1// SPDX-License-Identifier: GPL-2.0-only
  2/*
  3 * Copyright (C) 2005-2010 IBM Corporation
  4 *
  5 * Authors:
  6 * Mimi Zohar <zohar@us.ibm.com>
  7 * Kylene Hall <kjhall@us.ibm.com>
  8 *
  9 * File: evm_crypto.c
 10 *	 Using root's kernel master key (kmk), calculate the HMAC
 11 */
 12
 13#include <linux/export.h>
 14#include <linux/crypto.h>
 15#include <linux/xattr.h>
 16#include <linux/evm.h>
 17#include <keys/encrypted-type.h>
 18#include <crypto/hash.h>
 19#include <crypto/hash_info.h>
 20#include "evm.h"
 21
 22#define EVMKEY "evm-key"
 23#define MAX_KEY_SIZE 128
 24static unsigned char evmkey[MAX_KEY_SIZE];
 25static const int evmkey_len = MAX_KEY_SIZE;
 26
 27struct crypto_shash *hmac_tfm;
 28static struct crypto_shash *evm_tfm[HASH_ALGO__LAST];
 29
 30static DEFINE_MUTEX(mutex);
 31
 32#define EVM_SET_KEY_BUSY 0
 33
 34static unsigned long evm_set_key_flags;
 35
 36static const char evm_hmac[] = "hmac(sha1)";
 37
 38/**
 39 * evm_set_key() - set EVM HMAC key from the kernel
 40 * @key: pointer to a buffer with the key data
 41 * @size: length of the key data
 42 *
 43 * This function allows setting the EVM HMAC key from the kernel
 44 * without using the "encrypted" key subsystem keys. It can be used
 45 * by the crypto HW kernel module which has its own way of managing
 46 * keys.
 47 *
 48 * key length should be between 32 and 128 bytes long
 49 */
 50int evm_set_key(void *key, size_t keylen)
 51{
 52	int rc;
 53
 54	rc = -EBUSY;
 55	if (test_and_set_bit(EVM_SET_KEY_BUSY, &evm_set_key_flags))
 56		goto busy;
 57	rc = -EINVAL;
 58	if (keylen > MAX_KEY_SIZE)
 59		goto inval;
 60	memcpy(evmkey, key, keylen);
 61	evm_initialized |= EVM_INIT_HMAC;
 62	pr_info("key initialized\n");
 63	return 0;
 64inval:
 65	clear_bit(EVM_SET_KEY_BUSY, &evm_set_key_flags);
 66busy:
 67	pr_err("key initialization failed\n");
 68	return rc;
 69}
 70EXPORT_SYMBOL_GPL(evm_set_key);
 71
 72static struct shash_desc *init_desc(char type, uint8_t hash_algo)
 73{
 74	long rc;
 75	const char *algo;
 76	struct crypto_shash **tfm, *tmp_tfm;
 77	struct shash_desc *desc;
 78
 79	if (type == EVM_XATTR_HMAC) {
 80		if (!(evm_initialized & EVM_INIT_HMAC)) {
 81			pr_err_once("HMAC key is not set\n");
 82			return ERR_PTR(-ENOKEY);
 83		}
 84		tfm = &hmac_tfm;
 85		algo = evm_hmac;
 86	} else {
 87		if (hash_algo >= HASH_ALGO__LAST)
 88			return ERR_PTR(-EINVAL);
 89
 90		tfm = &evm_tfm[hash_algo];
 91		algo = hash_algo_name[hash_algo];
 92	}
 93
 94	if (*tfm)
 95		goto alloc;
 96	mutex_lock(&mutex);
 97	if (*tfm)
 98		goto unlock;
 99
100	tmp_tfm = crypto_alloc_shash(algo, 0, CRYPTO_NOLOAD);
101	if (IS_ERR(tmp_tfm)) {
102		pr_err("Can not allocate %s (reason: %ld)\n", algo,
103		       PTR_ERR(tmp_tfm));
104		mutex_unlock(&mutex);
105		return ERR_CAST(tmp_tfm);
106	}
107	if (type == EVM_XATTR_HMAC) {
108		rc = crypto_shash_setkey(tmp_tfm, evmkey, evmkey_len);
109		if (rc) {
110			crypto_free_shash(tmp_tfm);
111			mutex_unlock(&mutex);
112			return ERR_PTR(rc);
113		}
114	}
115	*tfm = tmp_tfm;
116unlock:
117	mutex_unlock(&mutex);
118alloc:
119	desc = kmalloc(sizeof(*desc) + crypto_shash_descsize(*tfm),
120			GFP_KERNEL);
121	if (!desc)
122		return ERR_PTR(-ENOMEM);
123
124	desc->tfm = *tfm;
125
126	rc = crypto_shash_init(desc);
127	if (rc) {
128		kfree(desc);
129		return ERR_PTR(rc);
130	}
131	return desc;
132}
133
134/* Protect against 'cutting & pasting' security.evm xattr, include inode
135 * specific info.
