xref: /openbmc/linux/net/mac80211/wep.c (revision 4800cd83)
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_blkcipher("ecb(arc4)", 0,
34 						CRYPTO_ALG_ASYNC);
35 	if (IS_ERR(local->wep_tx_tfm)) {
36 		local->wep_rx_tfm = ERR_PTR(-EINVAL);
37 		return PTR_ERR(local->wep_tx_tfm);
38 	}
39 
40 	local->wep_rx_tfm = crypto_alloc_blkcipher("ecb(arc4)", 0,
41 						CRYPTO_ALG_ASYNC);
42 	if (IS_ERR(local->wep_rx_tfm)) {
43 		crypto_free_blkcipher(local->wep_tx_tfm);
44 		local->wep_tx_tfm = ERR_PTR(-EINVAL);
45 		return PTR_ERR(local->wep_rx_tfm);
46 	}
47 
48 	return 0;
49 }
50 
51 void ieee80211_wep_free(struct ieee80211_local *local)
52 {
53 	if (!IS_ERR(local->wep_tx_tfm))
54 		crypto_free_blkcipher(local->wep_tx_tfm);
55 	if (!IS_ERR(local->wep_rx_tfm))
56 		crypto_free_blkcipher(local->wep_rx_tfm);
57 }
58 
59 static inline bool ieee80211_wep_weak_iv(u32 iv, int keylen)
60 {
61 	/*
62 	 * Fluhrer, Mantin, and Shamir have reported weaknesses in the
63 	 * key scheduling algorithm of RC4. At least IVs (KeyByte + 3,
64 	 * 0xff, N) can be used to speedup attacks, so avoid using them.
65 	 */
66 	if ((iv & 0xff00) == 0xff00) {
67 		u8 B = (iv >> 16) & 0xff;
68 		if (B >= 3 && B < 3 + keylen)
69 			return true;
70 	}
71 	return false;
72 }
73 
74 
75 static void ieee80211_wep_get_iv(struct ieee80211_local *local,
76 				 int keylen, int keyidx, u8 *iv)
77 {
78 	local->wep_iv++;
79 	if (ieee80211_wep_weak_iv(local->wep_iv, keylen))
80 		local->wep_iv += 0x0100;
81 
82 	if (!iv)
83 		return;
84 
85 	*iv++ = (local->wep_iv >> 16) & 0xff;
86 	*iv++ = (local->wep_iv >> 8) & 0xff;
87 	*iv++ = local->wep_iv & 0xff;
88 	*iv++ = keyidx << 6;
89 }
90 
91 
92 static u8 *ieee80211_wep_add_iv(struct ieee80211_local *local,
93 				struct sk_buff *skb,
94 				int keylen, int keyidx)
95 {
96 	struct ieee80211_hdr *hdr = (struct ieee80211_hdr *)skb->data;
97 	unsigned int hdrlen;
98 	u8 *newhdr;
99 
100 	hdr->frame_control |= cpu_to_le16(IEEE80211_FCTL_PROTECTED);
101 
102 	if (WARN_ON(skb_tailroom(skb) < WEP_ICV_LEN ||
103 		    skb_headroom(skb) < WEP_IV_LEN))
104 		return NULL;
105 
106 	hdrlen = ieee80211_hdrlen(hdr->frame_control);
107 	newhdr = skb_push(skb, WEP_IV_LEN);
108 	memmove(newhdr, newhdr + WEP_IV_LEN, hdrlen);
109 	ieee80211_wep_get_iv(local, keylen, keyidx, newhdr + hdrlen);
110 	return newhdr + hdrlen;
111 }
112 
113 
114 static void ieee80211_wep_remove_iv(struct ieee80211_local *local,
115 				    struct sk_buff *skb,
116 				    struct ieee80211_key *key)
117 {
118 	struct ieee80211_hdr *hdr = (struct ieee80211_hdr *)skb->data;
119 	unsigned int hdrlen;
120 
121 	hdrlen = ieee80211_hdrlen(hdr->frame_control);
122 	memmove(skb->data + WEP_IV_LEN, skb->data, hdrlen);
123 	skb_pull(skb, WEP_IV_LEN);
124 }
125 
126 
127 /* Perform WEP encryption using given key. data buffer must have tailroom
128  * for 4-byte ICV. data_len must not include this ICV. Note: this function
129  * does _not_ add IV. data = RC4(data | CRC32(data)) */
130 int ieee80211_wep_encrypt_data(struct crypto_blkcipher *tfm, u8 *rc4key,
131 			       size_t klen, u8 *data, size_t data_len)
132 {
133 	struct blkcipher_desc desc = { .tfm = tfm };
134 	struct scatterlist sg;
135 	__le32 icv;
136 
137 	if (IS_ERR(tfm))
138 		return -1;
139 
140 	icv = cpu_to_le32(~crc32_le(~0, data, data_len));
141 	put_unaligned(icv, (__le32 *)(data + data_len));
142 
143 	crypto_blkcipher_setkey(tfm, rc4key, klen);
144 	sg_init_one(&sg, data, data_len + WEP_ICV_LEN);
145 	crypto_blkcipher_encrypt(&desc, &sg, &sg, sg.length);
146 
147 	return 0;
148 }
149 
150 
151 /* Perform WEP encryption on given skb. 4 bytes of extra space (IV) in the
152  * beginning of the buffer 4 bytes of extra space (ICV) in the end of the
153  * buffer will be added. Both IV and ICV will be transmitted, so the
154  * payload length increases with 8 bytes.
