iob_net.c

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// SPDX-FileCopyrightText: 2014-2020 abcSup <zifan.tan@gmail.com>
// SPDX-License-Identifier: LGPL-3.0-only
#include <errno.h>
 
#include <rz_crypto.h>
#include <rz_hash.h>
#include <rz_socket.h>
#include <rz_util.h>
 
#include "kd.h"
#include "transport.h"
 
#define BUF_SIZE 4096
 
typedef struct iobnet_t {
    RzSocket *sock;
    bool hasDatakey;
 
    // Internal write buffer
    ut8 write_buf[BUF_SIZE];
    ut32 write_off;
    int write_size;
    // Internal read buffer
    ut8 read_buf[BUF_SIZE];
    ut32 read_off;
    int read_size;
 
    // AES-256 Control Key for enc/decrypting KDNet packets of type KDNET_PACKET_TYPE_CONTROL
    ut8 key[32];
    // AES-256 Data Key for enc/decrypting KDNet packets of type KDNET_PACKET_TYPE_DATA
    ut8 datakey[32];
    // HMAC Key
    ut8 hmackey[KDNET_HMACKEY_SIZE];
    // Lock that protects the above key fields
    RzThreadLock *key_lock;
    // KDNet Protocol version of the debuggee
    ut8 version;
    RzHash *hash;
} iobnet_t;
 
// Constants to convert ASCII to its base36 value
static const char d32[] = "[\\]^_`abcd$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$efghijklmnopqrstuvwxyz{|}~";
// The powers of 36 up to the 13th for 64-bit values
static const ut64 pow36[] = { 1, 36, 1296, 46656, 1679616, 60466176, 2176782336,
    78364164096, 2821109907456, 101559956668416, 3656158440062976,
    131621703842267136, 4738381338321616896 };
 
static ut64 base36_decode(const char *str) {
    ut64 ret = 0;
    size_t i;
    size_t len = strlen(str);
    // 64-bit base36 str has at most 13 characters
    if (len > 13) {
        eprintf("Error: base36_decode supports up to 64-bit values only\n");
        return 0;
    }
    for (i = 0; i < len; i++) {
        char c = str[len - i - 1];
        // "01234567890abcdefghijklmnopqrstuvwxyz"
        if (c < '0' || c > 'z' || ('9' < c && c < 'a')) {
            eprintf("Error: %s is not a valid base36 encoded string\n", str);
            return 0;
        }
        ut8 v = d32[c - '0'];
        // Character does not exist in base36 encoding
        if (v == '$') {
            eprintf("Error: %s is not a valid base36 encoded string\n", str);
            return 0;
        }
        v -= 91;
        // Check for overflow
        if (i == 12) {
            if (v > 3 || UT64_ADD_OVFCHK(ret, v * pow36[i])) {
                printf("Error: base36_decode supports up to 64-bit values only\n");
                return 0;
            }
        }
        ret += v * pow36[i];
    }
    return ret;
}
 
/*
 * @brief Initialize the key for enc/decrypting KDNet packet with the type Data.
 *
 * @param resbuf, the buffer that contains the KDNet Data of a Response packet.
 */
static bool _initializeDatakey(iobnet_t *obj, ut8 *resbuf, int size) {
    RzHashSize digest_size = 0;
    const ut8 *digest = NULL;
    RzHashCfg *md = rz_hash_cfg_new_with_algo2(obj->hash, "sha256");
    if (!md) {
        return false;
    }
 
    if (!rz_hash_cfg_update(md, obj->key, 32) ||
        !rz_hash_cfg_update(md, resbuf, size) ||
        !rz_hash_cfg_final(md) ||
        !(digest = rz_hash_cfg_get_result(md, "sha256", &digest_size))) {
 
        rz_hash_cfg_free(md);
        return false;
    }
 
    memcpy(obj->datakey, digest, digest_size);
    rz_hash_cfg_free(md);
 
    return true;
}
 
static void *iob_net_open(const char *path) {
    size_t i;
 
