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                 local->wep_rx_tfm = ERR_PTR(-EINVAL);
  37                 return PTR_ERR(local->wep_tx_tfm);
  38         }
  39
  40         local->wep_rx_tfm = crypto_alloc_blkcipher("ecb(arc4)", 0,
  41                                                 CRYPTO_ALG_ASYNC);
  42         if (IS_ERR(local->wep_rx_tfm)) {
  43                 crypto_free_blkcipher(local->wep_tx_tfm);
  44                 local->wep_tx_tfm = ERR_PTR(-EINVAL);
  45                 return PTR_ERR(local->wep_rx_tfm);
  46         }
  47
  48         return 0;
  49 }
  50
  51 void ieee80211_wep_free(struct ieee80211_local *local)
  52 {
  53         if (!IS_ERR(local->wep_tx_tfm))
  54                 crypto_free_blkcipher(local->wep_tx_tfm);
  55         if (!IS_ERR(local->wep_rx_tfm))
  56                 crypto_free_blkcipher(local->wep_rx_tfm);
  57 }
  58
  59 static inline bool ieee80211_wep_weak_iv(u32 iv, int keylen)
  60 {
  61         /*
  62          * Fluhrer, Mantin, and Shamir have reported weaknesses in the
  63          * key scheduling algorithm of RC4. At least IVs (KeyByte + 3,
  64          * 0xff, N) can be used to speedup attacks, so avoid using them.
  65          */
  66         if ((iv & 0xff00) == 0xff00) {
  67                 u8 B = (iv >> 16) & 0xff;
  68                 if (B >= 3 && B < 3 + keylen)
  69                         return true;
  70         }
  71         return false;
  72 }
  73
  74
  75 static void ieee80211_wep_get_iv(struct ieee80211_local *local,
  76                                  int keylen, int keyidx, u8 *iv)
  77 {
  78         local->wep_iv++;
  79         if (ieee80211_wep_weak_iv(local->wep_iv, keylen))
  80                 local->wep_iv += 0x0100;
  81
  82         if (!iv)
  83                 return;
  84
  85         *iv++ = (local->wep_iv >> 16) & 0xff;
  86         *iv++ = (local->wep_iv >> 8) & 0xff;
  87         *iv++ = local->wep_iv & 0xff;
  88         *iv++ = keyidx << 6;
  89 }
  90
  91
  92 static u8 *ieee80211_wep_add_iv(struct ieee80211_local *local,
  93                                 struct sk_buff *skb,
  94                                 int keylen, int keyidx)
  95 {
  96         struct ieee80211_hdr *hdr = (struct ieee80211_hdr *)skb->data;
  97         unsigned int hdrlen;
  98         u8 *newhdr;
  99
 100         hdr->frame_control |= cpu_to_le16(IEEE80211_FCTL_PROTECTED);
 101
 102         if (WARN_ON(skb_tailroom(skb) < WEP_ICV_LEN ||
 103                     skb_headroom(skb) < WEP_IV_LEN))
 104                 return NULL;
 105
 106         hdrlen = ieee80211_hdrlen(hdr->frame_control);
 107         newhdr = skb_push(skb, WEP_IV_LEN);
 108         memmove(newhdr, newhdr + WEP_IV_LEN, hdrlen);
 109         ieee80211_wep_get_iv(local, keylen, keyidx, newhdr + hdrlen);
 110         return newhdr + hdrlen;
 111 }
 112
 113
 114 static void ieee80211_wep_remove_iv(struct ieee80211_local *local,
 115                                     struct sk_buff *skb,
 116                                     struct ieee80211_key *key)
 117 {
 118         struct ieee80211_hdr *hdr = (struct ieee80211_hdr *)skb->data;
 119         unsigned int hdrlen;
 120
 121         hdrlen = ieee80211_hdrlen(hdr->frame_control);
 122         memmove(skb->data + WEP_IV_LEN, skb->data, hdrlen);
 123         skb_pull(skb, WEP_IV_LEN);
 124 }
 125
 126
 127 /* Perform WEP encryption using given key. data buffer must have tailroom
 128  * for 4-byte ICV. data_len must not include this ICV. Note: this function
 129  * does _not_ add IV. data = RC4(data | CRC32(data)) */
 130 int ieee80211_wep_encrypt_data(struct crypto_blkcipher *tfm, u8 *rc4key,
 131                                size_t klen, u8 *data, size_t data_len)
 132 {
 133         struct blkcipher_desc desc = { .tfm = tfm };
 134         struct scatterlist sg;
 135         __le32 icv;
 136
 137         if (IS_ERR(tfm))
 138                 return -1;
 139
 140         icv = cpu_to_le32(~crc32_le(~0, data, data_len));
 141         put_unaligned(icv, (__le32 *)(data + data_len));
 142
 143         crypto_blkcipher_setkey(tfm, rc4key, klen);
 144         sg_init_one(&sg, data, data_len + WEP_ICV_LEN);
 145         crypto_blkcipher_encrypt(&desc, &sg, &sg, sg.length);
 146
 147         return 0;
 148 }
 149
 150
 151 /* Perform WEP encryption on given skb. 4 bytes of extra space (IV) in the
 152  * beginning of the buffer 4 bytes of extra space (ICV) in the end of the
 153  * buffer will be added. Both IV and ICV will be transmitted, so the
 154  * payload length increases with 8 bytes.
