xref: /linux/net/mac80211/wep.c (revision c4c11dd160a8cc98f402c4e12f94b1572e822ffd) 
1 /*
2  * Software WEP encryption implementation
3  * Copyright 2002, Jouni Malinen <jkmaline@cc.hut.fi>
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 
28 int ieee80211_wep_init(struct ieee80211_local *local)
29 {
30 	/* start WEP IV from a random value */
31 	get_random_bytes(&local->wep_iv, IEEE80211_WEP_IV_LEN);
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 
49 void ieee80211_wep_free(struct ieee80211_local *local)
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 
99 	hdr->frame_control |= cpu_to_le16(IEEE80211_FCTL_PROTECTED);
100 
101 	if (WARN_ON(skb_tailroom(skb) < IEEE80211_WEP_ICV_LEN ||
102 		    skb_headroom(skb) < IEEE80211_WEP_IV_LEN))
103 		return NULL;
104 
105 	hdrlen = ieee80211_hdrlen(hdr->frame_control);
106 	newhdr = skb_push(skb, IEEE80211_WEP_IV_LEN);
107 	memmove(newhdr, newhdr + IEEE80211_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) +
115 				    IEEE80211_WEP_IV_LEN);
116 	ieee80211_wep_get_iv(local, keylen, keyidx, newhdr + hdrlen);
117 	return newhdr + hdrlen;
118 }
119 
120 
121 static void ieee80211_wep_remove_iv(struct ieee80211_local *local,
122 				    struct sk_buff *skb,
123 				    struct ieee80211_key *key)
124 {
125 	struct ieee80211_hdr *hdr = (struct ieee80211_hdr *)skb->data;
126 	unsigned int hdrlen;
127 
128 	hdrlen = ieee80211_hdrlen(hdr->frame_control);
129 	memmove(skb->data + IEEE80211_WEP_IV_LEN, skb->data, hdrlen);
130 	skb_pull(skb, IEEE80211_WEP_IV_LEN);
131 }
132 
133 
134 /* Perform WEP encryption using given key. data buffer must have tailroom
135  * for 4-byte ICV. data_len must not include this ICV. Note: this function
136  * does _not_ add IV. data = RC4(data | CRC32(data)) */
137 int ieee80211_wep_encrypt_data(struct crypto_cipher *tfm, u8 *rc4key,
138 			       size_t klen, u8 *data, size_t data_len)
139 {
140 	__le32 icv;
141 	int i;
142 
143 	if (IS_ERR(tfm))
144 		return -1;
145 
146 	icv = cpu_to_le32(~crc32_le(~0, data, data_len));
147 	put_unaligned(icv, (__le32 *)(data + data_len));
148 
149 	crypto_cipher_setkey(tfm, rc4key, klen);
150 	for (i = 0; i < data_len + IEEE80211_WEP_ICV_LEN; i++)
151 		crypto_cipher_encrypt_one(tfm, data + i, data + i);
152 
153 	return 0;
154 }
155 
156 
157 /* Perform WEP encryption on given skb. 4 bytes of extra space (IV) in the
158  * beginning of the buffer 4 bytes of extra space (ICV) in the end of the
159  * buffer will be added. Both IV and ICV will be transmitted, so the
160  * payload length increases with 8 bytes.
161  *
162  * WEP frame payload: IV + TX key idx, RC4(data), ICV = RC4(CRC32(data))
163  */
164 int ieee80211_wep_encrypt(struct ieee80211_local *local,
165 			  struct sk_buff *skb,
166 			  const u8 *key, int keylen, int keyidx)
167 {
168 	u8 *iv;
169 	size_t len;
170 	u8 rc4key[3 + WLAN_KEY_LEN_WEP104];
171 
172 	iv = ieee80211_wep_add_iv(local, skb, keylen, keyidx);
173 	if (!iv)
174 		return -1;
175 
176 	len = skb->len - (iv + IEEE80211_WEP_IV_LEN - skb->data);
177 
178 	/* Prepend 24-bit IV to RC4 key */
179 	memcpy(rc4key, iv, 3);
180 
181 	/* Copy rest of the WEP key (the secret part) */
182 	memcpy(rc4key + 3, key, keylen);
183 
184 	/* Add room for ICV */
185 	skb_put(skb, IEEE80211_WEP_ICV_LEN);
186 
187 	return ieee80211_wep_encrypt_data(local->wep_tx_tfm, rc4key, keylen + 3,
188 					  iv + IEEE80211_WEP_IV_LEN, len);
189 }
190 
191 
192 /* Perform WEP decryption using given key. data buffer includes encrypted
193  * payload, including 4-byte ICV, but _not_ IV. data_len must not include ICV.
