wpa.c

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/*
 * Copyright 2002-2004, Instant802 Networks, Inc.
 * Copyright 2008, Jouni Malinen <[email protected]>
 *
 * 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/skbuff.h>
#include <linux/compiler.h>
#include <linux/ieee80211.h>
#include <linux/gfp.h>
#include <asm/unaligned.h>
#include <net/mac80211.h>
#include <crypto/aes.h>

#include "ieee80211_i.h"
#include "michael.h"
#include "tkip.h"
#include "aes_ccm.h"
#include "aes_cmac.h"
#include "wpa.h"

ieee80211_tx_result
ieee80211_tx_h_michael_mic_add(struct ieee80211_tx_data *tx)
{
    u8 *data, *key, *mic;
    size_t data_len;
    unsigned int hdrlen;
    struct ieee80211_hdr *hdr;
    struct sk_buff *skb = tx->skb;
    struct ieee80211_tx_info *info = IEEE80211_SKB_CB(skb);
    int tail;

    hdr = (struct ieee80211_hdr *)skb->data;
    if (!tx->key || tx->key->conf.cipher != WLAN_CIPHER_SUITE_TKIP ||
        skb->len < 24 || !ieee80211_is_data_present(hdr->frame_control))
        return TX_CONTINUE;

    hdrlen = ieee80211_hdrlen(hdr->frame_control);
    if (skb->len < hdrlen)
        return TX_DROP;

    data = skb->data + hdrlen;
    data_len = skb->len - hdrlen;

    if (unlikely(info->flags & IEEE80211_TX_INTFL_TKIP_MIC_FAILURE)) {
        /* Need to use software crypto for the test */
        info->control.hw_key = NULL;
    }

    if (info->control.hw_key &&
        (info->flags & IEEE80211_TX_CTL_DONTFRAG ||
         tx->local->ops->set_frag_threshold) &&
        !(tx->key->conf.flags & IEEE80211_KEY_FLAG_GENERATE_MMIC)) {
        /* hwaccel - with no need for SW-generated MMIC */
        return TX_CONTINUE;
    }

    tail = MICHAEL_MIC_LEN;
    if (!info->control.hw_key)
        tail += TKIP_ICV_LEN;

    if (WARN_ON(skb_tailroom(skb) < tail ||
            skb_headroom(skb) < TKIP_IV_LEN))
        return TX_DROP;

    key = &tx->key->conf.key[NL80211_TKIP_DATA_OFFSET_TX_MIC_KEY];
    mic = skb_put(skb, MICHAEL_MIC_LEN);
    michael_mic(key, hdr, data, data_len, mic);
    if (unlikely(info->flags & IEEE80211_TX_INTFL_TKIP_MIC_FAILURE))
        mic[0]++;

    return TX_CONTINUE;
}


ieee80211_rx_result
ieee80211_rx_h_michael_mic_verify(struct ieee80211_rx_data *rx)
{
    u8 *data, *key = NULL;
    size_t data_len;
    unsigned int hdrlen;
    u8 mic[MICHAEL_MIC_LEN];
    struct sk_buff *skb = rx->skb;
    struct ieee80211_rx_status *status = IEEE80211_SKB_RXCB(skb);
    struct ieee80211_hdr *hdr = (struct ieee80211_hdr *)skb->data;

    /*
     * it makes no sense to check for MIC errors on anything other
     * than data frames.
     */
    if (!ieee80211_is_data_present(hdr->frame_control))
        return RX_CONTINUE;

    /*
     * No way to verify the MIC if the hardware stripped it or
     * the IV with the key index. In this case we have solely rely
     * on the driver to set RX_FLAG_MMIC_ERROR in the event of a
     * MIC failure report.
     */
    if (status->flag & (RX_FLAG_MMIC_STRIPPED | RX_FLAG_IV_STRIPPED)) {
        if (status->flag & RX_FLAG_MMIC_ERROR)
            goto mic_fail;

        if (!(status->flag & RX_FLAG_IV_STRIPPED) && rx->key &&
            rx->key->conf.cipher == WLAN_CIPHER_SUITE_TKIP)
            goto update_iv;

