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
  21 #include <net/mac80211.h>
  22 #include "ieee80211_i.h"
  23 #include "wep.h"
  24
  25
  26 int ieee80211_wep_init(struct ieee80211_local *local)
  27 {
  28         /* start WEP IV from a random value */
  29         get_random_bytes(&local->wep_iv, WEP_IV_LEN);
  30
  31         local->wep_tx_tfm = crypto_alloc_blkcipher("ecb(arc4)", 0,
  32                                                 CRYPTO_ALG_ASYNC);
  33         if (IS_ERR(local->wep_tx_tfm))
  34                 return PTR_ERR(local->wep_tx_tfm);
  35
  36         local->wep_rx_tfm = crypto_alloc_blkcipher("ecb(arc4)", 0,
  37                                                 CRYPTO_ALG_ASYNC);
  38         if (IS_ERR(local->wep_rx_tfm)) {
  39                 crypto_free_blkcipher(local->wep_tx_tfm);
  40                 return PTR_ERR(local->wep_rx_tfm);
  41         }
  42
  43         return 0;
  44 }
  45
  46 void ieee80211_wep_free(struct ieee80211_local *local)
  47 {
  48         crypto_free_blkcipher(local->wep_tx_tfm);
  49         crypto_free_blkcipher(local->wep_rx_tfm);
  50 }
  51
  52 static inline int ieee80211_wep_weak_iv(u32 iv, int keylen)
  53 {
  54         /* Fluhrer, Mantin, and Shamir have reported weaknesses in the
  55          * key scheduling algorithm of RC4. At least IVs (KeyByte + 3,
  56          * 0xff, N) can be used to speedup attacks, so avoid using them. */
  57         if ((iv & 0xff00) == 0xff00) {
  58                 u8 B = (iv >> 16) & 0xff;
  59                 if (B >= 3 && B < 3 + keylen)
  60                         return 1;
  61         }
  62         return 0;
  63 }
  64
  65
  66 static void ieee80211_wep_get_iv(struct ieee80211_local *local,
  67                                  struct ieee80211_key *key, u8 *iv)
  68 {
  69         local->wep_iv++;
  70         if (ieee80211_wep_weak_iv(local->wep_iv, key->conf.keylen))
  71                 local->wep_iv += 0x0100;
  72
  73         if (!iv)
  74                 return;
  75
  76         *iv++ = (local->wep_iv >> 16) & 0xff;
  77         *iv++ = (local->wep_iv >> 8) & 0xff;
  78         *iv++ = local->wep_iv & 0xff;
  79         *iv++ = key->conf.keyidx << 6;
  80 }
  81
  82
  83 static u8 *ieee80211_wep_add_iv(struct ieee80211_local *local,
  84                                 struct sk_buff *skb,
  85                                 struct ieee80211_key *key)
  86 {
  87         struct ieee80211_hdr *hdr = (struct ieee80211_hdr *)skb->data;
  88         unsigned int hdrlen;
  89         u8 *newhdr;
  90
  91         hdr->frame_control |= cpu_to_le16(IEEE80211_FCTL_PROTECTED);
  92
  93         if (WARN_ON(skb_tailroom(skb) < WEP_ICV_LEN ||
  94                     skb_headroom(skb) < WEP_IV_LEN))
  95                 return NULL;
  96
  97         hdrlen = ieee80211_hdrlen(hdr->frame_control);
  98         newhdr = skb_push(skb, WEP_IV_LEN);
  99         memmove(newhdr, newhdr + WEP_IV_LEN, hdrlen);
 100         ieee80211_wep_get_iv(local, key, newhdr + hdrlen);
 101         return newhdr + hdrlen;
 102 }
 103
 104
 105 static void ieee80211_wep_remove_iv(struct ieee80211_local *local,
 106                                     struct sk_buff *skb,
 107                                     struct ieee80211_key *key)
 108 {
 109         struct ieee80211_hdr *hdr = (struct ieee80211_hdr *)skb->data;
 110         unsigned int hdrlen;
 111
 112         hdrlen = ieee80211_hdrlen(hdr->frame_control);
 113         memmove(skb->data + WEP_IV_LEN, skb->data, hdrlen);
 114         skb_pull(skb, WEP_IV_LEN);
 115 }
 116
 117
 118 /* Perform WEP encryption using given key. data buffer must have tailroom
 119  * for 4-byte ICV. data_len must not include this ICV. Note: this function
 120  * does _not_ add IV. data = RC4(data | CRC32(data)) */
 121 void ieee80211_wep_encrypt_data(struct crypto_blkcipher *tfm, u8 *rc4key,
 122                                 size_t klen, u8 *data, size_t data_len)
 123 {
 124         struct blkcipher_desc desc = { .tfm = tfm };
 125         struct scatterlist sg;
 126         __le32 *icv;
 127
 128         icv = (__le32 *)(data + data_len);
 129         *icv = cpu_to_le32(~crc32_le(~0, data, data_len));
 130
 131         crypto_blkcipher_setkey(tfm, rc4key, klen);
 132         sg_init_one(&sg, data, data_len + WEP_ICV_LEN);
 133         crypto_blkcipher_encrypt(&desc, &sg, &sg, sg.length);
 134 }
 135
 136
 137 /* Perform WEP encryption on given skb. 4 bytes of extra space (IV) in the
 138  * beginning of the buffer 4 bytes of extra space (ICV) in the end of the
 139  * buffer will be added. Both IV and ICV will be transmitted, so the
 140  * payload length increases with 8 bytes.
