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wep.c
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1 /*
2  * Software WEP encryption implementation
3  * Copyright 2002, Jouni Malinen <[email protected]>
4  * Copyright 2003, Instant802 Networks, Inc.
5  *
6  * This program is free software; you can redistribute it and/or modify
7  * it under the terms of the GNU General Public License version 2 as
8  * published by the Free Software Foundation.
9  */
10 
11 #include <linux/netdevice.h>
12 #include <linux/types.h>
13 #include <linux/random.h>
14 #include <linux/compiler.h>
15 #include <linux/crc32.h>
16 #include <linux/crypto.h>
17 #include <linux/err.h>
18 #include <linux/mm.h>
19 #include <linux/scatterlist.h>
20 #include <linux/slab.h>
21 #include <asm/unaligned.h>
22 
23 #include <net/mac80211.h>
24 #include "ieee80211_i.h"
25 #include "wep.h"
26 
27 
29 {
30  /* start WEP IV from a random value */
32 
33  local->wep_tx_tfm = crypto_alloc_cipher("arc4", 0, CRYPTO_ALG_ASYNC);
34  if (IS_ERR(local->wep_tx_tfm)) {
35  local->wep_rx_tfm = ERR_PTR(-EINVAL);
36  return PTR_ERR(local->wep_tx_tfm);
37  }
38 
39  local->wep_rx_tfm = crypto_alloc_cipher("arc4", 0, CRYPTO_ALG_ASYNC);
40  if (IS_ERR(local->wep_rx_tfm)) {
41  crypto_free_cipher(local->wep_tx_tfm);
42  local->wep_tx_tfm = ERR_PTR(-EINVAL);
43  return PTR_ERR(local->wep_rx_tfm);
44  }
45 
46  return 0;
47 }
48 
50 {
51  if (!IS_ERR(local->wep_tx_tfm))
52  crypto_free_cipher(local->wep_tx_tfm);
53  if (!IS_ERR(local->wep_rx_tfm))
54  crypto_free_cipher(local->wep_rx_tfm);
55 }
56 
57 static inline bool ieee80211_wep_weak_iv(u32 iv, int keylen)
58 {
59  /*
60  * Fluhrer, Mantin, and Shamir have reported weaknesses in the
61  * key scheduling algorithm of RC4. At least IVs (KeyByte + 3,
62  * 0xff, N) can be used to speedup attacks, so avoid using them.
63  */
64  if ((iv & 0xff00) == 0xff00) {
65  u8 B = (iv >> 16) & 0xff;
66  if (B >= 3 && B < 3 + keylen)
67  return true;
68  }
69  return false;
70 }
71 
72 
73 static void ieee80211_wep_get_iv(struct ieee80211_local *local,
74  int keylen, int keyidx, u8 *iv)
75 {
76  local->wep_iv++;
77  if (ieee80211_wep_weak_iv(local->wep_iv, keylen))
78  local->wep_iv += 0x0100;
79 
80  if (!iv)
81  return;
82 
83  *iv++ = (local->wep_iv >> 16) & 0xff;
84  *iv++ = (local->wep_iv >> 8) & 0xff;
85  *iv++ = local->wep_iv & 0xff;
86  *iv++ = keyidx << 6;
87 }
88 
89 
90 static u8 *ieee80211_wep_add_iv(struct ieee80211_local *local,
91  struct sk_buff *skb,
92  int keylen, int keyidx)
93 {
94  struct ieee80211_hdr *hdr = (struct ieee80211_hdr *)skb->data;
95  struct ieee80211_tx_info *info = IEEE80211_SKB_CB(skb);
96  unsigned int hdrlen;
97  u8 *newhdr;
98 
100 
101  if (WARN_ON(skb_tailroom(skb) < WEP_ICV_LEN ||
102  skb_headroom(skb) < WEP_IV_LEN))
103  return NULL;
104 
105  hdrlen = ieee80211_hdrlen(hdr->frame_control);
106  newhdr = skb_push(skb, WEP_IV_LEN);
107  memmove(newhdr, newhdr + WEP_IV_LEN, hdrlen);
108 
109  /* the HW only needs room for the IV, but not the actual IV */
110  if (info->control.hw_key &&
111  (info->control.hw_key->flags & IEEE80211_KEY_FLAG_PUT_IV_SPACE))
112  return newhdr + hdrlen;
113 
114  skb_set_network_header(skb, skb_network_offset(skb) + WEP_IV_LEN);
115  ieee80211_wep_get_iv(local, keylen, keyidx, newhdr + hdrlen);
116  return newhdr + hdrlen;
117 }
118 
119 