136 *
137 * (Additional directory/file metadata needs to be added for more complete
138 * protection.)
139 */
140static void hmac_add_misc(struct shash_desc *desc, struct inode *inode,
141			  char type, char *digest)
142{
143	struct h_misc {
144		unsigned long ino;
145		__u32 generation;
146		uid_t uid;
147		gid_t gid;
148		umode_t mode;
149	} hmac_misc;
150
151	memset(&hmac_misc, 0, sizeof(hmac_misc));
152	/* Don't include the inode or generation number in portable
153	 * signatures
154	 */
155	if (type != EVM_XATTR_PORTABLE_DIGSIG) {
156		hmac_misc.ino = inode->i_ino;
157		hmac_misc.generation = inode->i_generation;
158	}
159	/* The hmac uid and gid must be encoded in the initial user
160	 * namespace (not the filesystems user namespace) as encoding
161	 * them in the filesystems user namespace allows an attack
162	 * where first they are written in an unprivileged fuse mount
163	 * of a filesystem and then the system is tricked to mount the
164	 * filesystem for real on next boot and trust it because
165	 * everything is signed.
166	 */
167	hmac_misc.uid = from_kuid(&init_user_ns, inode->i_uid);
168	hmac_misc.gid = from_kgid(&init_user_ns, inode->i_gid);
169	hmac_misc.mode = inode->i_mode;
170	crypto_shash_update(desc, (const u8 *)&hmac_misc, sizeof(hmac_misc));
171	if ((evm_hmac_attrs & EVM_ATTR_FSUUID) &&
172	    type != EVM_XATTR_PORTABLE_DIGSIG)
173		crypto_shash_update(desc, (u8 *)&inode->i_sb->s_uuid, UUID_SIZE);
174	crypto_shash_final(desc, digest);
175}
176
177/*
178 * Calculate the HMAC value across the set of protected security xattrs.
179 *
180 * Instead of retrieving the requested xattr, for performance, calculate
181 * the hmac using the requested xattr value. Don't alloc/free memory for
182 * each xattr, but attempt to re-use the previously allocated memory.
183 */
184static int evm_calc_hmac_or_hash(struct dentry *dentry,
185				 const char *req_xattr_name,
186				 const char *req_xattr_value,
187				 size_t req_xattr_value_len,
188				 uint8_t type, struct evm_digest *data)
189{
190	struct inode *inode = d_backing_inode(dentry);
191	struct xattr_list *xattr;
192	struct shash_desc *desc;
193	size_t xattr_size = 0;
194	char *xattr_value = NULL;
195	int error;
196	int size;
197	bool ima_present = false;
198
199	if (!(inode->i_opflags & IOP_XATTR) ||
200	    inode->i_sb->s_user_ns != &init_user_ns)
201		return -EOPNOTSUPP;
202
203	desc = init_desc(type, data->hdr.algo);
204	if (IS_ERR(desc))
205		return PTR_ERR(desc);
206
207	data->hdr.length = crypto_shash_digestsize(desc->tfm);
208
209	error = -ENODATA;
210	list_for_each_entry_lockless(xattr, &evm_config_xattrnames, list) {
211		bool is_ima = false;
212
213		if (strcmp(xattr->name, XATTR_NAME_IMA) == 0)
214			is_ima = true;
215
216		if ((req_xattr_name && req_xattr_value)
217		    && !strcmp(xattr->name, req_xattr_name)) {
218			error = 0;
219			crypto_shash_update(desc, (const u8 *)req_xattr_value,
220					     req_xattr_value_len);
221			if (is_ima)
222				ima_present = true;
223			continue;
224		}
225		size = vfs_getxattr_alloc(dentry, xattr->name,
226					  &xattr_value, xattr_size, GFP_NOFS);
227		if (size == -ENOMEM) {
228			error = -ENOMEM;
229			goto out;
230		}
231		if (size < 0)
232			continue;
233
234		error = 0;
235		xattr_size = size;
236		crypto_shash_update(desc, (const u8 *)xattr_value, xattr_size);
237		if (is_ima)
238			ima_present = true;
239	}
240	hmac_add_misc(desc, inode, type, data->digest);
241
242	/* Portable EVM signatures must include an IMA hash */
