linux/net/wireless/lib80211_crypt_wep.c
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   1// SPDX-License-Identifier: GPL-2.0-only
   2/*
   3 * lib80211 crypt: host-based WEP encryption implementation for lib80211
   4 *
   5 * Copyright (c) 2002-2004, Jouni Malinen <j@w1.fi>
   6 * Copyright (c) 2008, John W. Linville <linville@tuxdriver.com>
   7 */
   8
   9#include <linux/err.h>
  10#include <linux/fips.h>
  11#include <linux/module.h>
  12#include <linux/init.h>
  13#include <linux/slab.h>
  14#include <linux/random.h>
  15#include <linux/scatterlist.h>
  16#include <linux/skbuff.h>
  17#include <linux/mm.h>
  18#include <asm/string.h>
  19
  20#include <net/lib80211.h>
  21
  22#include <crypto/arc4.h>
  23#include <linux/crc32.h>
  24
  25MODULE_AUTHOR("Jouni Malinen");
  26MODULE_DESCRIPTION("lib80211 crypt: WEP");
  27MODULE_LICENSE("GPL");
  28
  29struct lib80211_wep_data {
  30        u32 iv;
  31#define WEP_KEY_LEN 13
  32        u8 key[WEP_KEY_LEN + 1];
  33        u8 key_len;
  34        u8 key_idx;
  35        struct arc4_ctx tx_ctx;
  36        struct arc4_ctx rx_ctx;
  37};
  38
  39static void *lib80211_wep_init(int keyidx)
  40{
  41        struct lib80211_wep_data *priv;
  42
  43        if (fips_enabled)
  44                return NULL;
  45
  46        priv = kzalloc(sizeof(*priv), GFP_ATOMIC);
  47        if (priv == NULL)
  48                return NULL;
  49        priv->key_idx = keyidx;
  50
  51        /* start WEP IV from a random value */
  52        get_random_bytes(&priv->iv, 4);
  53
  54        return priv;
  55}
  56
  57static void lib80211_wep_deinit(void *priv)
  58{
  59        kfree_sensitive(priv);
  60}
  61
  62/* Add WEP IV/key info to a frame that has at least 4 bytes of headroom */
  63static int lib80211_wep_build_iv(struct sk_buff *skb, int hdr_len,
  64                               u8 *key, int keylen, void *priv)
  65{
  66        struct lib80211_wep_data *wep = priv;
  67        u32 klen;
  68        u8 *pos;
  69
  70        if (skb_headroom(skb) < 4 || skb->len < hdr_len)
  71                return -1;
  72
  73        pos = skb_push(skb, 4);
  74        memmove(pos, pos + 4, hdr_len);
  75        pos += hdr_len;
  76
  77        klen = 3 + wep->key_len;
  78
  79        wep->iv++;
  80
  81        /* Fluhrer, Mantin, and Shamir have reported weaknesses in the key
  82         * scheduling algorithm of RC4. At least IVs (KeyByte + 3, 0xff, N)
  83         * can be used to speedup attacks, so avoid using them. */
  84        if ((wep->iv & 0xff00) == 0xff00) {
  85                u8 B = (wep->iv >> 16) & 0xff;
  86                if (B >= 3 && B < klen)
  87                        wep->iv += 0x0100;
  88        }
  89
  90        /* Prepend 24-bit IV to RC4 key and TX frame */
  91        *pos++ = (wep->iv >> 16) & 0xff;
  92        *pos++ = (wep->iv >> 8) & 0xff;
  93        *pos++ = wep->iv & 0xff;
  94        *pos++ = wep->key_idx << 6;
  95
  96        return 0;
  97}
  98
  99/* Perform WEP encryption on given skb that has at least 4 bytes of headroom
 100 * for IV and 4 bytes of tailroom for ICV. Both IV and ICV will be transmitted,
 101 * so the payload length increases with 8 bytes.
 102 *
 103 * WEP frame payload: IV + TX key idx, RC4(data), ICV = RC4(CRC32(data))
 104 */
 105static int lib80211_wep_encrypt(struct sk_buff *skb, int hdr_len, void *priv)
 106{
 107        struct lib80211_wep_data *wep = priv;
 108        u32 crc, klen, len;
 109        u8 *pos, *icv;
 110        u8 key[WEP_KEY_LEN + 3];
 111
 112        /* other checks are in lib80211_wep_build_iv */
 113        if (skb_tailroom(skb) < 4)
 114                return -1;
 115
 116        /* add the IV to the frame */
 117        if (lib80211_wep_build_iv(skb, hdr_len, NULL, 0, priv))
 118                return -1;
 119
 120        /* Copy the IV into the first 3 bytes of the key */
 121        skb_copy_from_linear_data_offset(skb, hdr_len, key, 3);
 122
 123        /* Copy rest of the WEP key (the secret part) */
 124        memcpy(key + 3, wep->key, wep->key_len);
 125
 126        len = skb->len - hdr_len - 4;
 127        pos = skb->data + hdr_len + 4;
 128        klen = 3 + wep->key_len;
 129
 130        /* Append little-endian CRC32 over only the data and encrypt it to produce ICV */
 131        crc = ~crc32_le(~0, pos, len);
 132        icv = skb_put(skb, 4);
 133        icv[0] = crc;
 134        icv[1] = crc >> 8;
 135        icv[2] = crc >> 16;
 136        icv[3] = crc >> 24;
 137
 138        arc4_setkey(&wep->tx_ctx, key, klen);
 139        arc4_crypt(&wep->tx_ctx, pos, pos, len + 4);
 140
 141        return 0;
 142}
 143
 144/* Perform WEP decryption on given buffer. Buffer includes whole WEP part of
 145 * the frame: IV (4 bytes), encrypted payload (including SNAP header),
 146 * ICV (4 bytes). len includes both IV and ICV.
