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 -ENOMEM;
  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 -ENOMEM;
  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         u16 fc;
  89         int hdrlen;
  90         u8 *newhdr;
  91
  92         fc = le16_to_cpu(hdr->frame_control);
  93         fc |= IEEE80211_FCTL_PROTECTED;
  94         hdr->frame_control = cpu_to_le16(fc);
  95
  96         if ((skb_headroom(skb) < WEP_IV_LEN ||
  97              skb_tailroom(skb) < WEP_ICV_LEN)) {
  98                 I802_DEBUG_INC(local->tx_expand_skb_head);
  99                 if (unlikely(pskb_expand_head(skb, WEP_IV_LEN, WEP_ICV_LEN,
 100                                               GFP_ATOMIC)))
 101                         return NULL;
 102         }
 103
 104         hdrlen = ieee80211_get_hdrlen(fc);
 105         newhdr = skb_push(skb, WEP_IV_LEN);
 106         memmove(newhdr, newhdr + WEP_IV_LEN, hdrlen);
 107         ieee80211_wep_get_iv(local, key, newhdr + hdrlen);
 108         return newhdr + hdrlen;
 109 }
 110
 111
 112 static void ieee80211_wep_remove_iv(struct ieee80211_local *local,
 113                                     struct sk_buff *skb,
 114                                     struct ieee80211_key *key)
 115 {
 116         struct ieee80211_hdr *hdr = (struct ieee80211_hdr *) skb->data;
 117         u16 fc;
 118         int hdrlen;
 119
 120         fc = le16_to_cpu(hdr->frame_control);
 121         hdrlen = ieee80211_get_hdrlen(fc);
 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 void 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         icv = (__le32 *)(data + data_len);
 138         *icv = cpu_to_le32(~crc32_le(~0, data, data_len));
 139
 140         crypto_blkcipher_setkey(tfm, rc4key, klen);
 141         sg_init_one(&sg, data, data_len + WEP_ICV_LEN);
 142         crypto_blkcipher_encrypt(&desc, &sg, &sg, sg.length);
 143 }
 144
 145
 146 /* Perform WEP encryption on given skb. 4 bytes of extra space (IV) in the
 147  * beginning of the buffer 4 bytes of extra space (ICV) in the end of the
 148  * buffer will be added. Both IV and ICV will be transmitted, so the
 149  * payload length increases with 8 bytes.
 150  *
 151  * WEP frame payload: IV + TX key idx, RC4(data), ICV = RC4(CRC32(data))
 152  */
 153 int ieee80211_wep_encrypt(struct ieee80211_local *local, struct sk_buff *skb,
 154                           struct ieee80211_key *key)
 155 {
 156         u32 klen;
 157         u8 *rc4key, *iv;
 158         size_t len;
 159
 160         if (!key || key->conf.alg != ALG_WEP)
 161                 return -1;
 162
 163         klen = 3 + key->conf.keylen;
 164         rc4key = kmalloc(klen, GFP_ATOMIC);
 165         if (!rc4key)
 166                 return -1;
 167
 168         iv = ieee80211_wep_add_iv(local, skb, key);
 169         if (!iv) {
 170                 kfree(rc4key);
 171                 return -1;
 172         }
 173
 174         len = skb->len - (iv + WEP_IV_LEN - skb->data);
 175
 176         /* Prepend 24-bit IV to RC4 key */
 177         memcpy(rc4key, iv, 3);
 178
 179         /* Copy rest of the WEP key (the secret part) */
 180         memcpy(rc4key + 3, key->conf.key, key->conf.keylen);
 181
 182         /* Add room for ICV */
 183         skb_put(skb, WEP_ICV_LEN);
 184
 185         ieee80211_wep_encrypt_data(local->wep_tx_tfm, rc4key, klen,
 186                                    iv + WEP_IV_LEN, len);
 187
 188         kfree(rc4key);
 189
 190         return 0;
 191 }
 192
 193
 194 /* Perform WEP decryption using given key. data buffer includes encrypted
 195  * payload, including 4-byte ICV, but _not_ IV. data_len must not include ICV.