        return RX_CONTINUE;
    }

    /*
     * Some hardware seems to generate Michael MIC failure reports; even
     * though, the frame was not encrypted with TKIP and therefore has no
     * MIC. Ignore the flag them to avoid triggering countermeasures.
     */
    if (!rx->key || rx->key->conf.cipher != WLAN_CIPHER_SUITE_TKIP ||
        !(status->flag & RX_FLAG_DECRYPTED))
        return RX_CONTINUE;

    if (rx->sdata->vif.type == NL80211_IFTYPE_AP && rx->key->conf.keyidx) {
        /*
         * APs with pairwise keys should never receive Michael MIC
         * errors for non-zero keyidx because these are reserved for
         * group keys and only the AP is sending real multicast
         * frames in the BSS. (
         */
        return RX_DROP_UNUSABLE;
    }

    if (status->flag & RX_FLAG_MMIC_ERROR)
        goto mic_fail;

    hdrlen = ieee80211_hdrlen(hdr->frame_control);
    if (skb->len < hdrlen + MICHAEL_MIC_LEN)
        return RX_DROP_UNUSABLE;

    if (skb_linearize(rx->skb))
        return RX_DROP_UNUSABLE;
    hdr = (void *)skb->data;

    data = skb->data + hdrlen;
    data_len = skb->len - hdrlen - MICHAEL_MIC_LEN;
    key = &rx->key->conf.key[NL80211_TKIP_DATA_OFFSET_RX_MIC_KEY];
    michael_mic(key, hdr, data, data_len, mic);
    if (memcmp(mic, data + data_len, MICHAEL_MIC_LEN) != 0)
        goto mic_fail;

    /* remove Michael MIC from payload */
    skb_trim(skb, skb->len - MICHAEL_MIC_LEN);

update_iv:
    /* update IV in key information to be able to detect replays */
    rx->key->u.tkip.rx[rx->security_idx].iv32 = rx->tkip_iv32;
    rx->key->u.tkip.rx[rx->security_idx].iv16 = rx->tkip_iv16;

    return RX_CONTINUE;

mic_fail:
    /*
     * In some cases the key can be unset - e.g. a multicast packet, in
     * a driver that supports HW encryption. Send up the key idx only if
     * the key is set.
     */
    mac80211_ev_michael_mic_failure(rx->sdata,
                    rx->key ? rx->key->conf.keyidx : -1,
                    (void *) skb->data, NULL, GFP_ATOMIC);
    return RX_DROP_UNUSABLE;
}


static int tkip_encrypt_skb(struct ieee80211_tx_data *tx, struct sk_buff *skb)
{
    struct ieee80211_hdr *hdr = (struct ieee80211_hdr *) skb->data;
    struct ieee80211_key *key = tx->key;
    struct ieee80211_tx_info *info = IEEE80211_SKB_CB(skb);
    unsigned long flags;
    unsigned int hdrlen;
    int len, tail;
    u8 *pos;

    if (info->control.hw_key &&
        !(info->control.hw_key->flags & IEEE80211_KEY_FLAG_GENERATE_IV) &&
        !(info->control.hw_key->flags & IEEE80211_KEY_FLAG_PUT_IV_SPACE)) {
        /* hwaccel - with no need for software-generated IV */
        return 0;
    }

    hdrlen = ieee80211_hdrlen(hdr->frame_control);
    len = skb->len - hdrlen;

    if (info->control.hw_key)
        tail = 0;
    else
        tail = TKIP_ICV_LEN;

    if (WARN_ON(skb_tailroom(skb) < tail ||
            skb_headroom(skb) < TKIP_IV_LEN))
        return -1;

    pos = skb_push(skb, TKIP_IV_LEN);
    memmove(pos, pos + TKIP_IV_LEN, hdrlen);
    skb_set_network_header(skb, skb_network_offset(skb) + TKIP_IV_LEN);
    pos += hdrlen;

    /* 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 0;

    /* Increase IV for the frame */
    spin_lock_irqsave(&key->u.tkip.txlock, flags);
    key->u.tkip.tx.iv16++;
    if (key->u.tkip.tx.iv16 == 0)
        key->u.tkip.tx.iv32++;
    pos = ieee80211_tkip_add_iv(pos, key);
    spin_unlock_irqrestore(&key->u.tkip.txlock, flags);

    /* hwaccel - with software IV */
    if (info->control.hw_key)
        return 0;

