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#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
 14
 15#include <linux/export.h>
 16#include <linux/crypto.h>
 17#include <linux/xattr.h>
 18#include <linux/evm.h>
 19#include <keys/encrypted-type.h>
 20#include <crypto/hash.h>
 21#include <crypto/hash_info.h>
 22#include "evm.h"
 23
 24#define EVMKEY "evm-key"
 25#define MAX_KEY_SIZE 128
 26static unsigned char evmkey[MAX_KEY_SIZE];
 27static const int evmkey_len = MAX_KEY_SIZE;
 28
 29struct crypto_shash *hmac_tfm;
 30static struct crypto_shash *evm_tfm[HASH_ALGO__LAST];
 31
 32static DEFINE_MUTEX(mutex);
 33
 34#define EVM_SET_KEY_BUSY 0
 35
 36static unsigned long evm_set_key_flags;
 37
 38static const char evm_hmac[] = "hmac(sha1)";
 39
 40/**
 41 * evm_set_key() - set EVM HMAC key from the kernel
 42 * @key: pointer to a buffer with the key data
 43 * @size: length of the key data
 44 *
 45 * This function allows setting the EVM HMAC key from the kernel
 46 * without using the "encrypted" key subsystem keys. It can be used
 47 * by the crypto HW kernel module which has its own way of managing
 48 * keys.
 49 *
 50 * key length should be between 32 and 128 bytes long
 51 */
 52int evm_set_key(void *key, size_t keylen)
 53{
 54	int rc;
 55
 56	rc = -EBUSY;
 57	if (test_and_set_bit(EVM_SET_KEY_BUSY, &evm_set_key_flags))
 58		goto busy;
 59	rc = -EINVAL;
 60	if (keylen > MAX_KEY_SIZE)
 61		goto inval;
 62	memcpy(evmkey, key, keylen);
 63	evm_initialized |= EVM_INIT_HMAC;
 64	pr_info("key initialized\n");
 65	return 0;
 66inval:
 67	clear_bit(EVM_SET_KEY_BUSY, &evm_set_key_flags);
 68busy:
 69	pr_err("key initialization failed\n");
 70	return rc;
 71}
 72EXPORT_SYMBOL_GPL(evm_set_key);
 73
 74static struct shash_desc *init_desc(char type, uint8_t hash_algo)
 75{
 76	long rc;
 77	const char *algo;
 78	struct crypto_shash **tfm;
 79	struct shash_desc *desc;
 80
 81	if (type == EVM_XATTR_HMAC) {
 82		if (!(evm_initialized & EVM_INIT_HMAC)) {
 83			pr_err_once("HMAC key is not set\n");
 84			return ERR_PTR(-ENOKEY);
 85		}
 86		tfm = &hmac_tfm;
 87		algo = evm_hmac;
 88	} else {
 89		if (hash_algo >= HASH_ALGO__LAST)
 90			return ERR_PTR(-EINVAL);
 91
 92		tfm = &evm_tfm[hash_algo];
 93		algo = hash_algo_name[hash_algo];
 94	}
 95
 96	if (*tfm == NULL) {
 97		mutex_lock(&mutex);
 98		if (*tfm)
 99			goto out;
100		*tfm = crypto_alloc_shash(algo, 0, CRYPTO_NOLOAD);
101		if (IS_ERR(*tfm)) {
102			rc = PTR_ERR(*tfm);
103			pr_err("Can not allocate %s (reason: %ld)\n", algo, rc);
104			*tfm = NULL;
105			mutex_unlock(&mutex);
106			return ERR_PTR(rc);
107		}
108		if (type == EVM_XATTR_HMAC) {
109			rc = crypto_shash_setkey(*tfm, evmkey, evmkey_len);
110			if (rc) {
111				crypto_free_shash(*tfm);
112				*tfm = NULL;
113				mutex_unlock(&mutex);
114				return ERR_PTR(rc);
115			}
116		}
117out:
118		mutex_unlock(&mutex);
119	}
120
121	desc = kmalloc(sizeof(*desc) + crypto_shash_descsize(*tfm),
122			GFP_KERNEL);
123	if (!desc)
124		return ERR_PTR(-ENOMEM);
125
126	desc->tfm = *tfm;
127
128	rc = crypto_shash_init(desc);
129	if (rc) {
130		kfree(desc);
131		return ERR_PTR(rc);
132	}
133	return desc;
134}
135
136/* Protect against 'cutting & pasting' security.evm xattr, include inode
137 * specific info.