 196  * Return 0 on success and -1 on ICV mismatch. */
 197 int ieee80211_wep_decrypt_data(struct crypto_blkcipher *tfm, u8 *rc4key,
 198                                size_t klen, u8 *data, size_t data_len)
 199 {
 200         struct blkcipher_desc desc = { .tfm = tfm };
 201         struct scatterlist sg;
 202         __le32 crc;
 203
 204         crypto_blkcipher_setkey(tfm, rc4key, klen);
 205         sg_init_one(&sg, data, data_len + WEP_ICV_LEN);
 206         crypto_blkcipher_decrypt(&desc, &sg, &sg, sg.length);
 207
 208         crc = cpu_to_le32(~crc32_le(~0, data, data_len));
 209         if (memcmp(&crc, data + data_len, 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 int ieee80211_wep_decrypt(struct ieee80211_local *local, struct sk_buff *skb,
 226                           struct ieee80211_key *key)
 227 {
 228         u32 klen;
 229         u8 *rc4key;
 230         u8 keyidx;
 231         struct ieee80211_hdr *hdr = (struct ieee80211_hdr *) skb->data;
 232         u16 fc;
 233         int hdrlen;
 234         size_t len;
 235         int ret = 0;
 236
 237         fc = le16_to_cpu(hdr->frame_control);
 238         if (!(fc & IEEE80211_FCTL_PROTECTED))
 239                 return -1;
 240
 241         hdrlen = ieee80211_get_hdrlen(fc);
 242
 243         if (skb->len < 8 + hdrlen)
 244                 return -1;
 245
 246         len = skb->len - hdrlen - 8;
 247
 248         keyidx = skb->data[hdrlen + 3] >> 6;
 249
 250         if (!key || keyidx != key->conf.keyidx || key->conf.alg != ALG_WEP)
 251                 return -1;
 252
 253         klen = 3 + key->conf.keylen;
 254
 255         rc4key = kmalloc(klen, GFP_ATOMIC);
 256         if (!rc4key)
 257                 return -1;
 258
 259         /* Prepend 24-bit IV to RC4 key */
 260         memcpy(rc4key, skb->data + hdrlen, 3);
 261
 262         /* Copy rest of the WEP key (the secret part) */
 263         memcpy(rc4key + 3, key->conf.key, key->conf.keylen);
 264
 265         if (ieee80211_wep_decrypt_data(local->wep_rx_tfm, rc4key, klen,
 266                                        skb->data + hdrlen + WEP_IV_LEN,
 267                                        len)) {
 268                 if (net_ratelimit())
 269                         printk(KERN_DEBUG "WEP decrypt failed (ICV)\n");
 270                 ret = -1;
 271         }
 272
 273         kfree(rc4key);
 274
 275         /* Trim ICV */
 276         skb_trim(skb, skb->len - WEP_ICV_LEN);
 277
 278         /* Remove IV */
 279         memmove(skb->data + WEP_IV_LEN, skb->data, hdrlen);
 280         skb_pull(skb, WEP_IV_LEN);
 281
 282         return ret;
 283 }
 284
 285
 286 u8 * ieee80211_wep_is_weak_iv(struct sk_buff *skb, struct ieee80211_key *key)
 287 {
 288         struct ieee80211_hdr *hdr = (struct ieee80211_hdr *) skb->data;
 289         u16 fc;
 290         int hdrlen;
 291         u8 *ivpos;
 292         u32 iv;
 293
 294         fc = le16_to_cpu(hdr->frame_control);
 295         if (!(fc & IEEE80211_FCTL_PROTECTED))
 296                 return NULL;
 297
 298         hdrlen = ieee80211_get_hdrlen(fc);
 299         ivpos = skb->data + hdrlen;
 300         iv = (ivpos[0] << 16) | (ivpos[1] << 8) | ivpos[2];
 301
 302         if (ieee80211_wep_weak_iv(iv, key->conf.keylen))
 303                 return ivpos;
 304
 305         return NULL;
 306 }
 307
 308 ieee80211_txrx_result
 309 ieee80211_crypto_wep_decrypt(struct ieee80211_txrx_data *rx)
 310 {
 311         if ((rx->fc & IEEE80211_FCTL_FTYPE) != IEEE80211_FTYPE_DATA &&
 312             ((rx->fc & IEEE80211_FCTL_FTYPE) != IEEE80211_FTYPE_MGMT ||
 313              (rx->fc & IEEE80211_FCTL_STYPE) != IEEE80211_STYPE_AUTH))
 314                 return TXRX_CONTINUE;
 315
 316         if (!(rx->u.rx.status->flag & RX_FLAG_DECRYPTED)) {
 317                 if (ieee80211_wep_decrypt(rx->local, rx->skb, rx->key)) {
 318 #ifdef CONFIG_MAC80211_DEBUG
 319                         if (net_ratelimit())
 320                                 printk(KERN_DEBUG "%s: RX WEP frame, decrypt "
 321                                        "failed\n", rx->dev->name);
 322 #endif /* CONFIG_MAC80211_DEBUG */
 323                         return TXRX_DROP;
 324                 }
 325         } else if (!(rx->u.rx.status->flag & RX_FLAG_IV_STRIPPED)) {
 326                 ieee80211_wep_remove_iv(rx->local, rx->skb, rx->key);
 327                 /* remove ICV */
 328                 skb_trim(rx->skb, rx->skb->len - 4);
 329         }
 330
 331         return TXRX_CONTINUE;
 332 }
 333
 334 static int wep_encrypt_skb(struct ieee80211_txrx_data *tx, struct sk_buff *skb)
 335 {
 336         if (!(tx->key->flags & KEY_FLAG_UPLOADED_TO_HARDWARE)) {
 337                 if (ieee80211_wep_encrypt(tx->local, skb, tx->key))
 338                         return -1;
 339         } else {
 340                 tx->u.tx.control->key_idx = tx->key->conf.hw_key_idx;
 341                 if (tx->key->conf.flags & IEEE80211_KEY_FLAG_GENERATE_IV) {
 342                         if (!ieee80211_wep_add_iv(tx->local, skb, tx->key))
 343                                 return -1;
 344                 }
 345         }
 346         return 0;
 347 }
 348
 349 ieee80211_txrx_result
 350 ieee80211_crypto_wep_encrypt(struct ieee80211_txrx_data *tx)
 351 {
 352         tx->u.tx.control->iv_len = WEP_IV_LEN;
 353         tx->u.tx.control->icv_len = WEP_ICV_LEN;
 354         ieee80211_tx_set_iswep(tx);
 355
 356         if (wep_encrypt_skb(tx, tx->skb) < 0) {
 357                 I802_DEBUG_INC(tx->local->tx_handlers_drop_wep);
 358                 return TXRX_DROP;
 359         }
 360
 361         if (tx->u.tx.extra_frag) {
 362                 int i;
 363                 for (i = 0; i < tx->u.tx.num_extra_frag; i++) {
 364                         if (wep_encrypt_skb(tx, tx->u.tx.extra_frag[i]) < 0) {
 365                                 I802_DEBUG_INC(tx->local->
 366                                                tx_handlers_drop_wep);
 367                                 return TXRX_DROP;
 368                         }
 369                 }
 370         }
 371
 372         return TXRX_CONTINUE;
 373 }