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

    return ieee80211_tkip_encrypt_data(tx->local->wep_tx_tfm,
                       key, skb, pos, len);
}


ieee80211_tx_result
ieee80211_crypto_tkip_encrypt(struct ieee80211_tx_data *tx)
{
    struct sk_buff *skb;

    ieee80211_tx_set_protected(tx);

    skb_queue_walk(&tx->skbs, skb) {
        if (tkip_encrypt_skb(tx, skb) < 0)
            return TX_DROP;
    }

    return TX_CONTINUE;
}


ieee80211_rx_result
ieee80211_crypto_tkip_decrypt(struct ieee80211_rx_data *rx)
{
    struct ieee80211_hdr *hdr = (struct ieee80211_hdr *) rx->skb->data;
    int hdrlen, res, hwaccel = 0;
    struct ieee80211_key *key = rx->key;
    struct sk_buff *skb = rx->skb;
    struct ieee80211_rx_status *status = IEEE80211_SKB_RXCB(skb);

    hdrlen = ieee80211_hdrlen(hdr->frame_control);

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

    if (!rx->sta || skb->len - hdrlen < 12)
        return RX_DROP_UNUSABLE;

    /* it may be possible to optimize this a bit more */
    if (skb_linearize(rx->skb))
        return RX_DROP_UNUSABLE;
    hdr = (void *)skb->data;

    /*
     * Let TKIP code verify IV, but skip decryption.
     * In the case where hardware checks the IV as well,
     * we don't even get here, see ieee80211_rx_h_decrypt()
     */
    if (status->flag & RX_FLAG_DECRYPTED)
        hwaccel = 1;

    res = ieee80211_tkip_decrypt_data(rx->local->wep_rx_tfm,
                      key, skb->data + hdrlen,
                      skb->len - hdrlen, rx->sta->sta.addr,
                      hdr->addr1, hwaccel, rx->security_idx,
                      &rx->tkip_iv32,
                      &rx->tkip_iv16);
    if (res != TKIP_DECRYPT_OK)
        return RX_DROP_UNUSABLE;

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

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

    return RX_CONTINUE;
}


static void ccmp_special_blocks(struct sk_buff *skb, u8 *pn, u8 *scratch,
                int encrypted)
{
    __le16 mask_fc;
    int a4_included, mgmt;
    u8 qos_tid;
    u8 *b_0, *aad;
    u16 data_len, len_a;
    unsigned int hdrlen;
    struct ieee80211_hdr *hdr = (struct ieee80211_hdr *)skb->data;

    memset(scratch, 0, 6 * AES_BLOCK_SIZE);

    b_0 = scratch + 3 * AES_BLOCK_SIZE;
    aad = scratch + 4 * AES_BLOCK_SIZE;

    /*
     * Mask FC: zero subtype b4 b5 b6 (if not mgmt)
     * Retry, PwrMgt, MoreData; set Protected
     */
    mgmt = ieee80211_is_mgmt(hdr->frame_control);
    mask_fc = hdr->frame_control;
    mask_fc &= ~cpu_to_le16(IEEE80211_FCTL_RETRY |
                IEEE80211_FCTL_PM | IEEE80211_FCTL_MOREDATA);
    if (!mgmt)
        mask_fc &= ~cpu_to_le16(0x0070);
    mask_fc |= cpu_to_le16(IEEE80211_FCTL_PROTECTED);

    hdrlen = ieee80211_hdrlen(hdr->frame_control);
    len_a = hdrlen - 2;
    a4_included = ieee80211_has_a4(hdr->frame_control);

    if (ieee80211_is_data_qos(hdr->frame_control))
        qos_tid = *ieee80211_get_qos_ctl(hdr) & IEEE80211_QOS_CTL_TID_MASK;
    else
        qos_tid = 0;

    data_len = skb->len - hdrlen - CCMP_HDR_LEN;
    if (encrypted)
        data_len -= CCMP_MIC_LEN;

