1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3 * FILS AEAD for (Re)Association Request/Response frames
4 * Copyright 2016, Qualcomm Atheros, Inc.
5 */
6
7 #include <crypto/aes.h>
8 #include <crypto/hash.h>
9 #include <crypto/skcipher.h>
10 #include <crypto/utils.h>
11
12 #include "ieee80211_i.h"
13 #include "aes_cmac.h"
14 #include "fils_aead.h"
15
16 static void gf_mulx(u8 *pad)
17 {
18 u64 a = get_unaligned_be64(pad);
19 u64 b = get_unaligned_be64(pad + 8);
20
21 put_unaligned_be64((a << 1) | (b >> 63), pad);
22 put_unaligned_be64((b << 1) ^ ((a >> 63) ? 0x87 : 0), pad + 8);
23 }
24
25 static int aes_s2v(struct crypto_shash *tfm,
26 size_t num_elem, const u8 *addr[], size_t len[], u8 *v)
27 {
28 u8 d[AES_BLOCK_SIZE], tmp[AES_BLOCK_SIZE] = {};
29 SHASH_DESC_ON_STACK(desc, tfm);
30 size_t i;
31
32 desc->tfm = tfm;
33
34 /* D = AES-CMAC(K, <zero>) */
35 crypto_shash_digest(desc, tmp, AES_BLOCK_SIZE, d);
36
37 for (i = 0; i < num_elem - 1; i++) {
38 /* D = dbl(D) xor AES_CMAC(K, Si) */
39 gf_mulx(d); /* dbl */
40 crypto_shash_digest(desc, addr[i], len[i], tmp);
41 crypto_xor(d, tmp, AES_BLOCK_SIZE);
42 }
43
44 crypto_shash_init(desc);
45
46 if (len[i] >= AES_BLOCK_SIZE) {
47 /* len(Sn) >= 128 */
48 /* T = Sn xorend D */
49 crypto_shash_update(desc, addr[i], len[i] - AES_BLOCK_SIZE);
50 crypto_xor(d, addr[i] + len[i] - AES_BLOCK_SIZE,
51 AES_BLOCK_SIZE);
52 } else {
53 /* len(Sn) < 128 */
54 /* T = dbl(D) xor pad(Sn) */
55 gf_mulx(d); /* dbl */
56 crypto_xor(d, addr[i], len[i]);
57 d[len[i]] ^= 0x80;
58 }
59 /* V = AES-CMAC(K, T) */
60 crypto_shash_finup(desc, d, AES_BLOCK_SIZE, v);
61
62 return 0;
63 }
64
65 /* Note: addr[] and len[] needs to have one extra slot at the end. */
66 static int aes_siv_encrypt(const u8 *key, size_t key_len,
67 const u8 *plain, size_t plain_len,
68 size_t num_elem, const u8 *addr[],
69 size_t len[], u8 *out)
70 {
71 u8 v[AES_BLOCK_SIZE];
72 struct crypto_shash *tfm;
73 struct crypto_skcipher *tfm2;
74 struct skcipher_request *req;
75 int res;
76 struct scatterlist src[1], dst[1];
77 u8 *tmp;
78
79 key_len /= 2; /* S2V key || CTR key */
80
81 addr[num_elem] = plain;
82 len[num_elem] = plain_len;
83 num_elem++;
84
85 /* S2V */
86
87 tfm = crypto_alloc_shash("cmac(aes)", 0, 0);
88 if (IS_ERR(tfm))
89 return PTR_ERR(tfm);
90 /* K1 for S2V */
91 res = crypto_shash_setkey(tfm, key, key_len);
92 if (!res)
93 res = aes_s2v(tfm, num_elem, addr, len, v);
94 crypto_free_shash(tfm);
95 if (res)
96 return res;
97
98 /* Use a temporary buffer of the plaintext to handle need for
99 * overwriting this during AES-CTR.
