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 * @keylen: 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_l(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
203static void dump_security_xattr(const char *name, const char *value,
204				size_t value_len)
205{
206	if (value_len < 64)
207		pr_debug("%s: (%zu) [%*phN]\n", name, value_len,
208			 (int)value_len, value);
209	else
210		dump_security_xattr_l(name, value, value_len);
211}
212
213/*
214 * Calculate the HMAC value across the set of protected security xattrs.
215 *
216 * Instead of retrieving the requested xattr, for performance, calculate
217 * the hmac using the requested xattr value. Don't alloc/free memory for
218 * each xattr, but attempt to re-use the previously allocated memory.
219 */
220static int evm_calc_hmac_or_hash(struct dentry *dentry,
221				 const char *req_xattr_name,
222				 const char *req_xattr_value,
223				 size_t req_xattr_value_len,
224				 uint8_t type, struct evm_digest *data,
225				 struct evm_iint_cache *iint)
226{
227	struct inode *inode = d_inode(d_real(dentry, D_REAL_METADATA));
228	struct xattr_list *xattr;
229	struct shash_desc *desc;
230	size_t xattr_size = 0;
231	char *xattr_value = NULL;
232	int error;
233	int size, user_space_size;
234	bool ima_present = false;
235	u64 i_version = 0;
236
237	if (!(inode->i_opflags & IOP_XATTR) ||
238	    inode->i_sb->s_user_ns != &init_user_ns)
239		return -EOPNOTSUPP;
240
241	desc = init_desc(type, data->hdr.algo);
242	if (IS_ERR(desc))
243		return PTR_ERR(desc);
244
245	data->hdr.length = crypto_shash_digestsize(desc->tfm);
246
247	error = -ENODATA;
248	list_for_each_entry_lockless(xattr, &evm_config_xattrnames, list) {
249		bool is_ima = false;
250
251		if (strcmp(xattr->name, XATTR_NAME_IMA) == 0)
252			is_ima = true;
253
254		/*
255		 * Skip non-enabled xattrs for locally calculated
256		 * signatures/HMACs.
257		 */
258		if (type != EVM_XATTR_PORTABLE_DIGSIG && !xattr->enabled)
259			continue;
260
261		if ((req_xattr_name && req_xattr_value)
262		    && !strcmp(xattr->name, req_xattr_name)) {
263			error = 0;
264			crypto_shash_update(desc, (const u8 *)req_xattr_value,
265					     req_xattr_value_len);
266			if (is_ima)
267				ima_present = true;
268
269			dump_security_xattr(req_xattr_name,
270					    req_xattr_value,
271					    req_xattr_value_len);
272			continue;
273		}
274		size = vfs_getxattr_alloc(&nop_mnt_idmap, dentry, xattr->name,
275					  &xattr_value, xattr_size, GFP_NOFS);
276		if (size == -ENOMEM) {
277			error = -ENOMEM;
278			goto out;
279		}
280		if (size < 0)
281			continue;
282
283		user_space_size = vfs_getxattr(&nop_mnt_idmap, dentry,
284					       xattr->name, NULL, 0);
285		if (user_space_size != size)
286			pr_debug("file %s: xattr %s size mismatch (kernel: %d, user: %d)\n",
287				 dentry->d_name.name, xattr->name, size,
288				 user_space_size);
289		error = 0;
290		xattr_size = size;
291		crypto_shash_update(desc, (const u8 *)xattr_value, xattr_size);
292		if (is_ima)
293			ima_present = true;
294
295		dump_security_xattr(xattr->name, xattr_value, xattr_size);
296	}
297	hmac_add_misc(desc, inode, type, data->digest);
298
299	if (inode != d_backing_inode(dentry) && iint) {
300		if (IS_I_VERSION(inode))
301			i_version = inode_query_iversion(inode);
302		integrity_inode_attrs_store(&iint->metadata_inode, i_version,
303					    inode);
304	}
305
306	/* Portable EVM signatures must include an IMA hash */
307	if (type == EVM_XATTR_PORTABLE_DIGSIG && !ima_present)
308		error = -EPERM;
309out:
310	kfree(xattr_value);
311	kfree(desc);
312	return error;
313}
314
315int evm_calc_hmac(struct dentry *dentry, const char *req_xattr_name,
