xref: /openbmc/linux/net/mac80211/wep.c (revision 22246614) 
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 
21 #include <net/mac80211.h>
22 #include "ieee80211_i.h"
23 #include "wep.h"
24 
25 
26 int ieee80211_wep_init(struct ieee80211_local *local)
27 {
28 	/* start WEP IV from a random value */
29 	get_random_bytes(&local->wep_iv, WEP_IV_LEN);
30 
31 	local->wep_tx_tfm = crypto_alloc_blkcipher("ecb(arc4)", 0,
32 						CRYPTO_ALG_ASYNC);
33 	if (IS_ERR(local->wep_tx_tfm))
34 		return -ENOMEM;
35 
36 	local->wep_rx_tfm = crypto_alloc_blkcipher("ecb(arc4)", 0,
37 						CRYPTO_ALG_ASYNC);
38 	if (IS_ERR(local->wep_rx_tfm)) {
39 		crypto_free_blkcipher(local->wep_tx_tfm);
40 		return -ENOMEM;
41 	}
42 
43 	return 0;
44 }
45 
46 void ieee80211_wep_free(struct ieee80211_local *local)
47 {
48 	crypto_free_blkcipher(local->wep_tx_tfm);
49 	crypto_free_blkcipher(local->wep_rx_tfm);
50 }
51 
52 static inline int ieee80211_wep_weak_iv(u32 iv, int keylen)
53 {
54 	/* Fluhrer, Mantin, and Shamir have reported weaknesses in the
55 	 * key scheduling algorithm of RC4. At least IVs (KeyByte + 3,
56 	 * 0xff, N) can be used to speedup attacks, so avoid using them. */
57 	if ((iv & 0xff00) == 0xff00) {
58 		u8 B = (iv >> 16) & 0xff;
59 		if (B >= 3 && B < 3 + keylen)
60 			return 1;
61 	}
62 	return 0;
63 }
64 
65 
66 static void ieee80211_wep_get_iv(struct ieee80211_local *local,
67 				 struct ieee80211_key *key, u8 *iv)
68 {
69 	local->wep_iv++;
70 	if (ieee80211_wep_weak_iv(local->wep_iv, key->conf.keylen))
71 		local->wep_iv += 0x0100;
72 
73 	if (!iv)
74 		return;
75 
76 	*iv++ = (local->wep_iv >> 16) & 0xff;
77 	*iv++ = (local->wep_iv >> 8) & 0xff;
78 	*iv++ = local->wep_iv & 0xff;
79 	*iv++ = key->conf.keyidx << 6;
80 }
81 
82 
83 static u8 *ieee80211_wep_add_iv(struct ieee80211_local *local,
84 				struct sk_buff *skb,
85 				struct ieee80211_key *key)
86 {
87 	struct ieee80211_hdr *hdr = (struct ieee80211_hdr *) skb->data;
88 	u16 fc;
89 	int hdrlen;
90 	u8 *newhdr;
91 
92 	fc = le16_to_cpu(hdr->frame_control);
93 	fc |= IEEE80211_FCTL_PROTECTED;
94 	hdr->frame_control = cpu_to_le16(fc);
95 
96 	if ((skb_headroom(skb) < WEP_IV_LEN ||
97 	     skb_tailroom(skb) < WEP_ICV_LEN)) {
98 		I802_DEBUG_INC(local->tx_expand_skb_head);
99 		if (unlikely(pskb_expand_head(skb, WEP_IV_LEN, WEP_ICV_LEN,
100 					      GFP_ATOMIC)))
101 			return NULL;
102 	}
103 
104 	hdrlen = ieee80211_get_hdrlen(fc);
105 	newhdr = skb_push(skb, WEP_IV_LEN);
106 	memmove(newhdr, newhdr + WEP_IV_LEN, hdrlen);
107 	ieee80211_wep_get_iv(local, key, newhdr + hdrlen);
108 	return newhdr + hdrlen;
109 }
110 
111 
112 static void ieee80211_wep_remove_iv(struct ieee80211_local *local,
113 				    struct sk_buff *skb,
114 				    struct ieee80211_key *key)
115 {
116 	struct ieee80211_hdr *hdr = (struct ieee80211_hdr *) skb->data;
117 	u16 fc;
118 	int hdrlen;
119 
120 	fc = le16_to_cpu(hdr->frame_control);
121 	hdrlen = ieee80211_get_hdrlen(fc);
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 void 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 	icv = (__le32 *)(data + data_len);
138 	*icv = cpu_to_le32(~crc32_le(~0, data, data_len));
139 
140 	crypto_blkcipher_setkey(tfm, rc4key, klen);
141 	sg_init_one(&sg, data, data_len + WEP_ICV_LEN);
142 	crypto_blkcipher_encrypt(&desc, &sg, &sg, sg.length);
143 }
144 
145 
146 /* Perform WEP encryption on given skb. 4 bytes of extra space (IV) in the
147  * beginning of the buffer 4 bytes of extra space (ICV) in the end of the
148  * buffer will be added. Both IV and ICV will be transmitted, so the
149  * payload length increases with 8 bytes.
