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 * @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 */
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_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
203 static 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 */
220 static 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;
309 out:
310 kfree(xattr_value);
311 kfree(desc);
312 return error;
313 }
314
315 int 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
324 int 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
332 static 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
355 out:
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 */
366 int 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
399 int 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 */
426 int 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 }
447
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