lib80211_crypt_ccmp.c

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/*
 * lib80211 crypt: host-based CCMP encryption implementation for lib80211
 *
 * Copyright (c) 2003-2004, Jouni Malinen <[email protected]>
 * Copyright (c) 2008, John W. Linville <[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. See README and COPYING for
 * more details.
 */

#include <linux/kernel.h>
#include <linux/err.h>
#include <linux/module.h>
#include <linux/init.h>
#include <linux/slab.h>
#include <linux/random.h>
#include <linux/skbuff.h>
#include <linux/netdevice.h>
#include <linux/if_ether.h>
#include <linux/if_arp.h>
#include <asm/string.h>
#include <linux/wireless.h>

#include <linux/ieee80211.h>

#include <linux/crypto.h>

#include <net/lib80211.h>

MODULE_AUTHOR("Jouni Malinen");
MODULE_DESCRIPTION("Host AP crypt: CCMP");
MODULE_LICENSE("GPL");

#define AES_BLOCK_LEN 16
#define CCMP_HDR_LEN 8
#define CCMP_MIC_LEN 8
#define CCMP_TK_LEN 16
#define CCMP_PN_LEN 6

struct lib80211_ccmp_data {
    u8 key[CCMP_TK_LEN];
    int key_set;

    u8 tx_pn[CCMP_PN_LEN];
    u8 rx_pn[CCMP_PN_LEN];

    u32 dot11RSNAStatsCCMPFormatErrors;
    u32 dot11RSNAStatsCCMPReplays;
    u32 dot11RSNAStatsCCMPDecryptErrors;

    int key_idx;

    struct crypto_cipher *tfm;

    /* scratch buffers for virt_to_page() (crypto API) */
    u8 tx_b0[AES_BLOCK_LEN], tx_b[AES_BLOCK_LEN],
        tx_e[AES_BLOCK_LEN], tx_s0[AES_BLOCK_LEN];
    u8 rx_b0[AES_BLOCK_LEN], rx_b[AES_BLOCK_LEN], rx_a[AES_BLOCK_LEN];
};

static inline void lib80211_ccmp_aes_encrypt(struct crypto_cipher *tfm,
                          const u8 pt[16], u8 ct[16])
{
    crypto_cipher_encrypt_one(tfm, ct, pt);
}

static void *lib80211_ccmp_init(int key_idx)
{
    struct lib80211_ccmp_data *priv;

    priv = kzalloc(sizeof(*priv), GFP_ATOMIC);
    if (priv == NULL)
        goto fail;
    priv->key_idx = key_idx;

    priv->tfm = crypto_alloc_cipher("aes", 0, CRYPTO_ALG_ASYNC);
    if (IS_ERR(priv->tfm)) {
        priv->tfm = NULL;
        goto fail;
    }

    return priv;

      fail:
    if (priv) {
        if (priv->tfm)
            crypto_free_cipher(priv->tfm);
        kfree(priv);
    }

    return NULL;
}

static void lib80211_ccmp_deinit(void *priv)
{
    struct lib80211_ccmp_data *_priv = priv;
    if (_priv && _priv->tfm)
        crypto_free_cipher(_priv->tfm);
    kfree(priv);
}

static inline void xor_block(u8 * b, u8 * a, size_t len)
{
    int i;
    for (i = 0; i < len; i++)
        b[i] ^= a[i];
}

static void ccmp_init_blocks(struct crypto_cipher *tfm,
                 struct ieee80211_hdr *hdr,
                 u8 * pn, size_t dlen, u8 * b0, u8 * auth, u8 * s0)
{
    u8 *pos, qc = 0;
    size_t aad_len;
    int a4_included, qc_included;
    u8 aad[2 * AES_BLOCK_LEN];

    a4_included = ieee80211_has_a4(hdr->frame_control);
    qc_included = ieee80211_is_data_qos(hdr->frame_control);

    aad_len = 22;
    if (a4_included)
        aad_len += 6;
    if (qc_included) {
        pos = (u8 *) & hdr->addr4;
        if (a4_included)
            pos += 6;
        qc = *pos & 0x0f;
        aad_len += 2;
    }

    /* CCM Initial Block:
     * Flag (Include authentication header, M=3 (8-octet MIC),
     *       L=1 (2-octet Dlen))
     * Nonce: 0x00 | A2 | PN
     * Dlen */
    b0[0] = 0x59;
    b0[1] = qc;
    memcpy(b0 + 2, hdr->addr2, ETH_ALEN);
    memcpy(b0 + 8, pn, CCMP_PN_LEN);
    b0[14] = (dlen >> 8) & 0xff;
    b0[15] = dlen & 0xff;