138 *
139 * (Additional directory/file metadata needs to be added for more complete
140 * protection.)
141 */
142static void hmac_add_misc(struct shash_desc *desc, struct inode *inode,
143			  char type, char *digest)
144{
145	struct h_misc {
146		unsigned long ino;
147		__u32 generation;
148		uid_t uid;
149		gid_t gid;
150		umode_t mode;
151	} hmac_misc;
152
153	memset(&hmac_misc, 0, sizeof(hmac_misc));
154	/* Don't include the inode or generation number in portable
155	 * signatures
156	 */
157	if (type != EVM_XATTR_PORTABLE_DIGSIG) {
158		hmac_misc.ino = inode->i_ino;
159		hmac_misc.generation = inode->i_generation;
160	}
161	/* The hmac uid and gid must be encoded in the initial user
162	 * namespace (not the filesystems user namespace) as encoding
163	 * them in the filesystems user namespace allows an attack
164	 * where first they are written in an unprivileged fuse mount
165	 * of a filesystem and then the system is tricked to mount the
166	 * filesystem for real on next boot and trust it because
167	 * everything is signed.
168	 */
169	hmac_misc.uid = from_kuid(&init_user_ns, inode->i_uid);
170	hmac_misc.gid = from_kgid(&init_user_ns, inode->i_gid);
171	hmac_misc.mode = inode->i_mode;
172	crypto_shash_update(desc, (const u8 *)&hmac_misc, sizeof(hmac_misc));
173	if ((evm_hmac_attrs & EVM_ATTR_FSUUID) &&
174	    type != EVM_XATTR_PORTABLE_DIGSIG)
175		crypto_shash_update(desc, (u8 *)&inode->i_sb->s_uuid, UUID_SIZE);
176	crypto_shash_final(desc, digest);
177}
178
179/*
180 * Calculate the HMAC value across the set of protected security xattrs.
181 *
182 * Instead of retrieving the requested xattr, for performance, calculate
183 * the hmac using the requested xattr value. Don't alloc/free memory for
184 * each xattr, but attempt to re-use the previously allocated memory.
185 */
186static int evm_calc_hmac_or_hash(struct dentry *dentry,
187				 const char *req_xattr_name,
188				 const char *req_xattr_value,
189				 size_t req_xattr_value_len,
190				 uint8_t type, struct evm_digest *data)
191{
192	struct inode *inode = d_backing_inode(dentry);
193	struct xattr_list *xattr;
194	struct shash_desc *desc;
195	size_t xattr_size = 0;
196	char *xattr_value = NULL;
197	int error;
198	int size;
199	bool ima_present = false;
200
201	if (!(inode->i_opflags & IOP_XATTR) ||
202	    inode->i_sb->s_user_ns != &init_user_ns)
203		return -EOPNOTSUPP;
204
205	desc = init_desc(type, data->hdr.algo);
206	if (IS_ERR(desc))
207		return PTR_ERR(desc);
208
209	data->hdr.length = crypto_shash_digestsize(desc->tfm);
210
211	error = -ENODATA;
212	list_for_each_entry_rcu(xattr, &evm_config_xattrnames, list) {
213		bool is_ima = false;
214
215		if (strcmp(xattr->name, XATTR_NAME_IMA) == 0)
216			is_ima = true;
217
218		if ((req_xattr_name && req_xattr_value)
219		    && !strcmp(xattr->name, req_xattr_name)) {
220			error = 0;
221			crypto_shash_update(desc, (const u8 *)req_xattr_value,
222					     req_xattr_value_len);
223			if (is_ima)
224				ima_present = true;
225			continue;
226		}
227		size = vfs_getxattr_alloc(dentry, xattr->name,
228					  &xattr_value, xattr_size, GFP_NOFS);
229		if (size == -ENOMEM) {
230			error = -ENOMEM;
231			goto out;
232		}
233		if (size < 0)
234			continue;
235
236		error = 0;
237		xattr_size = size;
238		crypto_shash_update(desc, (const u8 *)xattr_value, xattr_size);
239		if (is_ima)
240			ima_present = true;
241	}
242	hmac_add_misc(desc, inode, type, data->digest);
243
244	/* Portable EVM signatures must include an IMA hash */
