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_blkcipher("ecb(arc4)", 0,
  34                                                 CRYPTO_ALG_ASYNC);
  35         if (IS_ERR(local->wep_tx_tfm))
  36                 return PTR_ERR(local->wep_tx_tfm);
  37
  38         local->wep_rx_tfm = crypto_alloc_blkcipher("ecb(arc4)", 0,
  39                                                 CRYPTO_ALG_ASYNC);
  40         if (IS_ERR(local->wep_rx_tfm)) {
  41                 crypto_free_blkcipher(local->wep_tx_tfm);
  42                 return PTR_ERR(local->wep_rx_tfm);
  43         }
  44
  45         return 0;
  46 }
  47
  48 void ieee80211_wep_free(struct ieee80211_local *local)
  49 {
  50         crypto_free_blkcipher(local->wep_tx_tfm);
  51         crypto_free_blkcipher(local->wep_rx_tfm);
  52 }
  53
  54 static inline bool ieee80211_wep_weak_iv(u32 iv, int keylen)
  55 {
  56         /*
  57          * Fluhrer, Mantin, and Shamir have reported weaknesses in the
  58          * key scheduling algorithm of RC4. At least IVs (KeyByte + 3,
  59          * 0xff, N) can be used to speedup attacks, so avoid using them.
  60          */
  61         if ((iv & 0xff00) == 0xff00) {
  62                 u8 B = (iv >> 16) & 0xff;
  63                 if (B >= 3 && B < 3 + keylen)
  64                         return true;
  65         }
  66         return false;
  67 }
  68
  69
  70 static void ieee80211_wep_get_iv(struct ieee80211_local *local,
  71                                  int keylen, int keyidx, u8 *iv)
  72 {
  73         local->wep_iv++;
  74         if (ieee80211_wep_weak_iv(local->wep_iv, keylen))
  75                 local->wep_iv += 0x0100;
  76
  77         if (!iv)
  78                 return;
  79
  80         *iv++ = (local->wep_iv >> 16) & 0xff;
  81         *iv++ = (local->wep_iv >> 8) & 0xff;
  82         *iv++ = local->wep_iv & 0xff;
  83         *iv++ = keyidx << 6;
  84 }
  85
  86
  87 static u8 *ieee80211_wep_add_iv(struct ieee80211_local *local,
  88                                 struct sk_buff *skb,
  89                                 int keylen, int keyidx)
  90 {
  91         struct ieee80211_hdr *hdr = (struct ieee80211_hdr *)skb->data;
  92         unsigned int hdrlen;
  93         u8 *newhdr;
  94
  95         hdr->frame_control |= cpu_to_le16(IEEE80211_FCTL_PROTECTED);
  96
  97         if (WARN_ON(skb_tailroom(skb) < WEP_ICV_LEN ||
  98                     skb_headroom(skb) < WEP_IV_LEN))
  99                 return NULL;
 100
 101         hdrlen = ieee80211_hdrlen(hdr->frame_control);
 102         newhdr = skb_push(skb, WEP_IV_LEN);
 103         memmove(newhdr, newhdr + WEP_IV_LEN, hdrlen);
 104         ieee80211_wep_get_iv(local, keylen, keyidx, newhdr + hdrlen);
 105         return newhdr + hdrlen;
 106 }
 107
 108
 109 static void ieee80211_wep_remove_iv(struct ieee80211_local *local,
 110                                     struct sk_buff *skb,
 111                                     struct ieee80211_key *key)
 112 {
 113         struct ieee80211_hdr *hdr = (struct ieee80211_hdr *)skb->data;
 114         unsigned int hdrlen;
 115
 116         hdrlen = ieee80211_hdrlen(hdr->frame_control);
 117         memmove(skb->data + WEP_IV_LEN, skb->data, hdrlen);
 118         skb_pull(skb, WEP_IV_LEN);
 119 }
 120
 121
 122 /* Perform WEP encryption using given key. data buffer must have tailroom
 123  * for 4-byte ICV. data_len must not include this ICV. Note: this function
 124  * does _not_ add IV. data = RC4(data | CRC32(data)) */
 125 void ieee80211_wep_encrypt_data(struct crypto_blkcipher *tfm, u8 *rc4key,
 126                                 size_t klen, u8 *data, size_t data_len)
 127 {
 128         struct blkcipher_desc desc = { .tfm = tfm };
 129         struct scatterlist sg;
 130         __le32 icv;
 131
 132         icv = cpu_to_le32(~crc32_le(~0, data, data_len));
 133         put_unaligned(icv, (__le32 *)(data + data_len));
 134
 135         crypto_blkcipher_setkey(tfm, rc4key, klen);
 136         sg_init_one(&sg, data, data_len + WEP_ICV_LEN);
 137         crypto_blkcipher_encrypt(&desc, &sg, &sg, sg.length);
 138 }
 139
 140
 141 /* Perform WEP encryption on given skb. 4 bytes of extra space (IV) in the
 142  * beginning of the buffer 4 bytes of extra space (ICV) in the end of the
 143  * buffer will be added. Both IV and ICV will be transmitted, so the
 144  * payload length increases with 8 bytes.