194  * Return 0 on success and -1 on ICV mismatch. */
195 int ieee80211_wep_decrypt_data(struct crypto_cipher *tfm, u8 *rc4key,
196 			       size_t klen, u8 *data, size_t data_len)
197 {
198 	__le32 crc;
199 	int i;
200 
201 	if (IS_ERR(tfm))
202 		return -1;
203 
204 	crypto_cipher_setkey(tfm, rc4key, klen);
205 	for (i = 0; i < data_len + IEEE80211_WEP_ICV_LEN; i++)
206 		crypto_cipher_decrypt_one(tfm, data + i, data + i);
207 
208 	crc = cpu_to_le32(~crc32_le(~0, data, data_len));
209 	if (memcmp(&crc, data + data_len, IEEE80211_WEP_ICV_LEN) != 0)
210 		/* ICV mismatch */
211 		return -1;
212 
213 	return 0;
214 }
215 
216 
217 /* Perform WEP decryption on given skb. Buffer includes whole WEP part of
218  * the frame: IV (4 bytes), encrypted payload (including SNAP header),
219  * ICV (4 bytes). skb->len includes both IV and ICV.
220  *
221  * Returns 0 if frame was decrypted successfully and ICV was correct and -1 on
222  * failure. If frame is OK, IV and ICV will be removed, i.e., decrypted payload
223  * is moved to the beginning of the skb and skb length will be reduced.
224  */
225 static int ieee80211_wep_decrypt(struct ieee80211_local *local,
226 				 struct sk_buff *skb,
227 				 struct ieee80211_key *key)
228 {
229 	u32 klen;
230 	u8 rc4key[3 + WLAN_KEY_LEN_WEP104];
231 	u8 keyidx;
232 	struct ieee80211_hdr *hdr = (struct ieee80211_hdr *)skb->data;
233 	unsigned int hdrlen;
234 	size_t len;
235 	int ret = 0;
236 
237 	if (!ieee80211_has_protected(hdr->frame_control))
238 		return -1;
239 
240 	hdrlen = ieee80211_hdrlen(hdr->frame_control);
241 	if (skb->len < hdrlen + IEEE80211_WEP_IV_LEN + IEEE80211_WEP_ICV_LEN)
242 		return -1;
243 
244 	len = skb->len - hdrlen - IEEE80211_WEP_IV_LEN - IEEE80211_WEP_ICV_LEN;
245 
246 	keyidx = skb->data[hdrlen + 3] >> 6;
247 
248 	if (!key || keyidx != key->conf.keyidx)
249 		return -1;
250 
251 	klen = 3 + key->conf.keylen;
252 
253 	/* Prepend 24-bit IV to RC4 key */
254 	memcpy(rc4key, skb->data + hdrlen, 3);
255 
256 	/* Copy rest of the WEP key (the secret part) */
257 	memcpy(rc4key + 3, key->conf.key, key->conf.keylen);
258 
259 	if (ieee80211_wep_decrypt_data(local->wep_rx_tfm, rc4key, klen,
260 				       skb->data + hdrlen +
261 				       IEEE80211_WEP_IV_LEN, len))
262 		ret = -1;
263 
264 	/* Trim ICV */
265 	skb_trim(skb, skb->len - IEEE80211_WEP_ICV_LEN);
266 
267 	/* Remove IV */
268 	memmove(skb->data + IEEE80211_WEP_IV_LEN, skb->data, hdrlen);
269 	skb_pull(skb, IEEE80211_WEP_IV_LEN);
270 
271 	return ret;
272 }
273 
274 
275 static bool ieee80211_wep_is_weak_iv(struct sk_buff *skb,
276 				     struct ieee80211_key *key)