    /* First block, b_0 */
    b_0[0] = 0x59; /* flags: Adata: 1, M: 011, L: 001 */
    /* Nonce: Nonce Flags | A2 | PN
     * Nonce Flags: Priority (b0..b3) | Management (b4) | Reserved (b5..b7)
     */
    b_0[1] = qos_tid | (mgmt << 4);
    memcpy(&b_0[2], hdr->addr2, ETH_ALEN);
    memcpy(&b_0[8], pn, CCMP_PN_LEN);
    /* l(m) */
    put_unaligned_be16(data_len, &b_0[14]);

    /* AAD (extra authenticate-only data) / masked 802.11 header
     * FC | A1 | A2 | A3 | SC | [A4] | [QC] */
    put_unaligned_be16(len_a, &aad[0]);
    put_unaligned(mask_fc, (__le16 *)&aad[2]);
    memcpy(&aad[4], &hdr->addr1, 3 * ETH_ALEN);

    /* Mask Seq#, leave Frag# */
    aad[22] = *((u8 *) &hdr->seq_ctrl) & 0x0f;
    aad[23] = 0;

    if (a4_included) {
        memcpy(&aad[24], hdr->addr4, ETH_ALEN);
        aad[30] = qos_tid;
        aad[31] = 0;
    } else {
        memset(&aad[24], 0, ETH_ALEN + IEEE80211_QOS_CTL_LEN);
        aad[24] = qos_tid;
    }
}


static inline void ccmp_pn2hdr(u8 *hdr, u8 *pn, int key_id)
{
    hdr[0] = pn[5];
    hdr[1] = pn[4];
    hdr[2] = 0;
    hdr[3] = 0x20 | (key_id << 6);
    hdr[4] = pn[3];
    hdr[5] = pn[2];
    hdr[6] = pn[1];
    hdr[7] = pn[0];
}


static inline void ccmp_hdr2pn(u8 *pn, u8 *hdr)
{
    pn[0] = hdr[7];
    pn[1] = hdr[6];
    pn[2] = hdr[5];
    pn[3] = hdr[4];
    pn[4] = hdr[1];
    pn[5] = hdr[0];
}


static int ccmp_encrypt_skb(struct ieee80211_tx_data *tx, struct sk_buff *skb)
{
    struct ieee80211_hdr *hdr = (struct ieee80211_hdr *) skb->data;
    struct ieee80211_key *key = tx->key;
    struct ieee80211_tx_info *info = IEEE80211_SKB_CB(skb);
    int hdrlen, len, tail;
    u8 *pos;
    u8 pn[6];
    u64 pn64;
    u8 scratch[6 * AES_BLOCK_SIZE];

    if (info->control.hw_key &&
        !(info->control.hw_key->flags & IEEE80211_KEY_FLAG_GENERATE_IV) &&
        !(info->control.hw_key->flags & IEEE80211_KEY_FLAG_PUT_IV_SPACE)) {
        /*
         * hwaccel has no need for preallocated room for CCMP
         * header or MIC fields
         */
        return 0;
    }

    hdrlen = ieee80211_hdrlen(hdr->frame_control);
    len = skb->len - hdrlen;

    if (info->control.hw_key)
        tail = 0;
    else
        tail = CCMP_MIC_LEN;

    if (WARN_ON(skb_tailroom(skb) < tail ||
            skb_headroom(skb) < CCMP_HDR_LEN))
        return -1;

    pos = skb_push(skb, CCMP_HDR_LEN);
    memmove(pos, pos + CCMP_HDR_LEN, hdrlen);
    skb_set_network_header(skb, skb_network_offset(skb) + CCMP_HDR_LEN);

    /* 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 0;

    hdr = (struct ieee80211_hdr *) pos;
    pos += hdrlen;

    pn64 = atomic64_inc_return(&key->u.ccmp.tx_pn);

    pn[5] = pn64;
    pn[4] = pn64 >> 8;
    pn[3] = pn64 >> 16;
    pn[2] = pn64 >> 24;
    pn[1] = pn64 >> 32;
    pn[0] = pn64 >> 40;

    ccmp_pn2hdr(pos, pn, key->conf.keyidx);

