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 <asm/unaligned.h>
  21
  22 #include <net/mac80211.h>
  23 #include "ieee80211_i.h"
  24 #include "wep.h"
  25
  26
  27 int ieee80211_wep_init(struct ieee80211_local *local)
  28 {
  29         /* start WEP IV from a random value */
  30         get_random_bytes(&local->wep_iv, WEP_IV_LEN);
  31
  32         local->wep_tx_tfm = crypto_alloc_blkcipher("ecb(arc4)", 0,
  33                                                 CRYPTO_ALG_ASYNC);
  34         if (IS_ERR(local->wep_tx_tfm))
  35                 return PTR_ERR(local->wep_tx_tfm);
  36
  37         local->wep_rx_tfm = crypto_alloc_blkcipher("ecb(arc4)", 0,
  38                                                 CRYPTO_ALG_ASYNC);
  39         if (IS_ERR(local->wep_rx_tfm)) {
  40                 crypto_free_blkcipher(local->wep_tx_tfm);
  41                 return PTR_ERR(local->wep_rx_tfm);
  42         }
  43
  44         return 0;
  45 }
  46
  47 void ieee80211_wep_free(struct ieee80211_local *local)
  48 {
  49         crypto_free_blkcipher(local->wep_tx_tfm);
  50         crypto_free_blkcipher(local->wep_rx_tfm);
  51 }
  52
  53 static inline bool ieee80211_wep_weak_iv(u32 iv, int keylen)
  54 {
  55         /*
  56          * Fluhrer, Mantin, and Shamir have reported weaknesses in the
  57          * key scheduling algorithm of RC4. At least IVs (KeyByte + 3,
  58          * 0xff, N) can be used to speedup attacks, so avoid using them.
  59          */
  60         if ((iv & 0xff00) == 0xff00) {
  61                 u8 B = (iv >> 16) & 0xff;
  62                 if (B >= 3 && B < 3 + keylen)
  63                         return true;
  64         }
  65         return false;
  66 }
  67
  68
  69 static void ieee80211_wep_get_iv(struct ieee80211_local *local,
  70                                  int keylen, int keyidx, u8 *iv)
  71 {
  72         local->wep_iv++;
  73         if (ieee80211_wep_weak_iv(local->wep_iv, keylen))
  74                 local->wep_iv += 0x0100;
  75
  76         if (!iv)
  77                 return;
  78
  79         *iv++ = (local->wep_iv >> 16) & 0xff;
  80         *iv++ = (local->wep_iv >> 8) & 0xff;
  81         *iv++ = local->wep_iv & 0xff;
  82         *iv++ = keyidx << 6;
  83 }
  84
  85
  86 static u8 *ieee80211_wep_add_iv(struct ieee80211_local *local,
  87                                 struct sk_buff *skb,
  88                                 int keylen, int keyidx)
  89 {
  90         struct ieee80211_hdr *hdr = (struct ieee80211_hdr *)skb->data;
  91         unsigned int hdrlen;
  92         u8 *newhdr;
  93
  94         hdr->frame_control |= cpu_to_le16(IEEE80211_FCTL_PROTECTED);
  95
  96         if (WARN_ON(skb_tailroom(skb) < WEP_ICV_LEN ||
  97                     skb_headroom(skb) < WEP_IV_LEN))
  98                 return NULL;
  99
 100         hdrlen = ieee80211_hdrlen(hdr->frame_control);
 101         newhdr = skb_push(skb, WEP_IV_LEN);
 102         memmove(newhdr, newhdr + WEP_IV_LEN, hdrlen);
 103         ieee80211_wep_get_iv(local, keylen, keyidx, newhdr + hdrlen);
 104         return newhdr + hdrlen;
 105 }
 106
 107
 108 static void ieee80211_wep_remove_iv(struct ieee80211_local *local,
 109                                     struct sk_buff *skb,
 110                                     struct ieee80211_key *key)
 111 {
 112         struct ieee80211_hdr *hdr = (struct ieee80211_hdr *)skb->data;
 113         unsigned int hdrlen;
 114
 115         hdrlen = ieee80211_hdrlen(hdr->frame_control);
 116         memmove(skb->data + WEP_IV_LEN, skb->data, hdrlen);
 117         skb_pull(skb, WEP_IV_LEN);
 118 }
 119
 120
 121 /* Perform WEP encryption using given key. data buffer must have tailroom
 122  * for 4-byte ICV. data_len must not include this ICV. Note: this function
 123  * does _not_ add IV. data = RC4(data | CRC32(data)) */
 124 void ieee80211_wep_encrypt_data(struct crypto_blkcipher *tfm, u8 *rc4key,
 125                                 size_t klen, u8 *data, size_t data_len)
 126 {
 127         struct blkcipher_desc desc = { .tfm = tfm };
 128         struct scatterlist sg;
 129         __le32 icv;
 130
 131         icv = cpu_to_le32(~crc32_le(~0, data, data_len));
 132         put_unaligned(icv, (__le32 *)(data + data_len));
 133
 134         crypto_blkcipher_setkey(tfm, rc4key, klen);
 135         sg_init_one(&sg, data, data_len + WEP_ICV_LEN);
 136         crypto_blkcipher_encrypt(&desc, &sg, &sg, sg.length);
 137 }
 138
 139
 140 /* Perform WEP encryption on given skb. 4 bytes of extra space (IV) in the
 141  * beginning of the buffer 4 bytes of extra space (ICV) in the end of the
 142  * buffer will be added. Both IV and ICV will be transmitted, so the
 143  * payload length increases with 8 bytes.
