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, IEEE80211_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         struct ieee80211_tx_info *info = IEEE80211_SKB_CB(skb);
  96         unsigned int hdrlen;
  97         u8 *newhdr;
  98
  99         hdr->frame_control |= cpu_to_le16(IEEE80211_FCTL_PROTECTED);
 100
 101         if (WARN_ON(skb_tailroom(skb) < IEEE80211_WEP_ICV_LEN ||
 102                     skb_headroom(skb) < IEEE80211_WEP_IV_LEN))
 103                 return NULL;
 104
 105         hdrlen = ieee80211_hdrlen(hdr->frame_control);
 106         newhdr = skb_push(skb, IEEE80211_WEP_IV_LEN);
 107         memmove(newhdr, newhdr + IEEE80211_WEP_IV_LEN, hdrlen);
 108
 109         /* the HW only needs room for the IV, but not the actual IV */
 110         if (info->control.hw_key &&
 111             (info->control.hw_key->flags & IEEE80211_KEY_FLAG_PUT_IV_SPACE))
 112                 return newhdr + hdrlen;
 113
 114         skb_set_network_header(skb, skb_network_offset(skb) +
 115                                     IEEE80211_WEP_IV_LEN);
 116         ieee80211_wep_get_iv(local, keylen, keyidx, newhdr + hdrlen);
 117         return newhdr + hdrlen;
 118 }
 119
 120
 121 static void ieee80211_wep_remove_iv(struct ieee80211_local *local,
 122                                     struct sk_buff *skb,
 123                                     struct ieee80211_key *key)
 124 {
 125         struct ieee80211_hdr *hdr = (struct ieee80211_hdr *)skb->data;
 126         unsigned int hdrlen;
 127
 128         hdrlen = ieee80211_hdrlen(hdr->frame_control);
 129         memmove(skb->data + IEEE80211_WEP_IV_LEN, skb->data, hdrlen);
 130         skb_pull(skb, IEEE80211_WEP_IV_LEN);
 131 }
 132
 133
 134 /* Perform WEP encryption using given key. data buffer must have tailroom
 135  * for 4-byte ICV. data_len must not include this ICV. Note: this function
 136  * does _not_ add IV. data = RC4(data | CRC32(data)) */
 137 int ieee80211_wep_encrypt_data(struct crypto_cipher *tfm, u8 *rc4key,
 138                                size_t klen, u8 *data, size_t data_len)
 139 {
 140         __le32 icv;
 141         int i;
 142
 143         if (IS_ERR(tfm))
 144                 return -1;
 145
 146         icv = cpu_to_le32(~crc32_le(~0, data, data_len));
 147         put_unaligned(icv, (__le32 *)(data + data_len));
 148
 149         crypto_cipher_setkey(tfm, rc4key, klen);
 150         for (i = 0; i < data_len + IEEE80211_WEP_ICV_LEN; i++)
 151                 crypto_cipher_encrypt_one(tfm, data + i, data + i);
 152
 153         return 0;
 154 }
 155
 156
 157 /* Perform WEP encryption on given skb. 4 bytes of extra space (IV) in the
 158  * beginning of the buffer 4 bytes of extra space (ICV) in the end of the
 159  * buffer will be added. Both IV and ICV will be transmitted, so the
 160  * payload length increases with 8 bytes.
 161  *
 162  * WEP frame payload: IV + TX key idx, RC4(data), ICV = RC4(CRC32(data))
 163  */
 164 int ieee80211_wep_encrypt(struct ieee80211_local *local,
 165                           struct sk_buff *skb,
 166                           const u8 *key, int keylen, int keyidx)
 167 {
 168         u8 *iv;
 169         size_t len;
 170         u8 rc4key[3 + WLAN_KEY_LEN_WEP104];
 171
 172         iv = ieee80211_wep_add_iv(local, skb, keylen, keyidx);
 173         if (!iv)
 174                 return -1;
 175
 176         len = skb->len - (iv + IEEE80211_WEP_IV_LEN - skb->data);
 177
 178         /* Prepend 24-bit IV to RC4 key */
 179         memcpy(rc4key, iv, 3);
 180
 181         /* Copy rest of the WEP key (the secret part) */
 182         memcpy(rc4key + 3, key, keylen);
 183
 184         /* Add room for ICV */
 185         skb_put(skb, IEEE80211_WEP_ICV_LEN);
 186
 187         return ieee80211_wep_encrypt_data(local->wep_tx_tfm, rc4key, keylen + 3,
 188                                           iv + IEEE80211_WEP_IV_LEN, len);
 189 }
 190
 191
 192 /* Perform WEP decryption using given key. data buffer includes encrypted
 193  * payload, including 4-byte ICV, but _not_ IV. data_len must not include ICV.