    /* hwaccel - with software CCMP header */
    if (info->control.hw_key)
        return 0;

    pos += CCMP_HDR_LEN;
    ccmp_special_blocks(skb, pn, scratch, 0);
    ieee80211_aes_ccm_encrypt(key->u.ccmp.tfm, scratch, pos, len,
                  pos, skb_put(skb, CCMP_MIC_LEN));

    return 0;
}


ieee80211_tx_result
ieee80211_crypto_ccmp_encrypt(struct ieee80211_tx_data *tx)
{
    struct sk_buff *skb;

    ieee80211_tx_set_protected(tx);

    skb_queue_walk(&tx->skbs, skb) {
        if (ccmp_encrypt_skb(tx, skb) < 0)
            return TX_DROP;
    }

    return TX_CONTINUE;
}


ieee80211_rx_result
ieee80211_crypto_ccmp_decrypt(struct ieee80211_rx_data *rx)
{
    struct ieee80211_hdr *hdr = (struct ieee80211_hdr *)rx->skb->data;
    int hdrlen;
    struct ieee80211_key *key = rx->key;
    struct sk_buff *skb = rx->skb;
    struct ieee80211_rx_status *status = IEEE80211_SKB_RXCB(skb);
    u8 pn[CCMP_PN_LEN];
    int data_len;
    int queue;

    hdrlen = ieee80211_hdrlen(hdr->frame_control);

    if (!ieee80211_is_data(hdr->frame_control) &&
        !ieee80211_is_robust_mgmt_frame(hdr))
        return RX_CONTINUE;

    data_len = skb->len - hdrlen - CCMP_HDR_LEN - CCMP_MIC_LEN;
    if (!rx->sta || data_len < 0)
        return RX_DROP_UNUSABLE;

    if (status->flag & RX_FLAG_DECRYPTED) {
        if (!pskb_may_pull(rx->skb, hdrlen + CCMP_HDR_LEN))
            return RX_DROP_UNUSABLE;
    } else {
        if (skb_linearize(rx->skb))
            return RX_DROP_UNUSABLE;
    }

    ccmp_hdr2pn(pn, skb->data + hdrlen);

    queue = rx->security_idx;

    if (memcmp(pn, key->u.ccmp.rx_pn[queue], CCMP_PN_LEN) <= 0) {
        key->u.ccmp.replays++;
        return RX_DROP_UNUSABLE;
    }

    if (!(status->flag & RX_FLAG_DECRYPTED)) {
        u8 scratch[6 * AES_BLOCK_SIZE];
        /* hardware didn't decrypt/verify MIC */
        ccmp_special_blocks(skb, pn, scratch, 1);

        if (ieee80211_aes_ccm_decrypt(
                key->u.ccmp.tfm, scratch,
                skb->data + hdrlen + CCMP_HDR_LEN, data_len,
                skb->data + skb->len - CCMP_MIC_LEN,
                skb->data + hdrlen + CCMP_HDR_LEN))
            return RX_DROP_UNUSABLE;
    }

    memcpy(key->u.ccmp.rx_pn[queue], pn, CCMP_PN_LEN);

    /* Remove CCMP header and MIC */
    if (pskb_trim(skb, skb->len - CCMP_MIC_LEN))
        return RX_DROP_UNUSABLE;
    memmove(skb->data + CCMP_HDR_LEN, skb->data, hdrlen);
    skb_pull(skb, CCMP_HDR_LEN);

    return RX_CONTINUE;
}


static void bip_aad(struct sk_buff *skb, u8 *aad)
{
    __le16 mask_fc;
    struct ieee80211_hdr *hdr = (struct ieee80211_hdr *) skb->data;

    /* BIP AAD: FC(masked) || A1 || A2 || A3 */

    /* FC type/subtype */
    /* Mask FC Retry, PwrMgt, MoreData flags to zero */
    mask_fc = hdr->frame_control;
    mask_fc &= ~cpu_to_le16(IEEE80211_FCTL_RETRY | IEEE80211_FCTL_PM |
                IEEE80211_FCTL_MOREDATA);
    put_unaligned(mask_fc, (__le16 *) &aad[0]);
    /* A1 || A2 || A3 */
    memcpy(aad + 2, &hdr->addr1, 3 * ETH_ALEN);
}


static inline void bip_ipn_set64(u8 *d, u64 pn)
{
    *d++ = pn;
    *d++ = pn >> 8;
    *d++ = pn >> 16;
    *d++ = pn >> 24;
    *d++ = pn >> 32;
    *d = pn >> 40;
}

