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) "EVM: "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
 29static struct 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, *tmp_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)
 97		goto alloc;
 98	mutex_lock(&mutex);
 99	if (*tfm)
100		goto unlock;
101
102	tmp_tfm = crypto_alloc_shash(algo, 0, CRYPTO_NOLOAD);
103	if (IS_ERR(tmp_tfm)) {
104		pr_err("Can not allocate %s (reason: %ld)\n", algo,
105		       PTR_ERR(tmp_tfm));
106		mutex_unlock(&mutex);
107		return ERR_CAST(tmp_tfm);
108	}
109	if (type == EVM_XATTR_HMAC) {
110		rc = crypto_shash_setkey(tmp_tfm, evmkey, evmkey_len);
111		if (rc) {
112			crypto_free_shash(tmp_tfm);
113			mutex_unlock(&mutex);
114			return ERR_PTR(rc);
115		}
116	}
117	*tfm = tmp_tfm;
118unlock:
119	mutex_unlock(&mutex);
120alloc:
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	pr_debug("hmac_misc: (%zu) [%*phN]\n", sizeof(struct h_misc),
179		 (int)sizeof(struct h_misc), &hmac_misc);
180}
181
182/*
183 * Dump large security xattr values as a continuous ascii hexademical string.
184 * (pr_debug is limited to 64 bytes.)
185 */
186static void dump_security_xattr(const char *prefix, const void *src,
187				size_t count)
188{
189#if defined(DEBUG) || defined(CONFIG_DYNAMIC_DEBUG)
190	char *asciihex, *p;
191
192	p = asciihex = kmalloc(count * 2 + 1, GFP_KERNEL);
193	if (!asciihex)
194		return;
195
196	p = bin2hex(p, src, count);
197	*p = 0;
198	pr_debug("%s: (%zu) %.*s\n", prefix, count, (int)count * 2, asciihex);
199	kfree(asciihex);
200#endif
201}
202
203/*
204 * Calculate the HMAC value across the set of protected security xattrs.
205 *
206 * Instead of retrieving the requested xattr, for performance, calculate
207 * the hmac using the requested xattr value. Don't alloc/free memory for
208 * each xattr, but attempt to re-use the previously allocated memory.
209 */
210static int evm_calc_hmac_or_hash(struct dentry *dentry,
211				 const char *req_xattr_name,
212				 const char *req_xattr_value,
213				 size_t req_xattr_value_len,
214				 uint8_t type, struct evm_digest *data)
215{
216	struct inode *inode = d_backing_inode(dentry);
217	struct xattr_list *xattr;
218	struct shash_desc *desc;
219	size_t xattr_size = 0;
220	char *xattr_value = NULL;
221	int error;
222	int size, user_space_size;
223	bool ima_present = false;
224
225	if (!(inode->i_opflags & IOP_XATTR) ||
226	    inode->i_sb->s_user_ns != &init_user_ns)
227		return -EOPNOTSUPP;
228
229	desc = init_desc(type, data->hdr.algo);
230	if (IS_ERR(desc))
231		return PTR_ERR(desc);
232
233	data->hdr.length = crypto_shash_digestsize(desc->tfm);
234
235	error = -ENODATA;
236	list_for_each_entry_lockless(xattr, &evm_config_xattrnames, list) {
237		bool is_ima = false;
238
239		if (strcmp(xattr->name, XATTR_NAME_IMA) == 0)
240			is_ima = true;
241
242		/*
243		 * Skip non-enabled xattrs for locally calculated
244		 * signatures/HMACs.
245		 */
246		if (type != EVM_XATTR_PORTABLE_DIGSIG && !xattr->enabled)
247			continue;
248
249		if ((req_xattr_name && req_xattr_value)
250		    && !strcmp(xattr->name, req_xattr_name)) {
251			error = 0;
252			crypto_shash_update(desc, (const u8 *)req_xattr_value,
253					     req_xattr_value_len);
254			if (is_ima)
255				ima_present = true;
256
257			if (req_xattr_value_len < 64)
258				pr_debug("%s: (%zu) [%*phN]\n", req_xattr_name,
259					 req_xattr_value_len,
260					 (int)req_xattr_value_len,
261					 req_xattr_value);
262			else
263				dump_security_xattr(req_xattr_name,
264						    req_xattr_value,
265						    req_xattr_value_len);
266			continue;
267		}
268		size = vfs_getxattr_alloc(&init_user_ns, dentry, xattr->name,
269					  &xattr_value, xattr_size, GFP_NOFS);
270		if (size == -ENOMEM) {
271			error = -ENOMEM;
272			goto out;
273		}
274		if (size < 0)
275			continue;
276
277		user_space_size = vfs_getxattr(&init_user_ns, dentry,
278					       xattr->name, NULL, 0);
279		if (user_space_size != size)
280			pr_debug("file %s: xattr %s size mismatch (kernel: %d, user: %d)\n",
281				 dentry->d_name.name, xattr->name, size,
282				 user_space_size);
