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
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