static inline void bip_ipn_swap(u8 *d, const u8 *s)
{
    *d++ = s[5];
    *d++ = s[4];
    *d++ = s[3];
    *d++ = s[2];
    *d++ = s[1];
    *d = s[0];
}


ieee80211_tx_result
ieee80211_crypto_aes_cmac_encrypt(struct ieee80211_tx_data *tx)
{
    struct sk_buff *skb;
    struct ieee80211_tx_info *info;
    struct ieee80211_key *key = tx->key;
    struct ieee80211_mmie *mmie;
    u8 aad[20];
    u64 pn64;

    if (WARN_ON(skb_queue_len(&tx->skbs) != 1))
        return TX_DROP;

    skb = skb_peek(&tx->skbs);

    info = IEEE80211_SKB_CB(skb);

    if (info->control.hw_key)
        return TX_CONTINUE;

    if (WARN_ON(skb_tailroom(skb) < sizeof(*mmie)))
        return TX_DROP;

    mmie = (struct ieee80211_mmie *) skb_put(skb, sizeof(*mmie));
    mmie->element_id = WLAN_EID_MMIE;
    mmie->length = sizeof(*mmie) - 2;
    mmie->key_id = cpu_to_le16(key->conf.keyidx);

    /* PN = PN + 1 */
    pn64 = atomic64_inc_return(&key->u.aes_cmac.tx_pn);

    bip_ipn_set64(mmie->sequence_number, pn64);

    bip_aad(skb, aad);

    /*
     * MIC = AES-128-CMAC(IGTK, AAD || Management Frame Body || MMIE, 64)
     */
    ieee80211_aes_cmac(key->u.aes_cmac.tfm, aad,
               skb->data + 24, skb->len - 24, mmie->mic);

    return TX_CONTINUE;
}


ieee80211_rx_result
ieee80211_crypto_aes_cmac_decrypt(struct ieee80211_rx_data *rx)
{
    struct sk_buff *skb = rx->skb;
    struct ieee80211_rx_status *status = IEEE80211_SKB_RXCB(skb);
    struct ieee80211_key *key = rx->key;
    struct ieee80211_mmie *mmie;
    u8 aad[20], mic[8], ipn[6];
    struct ieee80211_hdr *hdr = (struct ieee80211_hdr *) skb->data;

    if (!ieee80211_is_mgmt(hdr->frame_control))
        return RX_CONTINUE;

    /* management frames are already linear */

    if (skb->len < 24 + sizeof(*mmie))
        return RX_DROP_UNUSABLE;

    mmie = (struct ieee80211_mmie *)
        (skb->data + skb->len - sizeof(*mmie));
    if (mmie->element_id != WLAN_EID_MMIE ||
        mmie->length != sizeof(*mmie) - 2)
        return RX_DROP_UNUSABLE; /* Invalid MMIE */

    bip_ipn_swap(ipn, mmie->sequence_number);

    if (memcmp(ipn, key->u.aes_cmac.rx_pn, 6) <= 0) {
        key->u.aes_cmac.replays++;
        return RX_DROP_UNUSABLE;
    }

    if (!(status->flag & RX_FLAG_DECRYPTED)) {
        /* hardware didn't decrypt/verify MIC */
        bip_aad(skb, aad);
        ieee80211_aes_cmac(key->u.aes_cmac.tfm, aad,
                   skb->data + 24, skb->len - 24, mic);
        if (memcmp(mic, mmie->mic, sizeof(mmie->mic)) != 0) {
            key->u.aes_cmac.icverrors++;
            return RX_DROP_UNUSABLE;
        }
    }

    memcpy(key->u.aes_cmac.rx_pn, ipn, 6);

    /* Remove MMIE */
    skb_trim(skb, skb->len - sizeof(*mmie));

    return RX_CONTINUE;
}

ieee80211_tx_result
ieee80211_crypto_hw_encrypt(struct ieee80211_tx_data *tx)
{
    struct sk_buff *skb;
    struct ieee80211_tx_info *info = NULL;

    skb_queue_walk(&tx->skbs, skb) {
        info  = IEEE80211_SKB_CB(skb);

        /* handle hw-only algorithm */
        if (!info->control.hw_key)
            return TX_DROP;
    }

    ieee80211_tx_set_protected(tx);

    return TX_CONTINUE;
}