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1 | /* | |
2 | * lib80211 crypt: host-based WEP encryption implementation for lib80211 | |
3 | * | |
4 | * Copyright (c) 2002-2004, Jouni Malinen <j@w1.fi> | |
5 | * Copyright (c) 2008, John W. Linville <linville@tuxdriver.com> | |
6 | * | |
7 | * This program is free software; you can redistribute it and/or modify | |
8 | * it under the terms of the GNU General Public License version 2 as | |
9 | * published by the Free Software Foundation. See README and COPYING for | |
10 | * more details. | |
11 | */ | |
12 | ||
13 | #include <linux/err.h> | |
14 | #include <linux/module.h> | |
15 | #include <linux/init.h> | |
16 | #include <linux/slab.h> | |
17 | #include <linux/random.h> | |
18 | #include <linux/scatterlist.h> | |
19 | #include <linux/skbuff.h> | |
20 | #include <linux/mm.h> | |
21 | #include <asm/string.h> | |
22 | ||
23 | #include <net/lib80211.h> | |
24 | ||
25 | #include <crypto/skcipher.h> | |
26 | #include <linux/crc32.h> | |
27 | ||
28 | MODULE_AUTHOR("Jouni Malinen"); | |
29 | MODULE_DESCRIPTION("lib80211 crypt: WEP"); | |
30 | MODULE_LICENSE("GPL"); | |
31 | ||
32 | struct lib80211_wep_data { | |
33 | u32 iv; | |
34 | #define WEP_KEY_LEN 13 | |
35 | u8 key[WEP_KEY_LEN + 1]; | |
36 | u8 key_len; | |
37 | u8 key_idx; | |
38 | struct crypto_skcipher *tx_tfm; | |
39 | struct crypto_skcipher *rx_tfm; | |
40 | }; | |
41 | ||
42 | static void *lib80211_wep_init(int keyidx) | |
43 | { | |
44 | struct lib80211_wep_data *priv; | |
45 | ||
46 | priv = kzalloc(sizeof(*priv), GFP_ATOMIC); | |
47 | if (priv == NULL) | |
48 | goto fail; | |
49 | priv->key_idx = keyidx; | |
50 | ||
51 | priv->tx_tfm = crypto_alloc_skcipher("ecb(arc4)", 0, CRYPTO_ALG_ASYNC); | |
52 | if (IS_ERR(priv->tx_tfm)) { | |
53 | priv->tx_tfm = NULL; | |
54 | goto fail; | |
55 | } | |
56 | ||
57 | priv->rx_tfm = crypto_alloc_skcipher("ecb(arc4)", 0, CRYPTO_ALG_ASYNC); | |
58 | if (IS_ERR(priv->rx_tfm)) { | |
59 | priv->rx_tfm = NULL; | |
60 | goto fail; | |
61 | } | |
62 | /* start WEP IV from a random value */ | |
63 | get_random_bytes(&priv->iv, 4); | |
64 | ||
65 | return priv; | |
66 | ||
67 | fail: | |
68 | if (priv) { | |
69 | crypto_free_skcipher(priv->tx_tfm); | |
70 | crypto_free_skcipher(priv->rx_tfm); | |
71 | kfree(priv); | |
72 | } | |
73 | return NULL; | |
74 | } | |
75 | ||
76 | static void lib80211_wep_deinit(void *priv) | |
77 | { | |
78 | struct lib80211_wep_data *_priv = priv; | |
79 | if (_priv) { | |
80 | crypto_free_skcipher(_priv->tx_tfm); | |
81 | crypto_free_skcipher(_priv->rx_tfm); | |
82 | } | |
83 | kfree(priv); | |
84 | } | |
85 | ||
86 | /* Add WEP IV/key info to a frame that has at least 4 bytes of headroom */ | |
87 | static int lib80211_wep_build_iv(struct sk_buff *skb, int hdr_len, | |
88 | u8 *key, int keylen, void *priv) | |
89 | { | |
90 | struct lib80211_wep_data *wep = priv; | |
91 | u32 klen; | |
92 | u8 *pos; | |
93 | ||
94 | if (skb_headroom(skb) < 4 || skb->len < hdr_len) | |
95 | return -1; | |
96 | ||
97 | pos = skb_push(skb, 4); | |
98 | memmove(pos, pos + 4, hdr_len); | |
99 | pos += hdr_len; | |
100 | ||
101 | klen = 3 + wep->key_len; | |
102 | ||
103 | wep->iv++; | |
104 | ||
105 | /* Fluhrer, Mantin, and Shamir have reported weaknesses in the key | |
106 | * scheduling algorithm of RC4. At least IVs (KeyByte + 3, 0xff, N) | |
