xref: /openbmc/linux/net/mac80211/wep.c (revision e868d61272caa648214046a096e5a6bfc068dc8c)
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 <asm/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 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->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->keyidx << 6;
80 }
81 
82 
83 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 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.page = virt_to_page(data);
142 	sg.offset = offset_in_page(data);
143 	sg.length = data_len + WEP_ICV_LEN;
144 	crypto_blkcipher_encrypt(&desc, &sg, &sg, sg.length);
145 }
146 
147 
148 /* Perform WEP encryption on given skb. 4 bytes of extra space (IV) in the
149  * beginning of the buffer 4 bytes of extra space (ICV) in the end of the
150  * buffer will be added. Both IV and ICV will be transmitted, so the
151  * payload length increases with 8 bytes.
152  *
153  * WEP frame payload: IV + TX key idx, RC4(data), ICV = RC4(CRC32(data))
154  */
155 int ieee80211_wep_encrypt(struct ieee80211_local *local, struct sk_buff *skb,
156 			  struct ieee80211_key *key)
157 {
158 	u32 klen;
159 	u8 *rc4key, *iv;
160 	size_t len;
161 
162 	if (!key || key->alg != ALG_WEP)
163 		return -1;
164 
165 	klen = 3 + key->keylen;
166 	rc4key = kmalloc(klen, GFP_ATOMIC);
167 	if (!rc4key)
168 		return -1;
169 
170 	iv = ieee80211_wep_add_iv(local, skb, key);
171 	if (!iv) {
172 		kfree(rc4key);
173 		return -1;
174 	}
175 
176 	len = skb->len - (iv + 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->key, key->keylen);
183 
184 	/* Add room for ICV */
185 	skb_put(skb, WEP_ICV_LEN);
186 
187 	ieee80211_wep_encrypt_data(local->wep_tx_tfm, rc4key, klen,
188 				   iv + WEP_IV_LEN, len);
189 
190 	kfree(rc4key);
191 
192 	return 0;
193 }
194 
195 
196 /* Perform WEP decryption using given key. data buffer includes encrypted
197  * payload, including 4-byte ICV, but _not_ IV. data_len must not include ICV.
198  * Return 0 on success and -1 on ICV mismatch. */
199 int ieee80211_wep_decrypt_data(struct crypto_blkcipher *tfm, u8 *rc4key,
200 			       size_t klen, u8 *data, size_t data_len)
201 {
202 	struct blkcipher_desc desc = { .tfm = tfm };
203 	struct scatterlist sg;
204 	__le32 crc;
205 
206 	crypto_blkcipher_setkey(tfm, rc4key, klen);
207 	sg.page = virt_to_page(data);
208 	sg.offset = offset_in_page(data);
209 	sg.length = data_len + WEP_ICV_LEN;
210 	crypto_blkcipher_decrypt(&desc, &sg, &sg, sg.length);
211 
212 	crc = cpu_to_le32(~crc32_le(~0, data, data_len));
213 	if (memcmp(&crc, data + data_len, WEP_ICV_LEN) != 0)
214 		/* ICV mismatch */
215 		return -1;
216 
217 	return 0;
218 }
219 
220 
221 /* Perform WEP decryption on given skb. Buffer includes whole WEP part of
222  * the frame: IV (4 bytes), encrypted payload (including SNAP header),
223  * ICV (4 bytes). skb->len includes both IV and ICV.
224  *
225  * Returns 0 if frame was decrypted successfully and ICV was correct and -1 on
226  * failure. If frame is OK, IV and ICV will be removed, i.e., decrypted payload
227  * is moved to the beginning of the skb and skb length will be reduced.
228  */
229 int ieee80211_wep_decrypt(struct ieee80211_local *local, struct sk_buff *skb,
230 			  struct ieee80211_key *key)
231 {
232 	u32 klen;
233 	u8 *rc4key;
234 	u8 keyidx;
235 	struct ieee80211_hdr *hdr = (struct ieee80211_hdr *) skb->data;
236 	u16 fc;
237 	int hdrlen;
238 	size_t len;
239 	int ret = 0;
240 
241 	fc = le16_to_cpu(hdr->frame_control);
242 	if (!(fc & IEEE80211_FCTL_PROTECTED))
243 		return -1;
244 
245 	hdrlen = ieee80211_get_hdrlen(fc);
246 
247 	if (skb->len < 8 + hdrlen)
248 		return -1;
249 
250 	len = skb->len - hdrlen - 8;
251 
252 	keyidx = skb->data[hdrlen + 3] >> 6;
253 
254 	if (!key || keyidx != key->keyidx || key->alg != ALG_WEP)
255 		return -1;
256 
257 	klen = 3 + key->keylen;
258 
259 	rc4key = kmalloc(klen, GFP_ATOMIC);
260 	if (!rc4key)
261 		return -1;
262 
263 	/* Prepend 24-bit IV to RC4 key */
264 	memcpy(rc4key, skb->data + hdrlen, 3);
265 
266 	/* Copy rest of the WEP key (the secret part) */
267 	memcpy(rc4key + 3, key->key, key->keylen);
268 
269 	if (ieee80211_wep_decrypt_data(local->wep_rx_tfm, rc4key, klen,
270 				       skb->data + hdrlen + WEP_IV_LEN,
271 				       len)) {
272 		printk(KERN_DEBUG "WEP decrypt failed (ICV)\n");
273 		ret = -1;
274 	}
275 
276 	kfree(rc4key);
277 
278 	/* Trim ICV */
279 	skb_trim(skb, skb->len - WEP_ICV_LEN);
280 
281 	/* Remove IV */
282 	memmove(skb->data + WEP_IV_LEN, skb->data, hdrlen);
283 	skb_pull(skb, WEP_IV_LEN);
284 
285 	return ret;
286 }
287 
288 
289 int ieee80211_wep_get_keyidx(struct sk_buff *skb)
290 {
291 	struct ieee80211_hdr *hdr = (struct ieee80211_hdr *) skb->data;
292 	u16 fc;
293 	int hdrlen;
294 
295 	fc = le16_to_cpu(hdr->frame_control);
296 	if (!(fc & IEEE80211_FCTL_PROTECTED))
297 		return -1;
298 
299 	hdrlen = ieee80211_get_hdrlen(fc);
300 
301 	if (skb->len < 8 + hdrlen)
302 		return -1;
303 
304 	return skb->data[hdrlen + 3] >> 6;
305 }
306 
307 
308 u8 * ieee80211_wep_is_weak_iv(struct sk_buff *skb, struct ieee80211_key *key)
309 {
310 	struct ieee80211_hdr *hdr = (struct ieee80211_hdr *) skb->data;
311 	u16 fc;
312 	int hdrlen;
313 	u8 *ivpos;
314 	u32 iv;
315 
316 	fc = le16_to_cpu(hdr->frame_control);
317 	if (!(fc & IEEE80211_FCTL_PROTECTED))
318 		return NULL;
319 
320 	hdrlen = ieee80211_get_hdrlen(fc);
321 	ivpos = skb->data + hdrlen;
322 	iv = (ivpos[0] << 16) | (ivpos[1] << 8) | ivpos[2];
323 
324 	if (ieee80211_wep_weak_iv(iv, key->keylen))
325 		return ivpos;
326 
327 	return NULL;
328 }
329