net/mac80211/wep.c

   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 <linux/scatterlist.h>
  20 #include <linux/slab.h>
  21 #include <asm/unaligned.h>
  22
  23 #include <net/mac80211.h>
  24 #include "ieee80211_i.h"
  25 #include "wep.h"
  26
  27
  28 int ieee80211_wep_init(struct ieee80211_local *local)
  29 {
  30         /* start WEP IV from a random value */
  31         get_random_bytes(&local->wep_iv, WEP_IV_LEN);
  32
  33         local->wep_tx_tfm = crypto_alloc_cipher("arc4", 0, CRYPTO_ALG_ASYNC);
  34         if (IS_ERR(local->wep_tx_tfm)) {
  35                 local->wep_rx_tfm = ERR_PTR(-EINVAL);
  36                 return PTR_ERR(local->wep_tx_tfm);
  37         }
  38
  39         local->wep_rx_tfm = crypto_alloc_cipher("arc4", 0, CRYPTO_ALG_ASYNC);
  40         if (IS_ERR(local->wep_rx_tfm)) {
  41                 crypto_free_cipher(local->wep_tx_tfm);
  42                 local->wep_tx_tfm = ERR_PTR(-EINVAL);
  43                 return PTR_ERR(local->wep_rx_tfm);
  44         }
  45
  46         return 0;
  47 }
  48
  49 void ieee80211_wep_free(struct ieee80211_local *local)
  50 {
  51         if (!IS_ERR(local->wep_tx_tfm))
  52                 crypto_free_cipher(local->wep_tx_tfm);
  53         if (!IS_ERR(local->wep_rx_tfm))
  54                 crypto_free_cipher(local->wep_rx_tfm);
  55 }
  56
  57 static inline bool ieee80211_wep_weak_iv(u32 iv, int keylen)
  58 {
  59         /*
  60          * Fluhrer, Mantin, and Shamir have reported weaknesses in the
  61          * key scheduling algorithm of RC4. At least IVs (KeyByte + 3,
  62          * 0xff, N) can be used to speedup attacks, so avoid using them.
  63          */
  64         if ((iv & 0xff00) == 0xff00) {
  65                 u8 B = (iv >> 16) & 0xff;
  66                 if (B >= 3 && B < 3 + keylen)
  67                         return true;
  68         }
  69         return false;
  70 }
  71
  72
  73 static void ieee80211_wep_get_iv(struct ieee80211_local *local,
  74                                  int keylen, int keyidx, u8 *iv)
  75 {
  76         local->wep_iv++;
  77         if (ieee80211_wep_weak_iv(local->wep_iv, keylen))
  78                 local->wep_iv += 0x0100;
  79
  80         if (!iv)
  81                 return;
  82
  83         *iv++ = (local->wep_iv >> 16) & 0xff;
  84         *iv++ = (local->wep_iv >> 8) & 0xff;
  85         *iv++ = local->wep_iv & 0xff;
  86         *iv++ = keyidx << 6;
  87 }
  88
  89
  90 static u8 *ieee80211_wep_add_iv(struct ieee80211_local *local,
  91                                 struct sk_buff *skb,
  92                                 int keylen, int keyidx)
  93 {
  94         struct ieee80211_hdr *hdr = (struct ieee80211_hdr *)skb->data;
  95         unsigned int hdrlen;
  96         u8 *newhdr;
  97
  98         hdr->frame_control |= cpu_to_le16(IEEE80211_FCTL_PROTECTED);
  99
 100         if (WARN_ON(skb_tailroom(skb) < WEP_ICV_LEN ||
 101                     skb_headroom(skb) < WEP_IV_LEN))
 102                 return NULL;
 103
 104         hdrlen = ieee80211_hdrlen(hdr->frame_control);
 105         newhdr = skb_push(skb, WEP_IV_LEN);
 106         memmove(newhdr, newhdr + WEP_IV_LEN, hdrlen);
 107         ieee80211_wep_get_iv(local, keylen, keyidx, newhdr + hdrlen);
 108         return newhdr + hdrlen;
 109 }
 110
 111
 112 static 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         unsigned int hdrlen;