 144  *
 145  * WEP frame payload: IV + TX key idx, RC4(data), ICV = RC4(CRC32(data))
 146  */
 147 int ieee80211_wep_encrypt(struct ieee80211_local *local,
 148                           struct sk_buff *skb,
 149                           const u8 *key, int keylen, int keyidx)
 150 {
 151         u8 *iv;
 152         size_t len;
 153         u8 rc4key[3 + WLAN_KEY_LEN_WEP104];
 154
 155         iv = ieee80211_wep_add_iv(local, skb, keylen, keyidx);
 156         if (!iv)
 157                 return -1;
 158
 159         len = skb->len - (iv + WEP_IV_LEN - skb->data);
 160
 161         /* Prepend 24-bit IV to RC4 key */
 162         memcpy(rc4key, iv, 3);
 163
 164         /* Copy rest of the WEP key (the secret part) */
 165         memcpy(rc4key + 3, key, keylen);
 166
 167         /* Add room for ICV */
 168         skb_put(skb, WEP_ICV_LEN);
 169
 170         ieee80211_wep_encrypt_data(local->wep_tx_tfm, rc4key, keylen + 3,
 171                                    iv + WEP_IV_LEN, len);
 172
 173         return 0;
 174 }
 175
 176
 177 /* Perform WEP decryption using given key. data buffer includes encrypted
 178  * payload, including 4-byte ICV, but _not_ IV. data_len must not include ICV.
 179  * Return 0 on success and -1 on ICV mismatch. */
 180 int ieee80211_wep_decrypt_data(struct crypto_blkcipher *tfm, u8 *rc4key,
 181                                size_t klen, u8 *data, size_t data_len)
 182 {
 183         struct blkcipher_desc desc = { .tfm = tfm };
 184         struct scatterlist sg;
 185         __le32 crc;
 186
 187         crypto_blkcipher_setkey(tfm, rc4key, klen);
 188         sg_init_one(&sg, data, data_len + WEP_ICV_LEN);
 189         crypto_blkcipher_decrypt(&desc, &sg, &sg, sg.length);
 190
 191         crc = cpu_to_le32(~crc32_le(~0, data, data_len));
 192         if (memcmp(&crc, data + data_len, WEP_ICV_LEN) != 0)
 193                 /* ICV mismatch */
 194                 return -1;
 195
 196         return 0;
 197 }
 198
 199
 200 /* Perform WEP decryption on given skb. Buffer includes whole WEP part of
 201  * the frame: IV (4 bytes), encrypted payload (including SNAP header),
 202  * ICV (4 bytes). skb->len includes both IV and ICV.
 203  *
 204  * Returns 0 if frame was decrypted successfully and ICV was correct and -1 on
 205  * failure. If frame is OK, IV and ICV will be removed, i.e., decrypted payload
 206  * is moved to the beginning of the skb and skb length will be reduced.