277 {
278 	struct ieee80211_hdr *hdr = (struct ieee80211_hdr *)skb->data;
279 	unsigned int hdrlen;
280 	u8 *ivpos;
281 	u32 iv;
282 
283 	hdrlen = ieee80211_hdrlen(hdr->frame_control);
284 	ivpos = skb->data + hdrlen;
285 	iv = (ivpos[0] << 16) | (ivpos[1] << 8) | ivpos[2];
286 
287 	return ieee80211_wep_weak_iv(iv, key->conf.keylen);
288 }
289 
290 ieee80211_rx_result
291 ieee80211_crypto_wep_decrypt(struct ieee80211_rx_data *rx)
292 {
293 	struct sk_buff *skb = rx->skb;
294 	struct ieee80211_rx_status *status = IEEE80211_SKB_RXCB(skb);
295 	struct ieee80211_hdr *hdr = (struct ieee80211_hdr *)skb->data;
296 	__le16 fc = hdr->frame_control;
297 
298 	if (!ieee80211_is_data(fc) && !ieee80211_is_auth(fc))
299 		return RX_CONTINUE;
300 
301 	if (!(status->flag & RX_FLAG_DECRYPTED)) {
302 		if (skb_linearize(rx->skb))
303 			return RX_DROP_UNUSABLE;
304 		if (rx->sta && ieee80211_wep_is_weak_iv(rx->skb, rx->key))
305 			rx->sta->wep_weak_iv_count++;
306 		if (ieee80211_wep_decrypt(rx->local, rx->skb, rx->key))
307 			return RX_DROP_UNUSABLE;
308 	} else if (!(status->flag & RX_FLAG_IV_STRIPPED)) {
309 		if (!pskb_may_pull(rx->skb, ieee80211_hdrlen(fc) +
310 					    IEEE80211_WEP_IV_LEN))
311 			return RX_DROP_UNUSABLE;
312 		if (rx->sta && ieee80211_wep_is_weak_iv(rx->skb, rx->key))
313 			rx->sta->wep_weak_iv_count++;
314 		ieee80211_wep_remove_iv(rx->local, rx->skb, rx->key);
315 		/* remove ICV */
316 		if (pskb_trim(rx->skb, rx->skb->len - IEEE80211_WEP_ICV_LEN))
317 			return RX_DROP_UNUSABLE;
318 	}
319 
320 	return RX_CONTINUE;
321 }
322 
323 static int wep_encrypt_skb(struct ieee80211_tx_data *tx, struct sk_buff *skb)
324 {
325 	struct ieee80211_tx_info *info = IEEE80211_SKB_CB(skb);
326 	struct ieee80211_key_conf *hw_key = info->control.hw_key;
327 
328 	if (!hw_key) {
329 		if (ieee80211_wep_encrypt(tx->local, skb, tx->key->conf.key,
330 					  tx->key->conf.keylen,
331 					  tx->key->conf.keyidx))
332 			return -1;
333 	} else if ((hw_key->flags & IEEE80211_KEY_FLAG_GENERATE_IV) ||
334 		   (hw_key->flags & IEEE80211_KEY_FLAG_PUT_IV_SPACE)) {
335 		if (!ieee80211_wep_add_iv(tx->local, skb,
336 					  tx->key->conf.keylen,
337 					  tx->key->conf.keyidx))
338 			return -1;
339 	}
340 
341 	return 0;
342 }
343 
344 ieee80211_tx_result
345 ieee80211_crypto_wep_encrypt(struct ieee80211_tx_data *tx)
346 {
347 	struct sk_buff *skb;
348 
349 	ieee80211_tx_set_protected(tx);
350 
351 	skb_queue_walk(&tx->skbs, skb) {
352 		if (wep_encrypt_skb(tx, skb) < 0) {
353 			I802_DEBUG_INC(tx->local->tx_handlers_drop_wep);
354 			return TX_DROP;
355 		}
356 	}
357 
358 	return TX_CONTINUE;
359 }
360