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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 <linux/crypto.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_blkcipher *tx_tfm;
 39         struct crypto_blkcipher *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_blkcipher("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_blkcipher("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                 if (priv->tx_tfm)
 70                         crypto_free_blkcipher(priv->tx_tfm);
 71                 if (priv->rx_tfm)
 72                         crypto_free_blkcipher(priv->rx_tfm);
 73                 kfree(priv);
 74         }
 75         return NULL;
 76 }
 77 
 78 static void lib80211_wep_deinit(void *priv)
 79 {
 80         struct lib80211_wep_data *_priv = priv;
 81         if (_priv) {
 82                 if (_priv->tx_tfm)
 83                         crypto_free_blkcipher(_priv->tx_tfm);
 84                 if (_priv->rx_tfm)
 85                         crypto_free_blkcipher(_priv->rx_tfm);
 86         }
 87         kfree(priv);
 88 }
 89 
 90 /* Add WEP IV/key info to a frame that has at least 4 bytes of headroom */
 91 static int lib80211_wep_build_iv(struct sk_buff *skb, int hdr_len,
 92                                u8 *key, int keylen, void *priv)
 93 {
 94         struct lib80211_wep_data *wep = priv;
 95         u32 klen;
 96         u8 *pos;
 97 
 98         if (skb_headroom(skb) < 4 || skb->len < hdr_len)
 99                 return -1;
100 
101         pos = skb_push(skb, 4);
102         memmove(pos, pos + 4, hdr_len);
103         pos += hdr_len;
104 
105         klen = 3 + wep->key_len;
106 
107         wep->iv++;
108 
109         /* Fluhrer, Mantin, and Shamir have reported weaknesses in the key
110          * scheduling algorithm of RC4. At least IVs (KeyByte + 3, 0xff, N)
111          * can be used to speedup attacks, so avoid using them. */
112         if ((wep->iv & 0xff00) == 0xff00) {
113                 u8 B = (wep->iv >> 16) & 0xff;
114                 if (B >= 3 && B < klen)
115                         wep->iv += 0x0100;
116         }
117 
118         /* Prepend 24-bit IV to RC4 key and TX frame */
119         *pos++ = (wep->iv >> 16) & 0xff;
120         *pos++ = (wep->iv >> 8) & 0xff;
121         *pos++ = wep->iv & 0xff;
122         *pos++ = wep->key_idx << 6;
123 
124         return 0;
125 }
126 
127 /* Perform WEP encryption on given skb that has at least 4 bytes of headroom
128  * for IV and 4 bytes of tailroom for ICV. Both IV and ICV will be transmitted,
129  * so the payload length increases with 8 bytes.
130  *
131  * WEP frame payload: IV + TX key idx, RC4(data), ICV = RC4(CRC32(data))
132  */
133 static int lib80211_wep_encrypt(struct sk_buff *skb, int hdr_len, void *priv)
134 {
135         struct lib80211_wep_data *wep = priv;
136         struct blkcipher_desc desc = { .tfm = wep->tx_tfm };
137         u32 crc, klen, len;
138         u8 *pos, *icv;
139         struct scatterlist sg;
140         u8 key[WEP_KEY_LEN + 3];
141 
142         /* other checks are in lib80211_wep_build_iv */
143         if (skb_tailroom(skb) < 4)
144                 return -1;
145 
146         /* add the IV to the frame */
147         if (lib80211_wep_build_iv(skb, hdr_len, NULL, 0, priv))
148                 return -1;
149 
150         /* Copy the IV into the first 3 bytes of the key */
151         skb_copy_from_linear_data_offset(skb, hdr_len, key, 3);
152 
153         /* Copy rest of the WEP key (the secret part) */
154         memcpy(key + 3, wep->key, wep->key_len);
155 
156         len = skb->len - hdr_len - 4;
157         pos = skb->data + hdr_len + 4;
158         klen = 3 + wep->key_len;
159 
160         /* Append little-endian CRC32 over only the data and encrypt it to produce ICV */
161         crc = ~crc32_le(~0, pos, len);
162         icv = skb_put(skb, 4);
163         icv[0] = crc;
164         icv[1] = crc >> 8;
165         icv[2] = crc >> 16;
166         icv[3] = crc >> 24;
167 
168         crypto_blkcipher_setkey(wep->tx_tfm, key, klen);
169         sg_init_one(&sg, pos, len + 4);
170         return crypto_blkcipher_encrypt(&desc, &sg, &sg, len + 4);
171 }
172 
173 /* Perform WEP decryption on given buffer. Buffer includes whole WEP part of
174  * the frame: IV (4 bytes), encrypted payload (including SNAP header),
175  * ICV (4 bytes). len includes both IV and ICV.
