_update_evmxattr(dentry, NULL, NULL, 0);
377	return;
378}
379
380/*
381 * evm_inode_init_security - initializes security.evm
382 */
383int evm_inode_init_security(struct inode *inode,
384				 const struct xattr *lsm_xattr,
385				 struct xattr *evm_xattr)
386{
387	struct evm_ima_xattr_data *xattr_data;
388	int rc;
389
390	if (!evm_initialized || !evm_protected_xattr(lsm_xattr->name))
391		return 0;
392
393	xattr_data = kzalloc(sizeof(*xattr_data), GFP_NOFS);
394	if (!xattr_data)
395		return -ENOMEM;
396
397	xattr_data->type = EVM_XATTR_HMAC;
398	rc = evm_init_hmac(inode, lsm_xattr, xattr_data->digest);
399	if (rc < 0)
400		goto out;
401
402	evm_xattr->value = xattr_data;
403	evm_xattr->value_len = sizeof(*xattr_data);
404	evm_xattr->name = kstrdup(XATTR_EVM_SUFFIX, GFP_NOFS);
405	return 0;
406out:
407	kfree(xattr_data);
408	return rc;
409}
410EXPORT_SYMBOL_GPL(evm_inode_init_security);
411
412static int __init init_evm(void)
413{
414	int error;
415
416	error = evm_init_secfs();
417	if (error < 0) {
418		printk(KERN_INFO "EVM: Error registering secfs\n");
419		goto err;
420	}
421
422	return 0;
423err:
424	return error;
425}
426
427static void __exit cleanup_evm(void)
428{
429	evm_cleanup_secfs();
430	if (hmac_tfm)
431		crypto_free_shash(hmac_tfm);
432	if (hash_tfm)
433		crypto_free_shash(hash_tfm);
434}
435
436/*
437 * evm_display_config - list the EVM protected security extended attributes
438 */
439static int __init evm_display_config(void)
440{
441	char **xattrname;
442
443	for (xattrname = evm_config_xattrnames; *xattrname != NULL; xattrname++)
444		printk(KERN_INFO "EVM: %s\n", *xattrname);
445	return 0;
446}
447
448pure_initcall(evm_display_config);
449late_initcall(init_evm);
450
451MODULE_DESCRIPTION("Extended Verification Module");
452MODULE_LICENSE("GPL");