net/wireless/lib80211_crypt_wep.c

   1 /*
   2  * lib80211 crypt: host-based WEP encryption implementation for lib80211
   3  *
   4  * Copyright (c) 2002-2004, Jouni Malinen <j@w1.fi>
   5  * Copyright (c) 2008, John W. Linville <linville@tuxdriver.com>
   6  *
   7  * This program is free software; you can redistribute it and/or modify
   8  * it under the terms of the GNU General Public License version 2 as
   9  * published by the Free Software Foundation. See README and COPYING for
  10  * more details.
  11  */
  12
  13 #include <linux/err.h>
  14 #include <linux/module.h>
  15 #include <linux/init.h>
  16 #include <linux/slab.h>
  17 #include <linux/random.h>
  18 #include <linux/scatterlist.h>
  19 #include <linux/skbuff.h>
  20 #include <linux/mm.h>
  21 #include <asm/string.h>
  22
  23 #include <net/lib80211.h>
  24
  25 #include <crypto/skcipher.h>
  26 #include <linux/crc32.h>
  27
  28 MODULE_AUTHOR("Jouni Malinen");
  29 MODULE_DESCRIPTION("lib80211 crypt: WEP");
  30 MODULE_LICENSE("GPL");
  31
  32 struct lib80211_wep_data {
  33         u32 iv;
  34 #define WEP_KEY_LEN 13
  35         u8 key[WEP_KEY_LEN + 1];
  36         u8 key_len;
  37         u8 key_idx;
  38         struct crypto_skcipher *tx_tfm;
  39         struct crypto_skcipher *rx_tfm;
  40 };
  41
  42 static void *lib80211_wep_init(int keyidx)
  43 {
  44         struct lib80211_wep_data *priv;
  45
  46         priv = kzalloc(sizeof(*priv), GFP_ATOMIC);
  47         if (priv == NULL)
  48                 goto fail;
  49         priv->key_idx = keyidx;
  50
  51         priv->tx_tfm = crypto_alloc_skcipher("ecb(arc4)", 0, CRYPTO_ALG_ASYNC);
  52         if (IS_ERR(priv->tx_tfm)) {
  53                 priv->tx_tfm = NULL;
  54                 goto fail;
  55         }
  56
  57         priv->rx_tfm = crypto_alloc_skcipher("ecb(arc4)", 0, CRYPTO_ALG_ASYNC);
  58         if (IS_ERR(priv->rx_tfm)) {
  59                 priv->rx_tfm = NULL;
  60                 goto fail;
  61         }
  62         /* start WEP IV from a random value */
  63         get_random_bytes(&priv->iv, 4);
  64
  65         return priv;
  66
  67       fail:
  68         if (priv) {
  69                 crypto_free_skcipher(priv->tx_tfm);
  70                 crypto_free_skcipher(priv->rx_tfm);
  71                 kfree(priv);
  72         }
  73         return NULL;
  74 }
  75
  76 static void lib80211_wep_deinit(void *priv)
  77 {
  78         struct lib80211_wep_data *_priv = priv;
  79         if (_priv) {
  80                 crypto_free_skcipher(_priv->tx_tfm);
  81                 crypto_free_skcipher(_priv->rx_tfm);
  82         }
  83         kfree(priv);
  84 }
  85
  86 /* Add WEP IV/key info to a frame that has at least 4 bytes of headroom */
  87 static int lib80211_wep_build_iv(struct sk_buff *skb, int hdr_len,
  88                                u8 *key, int keylen, void *priv)
  89 {
  90         struct lib80211_wep_data *wep = priv;
  91         u32 klen;
  92         u8 *pos;
  93
  94         if (skb_headroom(skb) < 4 || skb->len < hdr_len)
  95                 return -1;
  96
  97         pos = skb_push(skb, 4);
  98         memmove(pos, pos + 4, hdr_len);
  99         pos += hdr_len;
 100
 101         klen = 3 + wep->key_len;
 102
 103         wep->iv++;
 104
 105         /* Fluhrer, Mantin, and Shamir have reported weaknesses in the key
 106          * scheduling algorithm of RC4. At least IVs (KeyByte + 3, 0xff, N)
 107          * can be used to speedup attacks, so avoid using them. */
 108         if ((wep->iv & 0xff00) == 0xff00) {
 109                 u8 B = (wep->iv >> 16) & 0xff;
 110                 if (B >= 3 && B < klen)
 111                         wep->iv += 0x0100;
 112         }
 113
 114         /* Prepend 24-bit IV to RC4 key and TX frame */
 115         *pos++ = (wep->iv >> 16) & 0xff;
 116         *pos++ = (wep->iv >> 8) & 0xff;
 117         *pos++ = wep->iv & 0xff;
 118         *pos++ = wep->key_idx << 6;
 119
 120         return 0;
 121 }
 122
 123 /* Perform WEP encryption on given skb that has at least 4 bytes of headroom
 124  * for IV and 4 bytes of tailroom for ICV. Both IV and ICV will be transmitted,
 125  * so the payload length increases with 8 bytes.