150  *
151  * WEP frame payload: IV + TX key idx, RC4(data), ICV = RC4(CRC32(data))
152  */
153 int ieee80211_wep_encrypt(struct ieee80211_local *local, struct sk_buff *skb,
154 			  struct ieee80211_key *key)
155 {
156 	u32 klen;
157 	u8 *rc4key, *iv;
158 	size_t len;
159 
160 	if (!key || key->conf.alg != ALG_WEP)
161 		return -1;
162 
163 	klen = 3 + key->conf.keylen;
164 	rc4key = kmalloc(klen, GFP_ATOMIC);
165 	if (!rc4key)
166 		return -1;
167 
168 	iv = ieee80211_wep_add_iv(local, skb, key);
169 	if (!iv) {
170 		kfree(rc4key);
171 		return -1;
172 	}
173 
174 	len = skb->len - (iv + WEP_IV_LEN - skb->data);
175 
176 	/* Prepend 24-bit IV to RC4 key */
177 	memcpy(rc4key, iv, 3);
178 
179 	/* Copy rest of the WEP key (the secret part) */
180 	memcpy(rc4key + 3, key->conf.key, key->conf.keylen);
181 
182 	/* Add room for ICV */
183 	skb_put(skb, WEP_ICV_LEN);
184 
185 	ieee80211_wep_encrypt_data(local->wep_tx_tfm, rc4key, klen,
186 				   iv + WEP_IV_LEN, len);
187 
188 	kfree(rc4key);
189 
190 	return 0;
191 }
192 
193 
194 /* Perform WEP decryption using given key. data buffer includes encrypted
195  * payload, including 4-byte ICV, but _not_ IV. data_len must not include ICV.
196  * Return 0 on success and -1 on ICV mismatch. */
197 int ieee80211_wep_decrypt_data(struct crypto_blkcipher *tfm, u8 *rc4key,
198 			       size_t klen, u8 *data, size_t data_len)
199 {
200 	struct blkcipher_desc desc = { .tfm = tfm };
201 	struct scatterlist sg;
202 	__le32 crc;
203 
204 	crypto_blkcipher_setkey(tfm, rc4key, klen);
205 	sg_init_one(&sg, data, data_len + WEP_ICV_LEN);
206 	crypto_blkcipher_decrypt(&desc, &sg, &sg, sg.length);
207 
208 	crc = cpu_to_le32(~crc32_le(~0, data, data_len));
209 	if (memcmp(&crc, data + data_len, 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 int ieee80211_wep_decrypt(struct ieee80211_local *local, struct sk_buff *skb,
226 			  struct ieee80211_key *key)
227 {
228 	u32 klen;
229 	u8 *rc4key;
230 	u8 keyidx;
231 	struct ieee80211_hdr *hdr = (struct ieee80211_hdr *) skb->data;
232 	u16 fc;
233 	int hdrlen;
234 	size_t len;
235 	int ret = 0;
236 
237 	fc = le16_to_cpu(hdr->frame_control);
238 	if (!(fc & IEEE80211_FCTL_PROTECTED))
239 		return -1;
240 
241 	hdrlen = ieee80211_get_hdrlen(fc);
242 
243 	if (skb->len < 8 + hdrlen)
244 		return -1;
245 
246 	len = skb->len - hdrlen - 8;
247 
248 	keyidx = skb->data[hdrlen + 3] >> 6;
249 
250 	if (!key || keyidx != key->conf.keyidx || key->conf.alg != ALG_WEP)
251 		return -1;
252 
253 	klen = 3 + key->conf.keylen;
254 
255 	rc4key = kmalloc(klen, GFP_ATOMIC);
256 	if (!rc4key)
257 		return -1;
258 
259 	/* Prepend 24-bit IV to RC4 key */
260 	memcpy(rc4key, skb->data + hdrlen, 3);
261 
262 	/* Copy rest of the WEP key (the secret part) */
263 	memcpy(rc4key + 3, key->conf.key, key->conf.keylen);
264 
265 	if (ieee80211_wep_decrypt_data(local->wep_rx_tfm, rc4key, klen,
266 				       skb->data + hdrlen + WEP_IV_LEN,
267 				       len)) {