 147 *
 148 * Returns 0 if frame was decrypted successfully and ICV was correct and -1 on
 149 * failure. If frame is OK, IV and ICV will be removed.
 150 */
 151static int lib80211_wep_decrypt(struct sk_buff *skb, int hdr_len, void *priv)
 152{
 153        struct lib80211_wep_data *wep = priv;
 154        u32 crc, klen, plen;
 155        u8 key[WEP_KEY_LEN + 3];
 156        u8 keyidx, *pos, icv[4];
 157
 158        if (skb->len < hdr_len + 8)
 159                return -1;
 160
 161        pos = skb->data + hdr_len;
 162        key[0] = *pos++;
 163        key[1] = *pos++;
 164        key[2] = *pos++;
 165        keyidx = *pos++ >> 6;
 166        if (keyidx != wep->key_idx)
 167                return -1;
 168
 169        klen = 3 + wep->key_len;
 170
 171        /* Copy rest of the WEP key (the secret part) */
 172        memcpy(key + 3, wep->key, wep->key_len);
 173
 174        /* Apply RC4 to data and compute CRC32 over decrypted data */
 175        plen = skb->len - hdr_len - 8;
 176
 177        arc4_setkey(&wep->rx_ctx, key, klen);
 178        arc4_crypt(&wep->rx_ctx, pos, pos, plen + 4);
 179
 180        crc = ~crc32_le(~0, pos, plen);
 181        icv[0] = crc;
 182        icv[1] = crc >> 8;
 183        icv[2] = crc >> 16;
 184        icv[3] = crc >> 24;
 185        if (memcmp(icv, pos + plen, 4) != 0) {
 186                /* ICV mismatch - drop frame */
 187                return -2;
 188        }
 189
 190        /* Remove IV and ICV */
 191        memmove(skb->data + 4, skb->data, hdr_len);
 192        skb_pull(skb, 4);
 193        skb_trim(skb, skb->len - 4);
 194
 195        return 0;
 196}
 197
 198static int lib80211_wep_set_key(void *key, int len, u8 * seq, void *priv)
 199{
 200        struct lib80211_wep_data *wep = priv;
 201
 202        if (len < 0 || len > WEP_KEY_LEN)
 203                return -1;
 204
 205        memcpy(wep->key, key, len);
 206        wep->key_len = len;
 207
 208        return 0;
 209}
 210
 211static int lib80211_wep_get_key(void *key, int len, u8 * seq, void *priv)
 212{
 213        struct lib80211_wep_data *wep = priv;
 214
 215        if (len < wep->key_len)
 216                return -1;
 217
 218        memcpy(key, wep->key, wep->key_len);
 219
 220        return wep->key_len;
 221}
 222
 223static void lib80211_wep_print_stats(struct seq_file *m, void *priv)
 224{
 225        struct lib80211_wep_data *wep = priv;
 226        seq_printf(m, "key[%d] alg=WEP len=%d\n", wep->key_idx, wep->key_len);
 227}
 228
 229static struct lib80211_crypto_ops lib80211_crypt_wep = {
 230        .name = "WEP",
 231        .init = lib80211_wep_init,
 232        .deinit = lib80211_wep_deinit,
 233        .encrypt_mpdu = lib80211_wep_encrypt,
 234        .decrypt_mpdu = lib80211_wep_decrypt,
 235        .encrypt_msdu = NULL,
 236        .decrypt_msdu = NULL,
 237        .set_key = lib80211_wep_set_key,
 238        .get_key = lib80211_wep_get_key,
 239        .print_stats = lib80211_wep_print_stats,
 240        .extra_mpdu_prefix_len = 4,     /* IV */
 241        .extra_mpdu_postfix_len = 4,    /* ICV */
 242        .owner = THIS_MODULE,
 243};
 244
 245static int __init lib80211_crypto_wep_init(void)
 246{
 247        return lib80211_register_crypto_ops(&lib80211_crypt_wep);
 248}
 249
 250static void __exit lib80211_crypto_wep_exit(void)
 251{
 252        lib80211_unregister_crypto_ops(&lib80211_crypt_wep);
 253}
 254
 255module_init(lib80211_crypto_wep_init);
 256module_exit(lib80211_crypto_wep_exit);
 257