wep.c

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/*
 * Software WEP encryption implementation
 * Copyright 2002, Jouni Malinen <jkmaline@cc.hut.fi>
 * Copyright 2003, Instant802 Networks, Inc.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 */

#include <linux/netdevice.h>
#include <linux/types.h>
#include <linux/random.h>
#include <linux/compiler.h>
#include <linux/crc32.h>
#include <linux/crypto.h>
#include <linux/err.h>
#include <linux/mm.h>
#include <linux/scatterlist.h>
#include <linux/slab.h>
#include <asm/unaligned.h>

#include <net/mac80211.h>
#include "ieee80211_i.h"
#include "wep.h"


int ieee80211_wep_init(struct ieee80211_local *local)
{
        /* start WEP IV from a random value */
        get_random_bytes(&local->wep_iv, WEP_IV_LEN);

        local->wep_tx_tfm = crypto_alloc_cipher("arc4", 0, CRYPTO_ALG_ASYNC);
        if (IS_ERR(local->wep_tx_tfm)) {
                local->wep_rx_tfm = ERR_PTR(-EINVAL);
                return PTR_ERR(local->wep_tx_tfm);
        }

        local->wep_rx_tfm = crypto_alloc_cipher("arc4", 0, CRYPTO_ALG_ASYNC);
        if (IS_ERR(local->wep_rx_tfm)) {
                crypto_free_cipher(local->wep_tx_tfm);
                local->wep_tx_tfm = ERR_PTR(-EINVAL);
                return PTR_ERR(local->wep_rx_tfm);
        }

        return 0;
}

void ieee80211_wep_free(struct ieee80211_local *local)
{
        if (!IS_ERR(local->wep_tx_tfm))
                crypto_free_cipher(local->wep_tx_tfm);
        if (!IS_ERR(local->wep_rx_tfm))
                crypto_free_cipher(local->wep_rx_tfm);
}

static inline bool ieee80211_wep_weak_iv(u32 iv, int keylen)
{
        /*
         * Fluhrer, Mantin, and Shamir have reported weaknesses in the
         * key scheduling algorithm of RC4. At least IVs (KeyByte + 3,
         * 0xff, N) can be used to speedup attacks, so avoid using them.
         */
        if ((iv & 0xff00) == 0xff00) {
                u8 B = (iv >> 16) & 0xff;
                if (B >= 3 && B < 3 + keylen)
                        return true;
        }
        return false;
}


static void ieee80211_wep_get_iv(struct ieee80211_local *local,
                                 int keylen, int keyidx, u8 *iv)
{
        local->wep_iv++;
        if (ieee80211_wep_weak_iv(local->wep_iv, keylen))
                local->wep_iv += 0x0100;

        if (!iv)
                return;

        *iv++ = (local->wep_iv >> 16) & 0xff;
        *iv++ = (local->wep_iv >> 8) & 0xff;
        *iv++ = local->wep_iv & 0xff;
        *iv++ = keyidx << 6;
}


static u8 *ieee80211_wep_add_iv(struct ieee80211_local *local,
                                struct sk_buff *skb,
                                int keylen, int keyidx)
{
        struct ieee80211_hdr *hdr = (struct ieee80211_hdr *)skb->data;
        unsigned int hdrlen;
        u8 *newhdr;

        hdr->frame_control |= cpu_to_le16(IEEE80211_FCTL_PROTECTED);

        if (WARN_ON(skb_tailroom(skb) < WEP_ICV_LEN ||
                    skb_headroom(skb) < WEP_IV_LEN))
                return NULL;

        hdrlen = ieee80211_hdrlen(hdr->frame_control);
        newhdr = skb_push(skb, WEP_IV_LEN);
        memmove(newhdr, newhdr + WEP_IV_LEN, hdrlen);
        ieee80211_wep_get_iv(local, keylen, keyidx, newhdr + hdrlen);
        return newhdr + hdrlen;
}


static void ieee80211_wep_remove_iv(struct ieee80211_local *local,
                                    struct sk_buff *skb,
                                    struct ieee80211_key *key)
{
        struct ieee80211_hdr *hdr = (struct ieee80211_hdr *)skb->data;
        unsigned int hdrlen;

        hdrlen = ieee80211_hdrlen(hdr->frame_control);
        memmove(skb->data + WEP_IV_LEN, skb->data, hdrlen);
        skb_pull(skb, WEP_IV_LEN);
}