268 		if (net_ratelimit())
269 			printk(KERN_DEBUG "WEP decrypt failed (ICV)\n");
270 		ret = -1;
271 	}
272 
273 	kfree(rc4key);
274 
275 	/* Trim ICV */
276 	skb_trim(skb, skb->len - WEP_ICV_LEN);
277 
278 	/* Remove IV */
279 	memmove(skb->data + WEP_IV_LEN, skb->data, hdrlen);
280 	skb_pull(skb, WEP_IV_LEN);
281 
282 	return ret;
283 }
284 
285 
286 u8 * ieee80211_wep_is_weak_iv(struct sk_buff *skb, struct ieee80211_key *key)
287 {
288 	struct ieee80211_hdr *hdr = (struct ieee80211_hdr *) skb->data;
289 	u16 fc;
290 	int hdrlen;
291 	u8 *ivpos;
292 	u32 iv;
293 
294 	fc = le16_to_cpu(hdr->frame_control);
295 	if (!(fc & IEEE80211_FCTL_PROTECTED))
296 		return NULL;
297 
298 	hdrlen = ieee80211_get_hdrlen(fc);
299 	ivpos = skb->data + hdrlen;
300 	iv = (ivpos[0] << 16) | (ivpos[1] << 8) | ivpos[2];
301 
302 	if (ieee80211_wep_weak_iv(iv, key->conf.keylen))
303 		return ivpos;
304 
305 	return NULL;
306 }
307 
308 ieee80211_rx_result
309 ieee80211_crypto_wep_decrypt(struct ieee80211_rx_data *rx)
310 {
311 	if ((rx->fc & IEEE80211_FCTL_FTYPE) != IEEE80211_FTYPE_DATA &&
312 	    ((rx->fc & IEEE80211_FCTL_FTYPE) != IEEE80211_FTYPE_MGMT ||
313 	     (rx->fc & IEEE80211_FCTL_STYPE) != IEEE80211_STYPE_AUTH))
314 		return RX_CONTINUE;
315 
316 	if (!(rx->status->flag & RX_FLAG_DECRYPTED)) {
317 		if (ieee80211_wep_decrypt(rx->local, rx->skb, rx->key)) {
318 #ifdef CONFIG_MAC80211_DEBUG
319 			if (net_ratelimit())
320 				printk(KERN_DEBUG "%s: RX WEP frame, decrypt "
321 				       "failed\n", rx->dev->name);
322 #endif /* CONFIG_MAC80211_DEBUG */
323 			return RX_DROP_UNUSABLE;
324 		}
325 	} else if (!(rx->status->flag & RX_FLAG_IV_STRIPPED)) {
326 		ieee80211_wep_remove_iv(rx->local, rx->skb, rx->key);
327 		/* remove ICV */
328 		skb_trim(rx->skb, rx->skb->len - 4);
329 	}
330 
331 	return RX_CONTINUE;
332 }
333 
334 static int wep_encrypt_skb(struct ieee80211_tx_data *tx, struct sk_buff *skb)
335 {
336 	if (!(tx->key->flags & KEY_FLAG_UPLOADED_TO_HARDWARE)) {
337 		if (ieee80211_wep_encrypt(tx->local, skb, tx->key))
338 			return -1;
339 	} else {
340 		tx->control->key_idx = tx->key->conf.hw_key_idx;
341 		if (tx->key->conf.flags & IEEE80211_KEY_FLAG_GENERATE_IV) {
342 			if (!ieee80211_wep_add_iv(tx->local, skb, tx->key))
343 				return -1;
344 		}
345 	}
346 	return 0;
347 }
348 
349 ieee80211_tx_result
350 ieee80211_crypto_wep_encrypt(struct ieee80211_tx_data *tx)
351 {
352 	tx->control->iv_len = WEP_IV_LEN;
353 	tx->control->icv_len = WEP_ICV_LEN;
354 	ieee80211_tx_set_protected(tx);
355 
356 	if (wep_encrypt_skb(tx, tx->skb) < 0) {
357 		I802_DEBUG_INC(tx->local->tx_handlers_drop_wep);
358 		return TX_DROP;
359 	}
360 
361 	if (tx->extra_frag) {
362 		int i;
363 		for (i = 0; i < tx->num_extra_frag; i++) {
364 			if (wep_encrypt_skb(tx, tx->extra_frag[i]) < 0) {
365 				I802_DEBUG_INC(tx->local->
366 					       tx_handlers_drop_wep);
367 				return TX_DROP;
368 			}
369 		}
370 	}
371 
372 	return TX_CONTINUE;
373 }
374