120 static void ieee80211_wep_remove_iv(struct ieee80211_local *local,
121  struct sk_buff *skb,
122  struct ieee80211_key *key)
123 {
124  struct ieee80211_hdr *hdr = (struct ieee80211_hdr *)skb->data;
125  unsigned int hdrlen;
126 
127  hdrlen = ieee80211_hdrlen(hdr->frame_control);
128  memmove(skb->data + WEP_IV_LEN, skb->data, hdrlen);
129  skb_pull(skb, WEP_IV_LEN);
130 }
131 
132 
133 /* Perform WEP encryption using given key. data buffer must have tailroom
134  * for 4-byte ICV. data_len must not include this ICV. Note: this function
135  * does _not_ add IV. data = RC4(data | CRC32(data)) */
136 int ieee80211_wep_encrypt_data(struct crypto_cipher *tfm, u8 *rc4key,
137  size_t klen, u8 *data, size_t data_len)
138 {
139  __le32 icv;
140  int i;
141 
142  if (IS_ERR(tfm))
143  return -1;
144 
145  icv = cpu_to_le32(~crc32_le(~0, data, data_len));
146  put_unaligned(icv, (__le32 *)(data + data_len));
147 
148  crypto_cipher_setkey(tfm, rc4key, klen);
149  for (i = 0; i < data_len + WEP_ICV_LEN; i++)
150  crypto_cipher_encrypt_one(tfm, data + i, data + i);
151 
152  return 0;
153 }
154 
155 
156 /* Perform WEP encryption on given skb. 4 bytes of extra space (IV) in the
157  * beginning of the buffer 4 bytes of extra space (ICV) in the end of the
158  * buffer will be added. Both IV and ICV will be transmitted, so the
159  * payload length increases with 8 bytes.
160  *
161  * WEP frame payload: IV + TX key idx, RC4(data), ICV = RC4(CRC32(data))
162  */
164  struct sk_buff *skb,
165  const u8 *key, int keylen, int keyidx)
166 {
167  u8 *iv;
168  size_t len;
169  u8 rc4key[3 + WLAN_KEY_LEN_WEP104];
170 
171  iv = ieee80211_wep_add_iv(local, skb, keylen, keyidx);
172  if (!iv)
173  return -1;
174 
175  len = skb->len - (iv + WEP_IV_LEN - skb->data);
176 
177  /* Prepend 24-bit IV to RC4 key */
178  memcpy(rc4key, iv, 3);
179 
180  /* Copy rest of the WEP key (the secret part) */
181  memcpy(rc4key + 3, key, keylen);
182 
183  /* Add room for ICV */
184  skb_put(skb, WEP_ICV_LEN);
185 
186  return ieee80211_wep_encrypt_data(local->wep_tx_tfm, rc4key, keylen + 3,
187  iv + WEP_IV_LEN, len);
188 }
189 
190 
191 /* Perform WEP decryption using given key. data buffer includes encrypted
192  * payload, including 4-byte ICV, but _not_ IV. data_len must not include ICV.
193  * Return 0 on success and -1 on ICV mismatch. */
194 int ieee80211_wep_decrypt_data(struct crypto_cipher *tfm, u8 *rc4key,
195  size_t klen, u8 *data, size_t data_len)
196 {
197  __le32 crc;
198  int i;
199 
200  if (IS_ERR(tfm))
201  return -1;
202 
203  crypto_cipher_setkey(tfm, rc4key, klen);
204  for (i = 0; i < data_len + WEP_ICV_LEN; i++)
205  crypto_cipher_decrypt_one(tfm, data + i, data + i);
206 
207  crc = cpu_to_le32(~crc32_le(~0, data, data_len));
208  if (memcmp(&crc, data + data_len, WEP_ICV_LEN) != 0)
209  /* ICV mismatch */
210  return -1;
211 
212  return 0;
213 }
214 
215 
216 /* Perform WEP decryption on given skb. Buffer includes whole WEP part of
217  * the frame: IV (4 bytes), encrypted payload (including SNAP header),
218  * ICV (4 bytes). skb->len includes both IV and ICV.
219  *
220  * Returns 0 if frame was decrypted successfully and ICV was correct and -1 on
221  * failure. If frame is OK, IV and ICV will be removed, i.e., decrypted payload
222  * is moved to the beginning of the skb and skb length will be reduced.