176  *
177  * Returns 0 if frame was decrypted successfully and ICV was correct and -1 on
178  * failure. If frame is OK, IV and ICV will be removed.
179  */
180 static int lib80211_wep_decrypt(struct sk_buff *skb, int hdr_len, void *priv)
181 {
182         struct lib80211_wep_data *wep = priv;
183         struct blkcipher_desc desc = { .tfm = wep->rx_tfm };
184         u32 crc, klen, plen;
185         u8 key[WEP_KEY_LEN + 3];
186         u8 keyidx, *pos, icv[4];
187         struct scatterlist sg;
188 
189         if (skb->len < hdr_len + 8)
190                 return -1;
191 
192         pos = skb->data + hdr_len;
193         key[0] = *pos++;
194         key[1] = *pos++;
195         key[2] = *pos++;
196         keyidx = *pos++ >> 6;
197         if (keyidx != wep->key_idx)
198                 return -1;
199 
200         klen = 3 + wep->key_len;
201 
202         /* Copy rest of the WEP key (the secret part) */
203         memcpy(key + 3, wep->key, wep->key_len);
204 
205         /* Apply RC4 to data and compute CRC32 over decrypted data */
206         plen = skb->len - hdr_len - 8;
207 
208         crypto_blkcipher_setkey(wep->rx_tfm, key, klen);
209         sg_init_one(&sg, pos, plen + 4);
210         if (crypto_blkcipher_decrypt(&desc, &sg, &sg, plen + 4))
211                 return -7;
212 
213         crc = ~crc32_le(~0, pos, plen);
214         icv[0] = crc;
215         icv[1] = crc >> 8;
216         icv[2] = crc >> 16;
217         icv[3] = crc >> 24;
218         if (memcmp(icv, pos + plen, 4) != 0) {
219                 /* ICV mismatch - drop frame */
220                 return -2;
221         }
222 
223         /* Remove IV and ICV */
224         memmove(skb->data + 4, skb->data, hdr_len);
225         skb_pull(skb, 4);
226         skb_trim(skb, skb->len - 4);
227 
228         return 0;
229 }
230 
231 static int lib80211_wep_set_key(void *key, int len, u8 * seq, void *priv)
232 {
233         struct lib80211_wep_data *wep = priv;
234 
235         if (len < 0 || len > WEP_KEY_LEN)
236                 return -1;
237 
238         memcpy(wep->key, key, len);
239         wep->key_len = len;
240 
241         return 0;
242 }
243 
244 static int lib80211_wep_get_key(void *key, int len, u8 * seq, void *priv)
245 {
246         struct lib80211_wep_data *wep = priv;
247 
248         if (len < wep->key_len)
249                 return -1;
250 
251         memcpy(key, wep->key, wep->key_len);
252 
253         return wep->key_len;
254 }
255 
256 static void lib80211_wep_print_stats(struct seq_file *m, void *priv)
257 {
258         struct lib80211_wep_data *wep = priv;
259         seq_printf(m, "key[%d] alg=WEP len=%d\n", wep->key_idx, wep->key_len);
260 }
261 
262 static struct lib80211_crypto_ops lib80211_crypt_wep = {
263         .name = "WEP",
264         .init = lib80211_wep_init,
265         .deinit = lib80211_wep_deinit,
266         .encrypt_mpdu = lib80211_wep_encrypt,
267         .decrypt_mpdu = lib80211_wep_decrypt,
268         .encrypt_msdu = NULL,
269         .decrypt_msdu = NULL,
270         .set_key = lib80211_wep_set_key,
271         .get_key = lib80211_wep_get_key,
272         .print_stats = lib80211_wep_print_stats,
273         .extra_mpdu_prefix_len = 4,     /* IV */
274         .extra_mpdu_postfix_len = 4,    /* ICV */
275         .owner = THIS_MODULE,
276 };
277 
278 static int __init lib80211_crypto_wep_init(void)
279 {
280         return lib80211_register_crypto_ops(&lib80211_crypt_wep);
281 }
282 
283 static void __exit lib80211_crypto_wep_exit(void)
284 {
285         lib80211_unregister_crypto_ops(&lib80211_crypt_wep);
286 }
287 
288 module_init(lib80211_crypto_wep_init);
289 module_exit(lib80211_crypto_wep_exit);
290 

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