 145  *
 146  * WEP frame payload: IV + TX key idx, RC4(data), ICV = RC4(CRC32(data))
 147  */
 148 int ieee80211_wep_encrypt(struct ieee80211_local *local,
 149                           struct sk_buff *skb,
 150                           const u8 *key, int keylen, int keyidx)
 151 {
 152         u8 *iv;
 153         size_t len;
 154         u8 rc4key[3 + WLAN_KEY_LEN_WEP104];
 155
 156         iv = ieee80211_wep_add_iv(local, skb, keylen, keyidx);
 157         if (!iv)
 158                 return -1;
 159
 160         len = skb->len - (iv + WEP_IV_LEN - skb->data);
 161
 162         /* Prepend 24-bit IV to RC4 key */
 163         memcpy(rc4key, iv, 3);
 164
 165         /* Copy rest of the WEP key (the secret part) */
 166         memcpy(rc4key + 3, key, keylen);
 167
 168         /* Add room for ICV */
 169         skb_put(skb, WEP_ICV_LEN);
 170
 171         ieee80211_wep_encrypt_data(local->wep_tx_tfm, rc4key, keylen + 3,
 172                                    iv + WEP_IV_LEN, len);
 173
 174         return 0;
 175 }
 176
 177
 178 /* Perform WEP decryption using given key. data buffer includes encrypted
 179  * payload, including 4-byte ICV, but _not_ IV. data_len must not include ICV.
 180  * Return 0 on success and -1 on ICV mismatch. */
 181 int ieee80211_wep_decrypt_data(struct crypto_blkcipher *tfm, u8 *rc4key,
 182                                size_t klen, u8 *data, size_t data_len)
 183 {
 184         struct blkcipher_desc desc = { .tfm = tfm };
 185         struct scatterlist sg;
 186         __le32 crc;
 187
 188         crypto_blkcipher_setkey(tfm, rc4key, klen);
 189         sg_init_one(&sg, data, data_len + WEP_ICV_LEN);
 190         crypto_blkcipher_decrypt(&desc, &sg, &sg, sg.length);
 191
 192         crc = cpu_to_le32(~crc32_le(~0, data, data_len));
 193         if (memcmp(&crc, data + data_len, WEP_ICV_LEN) != 0)
 194                 /* ICV mismatch */
 195                 return -1;
 196
 197         return 0;
 198 }
 199
 200
 201 /* Perform WEP decryption on given skb. Buffer includes whole WEP part of
 202  * the frame: IV (4 bytes), encrypted payload (including SNAP header),
 203  * ICV (4 bytes). skb->len includes both IV and ICV.
 204  *
 205  * Returns 0 if frame was decrypted successfully and ICV was correct and -1 on
 206  * failure. If frame is OK, IV and ICV will be removed, i.e., decrypted payload
 207  * is moved to the beginning of the skb and skb length will be reduced.