 155  *
 156  * WEP frame payload: IV + TX key idx, RC4(data), ICV = RC4(CRC32(data))
 157  */
 158 int ieee80211_wep_encrypt(struct ieee80211_local *local,
 159                           struct sk_buff *skb,
 160                           const u8 *key, int keylen, int keyidx)
 161 {
 162         u8 *iv;
 163         size_t len;
 164         u8 rc4key[3 + WLAN_KEY_LEN_WEP104];
 165
 166         iv = ieee80211_wep_add_iv(local, skb, keylen, keyidx);
 167         if (!iv)
 168                 return -1;
 169
 170         len = skb->len - (iv + WEP_IV_LEN - skb->data);
 171
 172         /* Prepend 24-bit IV to RC4 key */
 173         memcpy(rc4key, iv, 3);
 174
 175         /* Copy rest of the WEP key (the secret part) */
 176         memcpy(rc4key + 3, key, keylen);
 177
 178         /* Add room for ICV */
 179         skb_put(skb, WEP_ICV_LEN);
 180
 181         return ieee80211_wep_encrypt_data(local->wep_tx_tfm, rc4key, keylen + 3,
 182                                           iv + WEP_IV_LEN, len);
 183 }
 184
 185
 186 /* Perform WEP decryption using given key. data buffer includes encrypted
 187  * payload, including 4-byte ICV, but _not_ IV. data_len must not include ICV.
 188  * Return 0 on success and -1 on ICV mismatch. */
 189 int ieee80211_wep_decrypt_data(struct crypto_blkcipher *tfm, u8 *rc4key,
 190                                size_t klen, u8 *data, size_t data_len)
 191 {
 192         struct blkcipher_desc desc = { .tfm = tfm };
 193         struct scatterlist sg;
 194         __le32 crc;
 195
 196         if (IS_ERR(tfm))
 197                 return -1;
 198
 199         crypto_blkcipher_setkey(tfm, rc4key, klen);
 200         sg_init_one(&sg, data, data_len + WEP_ICV_LEN);
 201         crypto_blkcipher_decrypt(&desc, &sg, &sg, sg.length);
 202
 203         crc = cpu_to_le32(~crc32_le(~0, data, data_len));
 204         if (memcmp(&crc, data + data_len, WEP_ICV_LEN) != 0)
 205                 /* ICV mismatch */
 206                 return -1;
 207
 208         return 0;
 209 }
 210
 211
 212 /* Perform WEP decryption on given skb. Buffer includes whole WEP part of
 213  * the frame: IV (4 bytes), encrypted payload (including SNAP header),
 214  * ICV (4 bytes). skb->len includes both IV and ICV.
 215  *
 216  * Returns 0 if frame was decrypted successfully and ICV was correct and -1 on
 217  * failure. If frame is OK, IV and ICV will be removed, i.e., decrypted payload
 218  * is moved to the beginning of the skb and skb length will be reduced.