    /* AAD:
     * FC with bits 4..6 and 11..13 masked to zero; 14 is always one
     * A1 | A2 | A3
     * SC with bits 4..15 (seq#) masked to zero
     * A4 (if present)
     * QC (if present)
     */
    pos = (u8 *) hdr;
    aad[0] = 0;     /* aad_len >> 8 */
    aad[1] = aad_len & 0xff;
    aad[2] = pos[0] & 0x8f;
    aad[3] = pos[1] & 0xc7;
    memcpy(aad + 4, hdr->addr1, 3 * ETH_ALEN);
    pos = (u8 *) & hdr->seq_ctrl;
    aad[22] = pos[0] & 0x0f;
    aad[23] = 0;        /* all bits masked */
    memset(aad + 24, 0, 8);
    if (a4_included)
        memcpy(aad + 24, hdr->addr4, ETH_ALEN);
    if (qc_included) {
        aad[a4_included ? 30 : 24] = qc;
        /* rest of QC masked */
    }

    /* Start with the first block and AAD */
    lib80211_ccmp_aes_encrypt(tfm, b0, auth);
    xor_block(auth, aad, AES_BLOCK_LEN);
    lib80211_ccmp_aes_encrypt(tfm, auth, auth);
    xor_block(auth, &aad[AES_BLOCK_LEN], AES_BLOCK_LEN);
    lib80211_ccmp_aes_encrypt(tfm, auth, auth);
    b0[0] &= 0x07;
    b0[14] = b0[15] = 0;
    lib80211_ccmp_aes_encrypt(tfm, b0, s0);
}

static int lib80211_ccmp_hdr(struct sk_buff *skb, int hdr_len,
                  u8 *aeskey, int keylen, void *priv)
{
    struct lib80211_ccmp_data *key = priv;
    int i;
    u8 *pos;

    if (skb_headroom(skb) < CCMP_HDR_LEN || skb->len < hdr_len)
        return -1;

    if (aeskey != NULL && keylen >= CCMP_TK_LEN)
        memcpy(aeskey, key->key, CCMP_TK_LEN);

    pos = skb_push(skb, CCMP_HDR_LEN);
    memmove(pos, pos + CCMP_HDR_LEN, hdr_len);
    pos += hdr_len;

    i = CCMP_PN_LEN - 1;
    while (i >= 0) {
        key->tx_pn[i]++;
        if (key->tx_pn[i] != 0)
            break;
        i--;
    }

    *pos++ = key->tx_pn[5];
    *pos++ = key->tx_pn[4];
    *pos++ = 0;
    *pos++ = (key->key_idx << 6) | (1 << 5) /* Ext IV included */ ;
    *pos++ = key->tx_pn[3];
    *pos++ = key->tx_pn[2];
    *pos++ = key->tx_pn[1];
    *pos++ = key->tx_pn[0];

    return CCMP_HDR_LEN;
}

static int lib80211_ccmp_encrypt(struct sk_buff *skb, int hdr_len, void *priv)
{
    struct lib80211_ccmp_data *key = priv;
    int data_len, i, blocks, last, len;
    u8 *pos, *mic;
    struct ieee80211_hdr *hdr;
    u8 *b0 = key->tx_b0;
    u8 *b = key->tx_b;
    u8 *e = key->tx_e;
    u8 *s0 = key->tx_s0;

    if (skb_tailroom(skb) < CCMP_MIC_LEN || skb->len < hdr_len)
        return -1;

    data_len = skb->len - hdr_len;
    len = lib80211_ccmp_hdr(skb, hdr_len, NULL, 0, priv);
    if (len < 0)
        return -1;

    pos = skb->data + hdr_len + CCMP_HDR_LEN;
    hdr = (struct ieee80211_hdr *)skb->data;
    ccmp_init_blocks(key->tfm, hdr, key->tx_pn, data_len, b0, b, s0);

    blocks = DIV_ROUND_UP(data_len, AES_BLOCK_LEN);
    last = data_len % AES_BLOCK_LEN;

    for (i = 1; i <= blocks; i++) {
        len = (i == blocks && last) ? last : AES_BLOCK_LEN;
        /* Authentication */
        xor_block(b, pos, len);
        lib80211_ccmp_aes_encrypt(key->tfm, b, b);
        /* Encryption, with counter */
        b0[14] = (i >> 8) & 0xff;
        b0[15] = i & 0xff;
        lib80211_ccmp_aes_encrypt(key->tfm, b0, e);
        xor_block(pos, e, len);
        pos += len;
    }