107 | * can be used to speedup attacks, so avoid using them. */ | |
108 | if ((wep->iv & 0xff00) == 0xff00) { | |
109 | u8 B = (wep->iv >> 16) & 0xff; | |
110 | if (B >= 3 && B < klen) | |
111 | wep->iv += 0x0100; | |
112 | } | |
113 | ||
114 | /* Prepend 24-bit IV to RC4 key and TX frame */ | |
115 | *pos++ = (wep->iv >> 16) & 0xff; | |
116 | *pos++ = (wep->iv >> 8) & 0xff; | |
117 | *pos++ = wep->iv & 0xff; | |
118 | *pos++ = wep->key_idx << 6; | |
119 | ||
120 | return 0; | |
121 | } | |
122 | ||
123 | /* Perform WEP encryption on given skb that has at least 4 bytes of headroom | |
124 | * for IV and 4 bytes of tailroom for ICV. Both IV and ICV will be transmitted, | |
125 | * so the payload length increases with 8 bytes. | |
126 | * | |
127 | * WEP frame payload: IV + TX key idx, RC4(data), ICV = RC4(CRC32(data)) | |
128 | */ | |
129 | static int lib80211_wep_encrypt(struct sk_buff *skb, int hdr_len, void *priv) | |
130 | { | |
131 | struct lib80211_wep_data *wep = priv; | |
132 | SKCIPHER_REQUEST_ON_STACK(req, wep->tx_tfm); | |
133 | u32 crc, klen, len; | |
134 | u8 *pos, *icv; | |
135 | struct scatterlist sg; | |
136 | u8 key[WEP_KEY_LEN + 3]; | |
137 | int err; | |
138 | ||
139 | /* other checks are in lib80211_wep_build_iv */ | |
140 | if (skb_tailroom(skb) < 4) | |
141 | return -1; | |
142 | ||
143 | /* add the IV to the frame */ | |
144 | if (lib80211_wep_build_iv(skb, hdr_len, NULL, 0, priv)) | |
145 | return -1; | |
146 | ||
147 | /* Copy the IV into the first 3 bytes of the key */ | |
148 | skb_copy_from_linear_data_offset(skb, hdr_len, key, 3); | |
149 | ||
150 | /* Copy rest of the WEP key (the secret part) */ | |
151 | memcpy(key + 3, wep->key, wep->key_len); | |
152 | ||
153 | len = skb->len - hdr_len - 4; | |
154 | pos = skb->data + hdr_len + 4; | |
155 | klen = 3 + wep->key_len; | |
156 | ||
157 | /* Append little-endian CRC32 over only the data and encrypt it to produce ICV */ | |
158 | crc = ~crc32_le(~0, pos, len); | |
159 | icv = skb_put(skb, 4); | |
160 | icv[0] = crc; | |
161 | icv[1] = crc >> 8; | |
162 | icv[2] = crc >> 16; | |
163 | icv[3] = crc >> 24; | |
164 | ||
165 | crypto_skcipher_setkey(wep->tx_tfm, key, klen); | |
166 | sg_init_one(&sg, pos, len + 4); | |
167 | skcipher_request_set_tfm(req, wep->tx_tfm); | |
168 | skcipher_request_set_callback(req, 0, NULL, NULL); | |
169 | skcipher_request_set_crypt(req, &sg, &sg, len + 4, NULL); | |
170 | err = crypto_skcipher_encrypt(req); | |
171 | skcipher_request_zero(req); | |
172 | return err; | |
173 | } | |
174 | ||
175 | /* Perform WEP decryption on given buffer. Buffer includes whole WEP part of | |
176 | * the frame: IV (4 bytes), encrypted payload (including SNAP header), | |
177 | * ICV (4 bytes). len includes both IV and ICV. | |
178 | * | |
179 | * Returns 0 if frame was decrypted successfully and ICV was correct and -1 on | |
180 | * failure. If frame is OK, IV and ICV will be removed. | |
181 | */ | |
182 | static int lib80211_wep_decrypt(struct sk_buff *skb, int hdr_len, void *priv) | |
183 | { | |
184 | struct lib80211_wep_data *wep = priv; | |
185 | SKCIPHER_REQUEST_ON_STACK(req, wep->rx_tfm); | |
186 | u32 crc, klen, plen; | |
187 | u8 key[WEP_KEY_LEN + 3]; | |
188 | u8 keyidx, *pos, icv[4]; | |
189 | struct scatterlist sg; | |
190 | int err; | |
191 | ||
192 | if (skb->len < hdr_len + 8) | |
193 | return -1; | |
