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 <linux/crypto.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_blkcipher *tx_tfm;
  39         struct crypto_blkcipher *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_blkcipher("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_blkcipher("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                 if (priv->tx_tfm)
  70                         crypto_free_blkcipher(priv->tx_tfm);
  71                 if (priv->rx_tfm)
  72                         crypto_free_blkcipher(priv->rx_tfm);
  73                 kfree(priv);
  74         }
  75         return NULL;
  76 }
  77
  78 static void lib80211_wep_deinit(void *priv)
  79 {
  80         struct lib80211_wep_data *_priv = priv;
  81         if (_priv) {
  82                 if (_priv->tx_tfm)
  83                         crypto_free_blkcipher(_priv->tx_tfm);
  84                 if (_priv->rx_tfm)
  85                         crypto_free_blkcipher(_priv->rx_tfm);
  86         }
  87         kfree(priv);
  88 }
  89
  90 /* Add WEP IV/key info to a frame that has at least 4 bytes of headroom */
  91 static int lib80211_wep_build_iv(struct sk_buff *skb, int hdr_len,
  92                                u8 *key, int keylen, void *priv)
  93 {
  94         struct lib80211_wep_data *wep = priv;
  95         u32 klen;
  96         u8 *pos;
  97
  98         if (skb_headroom(skb) < 4 || skb->len < hdr_len)
  99                 return -1;
 100
 101         pos = skb_push(skb, 4);
 102         memmove(pos, pos + 4, hdr_len);
 103         pos += hdr_len;
 104
 105         klen = 3 + wep->key_len;
 106
 107         wep->iv++;
 108
 109         /* Fluhrer, Mantin, and Shamir have reported weaknesses in the key
 110          * scheduling algorithm of RC4. At least IVs (KeyByte + 3, 0xff, N)
 111          * can be used to speedup attacks, so avoid using them. */
 112         if ((wep->iv & 0xff00) == 0xff00) {
 113                 u8 B = (wep->iv >> 16) & 0xff;
 114                 if (B >= 3 && B < klen)
 115                         wep->iv += 0x0100;
 116         }
 117
 118         /* Prepend 24-bit IV to RC4 key and TX frame */
 119         *pos++ = (wep->iv >> 16) & 0xff;
 120         *pos++ = (wep->iv >> 8) & 0xff;
 121         *pos++ = wep->iv & 0xff;
 122         *pos++ = wep->key_idx << 6;
 123
 124         return 0;
 125 }
 126
 127 /* Perform WEP encryption on given skb that has at least 4 bytes of headroom
 128  * for IV and 4 bytes of tailroom for ICV. Both IV and ICV will be transmitted,
 129  * so the payload length increases with 8 bytes.
 130  *
 131  * WEP frame payload: IV + TX key idx, RC4(data), ICV = RC4(CRC32(data))
 132  */
 133 static int lib80211_wep_encrypt(struct sk_buff *skb, int hdr_len, void *priv)
 134 {
 135         struct lib80211_wep_data *wep = priv;
 136         struct blkcipher_desc desc = { .tfm = wep->tx_tfm };
 137         u32 crc, klen, len;
 138         u8 *pos, *icv;
 139         struct scatterlist sg;
 140         u8 key[WEP_KEY_LEN + 3];
 141
 142         /* other checks are in lib80211_wep_build_iv */
 143         if (skb_tailroom(skb) < 4)
 144                 return -1;
 145
 146         /* add the IV to the frame */
 147         if (lib80211_wep_build_iv(skb, hdr_len, NULL, 0, priv))
 148                 return -1;
 149
 150         /* Copy the IV into the first 3 bytes of the key */
 151         skb_copy_from_linear_data_offset(skb, hdr_len, key, 3);
 152
 153         /* Copy rest of the WEP key (the secret part) */
 154         memcpy(key + 3, wep->key, wep->key_len);
 155
 156         len = skb->len - hdr_len - 4;
 157         pos = skb->data + hdr_len + 4;
 158         klen = 3 + wep->key_len;
 159
 160         /* Append little-endian CRC32 over only the data and encrypt it to produce ICV */
 161         crc = ~crc32_le(~0, pos, len);
 162         icv = skb_put(skb, 4);
 163         icv[0] = crc;
 164         icv[1] = crc >> 8;
 165         icv[2] = crc >> 16;
 166         icv[3] = crc >> 24;
 167
 168         crypto_blkcipher_setkey(wep->tx_tfm, key, klen);
 169         sg_init_one(&sg, pos, len + 4);
 170         return crypto_blkcipher_encrypt(&desc, &sg, &sg, len + 4);
 171 }
 172
 173 /* Perform WEP decryption on given buffer. Buffer includes whole WEP part of
 174  * the frame: IV (4 bytes), encrypted payload (including SNAP header),
 175  * ICV (4 bytes). len includes both IV and ICV.