 126  *
 127  * WEP frame payload: IV + TX key idx, RC4(data), ICV = RC4(CRC32(data))
 128  */
 129 static int lib80211_wep_encrypt(struct sk_buff *skb, int hdr_len, void *priv)
 130 {
 131         struct lib80211_wep_data *wep = priv;
 132         SKCIPHER_REQUEST_ON_STACK(req, wep->tx_tfm);
 133         u32 crc, klen, len;
 134         u8 *pos, *icv;
 135         struct scatterlist sg;
 136         u8 key[WEP_KEY_LEN + 3];
 137         int err;
 138
 139         /* other checks are in lib80211_wep_build_iv */
 140         if (skb_tailroom(skb) < 4)
 141                 return -1;
 142
 143         /* add the IV to the frame */
 144         if (lib80211_wep_build_iv(skb, hdr_len, NULL, 0, priv))
 145                 return -1;
 146
 147         /* Copy the IV into the first 3 bytes of the key */
 148         skb_copy_from_linear_data_offset(skb, hdr_len, key, 3);
 149
 150         /* Copy rest of the WEP key (the secret part) */
 151         memcpy(key + 3, wep->key, wep->key_len);
 152
 153         len = skb->len - hdr_len - 4;
 154         pos = skb->data + hdr_len + 4;
 155         klen = 3 + wep->key_len;
 156
 157         /* Append little-endian CRC32 over only the data and encrypt it to produce ICV */
 158         crc = ~crc32_le(~0, pos, len);
 159         icv = skb_put(skb, 4);
 160         icv[0] = crc;
 161         icv[1] = crc >> 8;
 162         icv[2] = crc >> 16;
 163         icv[3] = crc >> 24;
 164
 165         crypto_skcipher_setkey(wep->tx_tfm, key, klen);
 166         sg_init_one(&sg, pos, len + 4);
 167         skcipher_request_set_tfm(req, wep->tx_tfm);
 168         skcipher_request_set_callback(req, 0, NULL, NULL);
 169         skcipher_request_set_crypt(req, &sg, &sg, len + 4, NULL);
 170         err = crypto_skcipher_encrypt(req);
 171         skcipher_request_zero(req);
 172         return err;
 173 }
 174
 175 /* Perform WEP decryption on given buffer. Buffer includes whole WEP part of
 176  * the frame: IV (4 bytes), encrypted payload (including SNAP header),
 177  * ICV (4 bytes). len includes both IV and ICV.
 178  *
 179  * Returns 0 if frame was decrypted successfully and ICV was correct and -1 on
 180  * failure. If frame is OK, IV and ICV will be removed.