155  *
156  * WEP frame payload: IV + TX key idx, RC4(data), ICV = RC4(CRC32(data))
157  */
158 int ieee80211_wep_encrypt(struct ieee80211_local *local,
159 			  struct sk_buff *skb,
160 			  const u8 *key, int keylen, int keyidx)
161 {
162 	u8 *iv;
163 	size_t len;
164 	u8 rc4key[3 + WLAN_KEY_LEN_WEP104];
165 
166 	iv = ieee80211_wep_add_iv(local, skb, keylen, keyidx);
167 	if (!iv)
168 		return -1;
169 
170 	len = skb->len - (iv + WEP_IV_LEN - skb->data);
171 
172 	/* Prepend 24-bit IV to RC4 key */
173 	memcpy(rc4key, iv, 3);
174 
175 	/* Copy rest of the WEP key (the secret part) */
176 	memcpy(rc4key + 3, key, keylen);
177 
178 	/* Add room for ICV */
179 	skb_put(skb, WEP_ICV_LEN);
180 
181 	return ieee80211_wep_encrypt_data(local->wep_tx_tfm, rc4key, keylen + 3,
182 					  iv + WEP_IV_LEN, len);
183 }
184 
185 
186 /* Perform WEP decryption using given key. data buffer includes encrypted
187  * payload, including 4-byte ICV, but _not_ IV. data_len must not include ICV.
188  * Return 0 on success and -1 on ICV mismatch. */
189 int ieee80211_wep_decrypt_data(struct crypto_blkcipher *tfm, u8 *rc4key,
190 			       size_t klen, u8 *data, size_t data_len)
191 {
192 	struct blkcipher_desc desc = { .tfm = tfm };
193 	struct scatterlist sg;
194 	__le32 crc;
195 
196 	if (IS_ERR(tfm))
197 		return -1;
198 
199 	crypto_blkcipher_setkey(tfm, rc4key, klen);
200 	sg_init_one(&sg, data, data_len + WEP_ICV_LEN);
201 	crypto_blkcipher_decrypt(&desc, &sg, &sg, sg.length);
202 
203 	crc = cpu_to_le32(~crc32_le(~0, data, data_len));
204 	if (memcmp(&crc, data + data_len, WEP_ICV_LEN) != 0)
205 		/* ICV mismatch */
206 		return -1;
207 
208 	return 0;
209 }
210 
211 
212 /* Perform WEP decryption on given skb. Buffer includes whole WEP part of
213  * the frame: IV (4 bytes), encrypted payload (including SNAP header),
214  * ICV (4 bytes). skb->len includes both IV and ICV.
215  *
216  * Returns 0 if frame was decrypted successfully and ICV was correct and -1 on
217  * failure. If frame is OK, IV and ICV will be removed, i.e., decrypted payload
218  * is moved to the beginning of the skb and skb length will be reduced.