    iobnet_t *obj = RZ_NEW0(iobnet_t);
    if (!obj) {
        return NULL;
    }
    obj->hash = rz_hash_new();
    obj->key_lock = rz_th_lock_new(false);
    if (!obj->key_lock) {
        free(obj);
        return NULL;
    }
 
    char *host = strdup(path);
    char *port = strchr(host, ':');
    if (RZ_STR_ISEMPTY(port)) {
        free(host);
        free(obj);
        return NULL;
    }
    *port++ = 0;
    char *key = strchr(port, ':');
    if (RZ_STR_ISEMPTY(key)) {
        free(host);
        free(obj);
        return NULL;
    }
    *key++ = 0;
 
    // Decode AES-256 Control Key (x.x.x.x) from base36
    char *nkey;
    for (i = 0; i < 4 && key; key = nkey, i++) {
        nkey = strchr(key, '.');
        if (nkey) {
            *nkey++ = 0;
        }
        rz_write_le64(obj->key + i * 8, base36_decode(key));
    }
 
    // HMAC Key is the negation of AES-256 Control Key bytes
    for (i = 0; i < 32; i++) {
        obj->hmackey[i] = ~(obj->key[i]);
    }
 
    RzSocket *sock = rz_socket_new(0);
    if (!rz_socket_connect_udp(sock, host, port, 1)) {
        free(host);
        free(obj);
        return NULL;
    }
    obj->sock = sock;
 
    free(host);
    return (void *)obj;
}
 
static bool iob_net_close(void *p) {
    int ret = true;
    iobnet_t *obj = (iobnet_t *)p;
 
    if (rz_socket_close(obj->sock)) {
        ret = false;
    }
 
    rz_socket_free(obj->sock);
    rz_hash_free(obj->hash);
    free(obj);
    return ret;
}
 
static bool _encrypt(iobnet_t *obj, ut8 *buf, int size, int type) {
    bool ret = false;
    RzCrypto *cry = rz_crypto_new();
    if (!cry) {
        return false;
    }
    if (!rz_crypto_use(cry, "aes-cbc")) {
        goto end;
    }
 
    // Set AES-256 Key based on the KDNet packet type
    switch (type) {
    case KDNET_PACKET_TYPE_DATA:
        if (!rz_crypto_set_key(cry, obj->datakey, sizeof(obj->datakey), 0, 0)) {
            goto end;
        }
        break;
    case KDNET_PACKET_TYPE_CONTROL: // Control Channel
        if (!rz_crypto_set_key(cry, obj->key, sizeof(obj->key), 0, 0)) {
            goto end;
        }
        break;
    default:
        goto end;
    }
 
    // Set IV to the 16 bytes HMAC at the end of KDNet packet
    if (!rz_crypto_set_iv(cry, buf + size - KDNET_HMAC_SIZE, KDNET_HMAC_SIZE)) {
        goto end;
    }
 
    // Encrypt the buffer except HMAC
    if (rz_crypto_final(cry, buf, size - KDNET_HMAC_SIZE) == 0) {
        goto end;
    }
    // Overwrite the buffer with encrypted data
    int sz;
    const ut8 *encbuf = rz_crypto_get_output(cry, &sz);
    if (!encbuf) {
        goto end;
    }
    memcpy(buf, encbuf, size - KDNET_HMAC_SIZE);
 
    ret = true;
end:
    rz_crypto_free(cry);
    return ret;
}
 
/*
 * KDNet packet format:
 * - KDNet Header, struct kdnet_packet_t
 * - KDNet Data, 8 bytes (seqno (7 bytes) | direction (4 bits) | padsize (4 bits))
 * - KD packet (16-byte aligned)
 * - KDNet HMAC, HMAC generated with the decrypted KDNet Data and KD Packet.
 *
 * The KDNet Data and KD packet are encrypted together with key based on
 * the packet type in KDNet Header.
 */
static ut8 *_createKDNetPacket(iobnet_t *obj, const ut8 *buf, int size, int *osize, ut64 seqno, ut8 type) {
    // Calculate the pad size for KD packet.
    // The KD packet is 16-byte aligned in KDNet.
    ut8 padsize = -(size + 8) & 0x0F;
 
    int encsize = sizeof(kdnet_packet_t) + KDNET_DATA_SIZE + size + padsize + KDNET_HMAC_SIZE;
    ut8 *encbuf = calloc(1, encsize);
    if (!encbuf) {
        return NULL;
    }
 