 181  */
 182 static int lib80211_wep_decrypt(struct sk_buff *skb, int hdr_len, void *priv)
 183 {
 184         struct lib80211_wep_data *wep = priv;
 185         SKCIPHER_REQUEST_ON_STACK(req, wep->rx_tfm);
 186         u32 crc, klen, plen;
 187         u8 key[WEP_KEY_LEN + 3];
 188         u8 keyidx, *pos, icv[4];
 189         struct scatterlist sg;
 190         int err;
 191
 192         if (skb->len < hdr_len + 8)
 193                 return -1;
 194
 195         pos = skb->data + hdr_len;
 196         key[0] = *pos++;
 197         key[1] = *pos++;
 198         key[2] = *pos++;
 199         keyidx = *pos++ >> 6;
 200         if (keyidx != wep->key_idx)
 201                 return -1;
 202
 203         klen = 3 + wep->key_len;
 204
 205         /* Copy rest of the WEP key (the secret part) */
 206         memcpy(key + 3, wep->key, wep->key_len);
 207
 208         /* Apply RC4 to data and compute CRC32 over decrypted data */
 209         plen = skb->len - hdr_len - 8;
 210
 211         crypto_skcipher_setkey(wep->rx_tfm, key, klen);
 212         sg_init_one(&sg, pos, plen + 4);
 213         skcipher_request_set_tfm(req, wep->rx_tfm);
 214         skcipher_request_set_callback(req, 0, NULL, NULL);
 215         skcipher_request_set_crypt(req, &sg, &sg, plen + 4, NULL);
 216         err = crypto_skcipher_decrypt(req);
 217         skcipher_request_zero(req);
 218         if (err)
 219                 return -7;
 220
 221         crc = ~crc32_le(~0, pos, plen);
 222         icv[0] = crc;
 223         icv[1] = crc >> 8;
 224         icv[2] = crc >> 16;
 225         icv[3] = crc >> 24;
 226         if (memcmp(icv, pos + plen, 4) != 0) {
 227                 /* ICV mismatch - drop frame */
 228                 return -2;
 229         }
 230
 231         /* Remove IV and ICV */
 232         memmove(skb->data + 4, skb->data, hdr_len);
 233         skb_pull(skb, 4);
 234         skb_trim(skb, skb->len - 4);
 235
 236         return 0;
 237 }
 238
 239 static int lib80211_wep_set_key(void *key, int len, u8 * seq, void *priv)
 240 {
 241         struct lib80211_wep_data *wep = priv;
 242
 243         if (len < 0 || len > WEP_KEY_LEN)
 244                 return -1;
 245
 246         memcpy(wep->key, key, len);
 247         wep->key_len = len;
 248
 249         return 0;
 250 }
 251
 252 static int lib80211_wep_get_key(void *key, int len, u8 * seq, void *priv)
 253 {
 254         struct lib80211_wep_data *wep = priv;
 255
 256         if (len < wep->key_len)
 257                 return -1;
 258
 259         memcpy(key, wep->key, wep->key_len);
 260
 261         return wep->key_len;
 262 }
 263
 264 static void lib80211_wep_print_stats(struct seq_file *m, void *priv)
 265 {
 266         struct lib80211_wep_data *wep = priv;
 267         seq_printf(m, "key[%d] alg=WEP len=%d\n", wep->key_idx, wep->key_len);
 268 }
 269
 270 static struct lib80211_crypto_ops lib80211_crypt_wep = {
 271         .name = "WEP",
 272         .init = lib80211_wep_init,
 273         .deinit = lib80211_wep_deinit,
 274         .encrypt_mpdu = lib80211_wep_encrypt,
 275         .decrypt_mpdu = lib80211_wep_decrypt,
 276         .encrypt_msdu = NULL,
 277         .decrypt_msdu = NULL,
 278         .set_key = lib80211_wep_set_key,
 279         .get_key = lib80211_wep_get_key,
 280         .print_stats = lib80211_wep_print_stats,
 281         .extra_mpdu_prefix_len = 4,     /* IV */
 282         .extra_mpdu_postfix_len = 4,    /* ICV */
 283         .owner = THIS_MODULE,
 284 };
 285
 286 static int __init lib80211_crypto_wep_init(void)
 287 {
 288         return lib80211_register_crypto_ops(&lib80211_crypt_wep);
 289 }
 290
 291 static void __exit lib80211_crypto_wep_exit(void)
 292 {
 293         lib80211_unregister_crypto_ops(&lib80211_crypt_wep);
 294 }
 295
 296 module_init(lib80211_crypto_wep_init);
 297 module_exit(lib80211_crypto_wep_exit);