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
26 static unsigned char evmkey[MAX_KEY_SIZE];
27 static const int evmkey_len = MAX_KEY_SIZE;
28 
29 static struct crypto_shash *hmac_tfm;
30 static struct crypto_shash *evm_tfm[HASH_ALGO__LAST];
31 
32 static DEFINE_MUTEX(mutex);
33 
34 #define EVM_SET_KEY_BUSY 0
35 
36 static unsigned long evm_set_key_flags;
37 
38 static 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  */
52 int 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;
66 inval:
67 	clear_bit(EVM_SET_KEY_BUSY, &evm_set_key_flags);
68 busy:
69 	pr_err("key initialization failed\n");
70 	return rc;
71 }
72 EXPORT_SYMBOL_GPL(evm_set_key);
73 
74 static 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;
118 unlock:
119 	mutex_unlock(&mutex);
120 alloc:
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  */
142 static 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  */
186 static 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  */
210 static 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;
301 out:
302 	kfree(xattr_value);
303 	kfree(desc);
304 	return error;
305 }
306 
307 int 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 
315 int 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 
323 static 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 
346 out:
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  */
357 int 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 
389 int 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  */
409 int 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 }
430