    // Write KDNet Header
    rz_write_at_be32(encbuf, KDNET_MAGIC, 0); // Magic
    rz_write_at_be8(encbuf, obj->version, 4); // Protocol Number
    rz_write_at_be8(encbuf, type, 5); // Channel Type
    // Write KDNet Data (8 bytes)
    // seqno (7 bytes) | direction (4 bits) | padsize (4 bits)
    // seqno - sequence number
    // direction - 0x0 Debuggee -> Debugger, 0x8 Debugger -> Debuggee
    rz_write_at_be64(encbuf, ((seqno << 8) | 0x8 << 4 | padsize), 6);
 
    // Copy KD Packet from buffer
    memcpy(encbuf + sizeof(kdnet_packet_t) + KDNET_DATA_SIZE, buf, size);
 
    // Generate HMAC from KDNet Data to KD packet
    int off = sizeof(kdnet_packet_t) + KDNET_DATA_SIZE + size + padsize;
 
    const ut8 *digest = NULL;
    RzHashCfg *md = rz_hash_cfg_new_with_algo(obj->hash, "sha256", obj->hmackey, KDNET_HMACKEY_SIZE);
    if (!md) {
        free(encbuf);
        return NULL;
    }
 
    if (!rz_hash_cfg_update(md, encbuf, off) ||
        !rz_hash_cfg_final(md) ||
        !(digest = rz_hash_cfg_get_result(md, "sha256", NULL))) {
        free(encbuf);
        rz_hash_cfg_free(md);
        return NULL;
    }
 
    memcpy(encbuf + off, digest, KDNET_HMAC_SIZE);
    rz_hash_cfg_free(md);
 
    // Encrypt the KDNet Data, KD Packet and padding
    if (!_encrypt(obj, encbuf + sizeof(kdnet_packet_t), encsize - sizeof(kdnet_packet_t), type)) {
        free(encbuf);
        return NULL;
    }
 
    if (osize) {
        *osize = encsize;
    }
    return encbuf;
}
 
static bool _decrypt(iobnet_t *obj, ut8 *buf, int size, int type) {
    bool ret = false;
    RzCrypto *cry = rz_crypto_new();
    if (!cry) {
        return false;
    }
    if (!rz_crypto_use(cry, "aes-cbc")) {
        goto end;
    }
 
    // Set AES-256 Key based on the KDNet packet type
    switch (type) {
    case KDNET_PACKET_TYPE_DATA:
        if (!rz_crypto_set_key(cry, obj->datakey, sizeof(obj->datakey), 0, 1)) {
            goto end;
        }
        break;
    case KDNET_PACKET_TYPE_CONTROL:
        if (!rz_crypto_set_key(cry, obj->key, sizeof(obj->key), 0, 1)) {
            goto end;
        }
        break;
    default:
        goto end;
    }
 
    // Set IV to the 16 bytes HMAC at the end of KDNet packet
    if (!rz_crypto_set_iv(cry, buf + size - KDNET_HMAC_SIZE, KDNET_HMAC_SIZE)) {
        goto end;
    }
 
    // Decrypt the buffer except HMAC
    if (rz_crypto_final(cry, buf, size - KDNET_HMAC_SIZE) == 0) {
        goto end;
    }
    // Overwrite it with decrypted data
    int sz;
    const ut8 *decbuf = rz_crypto_get_output(cry, &sz);
    if (!decbuf) {
        goto end;
    }
    memcpy(buf, decbuf, size - KDNET_HMAC_SIZE);
    ret = true;
 
end:
    rz_crypto_free(cry);
    return ret;
}
 
/*
 * @brief Respond to the Poke packet with a Response packet
 *
 * @param pokedata, the buffer than contains the KDNet Data of a Poke packet
 */
static bool _sendResponsePacket(iobnet_t *obj, const ut8 *pokedata) {
    size_t i;
    int size;
 