 194  * Return 0 on success and -1 on ICV mismatch. */
 195 int ieee80211_wep_decrypt_data(struct crypto_cipher *tfm, u8 *rc4key,
 196                                size_t klen, u8 *data, size_t data_len)
 197 {
 198         __le32 crc;
 199         int i;
 200
 201         if (IS_ERR(tfm))
 202                 return -1;
 203
 204         crypto_cipher_setkey(tfm, rc4key, klen);
 205         for (i = 0; i < data_len + IEEE80211_WEP_ICV_LEN; i++)
 206                 crypto_cipher_decrypt_one(tfm, data + i, data + i);
 207
 208         crc = cpu_to_le32(~crc32_le(~0, data, data_len));
 209         if (memcmp(&crc, data + data_len, IEEE80211_WEP_ICV_LEN) != 0)
 210                 /* ICV mismatch */
 211                 return -1;
 212
 213         return 0;
 214 }
 215
 216
 217 /* Perform WEP decryption on given skb. Buffer includes whole WEP part of
 218  * the frame: IV (4 bytes), encrypted payload (including SNAP header),
 219  * ICV (4 bytes). skb->len includes both IV and ICV.
 220  *
 221  * Returns 0 if frame was decrypted successfully and ICV was correct and -1 on
 222  * failure. If frame is OK, IV and ICV will be removed, i.e., decrypted payload
 223  * is moved to the beginning of the skb and skb length will be reduced.
 224  */
 225 static int ieee80211_wep_decrypt(struct ieee80211_local *local,
 226                                  struct sk_buff *skb,
 227                                  struct ieee80211_key *key)
 228 {
 229         u32 klen;
 230         u8 rc4key[3 + WLAN_KEY_LEN_WEP104];
 231         u8 keyidx;
 232         struct ieee80211_hdr *hdr = (struct ieee80211_hdr *)skb->data;
 233         unsigned int hdrlen;
 234         size_t len;
 235         int ret = 0;
 236
 237         if (!ieee80211_has_protected(hdr->frame_control))
 238                 return -1;
 239
 240         hdrlen = ieee80211_hdrlen(hdr->frame_control);
 241         if (skb->len < hdrlen + IEEE80211_WEP_IV_LEN + IEEE80211_WEP_ICV_LEN)
 242                 return -1;
 243
 244         len = skb->len - hdrlen - IEEE80211_WEP_IV_LEN - IEEE80211_WEP_ICV_LEN;
 245
 246         keyidx = skb->data[hdrlen + 3] >> 6;
 247
 248         if (!key || keyidx != key->conf.keyidx)
 249                 return -1;
 250
 251         klen = 3 + key->conf.keylen;
 252
 253         /* Prepend 24-bit IV to RC4 key */
 254         memcpy(rc4key, skb->data + hdrlen, 3);
 255
 256         /* Copy rest of the WEP key (the secret part) */
 257         memcpy(rc4key + 3, key->conf.key, key->conf.keylen);
 258
 259         if (ieee80211_wep_decrypt_data(local->wep_rx_tfm, rc4key, klen,
 260                                        skb->data + hdrlen +
 261                                        IEEE80211_WEP_IV_LEN, len))
 262                 ret = -1;
 263
 264         /* Trim ICV */
 265         skb_trim(skb, skb->len - IEEE80211_WEP_ICV_LEN);
 266
 267         /* Remove IV */
 268         memmove(skb->data + IEEE80211_WEP_IV_LEN, skb->data, hdrlen);
 269         skb_pull(skb, IEEE80211_WEP_IV_LEN);
 270
 271         return ret;
 272 }
 273
 274
 275 static bool ieee80211_wep_is_weak_iv(struct sk_buff *skb,
 276                                      struct ieee80211_key *key)
 277 {
 278         struct ieee80211_hdr *hdr = (struct ieee80211_hdr *)skb->data;
 279         unsigned int hdrlen;
 280         u8 *ivpos;