/* Perform WEP encryption using given key. data buffer must have tailroom
 * for 4-byte ICV. data_len must not include this ICV. Note: this function
 * does _not_ add IV. data = RC4(data | CRC32(data)) */
int ieee80211_wep_encrypt_data(struct crypto_cipher *tfm, u8 *rc4key,
                               size_t klen, u8 *data, size_t data_len)
{
        __le32 icv;
        int i;

        if (IS_ERR(tfm))
                return -1;

        icv = cpu_to_le32(~crc32_le(~0, data, data_len));
        put_unaligned(icv, (__le32 *)(data + data_len));

        crypto_cipher_setkey(tfm, rc4key, klen);
        for (i = 0; i < data_len + WEP_ICV_LEN; i++)
                crypto_cipher_encrypt_one(tfm, data + i, data + i);

        return 0;
}


/* Perform WEP encryption on given skb. 4 bytes of extra space (IV) in the
 * beginning of the buffer 4 bytes of extra space (ICV) in the end of the
 * buffer will be added. Both IV and ICV will be transmitted, so the
 * payload length increases with 8 bytes.
 *
 * WEP frame payload: IV + TX key idx, RC4(data), ICV = RC4(CRC32(data))
 */
int ieee80211_wep_encrypt(struct ieee80211_local *local,
                          struct sk_buff *skb,
                          const u8 *key, int keylen, int keyidx)
{
        u8 *iv;
        size_t len;
        u8 rc4key[3 + WLAN_KEY_LEN_WEP104];

        iv = ieee80211_wep_add_iv(local, skb, keylen, keyidx);
        if (!iv)
                return -1;

        len = skb->len - (iv + WEP_IV_LEN - skb->data);

        /* Prepend 24-bit IV to RC4 key */
        memcpy(rc4key, iv, 3);

        /* Copy rest of the WEP key (the secret part) */
        memcpy(rc4key + 3, key, keylen);

        /* Add room for ICV */
        skb_put(skb, WEP_ICV_LEN);

        return ieee80211_wep_encrypt_data(local->wep_tx_tfm, rc4key, keylen + 3,
                                          iv + WEP_IV_LEN, len);
}


/* Perform WEP decryption using given key. data buffer includes encrypted
 * payload, including 4-byte ICV, but _not_ IV. data_len must not include ICV.
 * Return 0 on success and -1 on ICV mismatch. */
int ieee80211_wep_decrypt_data(struct crypto_cipher *tfm, u8 *rc4key,
                               size_t klen, u8 *data, size_t data_len)
{
        __le32 crc;
        int i;

        if (IS_ERR(tfm))
                return -1;

        crypto_cipher_setkey(tfm, rc4key, klen);
        for (i = 0; i < data_len + WEP_ICV_LEN; i++)
                crypto_cipher_decrypt_one(tfm, data + i, data + i);

        crc = cpu_to_le32(~crc32_le(~0, data, data_len));
        if (memcmp(&crc, data + data_len, WEP_ICV_LEN) != 0)
                /* ICV mismatch */
                return -1;

        return 0;
}


/* Perform WEP decryption on given skb. Buffer includes whole WEP part of
 * the frame: IV (4 bytes), encrypted payload (including SNAP header),
 * ICV (4 bytes). skb->len includes both IV and ICV.
 *
 * Returns 0 if frame was decrypted successfully and ICV was correct and -1 on
 * failure. If frame is OK, IV and ICV will be removed, i.e., decrypted payload
 * is moved to the beginning of the skb and skb length will be reduced.
 */
static int ieee80211_wep_decrypt(struct ieee80211_local *local,
                                 struct sk_buff *skb,
                                 struct ieee80211_key *key)
{
        u32 klen;
        u8 rc4key[3 + WLAN_KEY_LEN_WEP104];
        u8 keyidx;
        struct ieee80211_hdr *hdr = (struct ieee80211_hdr *)skb->data;
        unsigned int hdrlen;
        size_t len;
        int ret = 0;

        if (!ieee80211_has_protected(hdr->frame_control))
                return -1;

        hdrlen = ieee80211_hdrlen(hdr->frame_control);
        if (skb->len < hdrlen + WEP_IV_LEN + WEP_ICV_LEN)
                return -1;

        len = skb->len - hdrlen - WEP_IV_LEN - WEP_ICV_LEN;

        keyidx = skb->data[hdrlen + 3] >> 6;

        if (!key || keyidx != key->conf.keyidx)
                return -1;

        klen = 3 + key->conf.keylen;