 176  *
 177  * Returns 0 if frame was decrypted successfully and ICV was correct and -1 on
 178  * failure. If frame is OK, IV and ICV will be removed.
 179  */
 180 static int lib80211_wep_decrypt(struct sk_buff *skb, int hdr_len, void *priv)
 181 {
 182         struct lib80211_wep_data *wep = priv;
 183         struct blkcipher_desc desc = { .tfm = wep->rx_tfm };
 184         u32 crc, klen, plen;
 185         u8 key[WEP_KEY_LEN + 3];
 186         u8 keyidx, *pos, icv[4];
 187         struct scatterlist sg;
 188
 189         if (skb->len < hdr_len + 8)
 190                 return -1;
 191
 192         pos = skb->data + hdr_len;
 193         key[0] = *pos++;
 194         key[1] = *pos++;
 195         key[2] = *pos++;
 196         keyidx = *pos++ >> 6;
 197         if (keyidx != wep->key_idx)
 198                 return -1;
 199
 200         klen = 3 + wep->key_len;
 201
 202         /* Copy rest of the WEP key (the secret part) */
 203         memcpy(key + 3, wep->key, wep->key_len);
 204
 205         /* Apply RC4 to data and compute CRC32 over decrypted data */
 206         plen = skb->len - hdr_len - 8;
 207
 208         crypto_blkcipher_setkey(wep->rx_tfm, key, klen);
 209         sg_init_one(&sg, pos, plen + 4);
 210         if (crypto_blkcipher_decrypt(&desc, &sg, &sg, plen + 4))
 211                 return -7;
 212
 213         crc = ~crc32_le(~0, pos, plen);
 214         icv[0] = crc;
 215         icv[1] = crc >> 8;
 216         icv[2] = crc >> 16;
 217         icv[3] = crc >> 24;
 218         if (memcmp(icv, pos + plen, 4) != 0) {
 219                 /* ICV mismatch - drop frame */
 220                 return -2;
 221         }
 222
 223         /* Remove IV and ICV */
 224         memmove(skb->data + 4, skb->data, hdr_len);
 225         skb_pull(skb, 4);
 226         skb_trim(skb, skb->len - 4);
 227
 228         return 0;
 229 }
 230
 231 static int lib80211_wep_set_key(void *key, int len, u8 * seq, void *priv)
 232 {
 233         struct lib80211_wep_data *wep = priv;
 234
 235         if (len < 0 || len > WEP_KEY_LEN)
 236                 return -1;
 237
 238         memcpy(wep->key, key, len);
 239         wep->key_len = len;
 240
 241         return 0;
 242 }
 243
 244 static int lib80211_wep_get_key(void *key, int len, u8 * seq, void *priv)
 245 {
 246         struct lib80211_wep_data *wep = priv;
 247
 248         if (len < wep->key_len)
 249                 return -1;
 250
 251         memcpy(key, wep->key, wep->key_len);
 252
 253         return wep->key_len;
 254 }
 255
 256 static void lib80211_wep_print_stats(struct seq_file *m, void *priv)
 257 {
 258         struct lib80211_wep_data *wep = priv;
 259         seq_printf(m, "key[%d] alg=WEP len=%d\n", wep->key_idx, wep->key_len);
 260 }
 261
 262 static struct lib80211_crypto_ops lib80211_crypt_wep = {
 263         .name = "WEP",
 264         .init = lib80211_wep_init,
 265         .deinit = lib80211_wep_deinit,
 266         .encrypt_mpdu = lib80211_wep_encrypt,
 267         .decrypt_mpdu = lib80211_wep_decrypt,
 268         .encrypt_msdu = NULL,
 269         .decrypt_msdu = NULL,
 270         .set_key = lib80211_wep_set_key,
 271         .get_key = lib80211_wep_get_key,
 272         .print_stats = lib80211_wep_print_stats,
 273         .extra_mpdu_prefix_len = 4,     /* IV */
 274         .extra_mpdu_postfix_len = 4,    /* ICV */
 275         .owner = THIS_MODULE,
 276 };
 277
 278 static int __init lib80211_crypto_wep_init(void)
 279 {
 280         return lib80211_register_crypto_ops(&lib80211_crypt_wep);
 281 }
 282
 283 static void __exit lib80211_crypto_wep_exit(void)
 284 {
 285         lib80211_unregister_crypto_ops(&lib80211_crypt_wep);
 286 }
 287
 288 module_init(lib80211_crypto_wep_init);
 289 module_exit(lib80211_crypto_wep_exit);