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