    // Create the following buffer as the KD packet in the KDNet Response packet:
    // 0x01
    // 0x02
    // 32 bytes of Client Key from the first 32 bytes data of the Poke packet,
    // 32 bytes of Randomly generated Host Key,
    // 256 bytes of zeroes
    ut8 *resbuf = calloc(1, 322);
    if (!resbuf) {
        return false;
    }
    // 0x01 0x02
    resbuf[0] = 0x01;
    resbuf[1] = 0x02;
    // Copy 32 bytes Client Key after the KDNet Data
    memcpy(resbuf + 2, pokedata + 10, 32);
    // Generate 32 bytes random Host Key
    for (i = 0; i < 32; i++) {
        int rand = rz_num_rand(0xFF);
        resbuf[i + 34] = rand & 0xFF;
    }
 
    // Set seqno to the same seqno in Poke packet
    ut64 seqno = rz_read_be64(pokedata) >> 8;
    ut8 *pkt = _createKDNetPacket(obj, resbuf, 322, &size, seqno, 1);
    if (!pkt) {
        free(resbuf);
        return false;
    }
    rz_th_lock_enter(obj->key_lock);
    if (rz_socket_write(obj->sock, (void *)pkt, size) < 0) {
        free(pkt);
        free(resbuf);
        return false;
    }
 
    _initializeDatakey(obj, resbuf, 322);
    obj->hasDatakey = true;
    rz_th_lock_leave(obj->key_lock);
 
    free(pkt);
    free(resbuf);
    return true;
}
 
static bool _processControlPacket(iobnet_t *obj, const ut8 *ctrlbuf, int size) {
    if (obj->hasDatakey) {
        return true;
    }
    // Read KDNet Data to verify direction flag
    ut64 kdnetdata = rz_read_be64(ctrlbuf);
    if ((kdnetdata & 0x80) != 0) {
        eprintf("Error: KdNet wrong direction flag\n");
        return false;
    }
 
    // Respond to the control packet
    if (!_sendResponsePacket(obj, ctrlbuf)) {
        eprintf("Error: KdNet sending the response packet\n");
        return false;
    }
 
    return true;
}
 
bool _verifyhmac(iobnet_t *obj) {
    const ut8 *digest = NULL;
    RzHashCfg *md = rz_hash_cfg_new_with_algo(obj->hash, "sha256", obj->hmackey, KDNET_HMACKEY_SIZE);
    if (!md) {
        return false;
    }
 
    if (!rz_hash_cfg_update(md, obj->read_buf, obj->read_size - KDNET_HMAC_SIZE) ||
        !rz_hash_cfg_final(md) ||
        !(digest = rz_hash_cfg_get_result(md, "sha256", NULL))) {
        rz_hash_cfg_free(md);
        return false;
    }
 
    bool result = !memcmp(digest, obj->read_buf + obj->read_size - KDNET_HMAC_SIZE, KDNET_HMAC_SIZE);
    rz_hash_cfg_free(md);
 
    return result;
}
 
static int iob_net_read(void *p, uint8_t *obuf, const uint64_t count, const int timeout) {
    kdnet_packet_t pkt = { 0 };
    iobnet_t *obj = (iobnet_t *)p;
 
    if (obj->read_size == 0) {
        do {
            obj->read_size = rz_socket_read(obj->sock, obj->read_buf, BUF_SIZE);
            if (obj->read_size < sizeof(kdnet_packet_t) + KDNET_HMAC_SIZE) {
                // Continue if RzCons breaks
                if (errno == EINTR) {
                    continue;
                }
                goto fail;
            }
            memcpy(&pkt, obj->read_buf, sizeof(kdnet_packet_t));
 
            // Verify the KDNet Header magic
            if (rz_read_be32(obj->read_buf) != KDNET_MAGIC) {
                eprintf("Error: KdNet bad magic\n");
                goto fail;
            }
 