 118
 119         hdrlen = ieee80211_hdrlen(hdr->frame_control);
 120         memmove(skb->data + WEP_IV_LEN, skb->data, hdrlen);
 121         skb_pull(skb, WEP_IV_LEN);
 122 }
 123
 124
 125 /* Perform WEP encryption using given key. data buffer must have tailroom
 126  * for 4-byte ICV. data_len must not include this ICV. Note: this function
 127  * does _not_ add IV. data = RC4(data | CRC32(data)) */
 128 int ieee80211_wep_encrypt_data(struct crypto_cipher *tfm, u8 *rc4key,
 129                                size_t klen, u8 *data, size_t data_len)
 130 {
 131         __le32 icv;
 132         int i;
 133
 134         if (IS_ERR(tfm))
 135                 return -1;
 136
 137         icv = cpu_to_le32(~crc32_le(~0, data, data_len));
 138         put_unaligned(icv, (__le32 *)(data + data_len));
 139
 140         crypto_cipher_setkey(tfm, rc4key, klen);
 141         for (i = 0; i < data_len + WEP_ICV_LEN; i++)
 142                 crypto_cipher_encrypt_one(tfm, data + i, data + i);
 143
 144         return 0;
 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,
 156                           struct sk_buff *skb,
 157                           const u8 *key, int keylen, int keyidx)
 158 {
 159         u8 *iv;
 160         size_t len;
 161         u8 rc4key[3 + WLAN_KEY_LEN_WEP104];
 162
 163         iv = ieee80211_wep_add_iv(local, skb, keylen, keyidx);
 164         if (!iv)
 165                 return -1;
 166
 167         len = skb->len - (iv + WEP_IV_LEN - skb->data);
 168
 169         /* Prepend 24-bit IV to RC4 key */
 170         memcpy(rc4key, iv, 3);
 171
 172         /* Copy rest of the WEP key (the secret part) */
 173         memcpy(rc4key + 3, key, keylen);
 174
 175         /* Add room for ICV */
 176         skb_put(skb, WEP_ICV_LEN);
 177
 178         return ieee80211_wep_encrypt_data(local->wep_tx_tfm, rc4key, keylen + 3,
 179                                           iv + WEP_IV_LEN, len);
 180 }
 181
 182
 183 /* Perform WEP decryption using given key. data buffer includes encrypted
 184  * payload, including 4-byte ICV, but _not_ IV. data_len must not include ICV.
 185  * Return 0 on success and -1 on ICV mismatch. */
 186 int ieee80211_wep_decrypt_data(struct crypto_cipher *tfm, u8 *rc4key,
 187                                size_t klen, u8 *data, size_t data_len)
 188 {
 189         __le32 crc;
 190         int i;
 191
 192         if (IS_ERR(tfm))
 193                 return -1;
 194
 195         crypto_cipher_setkey(tfm, rc4key, klen);
 196         for (i = 0; i < data_len + WEP_ICV_LEN; i++)
 197                 crypto_cipher_decrypt_one(tfm, data + i, data + i);
 198
 199         crc = cpu_to_le32(~crc32_le(~0, data, data_len));
 200         if (memcmp(&crc, data + data_len, WEP_ICV_LEN) != 0)
 201                 /* ICV mismatch */
 202                 return -1;
 203
 204         return 0;
 205 }
 206
 207
 208 /* Perform WEP decryption on given skb. Buffer includes whole WEP part of
 209  * the frame: IV (4 bytes), encrypted payload (including SNAP header),
 210  * ICV (4 bytes). skb->len includes both IV and ICV.
 211  *
 212  * Returns 0 if frame was decrypted successfully and ICV was correct and -1 on
 213  * failure. If frame is OK, IV and ICV will be removed, i.e., decrypted payload
 214  * is moved to the beginning of the skb and skb length will be reduced.