100 */
101 tmp = kmemdup(plain, plain_len, GFP_KERNEL);
102 if (!tmp)
103 return -ENOMEM;
104
105 /* IV for CTR before encrypted data */
106 memcpy(out, v, AES_BLOCK_SIZE);
107
108 /* Synthetic IV to be used as the initial counter in CTR:
109 * Q = V bitand (1^64 || 0^1 || 1^31 || 0^1 || 1^31)
110 */
111 v[8] &= 0x7f;
112 v[12] &= 0x7f;
113
114 /* CTR */
115
116 tfm2 = crypto_alloc_skcipher("ctr(aes)", 0, CRYPTO_ALG_ASYNC);
117 if (IS_ERR(tfm2)) {
118 kfree(tmp);
119 return PTR_ERR(tfm2);
120 }
121 /* K2 for CTR */
122 res = crypto_skcipher_setkey(tfm2, key + key_len, key_len);
123 if (res)
124 goto fail;
125
126 req = skcipher_request_alloc(tfm2, GFP_KERNEL);
127 if (!req) {
128 res = -ENOMEM;
129 goto fail;
130 }
131
132 sg_init_one(src, tmp, plain_len);
133 sg_init_one(dst, out + AES_BLOCK_SIZE, plain_len);
134 skcipher_request_set_crypt(req, src, dst, plain_len, v);
135 res = crypto_skcipher_encrypt(req);
136 skcipher_request_free(req);
137 fail:
138 kfree(tmp);
139 crypto_free_skcipher(tfm2);
140 return res;
141 }
142
143 /* Note: addr[] and len[] needs to have one extra slot at the end. */
144 static int aes_siv_decrypt(const u8 *key, size_t key_len,
145 const u8 *iv_crypt, size_t iv_c_len,
146 size_t num_elem, const u8 *addr[], size_t len[],
147 u8 *out)
148 {
149 struct crypto_shash *tfm;
150 struct crypto_skcipher *tfm2;
151 struct skcipher_request *req;
152 struct scatterlist src[1], dst[1];
153 size_t crypt_len;
154 int res;
155 u8 frame_iv[AES_BLOCK_SIZE], iv[AES_BLOCK_SIZE];
156 u8 check[AES_BLOCK_SIZE];
157
158 crypt_len = iv_c_len - AES_BLOCK_SIZE;
159 key_len /= 2; /* S2V key || CTR key */
160 addr[num_elem] = out;
161 len[num_elem] = crypt_len;
162 num_elem++;
163
164 memcpy(iv, iv_crypt, AES_BLOCK_SIZE);
165 memcpy(frame_iv, iv_crypt, AES_BLOCK_SIZE);
166
167 /* Synthetic IV to be used as the initial counter in CTR:
168 * Q = V bitand (1^64 || 0^1 || 1^31 || 0^1 || 1^31)
169 */
170 iv[8] &= 0x7f;
171 iv[12] &= 0x7f;
172
173 /* CTR */
174
175 tfm2 = crypto_alloc_skcipher("ctr(aes)", 0, CRYPTO_ALG_ASYNC);
176 if (IS_ERR(tfm2))
177 return PTR_ERR(tfm2);
178 /* K2 for CTR */
179 res = crypto_skcipher_setkey(tfm2, key + key_len, key_len);
180 if (res) {
181 crypto_free_skcipher(tfm2);
182 return res;
183 }
184
185 req = skcipher_request_alloc(tfm2, GFP_KERNEL);
186 if (!req) {
187 crypto_free_skcipher(tfm2);
188 return -ENOMEM;
189 }
190
191 sg_init_one(src, iv_crypt + AES_BLOCK_SIZE, crypt_len);
192 sg_init_one(dst, out, crypt_len);
193 skcipher_request_set_crypt(req, src, dst, crypt_len, iv);
194 res = crypto_skcipher_decrypt(req);
195 skcipher_request_free(req);
196 crypto_free_skcipher(tfm2);
197 if (res)
198 return res;
199
200 /* S2V */
201
202 tfm = crypto_alloc_shash("cmac(aes)", 0, 0);
203 if (IS_ERR(tfm))
204 return PTR_ERR(tfm);
205 /* K1 for S2V */
206 res = crypto_shash_setkey(tfm, key, key_len);
207 if (!res)
208 res = aes_s2v(tfm, num_elem, addr, len, check);
209 crypto_free_shash(tfm);
210 if (res)
211 return res;
212 if (memcmp(check, frame_iv, AES_BLOCK_SIZE) != 0)
213 return -EINVAL;
214 return 0;
215 }
216
217 int fils_encrypt_assoc_req(struct sk_buff *skb,
218 struct ieee80211_mgd_assoc_data *assoc_data)
219 {
220 struct ieee80211_mgmt *mgmt = (void *)skb->data;
221 u8 *capab, *ies, *encr;
222 const u8 *addr[5 + 1];
223 const struct element *session;
224 size_t len[5 + 1];
225 size_t crypt_len;
226
227 if (ieee80211_is_reassoc_req(mgmt->frame_control)) {
228 capab = (u8 *)&mgmt->u.reassoc_req.capab_info;
229 ies = mgmt->u.reassoc_req.variable;
230 } else {
231 capab = (u8 *)&mgmt->u.assoc_req.capab_info;
232 ies = mgmt->u.assoc_req.variable;
233 }
234
235 session = cfg80211_find_ext_elem(WLAN_EID_EXT_FILS_SESSION,
236 ies, skb->data + skb->len - ies);
237 if (!session || session->datalen != 1 + 8)
238 return -EINVAL;
239 /* encrypt after FILS Session element */
240 encr = (u8 *)session->data + 1 + 8;
241
242 /* AES-SIV AAD vectors */
243
244 /* The STA's MAC address */
245 addr[0] = mgmt->sa;
246 len[0] = ETH_ALEN;
247 /* The AP's BSSID */
248 addr[1] = mgmt->da;
249 len[1] = ETH_ALEN;
250 /* The STA's nonce */
251 addr[2] = assoc_data->fils_nonces;
252 len[2] = FILS_NONCE_LEN;
253 /* The AP's nonce */
254 addr[3] = &assoc_data->fils_nonces[FILS_NONCE_LEN];
255 len[3] = FILS_NONCE_LEN;
256 /* The (Re)Association Request frame from the Capability Information
257 * field to the FILS Session element (both inclusive).