 219  */
 220 static int ieee80211_wep_decrypt(struct ieee80211_local *local,
 221                                  struct sk_buff *skb,
 222                                  struct ieee80211_key *key)
 223 {
 224         u32 klen;
 225         u8 rc4key[3 + WLAN_KEY_LEN_WEP104];
 226         u8 keyidx;
 227         struct ieee80211_hdr *hdr = (struct ieee80211_hdr *)skb->data;
 228         unsigned int hdrlen;
 229         size_t len;
 230         int ret = 0;
 231
 232         if (!ieee80211_has_protected(hdr->frame_control))
 233                 return -1;
 234
 235         hdrlen = ieee80211_hdrlen(hdr->frame_control);
 236         if (skb->len < hdrlen + WEP_IV_LEN + WEP_ICV_LEN)
 237                 return -1;
 238
 239         len = skb->len - hdrlen - WEP_IV_LEN - WEP_ICV_LEN;
 240
 241         keyidx = skb->data[hdrlen + 3] >> 6;
 242
 243         if (!key || keyidx != key->conf.keyidx)
 244                 return -1;
 245
 246         klen = 3 + key->conf.keylen;
 247
 248         /* Prepend 24-bit IV to RC4 key */
 249         memcpy(rc4key, skb->data + hdrlen, 3);
 250
 251         /* Copy rest of the WEP key (the secret part) */
 252         memcpy(rc4key + 3, key->conf.key, key->conf.keylen);
 253
 254         if (ieee80211_wep_decrypt_data(local->wep_rx_tfm, rc4key, klen,
 255                                        skb->data + hdrlen + WEP_IV_LEN,
 256                                        len))
 257                 ret = -1;
 258
 259         /* Trim ICV */
 260         skb_trim(skb, skb->len - WEP_ICV_LEN);
 261
 262         /* Remove IV */
 263         memmove(skb->data + WEP_IV_LEN, skb->data, hdrlen);
 264         skb_pull(skb, WEP_IV_LEN);
 265
 266         return ret;
 267 }
 268
 269
 270 bool ieee80211_wep_is_weak_iv(struct sk_buff *skb, struct ieee80211_key *key)
 271 {
 272         struct ieee80211_hdr *hdr = (struct ieee80211_hdr *)skb->data;
 273         unsigned int hdrlen;
 274         u8 *ivpos;
 275         u32 iv;
 276
 277         if (!ieee80211_has_protected(hdr->frame_control))
 278                 return false;
 279
 280         hdrlen = ieee80211_hdrlen(hdr->frame_control);
 281         ivpos = skb->data + hdrlen;
 282         iv = (ivpos[0] << 16) | (ivpos[1] << 8) | ivpos[2];
 283
 284         return ieee80211_wep_weak_iv(iv, key->conf.keylen);
 285 }
 286
 287 ieee80211_rx_result
 288 ieee80211_crypto_wep_decrypt(struct ieee80211_rx_data *rx)
 289 {
 290         struct sk_buff *skb = rx->skb;
 291         struct ieee80211_rx_status *status = IEEE80211_SKB_RXCB(skb);
 292         struct ieee80211_hdr *hdr = (struct ieee80211_hdr *)skb->data;
 293
 294         if (!ieee80211_is_data(hdr->frame_control) &&
 295             !ieee80211_is_auth(hdr->frame_control))
 296                 return RX_CONTINUE;
 297
 298         if (!(status->flag & RX_FLAG_DECRYPTED)) {
 299                 if (ieee80211_wep_decrypt(rx->local, rx->skb, rx->key))
 300                         return RX_DROP_UNUSABLE;
 301         } else if (!(status->flag & RX_FLAG_IV_STRIPPED)) {
 302                 ieee80211_wep_remove_iv(rx->local, rx->skb, rx->key);
 303                 /* remove ICV */
 304                 skb_trim(rx->skb, rx->skb->len - WEP_ICV_LEN);
 305         }
 306
 307         return RX_CONTINUE;
 308 }
 309
 310 static int wep_encrypt_skb(struct ieee80211_tx_data *tx, struct sk_buff *skb)
 311 {
 312         struct ieee80211_tx_info *info = IEEE80211_SKB_CB(skb);
 313
 314         if (!info->control.hw_key) {
 315                 if (ieee80211_wep_encrypt(tx->local, skb, tx->key->conf.key,
 316                                           tx->key->conf.keylen,
 317                                           tx->key->conf.keyidx))
 318                         return -1;
 319         } else if (info->control.hw_key->flags &
 320                         IEEE80211_KEY_FLAG_GENERATE_IV) {
 321                 if (!ieee80211_wep_add_iv(tx->local, skb,
 322                                           tx->key->conf.keylen,
 323                                           tx->key->conf.keyidx))
 324                         return -1;
 325         }
 326
 327         return 0;
 328 }
 329
 330 ieee80211_tx_result
 331 ieee80211_crypto_wep_encrypt(struct ieee80211_tx_data *tx)
 332 {
 333         struct sk_buff *skb;
 334
 335         ieee80211_tx_set_protected(tx);
 336
 337         skb = tx->skb;
 338         do {
 339                 if (wep_encrypt_skb(tx, skb) < 0) {
 340                         I802_DEBUG_INC(tx->local->tx_handlers_drop_wep);
 341                         return TX_DROP;
 342                 }
 343         } while ((skb = skb->next));
 344
 345         return TX_CONTINUE;
 346 }