duiaid.c

// Copyright 2014-2022 Nicholas J. Kain <njkain at gmail dot com>
// SPDX-License-Identifier: MIT
#include <string.h>
#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <arpa/inet.h>
#include <fcntl.h>
#include <limits.h>
#include <errno.h>
#include "nk/log.h"
#include "nk/hwrng.h"
#include "nk/io.h"
#include "duiaid.h"
#include "ndhc.h"

static void get_duid_path(char *duidfile, size_t dlen)
{
    int splen = snprintf(duidfile, dlen, "%s/DUID", state_dir);
    if (splen < 0 || (size_t)splen > dlen)
        suicide("%s: snprintf failed; return=%d\n", __func__, splen);
}

static void get_iaid_path(char *iaidfile, size_t ilen,
                          const uint8_t hwaddr[static 6], size_t hwaddrlen)
{
    if (hwaddrlen != 6)
        suicide("%s: Hardware address length=%zu != 6 bytes\n",
                __func__, hwaddrlen);
    int splen = snprintf
        (iaidfile, ilen,
         "%s/IAID-%2.2x:%2.2x:%2.2x:%2.2x:%2.2x:%2.2x",
         state_dir, hwaddr[0], hwaddr[1], hwaddr[2],
         hwaddr[3], hwaddr[4], hwaddr[5]);
    if (splen < 0 || (size_t)splen > ilen)
        suicide("%s: snprintf failed; return=%d\n", __func__, splen);
}

static int open_duidfile_read(void)
{
    char duidfile[PATH_MAX];
    get_duid_path(duidfile, sizeof duidfile);
    int fd = open(duidfile, O_RDONLY|O_CLOEXEC, 0);
    if (fd < 0) {
        log_line("Failed to open duidfile '%s' for reading: %s\n",
                 duidfile, strerror(errno));
    }
    return fd;
}

static int open_duidfile_write(void)
{
    char duidfile[PATH_MAX];
    get_duid_path(duidfile, sizeof duidfile);
    int fd = open(duidfile, O_WRONLY|O_TRUNC|O_CREAT|O_CLOEXEC, 0644);
    if (fd < 0)
        suicide("Failed to open duidfile '%s' for writing: %s\n",
                duidfile, strerror(errno));
    return fd;
}

static int open_iaidfile_read(const uint8_t hwaddr[static 6], size_t hwaddrlen)
{
    char iaidfile[PATH_MAX];
    get_iaid_path(iaidfile, sizeof iaidfile, hwaddr, hwaddrlen);
    int fd = open(iaidfile, O_RDONLY|O_CLOEXEC, 0);
    if (fd < 0) {
        log_line("Failed to open iaidfile '%s' for reading: %s\n",
                 iaidfile, strerror(errno));
    }
    return fd;
}

static int open_iaidfile_write(const uint8_t hwaddr[static 6],
                               size_t hwaddrlen)
{
    char iaidfile[PATH_MAX];
    get_iaid_path(iaidfile, sizeof iaidfile, hwaddr, hwaddrlen);
    int fd = open(iaidfile, O_WRONLY|O_TRUNC|O_CREAT|O_CLOEXEC, 0644);
    if (fd < 0)
        suicide("Failed to open iaidfile '%s' for writing: %s\n",
                iaidfile, strerror(errno));
    return fd;
}

// We use DUID-UUID (RFC6355)
// It is a 16-bit type=4 in network byte order followed by a 128-byte UUID.
// RFC6355 specifies a RFC4122 UUID, but I simply use a 128-byte random
// value, as the complexity of RFC4122 UUID generation is completely
// unwarranted for DHCPv4.
static size_t generate_duid(char *dest, size_t dlen)
{
    const size_t tlen = sizeof(uint16_t) + 4 * sizeof(uint32_t);
    if (dlen < tlen)
        suicide("%s: dlen < %zu\n", __func__, tlen);
    size_t off = 0;

    uint16_t typefield = htons(4);
    memcpy(dest+off, &typefield, sizeof typefield);
    off += sizeof typefield;

    nk_hwrng_bytes(dest+off, sizeof(uint32_t) * 4);
    off += sizeof(uint32_t) * 4;

    return off;
}

// RFC6355 specifies the IAID as a 32-bit value that uniquely identifies
// a hardware link for a given host.
static size_t generate_iaid(char *dest, size_t dlen)
{
    if (dlen < sizeof(uint32_t))
        suicide("%s: dlen < %zu\n", __func__, sizeof(uint32_t));
    size_t off = 0;

    nk_hwrng_bytes(dest+off, sizeof(uint32_t));
    off += sizeof(uint32_t);
    return off;
}

// Failures are all fatal.
void get_clientid(struct client_config_t *cc)
{
    if (cc->clientid_len > 0)
        return;
    char iaid[sizeof cc->clientid];
    char duid[sizeof cc->clientid];
    size_t iaid_len;
    size_t duid_len;

    int fd = open_iaidfile_read(cc->arp, sizeof cc->arp);
    if (fd < 0) {
        iaid_len = generate_iaid(iaid, sizeof iaid);
        fd = open_iaidfile_write(cc->arp, sizeof cc->arp);
        ssize_t r = safe_write(fd, iaid, iaid_len);
        if (r < 0 || (size_t)r != iaid_len)
            suicide("%s: (%s) failed to write generated IAID.\n",
                    cc->interface, __func__);
    } else {
        ssize_t r = safe_read(fd, iaid, sizeof iaid);
        if (r < 0)
            suicide("%s: (%s) failed to read IAID from file\n",
                    cc->interface, __func__);
        iaid_len = (size_t)r;
    }
    close(fd);

    fd = open_duidfile_read();
    if (fd < 0) {
        duid_len = generate_duid(duid, sizeof duid);
        fd = open_duidfile_write();
        ssize_t r = safe_write(fd, duid, duid_len);
        if (r < 0 || (size_t)r != duid_len)
            suicide("%s: (%s) failed to write generated DUID.\n",
                    cc->interface, __func__);
    } else {
        ssize_t r = safe_read(fd, duid, sizeof duid);
        if (r < 0)
            suicide("%s: (%s) failed to read DUID from file\n",
                    cc->interface, __func__);
        duid_len = (size_t)r;
    }
    close(fd);

    const uint8_t cid_type = 255;
    size_t cdl = sizeof cid_type + iaid_len + duid_len;
    if (cdl > sizeof cc->clientid)
        suicide("%s: (%s) clientid length %zu > %zu\n",
                cc->interface, __func__, cdl, sizeof cc->clientid);

    uint8_t cid_len = 0;
    memcpy(cc->clientid + cid_len, &cid_type, sizeof cid_type);
    cid_len += sizeof cid_type;
    memcpy(cc->clientid + cid_len, iaid, iaid_len);
    cid_len += iaid_len;
    memcpy(cc->clientid + cid_len, duid, duid_len);
    cid_len += duid_len;
    cc->clientid_len = cid_len;
}