219  */
220 static int ieee80211_wep_decrypt(struct ieee80211_local *local,
221 				 struct sk_buff *skb,
222 				 struct ieee80211_key *key)
223 {
224 	u32 klen;
225 	u8 rc4key[3 + WLAN_KEY_LEN_WEP104];
226 	u8 keyidx;
227 	struct ieee80211_hdr *hdr = (struct ieee80211_hdr *)skb->data;
228 	unsigned int hdrlen;
229 	size_t len;
230 	int ret = 0;
231 
232 	if (!ieee80211_has_protected(hdr->frame_control))
233 		return -1;
234 
235 	hdrlen = ieee80211_hdrlen(hdr->frame_control);
236 	if (skb->len < hdrlen + WEP_IV_LEN + WEP_ICV_LEN)
237 		return -1;
238 
239 	len = skb->len - hdrlen - WEP_IV_LEN - WEP_ICV_LEN;
240 
241 	keyidx = skb->data[hdrlen + 3] >> 6;
242 
243 	if (!key || keyidx != key->conf.keyidx)
244 		return -1;
245 
246 	klen = 3 + key->conf.keylen;
247 
248 	/* Prepend 24-bit IV to RC4 key */
249 	memcpy(rc4key, skb->data + hdrlen, 3);
250 
251 	/* Copy rest of the WEP key (the secret part) */
252 	memcpy(rc4key + 3, key->conf.key, key->conf.keylen);
253 
254 	if (ieee80211_wep_decrypt_data(local->wep_rx_tfm, rc4key, klen,
255 				       skb->data + hdrlen + WEP_IV_LEN,
256 				       len))
257 		ret = -1;
258 
259 	/* Trim ICV */
260 	skb_trim(skb, skb->len - WEP_ICV_LEN);
261 
262 	/* Remove IV */
263 	memmove(skb->data + WEP_IV_LEN, skb->data, hdrlen);
264 	skb_pull(skb, WEP_IV_LEN);
265 
266 	return ret;
267 }
268 
269 
270 bool ieee80211_wep_is_weak_iv(struct sk_buff *skb, struct ieee80211_key *key)
271 {
272 	struct ieee80211_hdr *hdr = (struct ieee80211_hdr *)skb->data;
273 	unsigned int hdrlen;
274 	u8 *ivpos;
275 	u32 iv;
276 
277 	if (!ieee80211_has_protected(hdr->frame_control))
278 		return false;
279 
280 	hdrlen = ieee80211_hdrlen(hdr->frame_control);
281 	ivpos = skb->data + hdrlen;
282 	iv = (ivpos[0] << 16) | (ivpos[1] << 8) | ivpos[2];
283 
284 	return ieee80211_wep_weak_iv(iv, key->conf.keylen);
285 }
286 
287 ieee80211_rx_result
288 ieee80211_crypto_wep_decrypt(struct ieee80211_rx_data *rx)
289 {
290 	struct sk_buff *skb = rx->skb;
291 	struct ieee80211_rx_status *status = IEEE80211_SKB_RXCB(skb);
292 	struct ieee80211_hdr *hdr = (struct ieee80211_hdr *)skb->data;
293 
294 	if (!ieee80211_is_data(hdr->frame_control) &&
295 	    !ieee80211_is_auth(hdr->frame_control))
296 		return RX_CONTINUE;
297 
298 	if (!(status->flag & RX_FLAG_DECRYPTED)) {
299 		if (ieee80211_wep_decrypt(rx->local, rx->skb, rx->key))
300 			return RX_DROP_UNUSABLE;
301 	} else if (!(status->flag & RX_FLAG_IV_STRIPPED)) {
302 		ieee80211_wep_remove_iv(rx->local, rx->skb, rx->key);
303 		/* remove ICV */
304 		skb_trim(rx->skb, rx->skb->len - WEP_ICV_LEN);
305 	}
306 
307 	return RX_CONTINUE;
308 }
309 
310 static int wep_encrypt_skb(struct ieee80211_tx_data *tx, struct sk_buff *skb)
311 {
312 	struct ieee80211_tx_info *info = IEEE80211_SKB_CB(skb);
313 
314 	if (!info->control.hw_key) {
315 		if (ieee80211_wep_encrypt(tx->local, skb, tx->key->conf.key,
316 					  tx->key->conf.keylen,
317 					  tx->key->conf.keyidx))
318 			return -1;
319 	} else if (info->control.hw_key->flags &
320 			IEEE80211_KEY_FLAG_GENERATE_IV) {
321 		if (!ieee80211_wep_add_iv(tx->local, skb,
322 					  tx->key->conf.keylen,
323 					  tx->key->conf.keyidx))
324 			return -1;
325 	}
326 
327 	return 0;
328 }
329 
330 ieee80211_tx_result
331 ieee80211_crypto_wep_encrypt(struct ieee80211_tx_data *tx)
332 {
333 	struct sk_buff *skb;
334 
335 	ieee80211_tx_set_protected(tx);
336 
337 	skb = tx->skb;
338 	do {
339 		if (wep_encrypt_skb(tx, skb) < 0) {
340 			I802_DEBUG_INC(tx->local->tx_handlers_drop_wep);
341 			return TX_DROP;
342 		}
343 	} while ((skb = skb->next));
344 
345 	return TX_CONTINUE;
346 }
347