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 <asm/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 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->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->keyidx << 6;
  80 }
  81
  82
  83 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 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.page = virt_to_page(data);
 142         sg.offset = offset_in_page(data);
 143         sg.length = data_len + WEP_ICV_LEN;
 144         crypto_blkcipher_encrypt(&desc, &sg, &sg, sg.length);
 145 }
 146
 147
 148 /* Perform WEP encryption on given skb. 4 bytes of extra space (IV) in the
 149  * beginning of the buffer 4 bytes of extra space (ICV) in the end of the
 150  * buffer will be added. Both IV and ICV will be transmitted, so the
 151  * payload length increases with 8 bytes.
 152  *
 153  * WEP frame payload: IV + TX key idx, RC4(data), ICV = RC4(CRC32(data))
 154  */
 155 int ieee80211_wep_encrypt(struct ieee80211_local *local, struct sk_buff *skb,
 156                           struct ieee80211_key *key)
 157 {
 158         u32 klen;
 159         u8 *rc4key, *iv;
 160         size_t len;
 161
 162         if (!key || key->alg != ALG_WEP)
 163                 return -1;
 164
 165         klen = 3 + key->keylen;
 166         rc4key = kmalloc(klen, GFP_ATOMIC);
 167         if (!rc4key)
 168                 return -1;
 169
 170         iv = ieee80211_wep_add_iv(local, skb, key);
 171         if (!iv) {
 172                 kfree(rc4key);
 173                 return -1;
 174         }
 175
 176         len = skb->len - (iv + WEP_IV_LEN - skb->data);
 177
 178         /* Prepend 24-bit IV to RC4 key */
 179         memcpy(rc4key, iv, 3);
 180
 181         /* Copy rest of the WEP key (the secret part) */
 182         memcpy(rc4key + 3, key->key, key->keylen);
 183
 184         /* Add room for ICV */
 185         skb_put(skb, WEP_ICV_LEN);
 186
 187         ieee80211_wep_encrypt_data(local->wep_tx_tfm, rc4key, klen,
 188                                    iv + WEP_IV_LEN, len);
 189
 190         kfree(rc4key);
 191
 192         return 0;
 193 }
 194
 195
 196 /* Perform WEP decryption using given key. data buffer includes encrypted
 197  * payload, including 4-byte ICV, but _not_ IV. data_len must not include ICV.
 198  * Return 0 on success and -1 on ICV mismatch. */
 199 int ieee80211_wep_decrypt_data(struct crypto_blkcipher *tfm, u8 *rc4key,
 200                                size_t klen, u8 *data, size_t data_len)
 201 {
 202         struct blkcipher_desc desc = { .tfm = tfm };
 203         struct scatterlist sg;
 204         __le32 crc;
 205
 206         crypto_blkcipher_setkey(tfm, rc4key, klen);
 207         sg.page = virt_to_page(data);
 208         sg.offset = offset_in_page(data);
 209         sg.length = data_len + WEP_ICV_LEN;
 210         crypto_blkcipher_decrypt(&desc, &sg, &sg, sg.length);
 211
 212         crc = cpu_to_le32(~crc32_le(~0, data, data_len));
 213         if (memcmp(&crc, data + data_len, WEP_ICV_LEN) != 0)
 214                 /* ICV mismatch */
 215                 return -1;
 216
 217         return 0;
 218 }
 219
 220
 221 /* Perform WEP decryption on given skb. Buffer includes whole WEP part of
 222  * the frame: IV (4 bytes), encrypted payload (including SNAP header),
 223  * ICV (4 bytes). skb->len includes both IV and ICV.
 224  *
 225  * Returns 0 if frame was decrypted successfully and ICV was correct and -1 on
 226  * failure. If frame is OK, IV and ICV will be removed, i.e., decrypted payload
 227  * is moved to the beginning of the skb and skb length will be reduced.
 228  */
 229 int ieee80211_wep_decrypt(struct ieee80211_local *local, struct sk_buff *skb,
 230                           struct ieee80211_key *key)
 231 {
 232         u32 klen;
 233         u8 *rc4key;
 234         u8 keyidx;
 235         struct ieee80211_hdr *hdr = (struct ieee80211_hdr *) skb->data;
 236         u16 fc;
 237         int hdrlen;
 238         size_t len;
 239         int ret = 0;
 240
 241         fc = le16_to_cpu(hdr->frame_control);
 242         if (!(fc & IEEE80211_FCTL_PROTECTED))
 243                 return -1;
 244
 245         hdrlen = ieee80211_get_hdrlen(fc);
 246
 247         if (skb->len < 8 + hdrlen)
 248                 return -1;
 249
 250         len = skb->len - hdrlen - 8;
 251
 252         keyidx = skb->data[hdrlen + 3] >> 6;
 253
 254         if (!key || keyidx != key->keyidx || key->alg != ALG_WEP)
 255                 return -1;
 256
 257         klen = 3 + key->keylen;
 258
 259         rc4key = kmalloc(klen, GFP_ATOMIC);
 260         if (!rc4key)
 261                 return -1;
 262
 263         /* Prepend 24-bit IV to RC4 key */
 264         memcpy(rc4key, skb->data + hdrlen, 3);
 265
 266         /* Copy rest of the WEP key (the secret part) */
 267         memcpy(rc4key + 3, key->key, key->keylen);
 268
 269         if (ieee80211_wep_decrypt_data(local->wep_rx_tfm, rc4key, klen,
 270                                        skb->data + hdrlen + WEP_IV_LEN,
 271                                        len)) {
 272                 printk(KERN_DEBUG "WEP decrypt failed (ICV)\n");
 273                 ret = -1;
 274         }
 275
 276         kfree(rc4key);
 277
 278         /* Trim ICV */
 279         skb_trim(skb, skb->len - WEP_ICV_LEN);
 280
 281         /* Remove IV */
 282         memmove(skb->data + WEP_IV_LEN, skb->data, hdrlen);
 283         skb_pull(skb, WEP_IV_LEN);
 284
 285         return ret;
 286 }
 287
 288
 289 int ieee80211_wep_get_keyidx(struct sk_buff *skb)
 290 {
 291         struct ieee80211_hdr *hdr = (struct ieee80211_hdr *) skb->data;
 292         u16 fc;
 293         int hdrlen;
 294
 295         fc = le16_to_cpu(hdr->frame_control);
 296         if (!(fc & IEEE80211_FCTL_PROTECTED))
 297                 return -1;
 298
 299         hdrlen = ieee80211_get_hdrlen(fc);
 300
 301         if (skb->len < 8 + hdrlen)
 302                 return -1;
 303
 304         return skb->data[hdrlen + 3] >> 6;
 305 }
 306
 307
 308 u8 * ieee80211_wep_is_weak_iv(struct sk_buff *skb, struct ieee80211_key *key)
 309 {
 310         struct ieee80211_hdr *hdr = (struct ieee80211_hdr *) skb->data;
 311         u16 fc;
 312         int hdrlen;
 313         u8 *ivpos;
 314         u32 iv;
 315
 316         fc = le16_to_cpu(hdr->frame_control);
 317         if (!(fc & IEEE80211_FCTL_PROTECTED))
 318                 return NULL;
 319
 320         hdrlen = ieee80211_get_hdrlen(fc);
 321         ivpos = skb->data + hdrlen;
 322         iv = (ivpos[0] << 16) | (ivpos[1] << 8) | ivpos[2];
 323
 324         if (ieee80211_wep_weak_iv(iv, key->keylen))
 325                 return ivpos;
 326
 327         return NULL;
 328 }