316		  const char *req_xattr_value, size_t req_xattr_value_len,
317		  struct evm_digest *data, struct evm_iint_cache *iint)
318{
319	return evm_calc_hmac_or_hash(dentry, req_xattr_name, req_xattr_value,
320				    req_xattr_value_len, EVM_XATTR_HMAC, data,
321				    iint);
322}
323
324int evm_calc_hash(struct dentry *dentry, const char *req_xattr_name,
325		  const char *req_xattr_value, size_t req_xattr_value_len,
326		  char type, struct evm_digest *data, struct evm_iint_cache *iint)
327{
328	return evm_calc_hmac_or_hash(dentry, req_xattr_name, req_xattr_value,
329				     req_xattr_value_len, type, data, iint);
330}
331
332static int evm_is_immutable(struct dentry *dentry, struct inode *inode)
333{
334	const struct evm_ima_xattr_data *xattr_data = NULL;
335	struct evm_iint_cache *iint;
336	int rc = 0;
337
338	iint = evm_iint_inode(inode);
339	if (iint && (iint->flags & EVM_IMMUTABLE_DIGSIG))
340		return 1;
341
342	/* Do this the hard way */
343	rc = vfs_getxattr_alloc(&nop_mnt_idmap, dentry, XATTR_NAME_EVM,
344				(char **)&xattr_data, 0, GFP_NOFS);
345	if (rc <= 0) {
346		if (rc == -ENODATA)
347			rc = 0;
348		goto out;
349	}
350	if (xattr_data->type == EVM_XATTR_PORTABLE_DIGSIG)
351		rc = 1;
352	else
353		rc = 0;
354
355out:
356	kfree(xattr_data);
357	return rc;
358}
359
360
361/*
362 * Calculate the hmac and update security.evm xattr
363 *
364 * Expects to be called with i_mutex locked.
365 */
366int evm_update_evmxattr(struct dentry *dentry, const char *xattr_name,
367			const char *xattr_value, size_t xattr_value_len)
368{
369	struct inode *inode = d_backing_inode(dentry);
370	struct evm_iint_cache *iint = evm_iint_inode(inode);
371	struct evm_digest data;
372	int rc = 0;
373
374	/*
375	 * Don't permit any transformation of the EVM xattr if the signature
376	 * is of an immutable type
377	 */
378	rc = evm_is_immutable(dentry, inode);
379	if (rc < 0)
380		return rc;
381	if (rc)
382		return -EPERM;
383
384	data.hdr.algo = HASH_ALGO_SHA1;
385	rc = evm_calc_hmac(dentry, xattr_name, xattr_value,
386			   xattr_value_len, &data, iint);
387	if (rc == 0) {
388		data.hdr.xattr.sha1.type = EVM_XATTR_HMAC;
389		rc = __vfs_setxattr_noperm(&nop_mnt_idmap, dentry,
390					   XATTR_NAME_EVM,
391					   &data.hdr.xattr.data[1],
392					   SHA1_DIGEST_SIZE + 1, 0);
393	} else if (rc == -ENODATA && (inode->i_opflags & IOP_XATTR)) {
394		rc = __vfs_removexattr(&nop_mnt_idmap, dentry, XATTR_NAME_EVM);
395	}
396	return rc;
397}
398
399int evm_init_hmac(struct inode *inode, const struct xattr *xattrs,
400		  char *hmac_val)
401{
402	struct shash_desc *desc;
403	const struct xattr *xattr;
404
405	desc = init_desc(EVM_XATTR_HMAC, HASH_ALGO_SHA1);
406	if (IS_ERR(desc)) {
407		pr_info("init_desc failed\n");
408		return PTR_ERR(desc);
409	}
410
411	for (xattr = xattrs; xattr->name; xattr++) {
412		if (!evm_protected_xattr(xattr->name))
413			continue;
414
415		crypto_shash_update(desc, xattr->value, xattr->value_len);
416	}
417
418	hmac_add_misc(desc, inode, EVM_XATTR_HMAC, hmac_val);
419	kfree(desc);
420	return 0;
421}
422
423/*
424 * Get the key from the TPM for the SHA1-HMAC
425 */
426int evm_init_key(void)
427{
428	struct key *evm_key;
429	struct encrypted_key_payload *ekp;
430	int rc;
431
432	evm_key = request_key(&key_type_encrypted, EVMKEY, NULL);
433	if (IS_ERR(evm_key))
434		return -ENOENT;
435
436	down_read(&evm_key->sem);
437	ekp = evm_key->payload.data[0];
438
439	rc = evm_set_key(ekp->decrypted_data, ekp->decrypted_datalen);
440
441	/* burn the original key contents */
442	memset(ekp->decrypted_data, 0, ekp->decrypted_datalen);
443	up_read(&evm_key->sem);
444	key_put(evm_key);
445	return rc;
446}