245	if (type == EVM_XATTR_PORTABLE_DIGSIG && !ima_present)
246		return -EPERM;
247out:
248	kfree(xattr_value);
249	kfree(desc);
250	return error;
251}
252
253int evm_calc_hmac(struct dentry *dentry, const char *req_xattr_name,
254		  const char *req_xattr_value, size_t req_xattr_value_len,
255		  struct evm_digest *data)
256{
257	return evm_calc_hmac_or_hash(dentry, req_xattr_name, req_xattr_value,
258				    req_xattr_value_len, EVM_XATTR_HMAC, data);
259}
260
261int evm_calc_hash(struct dentry *dentry, const char *req_xattr_name,
262		  const char *req_xattr_value, size_t req_xattr_value_len,
263		  char type, struct evm_digest *data)
264{
265	return evm_calc_hmac_or_hash(dentry, req_xattr_name, req_xattr_value,
266				     req_xattr_value_len, type, data);
267}
268
269static int evm_is_immutable(struct dentry *dentry, struct inode *inode)
270{
271	const struct evm_ima_xattr_data *xattr_data = NULL;
272	struct integrity_iint_cache *iint;
273	int rc = 0;
274
275	iint = integrity_iint_find(inode);
276	if (iint && (iint->flags & EVM_IMMUTABLE_DIGSIG))
277		return 1;
278
279	/* Do this the hard way */
280	rc = vfs_getxattr_alloc(dentry, XATTR_NAME_EVM, (char **)&xattr_data, 0,
281				GFP_NOFS);
282	if (rc <= 0) {
283		if (rc == -ENODATA)
284			return 0;
285		return rc;
286	}
287	if (xattr_data->type == EVM_XATTR_PORTABLE_DIGSIG)
288		rc = 1;
289	else
290		rc = 0;
291
292	kfree(xattr_data);
293	return rc;
294}
295
296
297/*
298 * Calculate the hmac and update security.evm xattr
299 *
300 * Expects to be called with i_mutex locked.
301 */
302int evm_update_evmxattr(struct dentry *dentry, const char *xattr_name,
303			const char *xattr_value, size_t xattr_value_len)
304{
305	struct inode *inode = d_backing_inode(dentry);
306	struct evm_digest data;
307	int rc = 0;
308
309	/*
310	 * Don't permit any transformation of the EVM xattr if the signature
311	 * is of an immutable type
312	 */
313	rc = evm_is_immutable(dentry, inode);
314	if (rc < 0)
315		return rc;
316	if (rc)
317		return -EPERM;
318
319	data.hdr.algo = HASH_ALGO_SHA1;
320	rc = evm_calc_hmac(dentry, xattr_name, xattr_value,
321			   xattr_value_len, &data);
322	if (rc == 0) {
323		data.hdr.xattr.sha1.type = EVM_XATTR_HMAC;
324		rc = __vfs_setxattr_noperm(dentry, XATTR_NAME_EVM,
325					   &data.hdr.xattr.data[1],
326					   SHA1_DIGEST_SIZE + 1, 0);
327	} else if (rc == -ENODATA && (inode->i_opflags & IOP_XATTR)) {
328		rc = __vfs_removexattr(dentry, XATTR_NAME_EVM);
329	}
330	return rc;
331}
332
333int evm_init_hmac(struct inode *inode, const struct xattr *lsm_xattr,
334		  char *hmac_val)
335{
336	struct shash_desc *desc;
337
338	desc = init_desc(EVM_XATTR_HMAC, HASH_ALGO_SHA1);
339	if (IS_ERR(desc)) {
340		pr_info("init_desc failed\n");
341		return PTR_ERR(desc);
342	}
343
344	crypto_shash_update(desc, lsm_xattr->value, lsm_xattr->value_len);
345	hmac_add_misc(desc, inode, EVM_XATTR_HMAC, hmac_val);
346	kfree(desc);
347	return 0;
348}
349
350/*
351 * Get the key from the TPM for the SHA1-HMAC
352 */
353int evm_init_key(void)
354{
355	struct key *evm_key;
356	struct encrypted_key_payload *ekp;
357	int rc;
358
359	evm_key = request_key(&key_type_encrypted, EVMKEY, NULL);
360	if (IS_ERR(evm_key))
361		return -ENOENT;
362
363	down_read(&evm_key->sem);
364	ekp = evm_key->payload.data[0];
365
366	rc = evm_set_key(ekp->decrypted_data, ekp->decrypted_datalen);
367
368	/* burn the original key contents */
369	memset(ekp->decrypted_data, 0, ekp->decrypted_datalen);
370	up_read(&evm_key->sem);
371	key_put(evm_key);
372	return rc;
373}