283		error = 0;
284		xattr_size = size;
285		crypto_shash_update(desc, (const u8 *)xattr_value, xattr_size);
286		if (is_ima)
287			ima_present = true;
288
289		if (xattr_size < 64)
290			pr_debug("%s: (%zu) [%*phN]", xattr->name, xattr_size,
291				 (int)xattr_size, xattr_value);
292		else
293			dump_security_xattr(xattr->name, xattr_value,
294					    xattr_size);
295	}
296	hmac_add_misc(desc, inode, type, data->digest);
297
298	/* Portable EVM signatures must include an IMA hash */
299	if (type == EVM_XATTR_PORTABLE_DIGSIG && !ima_present)
300		error = -EPERM;
301out:
302	kfree(xattr_value);
303	kfree(desc);
304	return error;
305}
306
307int evm_calc_hmac(struct dentry *dentry, const char *req_xattr_name,
308		  const char *req_xattr_value, size_t req_xattr_value_len,
309		  struct evm_digest *data)
310{
311	return evm_calc_hmac_or_hash(dentry, req_xattr_name, req_xattr_value,
312				    req_xattr_value_len, EVM_XATTR_HMAC, data);
313}
314
315int evm_calc_hash(struct dentry *dentry, const char *req_xattr_name,
316		  const char *req_xattr_value, size_t req_xattr_value_len,
317		  char type, struct evm_digest *data)
318{
319	return evm_calc_hmac_or_hash(dentry, req_xattr_name, req_xattr_value,
320				     req_xattr_value_len, type, data);
321}
322
323static int evm_is_immutable(struct dentry *dentry, struct inode *inode)
324{
325	const struct evm_ima_xattr_data *xattr_data = NULL;
326	struct integrity_iint_cache *iint;
327	int rc = 0;
328
329	iint = integrity_iint_find(inode);
330	if (iint && (iint->flags & EVM_IMMUTABLE_DIGSIG))
331		return 1;
332
333	/* Do this the hard way */
334	rc = vfs_getxattr_alloc(&init_user_ns, dentry, XATTR_NAME_EVM,
335				(char **)&xattr_data, 0, GFP_NOFS);
336	if (rc <= 0) {
337		if (rc == -ENODATA)
338			rc = 0;
339		goto out;
340	}
341	if (xattr_data->type == EVM_XATTR_PORTABLE_DIGSIG)
342		rc = 1;
343	else
344		rc = 0;
345
346out:
347	kfree(xattr_data);
348	return rc;
349}
350
351
352/*
353 * Calculate the hmac and update security.evm xattr
354 *
355 * Expects to be called with i_mutex locked.
356 */
357int evm_update_evmxattr(struct dentry *dentry, const char *xattr_name,
358			const char *xattr_value, size_t xattr_value_len)
359{
360	struct inode *inode = d_backing_inode(dentry);
361	struct evm_digest data;
362	int rc = 0;
363
364	/*
365	 * Don't permit any transformation of the EVM xattr if the signature
366	 * is of an immutable type
367	 */
368	rc = evm_is_immutable(dentry, inode);
369	if (rc < 0)
370		return rc;
371	if (rc)
372		return -EPERM;
373
374	data.hdr.algo = HASH_ALGO_SHA1;
375	rc = evm_calc_hmac(dentry, xattr_name, xattr_value,
376			   xattr_value_len, &data);
377	if (rc == 0) {
378		data.hdr.xattr.sha1.type = EVM_XATTR_HMAC;
379		rc = __vfs_setxattr_noperm(&init_user_ns, dentry,
380					   XATTR_NAME_EVM,
381					   &data.hdr.xattr.data[1],
382					   SHA1_DIGEST_SIZE + 1, 0);
383	} else if (rc == -ENODATA && (inode->i_opflags & IOP_XATTR)) {
384		rc = __vfs_removexattr(&init_user_ns, dentry, XATTR_NAME_EVM);
385	}
386	return rc;
387}
388
389int evm_init_hmac(struct inode *inode, const struct xattr *lsm_xattr,
390		  char *hmac_val)
391{
392	struct shash_desc *desc;
393
394	desc = init_desc(EVM_XATTR_HMAC, HASH_ALGO_SHA1);
395	if (IS_ERR(desc)) {
396		pr_info("init_desc failed\n");
397		return PTR_ERR(desc);
398	}
399
400	crypto_shash_update(desc, lsm_xattr->value, lsm_xattr->value_len);
401	hmac_add_misc(desc, inode, EVM_XATTR_HMAC, hmac_val);
402	kfree(desc);
403	return 0;
404}
405
406/*
407 * Get the key from the TPM for the SHA1-HMAC
408 */
409int evm_init_key(void)
410{
411	struct key *evm_key;
412	struct encrypted_key_payload *ekp;
413	int rc;
414
415	evm_key = request_key(&key_type_encrypted, EVMKEY, NULL);
416	if (IS_ERR(evm_key))
417		return -ENOENT;
418
419	down_read(&evm_key->sem);
420	ekp = evm_key->payload.data[0];
421
422	rc = evm_set_key(ekp->decrypted_data, ekp->decrypted_datalen);
423
424	/* burn the original key contents */
425	memset(ekp->decrypted_data, 0, ekp->decrypted_datalen);
426	up_read(&evm_key->sem);
427	key_put(evm_key);
428	return rc;
429}