wep.c 8.31 KB
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// SPDX-License-Identifier: GPL-2.0-only
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/*
 * Software WEP encryption implementation
 * Copyright 2002, Jouni Malinen <jkmaline@cc.hut.fi>
 * Copyright 2003, Instant802 Networks, Inc.
 */

#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>
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#include <linux/scatterlist.h>
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#include <linux/slab.h>
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#include <asm/unaligned.h>
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#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 */
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	get_random_bytes(&local->wep_iv, IEEE80211_WEP_IV_LEN);
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	return 0;
}

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


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

	if (!iv)
		return;

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


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static u8 *ieee80211_wep_add_iv(struct ieee80211_local *local,
				struct sk_buff *skb,
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				int keylen, int keyidx)
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{
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	struct ieee80211_hdr *hdr = (struct ieee80211_hdr *)skb->data;
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	struct ieee80211_tx_info *info = IEEE80211_SKB_CB(skb);
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	unsigned int hdrlen;
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	u8 *newhdr;

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	hdr->frame_control |= cpu_to_le16(IEEE80211_FCTL_PROTECTED);
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	if (WARN_ON(skb_headroom(skb) < IEEE80211_WEP_IV_LEN))
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		return NULL;
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	hdrlen = ieee80211_hdrlen(hdr->frame_control);
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	newhdr = skb_push(skb, IEEE80211_WEP_IV_LEN);
	memmove(newhdr, newhdr + IEEE80211_WEP_IV_LEN, hdrlen);
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	/* the HW only needs room for the IV, but not the actual IV */
	if (info->control.hw_key &&
	    (info->control.hw_key->flags & IEEE80211_KEY_FLAG_PUT_IV_SPACE))
		return newhdr + hdrlen;

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	ieee80211_wep_get_iv(local, keylen, keyidx, newhdr + hdrlen);
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	return newhdr + hdrlen;
}


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static void ieee80211_wep_remove_iv(struct ieee80211_local *local,
				    struct sk_buff *skb,
				    struct ieee80211_key *key)
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{
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	struct ieee80211_hdr *hdr = (struct ieee80211_hdr *)skb->data;
	unsigned int hdrlen;
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	hdrlen = ieee80211_hdrlen(hdr->frame_control);
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	memmove(skb->data + IEEE80211_WEP_IV_LEN, skb->data, hdrlen);
	skb_pull(skb, IEEE80211_WEP_IV_LEN);
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}


/* 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)) */
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int ieee80211_wep_encrypt_data(struct arc4_ctx *ctx, u8 *rc4key,
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			       size_t klen, u8 *data, size_t data_len)
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{
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	__le32 icv;
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	icv = cpu_to_le32(~crc32_le(~0, data, data_len));
	put_unaligned(icv, (__le32 *)(data + data_len));
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	arc4_setkey(ctx, rc4key, klen);
	arc4_crypt(ctx, data, data, data_len + IEEE80211_WEP_ICV_LEN);
	memzero_explicit(ctx, sizeof(*ctx));
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	return 0;
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}


/* 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))
 */
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int ieee80211_wep_encrypt(struct ieee80211_local *local,
			  struct sk_buff *skb,
			  const u8 *key, int keylen, int keyidx)
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{
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	u8 *iv;
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	size_t len;
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	u8 rc4key[3 + WLAN_KEY_LEN_WEP104];
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	if (WARN_ON(skb_tailroom(skb) < IEEE80211_WEP_ICV_LEN))
		return -1;

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

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	len = skb->len - (iv + IEEE80211_WEP_IV_LEN - skb->data);
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	/* Prepend 24-bit IV to RC4 key */
	memcpy(rc4key, iv, 3);

	/* Copy rest of the WEP key (the secret part) */
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	memcpy(rc4key + 3, key, keylen);
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	/* Add room for ICV */
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	skb_put(skb, IEEE80211_WEP_ICV_LEN);
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	return ieee80211_wep_encrypt_data(&local->wep_tx_ctx, rc4key, keylen + 3,
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					  iv + IEEE80211_WEP_IV_LEN, len);
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}


/* 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. */
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int ieee80211_wep_decrypt_data(struct arc4_ctx *ctx, u8 *rc4key,
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			       size_t klen, u8 *data, size_t data_len)
{
	__le32 crc;
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	arc4_setkey(ctx, rc4key, klen);
	arc4_crypt(ctx, data, data, data_len + IEEE80211_WEP_ICV_LEN);
	memzero_explicit(ctx, sizeof(*ctx));
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	crc = cpu_to_le32(~crc32_le(~0, data, data_len));
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	if (memcmp(&crc, data + data_len, IEEE80211_WEP_ICV_LEN) != 0)
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		/* 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.
 */
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static int ieee80211_wep_decrypt(struct ieee80211_local *local,
				 struct sk_buff *skb,
				 struct ieee80211_key *key)
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{
	u32 klen;
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	u8 rc4key[3 + WLAN_KEY_LEN_WEP104];
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	u8 keyidx;
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	struct ieee80211_hdr *hdr = (struct ieee80211_hdr *)skb->data;
	unsigned int hdrlen;
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	size_t len;
	int ret = 0;