            // Decrypt the KDNet Data and KD Packet
            if (!_decrypt(obj, obj->read_buf + sizeof(kdnet_packet_t), obj->read_size - sizeof(kdnet_packet_t), pkt.type)) {
                goto fail;
            }
 
            // Verify the KDNet HMAC
            if (!_verifyhmac(obj)) {
                eprintf("Error: KdNet failed authentication\n");
                goto fail;
            }
 
            // Process KDNet Control Packets
            if (pkt.type == KDNET_PACKET_TYPE_CONTROL) {
                obj->version = pkt.version;
                if (!_processControlPacket(obj, obj->read_buf + sizeof(kdnet_packet_t), obj->read_size)) {
                    eprintf("Error: KdNet failed to process Control packet\n");
                    goto fail;
                };
                obj->read_size = 0;
            }
        } while (pkt.type == KDNET_PACKET_TYPE_CONTROL);
 
        // Remove padding from the buffer
        ut8 padsize = rz_read_at_be64(obj->read_buf, sizeof(kdnet_packet_t)) & 0xF;
        obj->read_size -= KDNET_HMAC_SIZE + padsize;
 
        // Seek to KD packet
        obj->read_off = sizeof(kdnet_packet_t) + KDNET_DATA_SIZE;
 
        // KD_PACKET_TYPE_UNUSED KD packet does not have a checksum,
        // but kd_read_packet always read for the 4-byte checksum
        if (rz_read_at_be16(obj->read_buf, obj->read_off + 4) == KD_PACKET_TYPE_UNUSED) {
            obj->read_size += 4;
        }
    }
 
    if (count + obj->read_off > obj->read_size) {
        eprintf("Error: KdNet out-of-bounds read\n");
        goto fail;
    }
 
    // Copy remaining data in buffer
    size_t c = RZ_MIN(count, obj->read_size - obj->read_off);
    memcpy(obuf, obj->read_buf + obj->read_off, c);
    obj->read_off += c;
 
    // Reset the internal buffer when finished
    if (obj->read_off == obj->read_size) {
        obj->read_size = 0;
    }
 
    return count;
fail:
    obj->read_size = 0;
    return -1;
}
 
static int iob_net_write(void *p, const uint8_t *buf, const uint64_t count, const int timeout) {
    static ut64 seqno = 1;
    iobnet_t *obj = (iobnet_t *)p;
    if (obj->write_size == 0) {
        // kd_packet_t
        if (count == sizeof(kd_packet_t)) {
            kd_packet_t pkt;
            memcpy(&pkt, buf, sizeof(kd_packet_t));
 
            obj->write_size = sizeof(kd_packet_t) + pkt.length;
            obj->write_off = count;
            memcpy(obj->write_buf, buf, count);
        } else { // breakin packet "b"
            memcpy(obj->write_buf, buf, count);
            obj->write_size = count;
            obj->write_off = count;
        }
    } else {
        memcpy(obj->write_buf + obj->write_off, buf, count);
        obj->write_off += count;
    }
 
    if (obj->write_off == obj->write_size) {
        int size;
        rz_th_lock_enter(obj->key_lock);
        ut8 *pkt = _createKDNetPacket(obj, obj->write_buf, obj->write_size, &size, seqno, 0);
        if (!pkt) {
            rz_th_lock_leave(obj->key_lock);
            return -1;
        }
        if (rz_socket_write(obj->sock, (void *)pkt, size) < 0) {
            free(pkt);
            rz_th_lock_leave(obj->key_lock);
            return -1;
        }
        rz_th_lock_leave(obj->key_lock);
        seqno++;
 
        obj->write_size = 0;
        free(pkt);
    }
 
    return count;
}
 
io_backend_t iob_net = {
    .name = "kdnet",
    .type = KD_IO_NET,
    .init = NULL,
    .deinit = NULL,
    .config = NULL,
    .open = &iob_net_open,
    .close = &iob_net_close,
    .read = &iob_net_read,
    .write = &iob_net_write,
};