 207  */
 208 static int ieee80211_wep_decrypt(struct ieee80211_local *local,
 209                                  struct sk_buff *skb,
 210                                  struct ieee80211_key *key)
 211 {
 212         u32 klen;
 213         u8 *rc4key;
 214         u8 keyidx;
 215         struct ieee80211_hdr *hdr = (struct ieee80211_hdr *)skb->data;
 216         unsigned int hdrlen;
 217         size_t len;
 218         int ret = 0;
 219
 220         if (!ieee80211_has_protected(hdr->frame_control))
 221                 return -1;
 222
 223         hdrlen = ieee80211_hdrlen(hdr->frame_control);
 224         if (skb->len < hdrlen + WEP_IV_LEN + WEP_ICV_LEN)
 225                 return -1;
 226
 227         len = skb->len - hdrlen - WEP_IV_LEN - WEP_ICV_LEN;
 228
 229         keyidx = skb->data[hdrlen + 3] >> 6;
 230
 231         if (!key || keyidx != key->conf.keyidx || key->conf.alg != ALG_WEP)
 232                 return -1;
 233
 234         klen = 3 + key->conf.keylen;
 235
 236         rc4key = kmalloc(klen, GFP_ATOMIC);
 237         if (!rc4key)
 238                 return -1;
 239
 240         /* Prepend 24-bit IV to RC4 key */
 241         memcpy(rc4key, skb->data + hdrlen, 3);
 242
 243         /* Copy rest of the WEP key (the secret part) */
 244         memcpy(rc4key + 3, key->conf.key, key->conf.keylen);
 245
 246         if (ieee80211_wep_decrypt_data(local->wep_rx_tfm, rc4key, klen,
 247                                        skb->data + hdrlen + WEP_IV_LEN,
 248                                        len))
 249                 ret = -1;
 250
 251         kfree(rc4key);
 252
 253         /* Trim ICV */
 254         skb_trim(skb, skb->len - WEP_ICV_LEN);
 255
 256         /* Remove IV */
 257         memmove(skb->data + WEP_IV_LEN, skb->data, hdrlen);
 258         skb_pull(skb, WEP_IV_LEN);
 259
 260         return ret;
 261 }
 262
 263
 264 bool ieee80211_wep_is_weak_iv(struct sk_buff *skb, struct ieee80211_key *key)
 265 {
 266         struct ieee80211_hdr *hdr = (struct ieee80211_hdr *)skb->data;
 267         unsigned int hdrlen;
 268         u8 *ivpos;
 269         u32 iv;
 270
 271         if (!ieee80211_has_protected(hdr->frame_control))
 272                 return false;
 273
 274         hdrlen = ieee80211_hdrlen(hdr->frame_control);
 275         ivpos = skb->data + hdrlen;
 276         iv = (ivpos[0] << 16) | (ivpos[1] << 8) | ivpos[2];
 277
 278         return ieee80211_wep_weak_iv(iv, key->conf.keylen);
 279 }
 280
 281 ieee80211_rx_result
 282 ieee80211_crypto_wep_decrypt(struct ieee80211_rx_data *rx)
 283 {
 284         struct sk_buff *skb = rx->skb;
 285         struct ieee80211_rx_status *status = IEEE80211_SKB_RXCB(skb);
 286         struct ieee80211_hdr *hdr = (struct ieee80211_hdr *)skb->data;
 287
 288         if (!ieee80211_is_data(hdr->frame_control) &&
 289             !ieee80211_is_auth(hdr->frame_control))
 290                 return RX_CONTINUE;
 291
 292         if (!(status->flag & RX_FLAG_DECRYPTED)) {
 293                 if (ieee80211_wep_decrypt(rx->local, rx->skb, rx->key))
 294                         return RX_DROP_UNUSABLE;
 295         } else if (!(status->flag & RX_FLAG_IV_STRIPPED)) {
 296                 ieee80211_wep_remove_iv(rx->local, rx->skb, rx->key);
 297                 /* remove ICV */
 298                 skb_trim(rx->skb, rx->skb->len - WEP_ICV_LEN);
 299         }
 300
 301         return RX_CONTINUE;
 302 }
 303
 304 static int wep_encrypt_skb(struct ieee80211_tx_data *tx, struct sk_buff *skb)
 305 {
 306         struct ieee80211_tx_info *info = IEEE80211_SKB_CB(skb);
 307
 308         if (!info->control.hw_key) {
 309                 if (ieee80211_wep_encrypt(tx->local, skb, tx->key->conf.key,
 310                                           tx->key->conf.keylen,
 311                                           tx->key->conf.keyidx))
 312                         return -1;
 313         } else if (info->control.hw_key->flags &
 314                         IEEE80211_KEY_FLAG_GENERATE_IV) {
 315                 if (!ieee80211_wep_add_iv(tx->local, skb,
 316                                           tx->key->conf.keylen,
 317                                           tx->key->conf.keyidx))
 318                         return -1;
 319         }
 320
 321         return 0;
 322 }
 323
 324 ieee80211_tx_result
 325 ieee80211_crypto_wep_encrypt(struct ieee80211_tx_data *tx)
 326 {
 327         struct sk_buff *skb;
 328
 329         ieee80211_tx_set_protected(tx);
 330
 331         skb = tx->skb;
 332         do {
 333                 if (wep_encrypt_skb(tx, skb) < 0) {
 334                         I802_DEBUG_INC(tx->local->tx_handlers_drop_wep);
 335                         return TX_DROP;
 336                 }
 337         } while ((skb = skb->next));
 338
 339         return TX_CONTINUE;
 340 }