258 */
259 addr[4] = capab;
260 len[4] = encr - capab;
261
262 crypt_len = skb->data + skb->len - encr;
263 skb_put(skb, AES_BLOCK_SIZE);
264 return aes_siv_encrypt(assoc_data->fils_kek, assoc_data->fils_kek_len,
265 encr, crypt_len, 5, addr, len, encr);
266 }
267
268 int fils_decrypt_assoc_resp(struct ieee80211_sub_if_data *sdata,
269 u8 *frame, size_t *frame_len,
270 struct ieee80211_mgd_assoc_data *assoc_data)
271 {
272 struct ieee80211_mgmt *mgmt = (void *)frame;
273 u8 *capab, *ies, *encr;
274 const u8 *addr[5 + 1];
275 const struct element *session;
276 size_t len[5 + 1];
277 int res;
278 size_t crypt_len;
279
280 if (*frame_len < 24 + 6)
281 return -EINVAL;
282
283 capab = (u8 *)&mgmt->u.assoc_resp.capab_info;
284 ies = mgmt->u.assoc_resp.variable;
285 session = cfg80211_find_ext_elem(WLAN_EID_EXT_FILS_SESSION,
286 ies, frame + *frame_len - ies);
287 if (!session || session->datalen != 1 + 8) {
288 mlme_dbg(sdata,
289 "No (valid) FILS Session element in (Re)Association Response frame from %pM",
290 mgmt->sa);
291 return -EINVAL;
292 }
293 /* decrypt after FILS Session element */
294 encr = (u8 *)session->data + 1 + 8;
295
296 /* AES-SIV AAD vectors */
297
298 /* The AP's BSSID */
299 addr[0] = mgmt->sa;
300 len[0] = ETH_ALEN;
301 /* The STA's MAC address */
302 addr[1] = mgmt->da;
303 len[1] = ETH_ALEN;
304 /* The AP's nonce */
305 addr[2] = &assoc_data->fils_nonces[FILS_NONCE_LEN];
306 len[2] = FILS_NONCE_LEN;
307 /* The STA's nonce */
308 addr[3] = assoc_data->fils_nonces;
309 len[3] = FILS_NONCE_LEN;
310 /* The (Re)Association Response frame from the Capability Information
311 * field to the FILS Session element (both inclusive).
312 */
313 addr[4] = capab;
314 len[4] = encr - capab;
315
316 crypt_len = frame + *frame_len - encr;
317 if (crypt_len < AES_BLOCK_SIZE) {
318 mlme_dbg(sdata,
319 "Not enough room for AES-SIV data after FILS Session element in (Re)Association Response frame from %pM",
320 mgmt->sa);
321 return -EINVAL;
322 }
323 res = aes_siv_decrypt(assoc_data->fils_kek, assoc_data->fils_kek_len,
324 encr, crypt_len, 5, addr, len, encr);
325 if (res != 0) {
326 mlme_dbg(sdata,
327 "AES-SIV decryption of (Re)Association Response frame from %pM failed",
328 mgmt->sa);
329 return res;
330 }
331 *frame_len -= AES_BLOCK_SIZE;
332 return 0;
333 }
334
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