 208  */
 209 static int ieee80211_wep_decrypt(struct ieee80211_local *local,
 210                                  struct sk_buff *skb,
 211                                  struct ieee80211_key *key)
 212 {
 213         u32 klen;
 214         u8 *rc4key;
 215         u8 keyidx;
 216         struct ieee80211_hdr *hdr = (struct ieee80211_hdr *)skb->data;
 217         unsigned int hdrlen;
 218         size_t len;
 219         int ret = 0;
 220
 221         if (!ieee80211_has_protected(hdr->frame_control))
 222                 return -1;
 223
 224         hdrlen = ieee80211_hdrlen(hdr->frame_control);
 225         if (skb->len < hdrlen + WEP_IV_LEN + WEP_ICV_LEN)
 226                 return -1;
 227
 228         len = skb->len - hdrlen - WEP_IV_LEN - WEP_ICV_LEN;
 229
 230         keyidx = skb->data[hdrlen + 3] >> 6;
 231
 232         if (!key || keyidx != key->conf.keyidx || key->conf.alg != ALG_WEP)
 233                 return -1;
 234
 235         klen = 3 + key->conf.keylen;
 236
 237         rc4key = kmalloc(klen, GFP_ATOMIC);
 238         if (!rc4key)
 239                 return -1;
 240
 241         /* Prepend 24-bit IV to RC4 key */
 242         memcpy(rc4key, skb->data + hdrlen, 3);
 243
 244         /* Copy rest of the WEP key (the secret part) */
 245         memcpy(rc4key + 3, key->conf.key, key->conf.keylen);
 246
 247         if (ieee80211_wep_decrypt_data(local->wep_rx_tfm, rc4key, klen,
 248                                        skb->data + hdrlen + WEP_IV_LEN,
 249                                        len))
 250                 ret = -1;
 251
 252         kfree(rc4key);
 253
 254         /* Trim ICV */
 255         skb_trim(skb, skb->len - WEP_ICV_LEN);
 256
 257         /* Remove IV */
 258         memmove(skb->data + WEP_IV_LEN, skb->data, hdrlen);
 259         skb_pull(skb, WEP_IV_LEN);
 260
 261         return ret;
 262 }
 263
 264
 265 bool ieee80211_wep_is_weak_iv(struct sk_buff *skb, struct ieee80211_key *key)
 266 {
 267         struct ieee80211_hdr *hdr = (struct ieee80211_hdr *)skb->data;
 268         unsigned int hdrlen;
 269         u8 *ivpos;
 270         u32 iv;
 271
 272         if (!ieee80211_has_protected(hdr->frame_control))
 273                 return false;
 274
 275         hdrlen = ieee80211_hdrlen(hdr->frame_control);
 276         ivpos = skb->data + hdrlen;
 277         iv = (ivpos[0] << 16) | (ivpos[1] << 8) | ivpos[2];
 278
 279         return ieee80211_wep_weak_iv(iv, key->conf.keylen);
 280 }
 281
 282 ieee80211_rx_result
 283 ieee80211_crypto_wep_decrypt(struct ieee80211_rx_data *rx)
 284 {
 285         struct sk_buff *skb = rx->skb;
 286         struct ieee80211_rx_status *status = IEEE80211_SKB_RXCB(skb);
 287         struct ieee80211_hdr *hdr = (struct ieee80211_hdr *)skb->data;
 288
 289         if (!ieee80211_is_data(hdr->frame_control) &&
 290             !ieee80211_is_auth(hdr->frame_control))
 291                 return RX_CONTINUE;
 292
 293         if (!(status->flag & RX_FLAG_DECRYPTED)) {
 294                 if (ieee80211_wep_decrypt(rx->local, rx->skb, rx->key))
 295                         return RX_DROP_UNUSABLE;
 296         } else if (!(status->flag & RX_FLAG_IV_STRIPPED)) {
 297                 ieee80211_wep_remove_iv(rx->local, rx->skb, rx->key);
 298                 /* remove ICV */
 299                 skb_trim(rx->skb, rx->skb->len - WEP_ICV_LEN);
 300         }
 301
 302         return RX_CONTINUE;
 303 }
 304
 305 static int wep_encrypt_skb(struct ieee80211_tx_data *tx, struct sk_buff *skb)
 306 {
 307         struct ieee80211_tx_info *info = IEEE80211_SKB_CB(skb);
 308
 309         if (!info->control.hw_key) {
 310                 if (ieee80211_wep_encrypt(tx->local, skb, tx->key->conf.key,
 311                                           tx->key->conf.keylen,
 312                                           tx->key->conf.keyidx))
 313                         return -1;
 314         } else if (info->control.hw_key->flags &
 315                         IEEE80211_KEY_FLAG_GENERATE_IV) {
 316                 if (!ieee80211_wep_add_iv(tx->local, skb,
 317                                           tx->key->conf.keylen,
 318                                           tx->key->conf.keyidx))
 319                         return -1;
 320         }
 321
 322         return 0;
 323 }
 324
 325 ieee80211_tx_result
 326 ieee80211_crypto_wep_encrypt(struct ieee80211_tx_data *tx)
 327 {
 328         struct sk_buff *skb;
 329
 330         ieee80211_tx_set_protected(tx);
 331
 332         skb = tx->skb;
 333         do {
 334                 if (wep_encrypt_skb(tx, skb) < 0) {
 335                         I802_DEBUG_INC(tx->local->tx_handlers_drop_wep);
 336                         return TX_DROP;
 337                 }
 338         } while ((skb = skb->next));
 339
 340         return TX_CONTINUE;
 341 }