 141  *
 142  * WEP frame payload: IV + TX key idx, RC4(data), ICV = RC4(CRC32(data))
 143  */
 144 int ieee80211_wep_encrypt(struct ieee80211_local *local, struct sk_buff *skb,
 145                           struct ieee80211_key *key)
 146 {
 147         u32 klen;
 148         u8 *rc4key, *iv;
 149         size_t len;
 150
 151         if (!key || key->conf.alg != ALG_WEP)
 152                 return -1;
 153
 154         klen = 3 + key->conf.keylen;
 155         rc4key = kmalloc(klen, GFP_ATOMIC);
 156         if (!rc4key)
 157                 return -1;
 158
 159         iv = ieee80211_wep_add_iv(local, skb, key);
 160         if (!iv) {
 161                 kfree(rc4key);
 162                 return -1;
 163         }
 164
 165         len = skb->len - (iv + WEP_IV_LEN - skb->data);
 166
 167         /* Prepend 24-bit IV to RC4 key */
 168         memcpy(rc4key, iv, 3);
 169
 170         /* Copy rest of the WEP key (the secret part) */
 171         memcpy(rc4key + 3, key->conf.key, key->conf.keylen);
 172
 173         /* Add room for ICV */
 174         skb_put(skb, WEP_ICV_LEN);
 175
 176         ieee80211_wep_encrypt_data(local->wep_tx_tfm, rc4key, klen,
 177                                    iv + WEP_IV_LEN, len);
 178
 179         kfree(rc4key);
 180
 181         return 0;
 182 }
 183
 184
 185 /* Perform WEP decryption using given key. data buffer includes encrypted
 186  * payload, including 4-byte ICV, but _not_ IV. data_len must not include ICV.
 187  * Return 0 on success and -1 on ICV mismatch. */
 188 int ieee80211_wep_decrypt_data(struct crypto_blkcipher *tfm, u8 *rc4key,
 189                                size_t klen, u8 *data, size_t data_len)
 190 {
 191         struct blkcipher_desc desc = { .tfm = tfm };
 192         struct scatterlist sg;
 193         __le32 crc;
 194
 195         crypto_blkcipher_setkey(tfm, rc4key, klen);
 196         sg_init_one(&sg, data, data_len + WEP_ICV_LEN);
 197         crypto_blkcipher_decrypt(&desc, &sg, &sg, sg.length);
 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 int ieee80211_wep_decrypt(struct ieee80211_local *local, struct sk_buff *skb,
 217                           struct ieee80211_key *key)
 218 {
 219         u32 klen;
 220         u8 *rc4key;
 221         u8 keyidx;
 222         struct ieee80211_hdr *hdr = (struct ieee80211_hdr *)skb->data;
 223         unsigned int hdrlen;
 224         size_t len;
 225         int ret = 0;
 226
 227         if (!ieee80211_has_protected(hdr->frame_control))
 228                 return -1;
 229
 230         hdrlen = ieee80211_hdrlen(hdr->frame_control);
 231         if (skb->len < hdrlen + WEP_IV_LEN + WEP_ICV_LEN)
 232                 return -1;
 233
 234         len = skb->len - hdrlen - WEP_IV_LEN - WEP_ICV_LEN;
 235
 236         keyidx = skb->data[hdrlen + 3] >> 6;
 237
 238         if (!key || keyidx != key->conf.keyidx || key->conf.alg != ALG_WEP)
 239                 return -1;
 240
 241         klen = 3 + key->conf.keylen;
 242
 243         rc4key = kmalloc(klen, GFP_ATOMIC);
 244         if (!rc4key)
 245                 return -1;
 246
 247         /* Prepend 24-bit IV to RC4 key */
 248         memcpy(rc4key, skb->data + hdrlen, 3);
 249
 250         /* Copy rest of the WEP key (the secret part) */
 251         memcpy(rc4key + 3, key->conf.key, key->conf.keylen);
 252
 253         if (ieee80211_wep_decrypt_data(local->wep_rx_tfm, rc4key, klen,
 254                                        skb->data + hdrlen + WEP_IV_LEN,
