xref: /openbmc/linux/net/mac80211/wep.c (revision 95e9fd10) 
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, 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) < 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  */
163 int ieee80211_wep_encrypt(struct ieee80211_local *local,
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 
289 ieee80211_rx_result
290 ieee80211_crypto_wep_decrypt(struct ieee80211_rx_data *rx)
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) ||
332 		   (hw_key->flags & IEEE80211_KEY_FLAG_PUT_IV_SPACE)) {
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 
342 ieee80211_tx_result
343 ieee80211_crypto_wep_encrypt(struct ieee80211_tx_data *tx)
344 {
345 	struct sk_buff *skb;
346 
347 	ieee80211_tx_set_protected(tx);
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 }
358