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TOMOYO Linux Cross Reference
Linux/net/wireless/lib80211_crypt_wep.c

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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);
298 

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