194 | ||
195 | pos = skb->data + hdr_len; | |
196 | key[0] = *pos++; | |
197 | key[1] = *pos++; | |
198 | key[2] = *pos++; | |
199 | keyidx = *pos++ >> 6; | |
200 | if (keyidx != wep->key_idx) | |
201 | return -1; | |
202 | ||
203 | klen = 3 + wep->key_len; | |
204 | ||
205 | /* Copy rest of the WEP key (the secret part) */ | |
206 | memcpy(key + 3, wep->key, wep->key_len); | |
207 | ||
208 | /* Apply RC4 to data and compute CRC32 over decrypted data */ | |
209 | plen = skb->len - hdr_len - 8; | |
210 | ||
211 | crypto_skcipher_setkey(wep->rx_tfm, key, klen); | |
212 | sg_init_one(&sg, pos, plen + 4); | |
213 | skcipher_request_set_tfm(req, wep->rx_tfm); | |
214 | skcipher_request_set_callback(req, 0, NULL, NULL); | |
215 | skcipher_request_set_crypt(req, &sg, &sg, plen + 4, NULL); | |
216 | err = crypto_skcipher_decrypt(req); | |
217 | skcipher_request_zero(req); | |
218 | if (err) | |
219 | return -7; | |
220 | ||
221 | crc = ~crc32_le(~0, pos, plen); | |
222 | icv[0] = crc; | |
223 | icv[1] = crc >> 8; | |
224 | icv[2] = crc >> 16; | |
225 | icv[3] = crc >> 24; | |
226 | if (memcmp(icv, pos + plen, 4) != 0) { | |
227 | /* ICV mismatch - drop frame */ | |
228 | return -2; | |
229 | } | |
230 | ||
231 | /* Remove IV and ICV */ | |
232 | memmove(skb->data + 4, skb->data, hdr_len); | |
233 | skb_pull(skb, 4); | |
234 | skb_trim(skb, skb->len - 4); | |
235 | ||
236 | return 0; | |
237 | } | |
238 | ||
239 | static int lib80211_wep_set_key(void *key, int len, u8 * seq, void *priv) | |
240 | { | |
241 | struct lib80211_wep_data *wep = priv; | |
242 | ||
243 | if (len < 0 || len > WEP_KEY_LEN) | |
244 | return -1; | |
245 | ||
246 | memcpy(wep->key, key, len); | |
247 | wep->key_len = len; | |
248 | ||
249 | return 0; | |
250 | } | |
251 | ||
252 | static int lib80211_wep_get_key(void *key, int len, u8 * seq, void *priv) | |
253 | { | |
254 | struct lib80211_wep_data *wep = priv; | |
255 | ||
256 | if (len < wep->key_len) | |
257 | return -1; | |
258 | ||
259 | memcpy(key, wep->key, wep->key_len); | |
260 | ||
261 | return wep->key_len; | |
262 | } | |
263 | ||
264 | static void lib80211_wep_print_stats(struct seq_file *m, void *priv) | |
265 | { | |
266 | struct lib80211_wep_data *wep = priv; | |
267 | seq_printf(m, "key[%d] alg=WEP len=%d\n", wep->key_idx, wep->key_len); | |
268 | } | |
269 | ||
270 | static struct lib80211_crypto_ops lib80211_crypt_wep = { | |
271 | .name = "WEP", | |
272 | .init = lib80211_wep_init, | |
273 | .deinit = lib80211_wep_deinit, | |
274 | .encrypt_mpdu = lib80211_wep_encrypt, | |
275 | .decrypt_mpdu = lib80211_wep_decrypt, | |
276 | .encrypt_msdu = NULL, | |
277 | .decrypt_msdu = NULL, | |
278 | .set_key = lib80211_wep_set_key, | |
279 | .get_key = lib80211_wep_get_key, | |
280 | .print_stats = lib80211_wep_print_stats, | |
281 | .extra_mpdu_prefix_len = 4, /* IV */ | |
282 | .extra_mpdu_postfix_len = 4, /* ICV */ | |
283 | .owner = THIS_MODULE, | |
284 | }; | |
285 | ||
286 | static int __init lib80211_crypto_wep_init(void) | |
287 | { | |
288 | return lib80211_register_crypto_ops(&lib80211_crypt_wep); | |
289 | } | |
290 | ||
291 | static void __exit lib80211_crypto_wep_exit(void) | |
292 | { | |
293 | lib80211_unregister_crypto_ops(&lib80211_crypt_wep); | |
294 | } | |
295 | ||
296 | module_init(lib80211_crypto_wep_init); | |
297 | module_exit(lib80211_crypto_wep_exit); |