 215  */
 216 static int ieee80211_wep_decrypt(struct ieee80211_local *local,
 217                                  struct sk_buff *skb,
 218                                  struct ieee80211_key *key)
 219 {
 220         u32 klen;
 221         u8 rc4key[3 + WLAN_KEY_LEN_WEP104];
 222         u8 keyidx;
 223         struct ieee80211_hdr *hdr = (struct ieee80211_hdr *)skb->data;
 224         unsigned int hdrlen;
 225         size_t len;
 226         int ret = 0;
 227
 228         if (!ieee80211_has_protected(hdr->frame_control))
 229                 return -1;
 230
 231         hdrlen = ieee80211_hdrlen(hdr->frame_control);
 232         if (skb->len < hdrlen + WEP_IV_LEN + WEP_ICV_LEN)
 233                 return -1;
 234
 235         len = skb->len - hdrlen - WEP_IV_LEN - WEP_ICV_LEN;
 236
 237         keyidx = skb->data[hdrlen + 3] >> 6;
 238
 239         if (!key || keyidx != key->conf.keyidx)
 240                 return -1;
 241
 242         klen = 3 + key->conf.keylen;
 243
 244         /* Prepend 24-bit IV to RC4 key */
 245         memcpy(rc4key, skb->data + hdrlen, 3);
 246
 247         /* Copy rest of the WEP key (the secret part) */
 248         memcpy(rc4key + 3, key->conf.key, key->conf.keylen);
 249
 250         if (ieee80211_wep_decrypt_data(local->wep_rx_tfm, rc4key, klen,
 251                                        skb->data + hdrlen + WEP_IV_LEN,
 252                                        len))
 253                 ret = -1;
 254
 255         /* Trim ICV */
 256         skb_trim(skb, skb->len - WEP_ICV_LEN);
 257
 258         /* Remove IV */
 259         memmove(skb->data + WEP_IV_LEN, skb->data, hdrlen);
 260         skb_pull(skb, WEP_IV_LEN);
 261
 262         return ret;
 263 }
 264
 265
 266 bool ieee80211_wep_is_weak_iv(struct sk_buff *skb, struct ieee80211_key *key)
 267 {
 268         struct ieee80211_hdr *hdr = (struct ieee80211_hdr *)skb->data;
 269         unsigned int hdrlen;
 270         u8 *ivpos;
 271         u32 iv;
 272
 273         if (!ieee80211_has_protected(hdr->frame_control))
 274                 return false;
 275
 276         hdrlen = ieee80211_hdrlen(hdr->frame_control);
 277         ivpos = skb->data + hdrlen;
 278         iv = (ivpos[0] << 16) | (ivpos[1] << 8) | ivpos[2];
 279
 280         return ieee80211_wep_weak_iv(iv, key->conf.keylen);
 281 }
 282
 283 ieee80211_rx_result
 284 ieee80211_crypto_wep_decrypt(struct ieee80211_rx_data *rx)
 285 {
 286         struct sk_buff *skb = rx->skb;
 287         struct ieee80211_rx_status *status = IEEE80211_SKB_RXCB(skb);
 288         struct ieee80211_hdr *hdr = (struct ieee80211_hdr *)skb->data;
 289
 290         if (!ieee80211_is_data(hdr->frame_control) &&
 291             !ieee80211_is_auth(hdr->frame_control))
 292                 return RX_CONTINUE;
 293
 294         if (!(status->flag & RX_FLAG_DECRYPTED)) {
 295                 if (ieee80211_wep_decrypt(rx->local, rx->skb, rx->key))
 296                         return RX_DROP_UNUSABLE;
 297         } else if (!(status->flag & RX_FLAG_IV_STRIPPED)) {
 298                 ieee80211_wep_remove_iv(rx->local, rx->skb, rx->key);
 299                 /* remove ICV */
 300                 skb_trim(rx->skb, rx->skb->len - WEP_ICV_LEN);
 301         }
 302
 303         return RX_CONTINUE;
 304 }
 305
 306 static int wep_encrypt_skb(struct ieee80211_tx_data *tx, struct sk_buff *skb)
 307 {
 308         struct ieee80211_tx_info *info = IEEE80211_SKB_CB(skb);
 309
 310         if (!info->control.hw_key) {
 311                 if (ieee80211_wep_encrypt(tx->local, skb, tx->key->conf.key,
 312                                           tx->key->conf.keylen,
 313                                           tx->key->conf.keyidx))
 314                         return -1;
 315         } else if (info->control.hw_key->flags &
 316                         IEEE80211_KEY_FLAG_GENERATE_IV) {
 317                 if (!ieee80211_wep_add_iv(tx->local, skb,
 318                                           tx->key->conf.keylen,
 319                                           tx->key->conf.keyidx))
 320                         return -1;
 321         }
 322
 323         return 0;
 324 }
 325
 326 ieee80211_tx_result
 327 ieee80211_crypto_wep_encrypt(struct ieee80211_tx_data *tx)
 328 {
 329         struct sk_buff *skb;
 330
 331         ieee80211_tx_set_protected(tx);
 332
 333         skb_queue_walk(&tx->skbs, skb) {
 334                 if (wep_encrypt_skb(tx, skb) < 0) {
 335                         I802_DEBUG_INC(tx->local->tx_handlers_drop_wep);
 336                         return TX_DROP;
 337                 }
 338         }
 339
 340         return TX_CONTINUE;
 341 }