1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3  * lib80211 crypt: host-based WEP encryption implementation for lib80211
4  *
5  * Copyright (c) 2002-2004, Jouni Malinen <j@w1.fi>
6  * Copyright (c) 2008, John W. Linville <linville@tuxdriver.com>
7  */
8 
9 #include <linux/err.h>
10 #include <linux/fips.h>
11 #include <linux/module.h>
12 #include <linux/init.h>
13 #include <linux/slab.h>
14 #include <linux/random.h>
15 #include <linux/scatterlist.h>
16 #include <linux/skbuff.h>
17 #include <linux/mm.h>
18 #include <asm/string.h>
19 
20 #include <net/lib80211.h>
21 
22 #include <crypto/arc4.h>
23 #include <linux/crc32.h>
24 
25 MODULE_AUTHOR("Jouni Malinen");
26 MODULE_DESCRIPTION("lib80211 crypt: WEP");
27 MODULE_LICENSE("GPL");
28 
29 struct lib80211_wep_data {
30 	u32 iv;
31 #define WEP_KEY_LEN 13
32 	u8 key[WEP_KEY_LEN + 1];
33 	u8 key_len;
34 	u8 key_idx;
35 	struct arc4_ctx tx_ctx;
36 	struct arc4_ctx rx_ctx;
37 };
38 
39 static void *lib80211_wep_init(int keyidx)
40 {
41 	struct lib80211_wep_data *priv;
42 
43 	if (fips_enabled)
44 		return NULL;
45 
46 	priv = kzalloc(sizeof(*priv), GFP_ATOMIC);
47 	if (priv == NULL)
48 		return NULL;
49 	priv->key_idx = keyidx;
50 
51 	/* start WEP IV from a random value */
52 	get_random_bytes(&priv->iv, 4);
53 
54 	return priv;
55 }
56 
57 static void lib80211_wep_deinit(void *priv)
58 {
59 	kfree_sensitive(priv);
60 }
61 
62 /* Add WEP IV/key info to a frame that has at least 4 bytes of headroom */
63 static int lib80211_wep_build_iv(struct sk_buff *skb, int hdr_len,
64 			       u8 *key, int keylen, void *priv)
65 {
66 	struct lib80211_wep_data *wep = priv;
67 	u32 klen;
68 	u8 *pos;
69 
70 	if (skb_headroom(skb) < 4 || skb->len < hdr_len)
71 		return -1;
72 
73 	pos = skb_push(skb, 4);
74 	memmove(pos, pos + 4, hdr_len);
75 	pos += hdr_len;
76 
77 	klen = 3 + wep->key_len;
78 
79 	wep->iv++;
80 
81 	/* Fluhrer, Mantin, and Shamir have reported weaknesses in the key
82 	 * scheduling algorithm of RC4. At least IVs (KeyByte + 3, 0xff, N)
83 	 * can be used to speedup attacks, so avoid using them. */
84 	if ((wep->iv & 0xff00) == 0xff00) {
85 		u8 B = (wep->iv >> 16) & 0xff;
86 		if (B >= 3 && B < klen)
87 			wep->iv += 0x0100;
88 	}
89 
90 	/* Prepend 24-bit IV to RC4 key and TX frame */
91 	*pos++ = (wep->iv >> 16) & 0xff;
92 	*pos++ = (wep->iv >> 8) & 0xff;
93 	*pos++ = wep->iv & 0xff;
94 	*pos++ = wep->key_idx << 6;
95 
96 	return 0;
97 }
98 
99 /* Perform WEP encryption on given skb that has at least 4 bytes of headroom
100  * for IV and 4 bytes of tailroom for ICV. Both IV and ICV will be transmitted,
101  * so the payload length increases with 8 bytes.
102  *
103  * WEP frame payload: IV + TX key idx, RC4(data), ICV = RC4(CRC32(data))
104  */
105 static int lib80211_wep_encrypt(struct sk_buff *skb, int hdr_len, void *priv)
106 {
107 	struct lib80211_wep_data *wep = priv;
108 	u32 crc, klen, len;
109 	u8 *pos, *icv;
110 	u8 key[WEP_KEY_LEN + 3];
111 
112 	/* other checks are in lib80211_wep_build_iv */
113 	if (skb_tailroom(skb) < 4)
114 		return -1;
115 
116 	/* add the IV to the frame */
117 	if (lib80211_wep_build_iv(skb, hdr_len, NULL, 0, priv))
118 		return -1;
119 
120 	/* Copy the IV into the first 3 bytes of the key */
121 	skb_copy_from_linear_data_offset(skb, hdr_len, key, 3);
122 
123 	/* Copy rest of the WEP key (the secret part) */
124 	memcpy(key + 3, wep->key, wep->key_len);
125 
126 	len = skb->len - hdr_len - 4;
127 	pos = skb->data + hdr_len + 4;
128 	klen = 3 + wep->key_len;
129 
130 	/* Append little-endian CRC32 over only the data and encrypt it to produce ICV */
131 	crc = ~crc32_le(~0, pos, len);
132 	icv = skb_put(skb, 4);
133 	icv[0] = crc;
134 	icv[1] = crc >> 8;
135 	icv[2] = crc >> 16;
136 	icv[3] = crc >> 24;
137 
138 	arc4_setkey(&wep->tx_ctx, key, klen);
139 	arc4_crypt(&wep->tx_ctx, pos, pos, len + 4);
140 
141 	return 0;
142 }
143 
144 /* Perform WEP decryption on given buffer. Buffer includes whole WEP part of
145  * the frame: IV (4 bytes), encrypted payload (including SNAP header),
146  * ICV (4 bytes). len includes both IV and ICV.