223  */
224 static int ieee80211_wep_decrypt(struct ieee80211_local *local,
225  struct sk_buff *skb,
226  struct ieee80211_key *key)
227 {
228  u32 klen;
229  u8 rc4key[3 + WLAN_KEY_LEN_WEP104];
230  u8 keyidx;
231  struct ieee80211_hdr *hdr = (struct ieee80211_hdr *)skb->data;
232  unsigned int hdrlen;
233  size_t len;
234  int ret = 0;
235 
236  if (!ieee80211_has_protected(hdr->frame_control))
237  return -1;
238 
239  hdrlen = ieee80211_hdrlen(hdr->frame_control);
240  if (skb->len < hdrlen + WEP_IV_LEN + WEP_ICV_LEN)
241  return -1;
242 
243  len = skb->len - hdrlen - WEP_IV_LEN - WEP_ICV_LEN;
244 
245  keyidx = skb->data[hdrlen + 3] >> 6;
246 
247  if (!key || keyidx != key->conf.keyidx)
248  return -1;
249 
250  klen = 3 + key->conf.keylen;
251 
252  /* Prepend 24-bit IV to RC4 key */
253  memcpy(rc4key, skb->data + hdrlen, 3);
254 
255  /* Copy rest of the WEP key (the secret part) */
256  memcpy(rc4key + 3, key->conf.key, key->conf.keylen);
257 
258  if (ieee80211_wep_decrypt_data(local->wep_rx_tfm, rc4key, klen,
259  skb->data + hdrlen + WEP_IV_LEN,
260  len))
261  ret = -1;
262 
263  /* Trim ICV */
264  skb_trim(skb, skb->len - WEP_ICV_LEN);
265 
266  /* Remove IV */
267  memmove(skb->data + WEP_IV_LEN, skb->data, hdrlen);
268  skb_pull(skb, WEP_IV_LEN);
269 
270  return ret;
271 }
272 
273 
274 static bool ieee80211_wep_is_weak_iv(struct sk_buff *skb,
275  struct ieee80211_key *key)
276 {
277  struct ieee80211_hdr *hdr = (struct ieee80211_hdr *)skb->data;
278  unsigned int hdrlen;
279  u8 *ivpos;
280  u32 iv;
281 
282  hdrlen = ieee80211_hdrlen(hdr->frame_control);
283  ivpos = skb->data + hdrlen;
284  iv = (ivpos[0] << 16) | (ivpos[1] << 8) | ivpos[2];
285 
286  return ieee80211_wep_weak_iv(iv, key->conf.keylen);
287 }
288 
291 {
292  struct sk_buff *skb = rx->skb;
293  struct ieee80211_rx_status *status = IEEE80211_SKB_RXCB(skb);
294  struct ieee80211_hdr *hdr = (struct ieee80211_hdr *)skb->data;
295  __le16 fc = hdr->frame_control;
296 
297  if (!ieee80211_is_data(fc) && !ieee80211_is_auth(fc))
298  return RX_CONTINUE;
299 
300  if (!(status->flag & RX_FLAG_DECRYPTED)) {
301  if (skb_linearize(rx->skb))
302  return RX_DROP_UNUSABLE;
303  if (rx->sta && ieee80211_wep_is_weak_iv(rx->skb, rx->key))
304  rx->sta->wep_weak_iv_count++;
305  if (ieee80211_wep_decrypt(rx->local, rx->skb, rx->key))
306  return RX_DROP_UNUSABLE;
307  } else if (!(status->flag & RX_FLAG_IV_STRIPPED)) {
308  if (!pskb_may_pull(rx->skb, ieee80211_hdrlen(fc) + WEP_IV_LEN))
309  return RX_DROP_UNUSABLE;
310  if (rx->sta && ieee80211_wep_is_weak_iv(rx->skb, rx->key))
311  rx->sta->wep_weak_iv_count++;
312  ieee80211_wep_remove_iv(rx->local, rx->skb, rx->key);
313  /* remove ICV */
314  if (pskb_trim(rx->skb, rx->skb->len - WEP_ICV_LEN))
315  return RX_DROP_UNUSABLE;
316  }
317 
318  return RX_CONTINUE;
319 }
320 
321 static int wep_encrypt_skb(struct ieee80211_tx_data *tx, struct sk_buff *skb)
322 {
323  struct ieee80211_tx_info *info = IEEE80211_SKB_CB(skb);
324  struct ieee80211_key_conf *hw_key = info->control.hw_key;
325 
326  if (!hw_key) {
327  if (ieee80211_wep_encrypt(tx->local, skb, tx->key->conf.key,
328  tx->key->conf.keylen,
329  tx->key->conf.keyidx))
330  return -1;
331  } else if ((hw_key->flags & IEEE80211_KEY_FLAG_GENERATE_IV) ||
333  if (!ieee80211_wep_add_iv(tx->local, skb,
334  tx->key->conf.keylen,
335  tx->key->conf.keyidx))
336  return -1;
337  }
338 
339  return 0;
340 }
341 
344 {
345  struct sk_buff *skb;
346 
348 
349  skb_queue_walk(&tx->skbs, skb) {
350  if (wep_encrypt_skb(tx, skb) < 0) {
351  I802_DEBUG_INC(tx->local->tx_handlers_drop_wep);
352  return TX_DROP;
353  }
354  }
355 
356  return TX_CONTINUE;
357 }