243	if (type == EVM_XATTR_PORTABLE_DIGSIG && !ima_present)
244		error = -EPERM;
245out:
246	kfree(xattr_value);
247	kfree(desc);
248	return error;
249}
250
251int evm_calc_hmac(struct dentry *dentry, const char *req_xattr_name,
252		  const char *req_xattr_value, size_t req_xattr_value_len,
253		  struct evm_digest *data)
254{
255	return evm_calc_hmac_or_hash(dentry, req_xattr_name, req_xattr_value,
256				    req_xattr_value_len, EVM_XATTR_HMAC, data);
257}
258
259int evm_calc_hash(struct dentry *dentry, const char *req_xattr_name,
260		  const char *req_xattr_value, size_t req_xattr_value_len,
261		  char type, struct evm_digest *data)
262{
263	return evm_calc_hmac_or_hash(dentry, req_xattr_name, req_xattr_value,
264				     req_xattr_value_len, type, data);
265}
266
267static int evm_is_immutable(struct dentry *dentry, struct inode *inode)
268{
269	const struct evm_ima_xattr_data *xattr_data = NULL;
270	struct integrity_iint_cache *iint;
271	int rc = 0;
272
273	iint = integrity_iint_find(inode);
274	if (iint && (iint->flags & EVM_IMMUTABLE_DIGSIG))
275		return 1;
276
277	/* Do this the hard way */
278	rc = vfs_getxattr_alloc(dentry, XATTR_NAME_EVM, (char **)&xattr_data, 0,
279				GFP_NOFS);
280	if (rc <= 0) {
281		if (rc == -ENODATA)
282			return 0;
283		return rc;
284	}
285	if (xattr_data->type == EVM_XATTR_PORTABLE_DIGSIG)
286		rc = 1;
287	else
288		rc = 0;
289
290	kfree(xattr_data);
291	return rc;
292}
293
294
295/*
296 * Calculate the hmac and update security.evm xattr
297 *
298 * Expects to be called with i_mutex locked.
299 */
300int evm_update_evmxattr(struct dentry *dentry, const char *xattr_name,
301			const char *xattr_value, size_t xattr_value_len)
302{
303	struct inode *inode = d_backing_inode(dentry);
304	struct evm_digest data;
305	int rc = 0;
306
307	/*
308	 * Don't permit any transformation of the EVM xattr if the signature
309	 * is of an immutable type
310	 */
311	rc = evm_is_immutable(dentry, inode);
312	if (rc < 0)
313		return rc;
314	if (rc)
315		return -EPERM;
316
317	data.hdr.algo = HASH_ALGO_SHA1;
318	rc = evm_calc_hmac(dentry, xattr_name, xattr_value,
319			   xattr_value_len, &data);
320	if (rc == 0) {
321		data.hdr.xattr.sha1.type = EVM_XATTR_HMAC;
322		rc = __vfs_setxattr_noperm(dentry, XATTR_NAME_EVM,
323					   &data.hdr.xattr.data[1],
324					   SHA1_DIGEST_SIZE + 1, 0);
325	} else if (rc == -ENODATA && (inode->i_opflags & IOP_XATTR)) {
326		rc = __vfs_removexattr(dentry, XATTR_NAME_EVM);
327	}
328	return rc;
329}
330
331int evm_init_hmac(struct inode *inode, const struct xattr *lsm_xattr,
332		  char *hmac_val)
333{
334	struct shash_desc *desc;
335
336	desc = init_desc(EVM_XATTR_HMAC, HASH_ALGO_SHA1);
337	if (IS_ERR(desc)) {
338		pr_info("init_desc failed\n");
339		return PTR_ERR(desc);
340	}
341
342	crypto_shash_update(desc, lsm_xattr->value, lsm_xattr->value_len);
343	hmac_add_misc(desc, inode, EVM_XATTR_HMAC, hmac_val);
344	kfree(desc);
345	return 0;
346}
347
348/*
349 * Get the key from the TPM for the SHA1-HMAC
350 */
351int evm_init_key(void)
352{
353	struct key *evm_key;
354	struct encrypted_key_payload *ekp;
355	int rc;
356
357	evm_key = request_key(&key_type_encrypted, EVMKEY, NULL);
358	if (IS_ERR(evm_key))
359		return -ENOENT;
360
361	down_read(&evm_key->sem);
362	ekp = evm_key->payload.data[0];
363
364	rc = evm_set_key(ekp->decrypted_data, ekp->decrypted_datalen);
365
366	/* burn the original key contents */
367	memset(ekp->decrypted_data, 0, ekp->decrypted_datalen);
368	up_read(&evm_key->sem);
369	key_put(evm_key);
370	return rc;
371}