 281         u32 iv;
 282
 283         hdrlen = ieee80211_hdrlen(hdr->frame_control);
 284         ivpos = skb->data + hdrlen;
 285         iv = (ivpos[0] << 16) | (ivpos[1] << 8) | ivpos[2];
 286
 287         return ieee80211_wep_weak_iv(iv, key->conf.keylen);
 288 }
 289
 290 ieee80211_rx_result
 291 ieee80211_crypto_wep_decrypt(struct ieee80211_rx_data *rx)
 292 {
 293         struct sk_buff *skb = rx->skb;
 294         struct ieee80211_rx_status *status = IEEE80211_SKB_RXCB(skb);
 295         struct ieee80211_hdr *hdr = (struct ieee80211_hdr *)skb->data;
 296         __le16 fc = hdr->frame_control;
 297
 298         if (!ieee80211_is_data(fc) && !ieee80211_is_auth(fc))
 299                 return RX_CONTINUE;
 300
 301         if (!(status->flag & RX_FLAG_DECRYPTED)) {
 302                 if (skb_linearize(rx->skb))
 303                         return RX_DROP_UNUSABLE;
 304                 if (rx->sta && ieee80211_wep_is_weak_iv(rx->skb, rx->key))
 305                         rx->sta->wep_weak_iv_count++;
 306                 if (ieee80211_wep_decrypt(rx->local, rx->skb, rx->key))
 307                         return RX_DROP_UNUSABLE;
 308         } else if (!(status->flag & RX_FLAG_IV_STRIPPED)) {
 309                 if (!pskb_may_pull(rx->skb, ieee80211_hdrlen(fc) +
 310                                             IEEE80211_WEP_IV_LEN))
 311                         return RX_DROP_UNUSABLE;
 312                 if (rx->sta && ieee80211_wep_is_weak_iv(rx->skb, rx->key))
 313                         rx->sta->wep_weak_iv_count++;
 314                 ieee80211_wep_remove_iv(rx->local, rx->skb, rx->key);
 315                 /* remove ICV */
 316                 if (pskb_trim(rx->skb, rx->skb->len - IEEE80211_WEP_ICV_LEN))
 317                         return RX_DROP_UNUSABLE;
 318         }
 319
 320         return RX_CONTINUE;
 321 }
 322
 323 static int wep_encrypt_skb(struct ieee80211_tx_data *tx, struct sk_buff *skb)
 324 {
 325         struct ieee80211_tx_info *info = IEEE80211_SKB_CB(skb);
 326         struct ieee80211_key_conf *hw_key = info->control.hw_key;
 327
 328         if (!hw_key) {
 329                 if (ieee80211_wep_encrypt(tx->local, skb, tx->key->conf.key,
 330                                           tx->key->conf.keylen,
 331                                           tx->key->conf.keyidx))
 332                         return -1;
 333         } else if ((hw_key->flags & IEEE80211_KEY_FLAG_GENERATE_IV) ||
 334                    (hw_key->flags & IEEE80211_KEY_FLAG_PUT_IV_SPACE)) {
 335                 if (!ieee80211_wep_add_iv(tx->local, skb,
 336                                           tx->key->conf.keylen,
 337                                           tx->key->conf.keyidx))
 338                         return -1;
 339         }
 340
 341         return 0;
 342 }
 343
 344 ieee80211_tx_result
 345 ieee80211_crypto_wep_encrypt(struct ieee80211_tx_data *tx)
 346 {
 347         struct sk_buff *skb;
 348
 349         ieee80211_tx_set_protected(tx);
 350
 351         skb_queue_walk(&tx->skbs, skb) {
 352                 if (wep_encrypt_skb(tx, skb) < 0) {
 353                         I802_DEBUG_INC(tx->local->tx_handlers_drop_wep);
 354                         return TX_DROP;
 355                 }
 356         }
 357
 358         return TX_CONTINUE;
 359 }