        /* Prepend 24-bit IV to RC4 key */
        memcpy(rc4key, skb->data + hdrlen, 3);

        /* Copy rest of the WEP key (the secret part) */
        memcpy(rc4key + 3, key->conf.key, key->conf.keylen);

        if (ieee80211_wep_decrypt_data(local->wep_rx_tfm, rc4key, klen,
                                       skb->data + hdrlen + WEP_IV_LEN,
                                       len))
                ret = -1;

        /* Trim ICV */
        skb_trim(skb, skb->len - WEP_ICV_LEN);

        /* Remove IV */
        memmove(skb->data + WEP_IV_LEN, skb->data, hdrlen);
        skb_pull(skb, WEP_IV_LEN);

        return ret;
}


bool ieee80211_wep_is_weak_iv(struct sk_buff *skb, struct ieee80211_key *key)
{
        struct ieee80211_hdr *hdr = (struct ieee80211_hdr *)skb->data;
        unsigned int hdrlen;
        u8 *ivpos;
        u32 iv;

        if (!ieee80211_has_protected(hdr->frame_control))
                return false;

        hdrlen = ieee80211_hdrlen(hdr->frame_control);
        ivpos = skb->data + hdrlen;
        iv = (ivpos[0] << 16) | (ivpos[1] << 8) | ivpos[2];

        return ieee80211_wep_weak_iv(iv, key->conf.keylen);
}

ieee80211_rx_result
ieee80211_crypto_wep_decrypt(struct ieee80211_rx_data *rx)
{
        struct sk_buff *skb = rx->skb;
        struct ieee80211_rx_status *status = IEEE80211_SKB_RXCB(skb);
        struct ieee80211_hdr *hdr = (struct ieee80211_hdr *)skb->data;

        if (!ieee80211_is_data(hdr->frame_control) &&
            !ieee80211_is_auth(hdr->frame_control))
                return RX_CONTINUE;

        if (!(status->flag & RX_FLAG_DECRYPTED)) {
                if (ieee80211_wep_decrypt(rx->local, rx->skb, rx->key))
                        return RX_DROP_UNUSABLE;
        } else if (!(status->flag & RX_FLAG_IV_STRIPPED)) {
                ieee80211_wep_remove_iv(rx->local, rx->skb, rx->key);
                /* remove ICV */
                skb_trim(rx->skb, rx->skb->len - WEP_ICV_LEN);
        }

        return RX_CONTINUE;
}

static int wep_encrypt_skb(struct ieee80211_tx_data *tx, struct sk_buff *skb)
{
        struct ieee80211_tx_info *info = IEEE80211_SKB_CB(skb);

        if (!info->control.hw_key) {
                if (ieee80211_wep_encrypt(tx->local, skb, tx->key->conf.key,
                                          tx->key->conf.keylen,
                                          tx->key->conf.keyidx))
                        return -1;
        } else if (info->control.hw_key->flags &
                        IEEE80211_KEY_FLAG_GENERATE_IV) {
                if (!ieee80211_wep_add_iv(tx->local, skb,
                                          tx->key->conf.keylen,
                                          tx->key->conf.keyidx))
                        return -1;
        }

        return 0;
}

ieee80211_tx_result
ieee80211_crypto_wep_encrypt(struct ieee80211_tx_data *tx)
{
        struct sk_buff *skb;

        ieee80211_tx_set_protected(tx);

        skb = tx->skb;
        do {
                if (wep_encrypt_skb(tx, skb) < 0) {
                        I802_DEBUG_INC(tx->local->tx_handlers_drop_wep);
                        return TX_DROP;
                }
        } while ((skb = skb->next));

        return TX_CONTINUE;
}