    mic = skb_put(skb, CCMP_MIC_LEN);
    for (i = 0; i < CCMP_MIC_LEN; i++)
        mic[i] = b[i] ^ s0[i];

    return 0;
}

/*
 * deal with seq counter wrapping correctly.
 * refer to timer_after() for jiffies wrapping handling
 */
static inline int ccmp_replay_check(u8 *pn_n, u8 *pn_o)
{
    u32 iv32_n, iv16_n;
    u32 iv32_o, iv16_o;

    iv32_n = (pn_n[0] << 24) | (pn_n[1] << 16) | (pn_n[2] << 8) | pn_n[3];
    iv16_n = (pn_n[4] << 8) | pn_n[5];

    iv32_o = (pn_o[0] << 24) | (pn_o[1] << 16) | (pn_o[2] << 8) | pn_o[3];
    iv16_o = (pn_o[4] << 8) | pn_o[5];

    if ((s32)iv32_n - (s32)iv32_o < 0 ||
        (iv32_n == iv32_o && iv16_n <= iv16_o))
        return 1;
    return 0;
}

static int lib80211_ccmp_decrypt(struct sk_buff *skb, int hdr_len, void *priv)
{
    struct lib80211_ccmp_data *key = priv;
    u8 keyidx, *pos;
    struct ieee80211_hdr *hdr;
    u8 *b0 = key->rx_b0;
    u8 *b = key->rx_b;
    u8 *a = key->rx_a;
    u8 pn[6];
    int i, blocks, last, len;
    size_t data_len = skb->len - hdr_len - CCMP_HDR_LEN - CCMP_MIC_LEN;
    u8 *mic = skb->data + skb->len - CCMP_MIC_LEN;

    if (skb->len < hdr_len + CCMP_HDR_LEN + CCMP_MIC_LEN) {
        key->dot11RSNAStatsCCMPFormatErrors++;
        return -1;
    }

    hdr = (struct ieee80211_hdr *)skb->data;
    pos = skb->data + hdr_len;
    keyidx = pos[3];
    if (!(keyidx & (1 << 5))) {
        net_dbg_ratelimited("CCMP: received packet without ExtIV flag from %pM\n",
                    hdr->addr2);
        key->dot11RSNAStatsCCMPFormatErrors++;
        return -2;
    }
    keyidx >>= 6;
    if (key->key_idx != keyidx) {
        printk(KERN_DEBUG "CCMP: RX tkey->key_idx=%d frame "
               "keyidx=%d priv=%p\n", key->key_idx, keyidx, priv);
        return -6;
    }
    if (!key->key_set) {
        net_dbg_ratelimited("CCMP: received packet from %pM with keyid=%d that does not have a configured key\n",
                    hdr->addr2, keyidx);
        return -3;
    }

    pn[0] = pos[7];
    pn[1] = pos[6];
    pn[2] = pos[5];
    pn[3] = pos[4];
    pn[4] = pos[1];
    pn[5] = pos[0];
    pos += 8;

    if (ccmp_replay_check(pn, key->rx_pn)) {
#ifdef CONFIG_LIB80211_DEBUG
        net_dbg_ratelimited("CCMP: replay detected: STA=%pM previous PN %02x%02x%02x%02x%02x%02x received PN %02x%02x%02x%02x%02x%02x\n",
                    hdr->addr2,
                    key->rx_pn[0], key->rx_pn[1], key->rx_pn[2],
                    key->rx_pn[3], key->rx_pn[4], key->rx_pn[5],
                    pn[0], pn[1], pn[2], pn[3], pn[4], pn[5]);
#endif
        key->dot11RSNAStatsCCMPReplays++;
        return -4;
    }

    ccmp_init_blocks(key->tfm, hdr, pn, data_len, b0, a, b);
    xor_block(mic, b, CCMP_MIC_LEN);

    blocks = DIV_ROUND_UP(data_len, AES_BLOCK_LEN);
    last = data_len % AES_BLOCK_LEN;

    for (i = 1; i <= blocks; i++) {
        len = (i == blocks && last) ? last : AES_BLOCK_LEN;
        /* Decrypt, with counter */
        b0[14] = (i >> 8) & 0xff;
        b0[15] = i & 0xff;
        lib80211_ccmp_aes_encrypt(key->tfm, b0, b);
        xor_block(pos, b, len);
        /* Authentication */
        xor_block(a, pos, len);
        lib80211_ccmp_aes_encrypt(key->tfm, a, a);
        pos += len;
    }

    if (memcmp(mic, a, CCMP_MIC_LEN) != 0) {
        net_dbg_ratelimited("CCMP: decrypt failed: STA=%pM\n",
                    hdr->addr2);
        key->dot11RSNAStatsCCMPDecryptErrors++;
        return -5;
    }

    memcpy(key->rx_pn, pn, CCMP_PN_LEN);