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

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	hdrlen = ieee80211_hdrlen(hdr->frame_control);
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	if (skb->len < hdrlen + IEEE80211_WEP_IV_LEN + IEEE80211_WEP_ICV_LEN)
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		return -1;

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	len = skb->len - hdrlen - IEEE80211_WEP_IV_LEN - IEEE80211_WEP_ICV_LEN;
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	keyidx = skb->data[hdrlen + 3] >> 6;

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

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

	/* Copy rest of the WEP key (the secret part) */
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	memcpy(rc4key + 3, key->conf.key, key->conf.keylen);
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	if (ieee80211_wep_decrypt_data(&local->wep_rx_ctx, rc4key, klen,
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				       skb->data + hdrlen +
				       IEEE80211_WEP_IV_LEN, len))
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		ret = -1;

	/* Trim ICV */
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	skb_trim(skb, skb->len - IEEE80211_WEP_ICV_LEN);
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	/* Remove IV */
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	memmove(skb->data + IEEE80211_WEP_IV_LEN, skb->data, hdrlen);
	skb_pull(skb, IEEE80211_WEP_IV_LEN);
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	return ret;
}

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ieee80211_rx_result
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ieee80211_crypto_wep_decrypt(struct ieee80211_rx_data *rx)
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{
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	struct sk_buff *skb = rx->skb;
	struct ieee80211_rx_status *status = IEEE80211_SKB_RXCB(skb);
	struct ieee80211_hdr *hdr = (struct ieee80211_hdr *)skb->data;
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	__le16 fc = hdr->frame_control;
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	if (!ieee80211_is_data(fc) && !ieee80211_is_auth(fc))
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		return RX_CONTINUE;
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	if (!(status->flag & RX_FLAG_DECRYPTED)) {
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		if (skb_linearize(rx->skb))
			return RX_DROP_UNUSABLE;
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		if (ieee80211_wep_decrypt(rx->local, rx->skb, rx->key))
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			return RX_DROP_UNUSABLE;
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	} else if (!(status->flag & RX_FLAG_IV_STRIPPED)) {
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		if (!pskb_may_pull(rx->skb, ieee80211_hdrlen(fc) +
					    IEEE80211_WEP_IV_LEN))
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			return RX_DROP_UNUSABLE;
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		ieee80211_wep_remove_iv(rx->local, rx->skb, rx->key);
		/* remove ICV */
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		if (!(status->flag & RX_FLAG_ICV_STRIPPED) &&
		    pskb_trim(rx->skb, rx->skb->len - IEEE80211_WEP_ICV_LEN))
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			return RX_DROP_UNUSABLE;
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	}

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	return RX_CONTINUE;
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}
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static int wep_encrypt_skb(struct ieee80211_tx_data *tx, struct sk_buff *skb)
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{
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	struct ieee80211_tx_info *info = IEEE80211_SKB_CB(skb);
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	struct ieee80211_key_conf *hw_key = info->control.hw_key;
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	if (!hw_key) {
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		if (ieee80211_wep_encrypt(tx->local, skb, tx->key->conf.key,
					  tx->key->conf.keylen,
					  tx->key->conf.keyidx))
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			return -1;
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	} else if ((hw_key->flags & IEEE80211_KEY_FLAG_GENERATE_IV) ||
		   (hw_key->flags & IEEE80211_KEY_FLAG_PUT_IV_SPACE)) {
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		if (!ieee80211_wep_add_iv(tx->local, skb,
					  tx->key->conf.keylen,
					  tx->key->conf.keyidx))
			return -1;
	}

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	return 0;
}

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ieee80211_tx_result
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ieee80211_crypto_wep_encrypt(struct ieee80211_tx_data *tx)
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{
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	struct sk_buff *skb;
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	ieee80211_tx_set_protected(tx);
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	skb_queue_walk(&tx->skbs, skb) {
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		if (wep_encrypt_skb(tx, skb) < 0) {
			I802_DEBUG_INC(tx->local->tx_handlers_drop_wep);
			return TX_DROP;
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		}
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	}
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	return TX_CONTINUE;
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}