147  *
148  * Returns 0 if frame was decrypted successfully and ICV was correct and -1 on
149  * failure. If frame is OK, IV and ICV will be removed.
150  */
151 static int lib80211_wep_decrypt(struct sk_buff *skb, int hdr_len, void *priv)
152 {
153 	struct lib80211_wep_data *wep = priv;
154 	u32 crc, klen, plen;
155 	u8 key[WEP_KEY_LEN + 3];
156 	u8 keyidx, *pos, icv[4];
157 
158 	if (skb->len < hdr_len + 8)
159 		return -1;
160 
161 	pos = skb->data + hdr_len;
162 	key[0] = *pos++;
163 	key[1] = *pos++;
164 	key[2] = *pos++;
165 	keyidx = *pos++ >> 6;
166 	if (keyidx != wep->key_idx)
167 		return -1;
168 
169 	klen = 3 + wep->key_len;
170 
171 	/* Copy rest of the WEP key (the secret part) */
172 	memcpy(key + 3, wep->key, wep->key_len);
173 
174 	/* Apply RC4 to data and compute CRC32 over decrypted data */
175 	plen = skb->len - hdr_len - 8;
176 
177 	arc4_setkey(&wep->rx_ctx, key, klen);
178 	arc4_crypt(&wep->rx_ctx, pos, pos, plen + 4);
179 
180 	crc = ~crc32_le(~0, pos, plen);
181 	icv[0] = crc;
182 	icv[1] = crc >> 8;
183 	icv[2] = crc >> 16;
184 	icv[3] = crc >> 24;
185 	if (memcmp(icv, pos + plen, 4) != 0) {
186 		/* ICV mismatch - drop frame */
187 		return -2;
188 	}
189 
190 	/* Remove IV and ICV */
191 	memmove(skb->data + 4, skb->data, hdr_len);
192 	skb_pull(skb, 4);
193 	skb_trim(skb, skb->len - 4);
194 
195 	return 0;
196 }
197 
198 static int lib80211_wep_set_key(void *key, int len, u8 * seq, void *priv)
199 {
200 	struct lib80211_wep_data *wep = priv;
201 
202 	if (len < 0 || len > WEP_KEY_LEN)
203 		return -1;
204 
205 	memcpy(wep->key, key, len);
206 	wep->key_len = len;
207 
208 	return 0;
209 }
210 
211 static int lib80211_wep_get_key(void *key, int len, u8 * seq, void *priv)
212 {
213 	struct lib80211_wep_data *wep = priv;
214 
215 	if (len < wep->key_len)
216 		return -1;
217 
218 	memcpy(key, wep->key, wep->key_len);
219 
220 	return wep->key_len;
221 }
222 
223 static void lib80211_wep_print_stats(struct seq_file *m, void *priv)
224 {
225 	struct lib80211_wep_data *wep = priv;
226 	seq_printf(m, "key[%d] alg=WEP len=%d\n", wep->key_idx, wep->key_len);
227 }
228 
229 static struct lib80211_crypto_ops lib80211_crypt_wep = {
230 	.name = "WEP",
231 	.init = lib80211_wep_init,
232 	.deinit = lib80211_wep_deinit,
233 	.encrypt_mpdu = lib80211_wep_encrypt,
234 	.decrypt_mpdu = lib80211_wep_decrypt,
235 	.encrypt_msdu = NULL,
236 	.decrypt_msdu = NULL,
237 	.set_key = lib80211_wep_set_key,
238 	.get_key = lib80211_wep_get_key,
239 	.print_stats = lib80211_wep_print_stats,
240 	.extra_mpdu_prefix_len = 4,	/* IV */
241 	.extra_mpdu_postfix_len = 4,	/* ICV */
242 	.owner = THIS_MODULE,
243 };
244 
245 static int __init lib80211_crypto_wep_init(void)
246 {
247 	return lib80211_register_crypto_ops(&lib80211_crypt_wep);
248 }
249 
250 static void __exit lib80211_crypto_wep_exit(void)
251 {
252 	lib80211_unregister_crypto_ops(&lib80211_crypt_wep);
253 }
254 
255 module_init(lib80211_crypto_wep_init);
256 module_exit(lib80211_crypto_wep_exit);
257