    /* Remove hdr and MIC */
    memmove(skb->data + CCMP_HDR_LEN, skb->data, hdr_len);
    skb_pull(skb, CCMP_HDR_LEN);
    skb_trim(skb, skb->len - CCMP_MIC_LEN);

    return keyidx;
}

static int lib80211_ccmp_set_key(void *key, int len, u8 * seq, void *priv)
{
    struct lib80211_ccmp_data *data = priv;
    int keyidx;
    struct crypto_cipher *tfm = data->tfm;

    keyidx = data->key_idx;
    memset(data, 0, sizeof(*data));
    data->key_idx = keyidx;
    data->tfm = tfm;
    if (len == CCMP_TK_LEN) {
        memcpy(data->key, key, CCMP_TK_LEN);
        data->key_set = 1;
        if (seq) {
            data->rx_pn[0] = seq[5];
            data->rx_pn[1] = seq[4];
            data->rx_pn[2] = seq[3];
            data->rx_pn[3] = seq[2];
            data->rx_pn[4] = seq[1];
            data->rx_pn[5] = seq[0];
        }
        crypto_cipher_setkey(data->tfm, data->key, CCMP_TK_LEN);
    } else if (len == 0)
        data->key_set = 0;
    else
        return -1;

    return 0;
}

static int lib80211_ccmp_get_key(void *key, int len, u8 * seq, void *priv)
{
    struct lib80211_ccmp_data *data = priv;

    if (len < CCMP_TK_LEN)
        return -1;

    if (!data->key_set)
        return 0;
    memcpy(key, data->key, CCMP_TK_LEN);

    if (seq) {
        seq[0] = data->tx_pn[5];
        seq[1] = data->tx_pn[4];
        seq[2] = data->tx_pn[3];
        seq[3] = data->tx_pn[2];
        seq[4] = data->tx_pn[1];
        seq[5] = data->tx_pn[0];
    }

    return CCMP_TK_LEN;
}

static char *lib80211_ccmp_print_stats(char *p, void *priv)
{
    struct lib80211_ccmp_data *ccmp = priv;

    p += sprintf(p, "key[%d] alg=CCMP key_set=%d "
             "tx_pn=%02x%02x%02x%02x%02x%02x "
             "rx_pn=%02x%02x%02x%02x%02x%02x "
             "format_errors=%d replays=%d decrypt_errors=%d\n",
             ccmp->key_idx, ccmp->key_set,
             ccmp->tx_pn[0], ccmp->tx_pn[1], ccmp->tx_pn[2],
             ccmp->tx_pn[3], ccmp->tx_pn[4], ccmp->tx_pn[5],
             ccmp->rx_pn[0], ccmp->rx_pn[1], ccmp->rx_pn[2],
             ccmp->rx_pn[3], ccmp->rx_pn[4], ccmp->rx_pn[5],
             ccmp->dot11RSNAStatsCCMPFormatErrors,
             ccmp->dot11RSNAStatsCCMPReplays,
             ccmp->dot11RSNAStatsCCMPDecryptErrors);

    return p;
}

static struct lib80211_crypto_ops lib80211_crypt_ccmp = {
    .name = "CCMP",
    .init = lib80211_ccmp_init,
    .deinit = lib80211_ccmp_deinit,
    .encrypt_mpdu = lib80211_ccmp_encrypt,
    .decrypt_mpdu = lib80211_ccmp_decrypt,
    .encrypt_msdu = NULL,
    .decrypt_msdu = NULL,
    .set_key = lib80211_ccmp_set_key,
    .get_key = lib80211_ccmp_get_key,
    .print_stats = lib80211_ccmp_print_stats,
    .extra_mpdu_prefix_len = CCMP_HDR_LEN,
    .extra_mpdu_postfix_len = CCMP_MIC_LEN,
    .owner = THIS_MODULE,
};

static int __init lib80211_crypto_ccmp_init(void)
{
    return lib80211_register_crypto_ops(&lib80211_crypt_ccmp);
}

static void __exit lib80211_crypto_ccmp_exit(void)
{
    lib80211_unregister_crypto_ops(&lib80211_crypt_ccmp);
}

module_init(lib80211_crypto_ccmp_init);
module_exit(lib80211_crypto_ccmp_exit);