 255                                        len))
 256                 ret = -1;
 257
 258         kfree(rc4key);
 259
 260         /* Trim ICV */
 261         skb_trim(skb, skb->len - WEP_ICV_LEN);
 262
 263         /* Remove IV */
 264         memmove(skb->data + WEP_IV_LEN, skb->data, hdrlen);
 265         skb_pull(skb, WEP_IV_LEN);
 266
 267         return ret;
 268 }
 269
 270
 271 u8 * ieee80211_wep_is_weak_iv(struct sk_buff *skb, struct ieee80211_key *key)
 272 {
 273         struct ieee80211_hdr *hdr = (struct ieee80211_hdr *)skb->data;
 274         unsigned int hdrlen;
 275         u8 *ivpos;
 276         u32 iv;
 277
 278         if (!ieee80211_has_protected(hdr->frame_control))
 279                 return NULL;
 280
 281         hdrlen = ieee80211_hdrlen(hdr->frame_control);
 282         ivpos = skb->data + hdrlen;
 283         iv = (ivpos[0] << 16) | (ivpos[1] << 8) | ivpos[2];
 284
 285         if (ieee80211_wep_weak_iv(iv, key->conf.keylen))
 286                 return ivpos;
 287
 288         return NULL;
 289 }
 290
 291 ieee80211_rx_result
 292 ieee80211_crypto_wep_decrypt(struct ieee80211_rx_data *rx)
 293 {
 294         struct ieee80211_hdr *hdr = (struct ieee80211_hdr *)rx->skb->data;
 295
 296         if (!ieee80211_is_data(hdr->frame_control) &&
 297             !ieee80211_is_auth(hdr->frame_control))
 298                 return RX_CONTINUE;
 299
 300         if (!(rx->status->flag & RX_FLAG_DECRYPTED)) {
 301                 if (ieee80211_wep_decrypt(rx->local, rx->skb, rx->key))
 302                         return RX_DROP_UNUSABLE;
 303         } else if (!(rx->status->flag & RX_FLAG_IV_STRIPPED)) {
 304                 ieee80211_wep_remove_iv(rx->local, rx->skb, rx->key);
 305                 /* remove ICV */
 306                 skb_trim(rx->skb, rx->skb->len - WEP_ICV_LEN);
 307         }
 308
 309         return RX_CONTINUE;
 310 }
 311
 312 static int wep_encrypt_skb(struct ieee80211_tx_data *tx, struct sk_buff *skb)
 313 {
 314         struct ieee80211_tx_info *info = IEEE80211_SKB_CB(skb);
 315
 316         if (!(tx->key->flags & KEY_FLAG_UPLOADED_TO_HARDWARE)) {
 317                 if (ieee80211_wep_encrypt(tx->local, skb, tx->key))
 318                         return -1;
 319         } else {
 320                 info->control.hw_key = &tx->key->conf;
 321                 if (tx->key->conf.flags & IEEE80211_KEY_FLAG_GENERATE_IV) {
 322                         if (!ieee80211_wep_add_iv(tx->local, skb, tx->key))
 323                                 return -1;
 324                 }
 325         }
 326         return 0;
 327 }
 328
 329 ieee80211_tx_result
 330 ieee80211_crypto_wep_encrypt(struct ieee80211_tx_data *tx)
 331 {
 332         ieee80211_tx_set_protected(tx);
 333
 334         if (wep_encrypt_skb(tx, tx->skb) < 0) {
 335                 I802_DEBUG_INC(tx->local->tx_handlers_drop_wep);
 336                 return TX_DROP;
 337         }
 338
 339         if (tx->extra_frag) {
 340                 int i;
 341                 for (i = 0; i < tx->num_extra_frag; i++) {
 342                         if (wep_encrypt_skb(tx, tx->extra_frag[i]) < 0) {
 343                                 I802_DEBUG_INC(tx->local->
 344                                                tx_handlers_drop_wep);
 345                                 return TX_DROP;
 346                         }
 347                 }
 348         }
 349
 350         return TX_CONTINUE;
 351 }