src/tcpedit/checksum.c

/* $Id$ */

/*
 *   Copyright (c) 2001-2010 Aaron Turner <aturner at synfin dot net>
 *   Copyright (c) 2013-2022 Fred Klassen <tcpreplay at appneta dot com> - AppNeta
 *
 *   The Tcpreplay Suite of tools is free software: you can redistribute it
 *   and/or modify it under the terms of the GNU General Public License as
 *   published by the Free Software Foundation, either version 3 of the
 *   License, or with the authors permission any later version.
 *
 *   The Tcpreplay Suite is distributed in the hope that it will be useful,
 *   but WITHOUT ANY WARRANTY; without even the implied warranty of
 *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *   GNU General Public License for more details.
 *
 *   You should have received a copy of the GNU General Public License
 *   along with the Tcpreplay Suite.  If not, see <http://www.gnu.org/licenses/>.
 */

/*
 * This code is heavily based on (some might even say stolen from) Mike Shiffman's
 * checksumming code from Libnet 1.1.3
 */

#include "checksum.h"
#include "config.h"

static int do_checksum_math(uint16_t *, int);

/**
 * Returns -1 on error and 0 on success, 1 on warn
 */
int
do_checksum(tcpedit_t *tcpedit, uint8_t *data, int proto, int len, const u_char *end_ptr)
{
    ipv4_hdr_t *ipv4;
    ipv6_hdr_t *ipv6;
    tcp_hdr_t *tcp;
    udp_hdr_t *udp;
    icmpv4_hdr_t *icmp;
    icmpv6_hdr_t *icmp6;
    u_char *layer;
    int ip_hl;
    int sum;

    sum = 0;
    ipv4 = NULL;
    ipv6 = NULL;
    assert(data);

    if (!data || len <= 0) {
        tcpedit_seterr(tcpedit, "%s", "length of data must be > 0");
        return TCPEDIT_ERROR;
    }

    ipv4 = (ipv4_hdr_t *)data;
    if (ipv4->ip_v == 6) {
        ipv6 = (ipv6_hdr_t *)data;
        ipv4 = NULL;

        proto = get_ipv6_l4proto(ipv6, end_ptr);
        dbgx(3, "layer4 proto is 0x%hx", (uint16_t)proto);

        layer = (u_char *)get_layer4_v6(ipv6, end_ptr);
        if (!layer) {
            tcpedit_setwarn(tcpedit, "%s", "Packet to short for checksum");
            return TCPEDIT_WARN;
        }

        ip_hl = (int)(layer - (u_char *)data);
        dbgx(3, "ip_hl proto is 0x%d", ip_hl);

        len -= (ip_hl - TCPR_IPV6_H);
    } else {
        ip_hl = ipv4->ip_hl << 2;
    }

    switch (proto) {
    case IPPROTO_TCP:
        if (len < (int)sizeof(tcp_hdr_t)) {
            tcpedit_setwarn(tcpedit, "%s", "Unable to checksum TCP with insufficient L4 data");
            return TCPEDIT_WARN;
        }

        tcp = (tcp_hdr_t *)(data + ip_hl);
#ifdef STUPID_SOLARIS_CHECKSUM_BUG
        tcp->th_sum = tcp->th_off << 2;
        return (TCPEDIT_OK);
#endif
        tcp->th_sum = 0;

        /* Note, we do both src & dst IP's at the same time, that's why the
         * length is 2x a single IP
         */
        if (ipv6 != NULL) {
            sum = do_checksum_math((uint16_t *)&ipv6->ip_src, 32);
        } else {
            sum = do_checksum_math((uint16_t *)&ipv4->ip_src, 8);
        }
        sum += ntohs(IPPROTO_TCP + len);
        sum += do_checksum_math((uint16_t *)tcp, len);
        tcp->th_sum = CHECKSUM_CARRY(sum);
        break;

    case IPPROTO_UDP:
        if (len < (int)sizeof(udp_hdr_t)) {
            tcpedit_setwarn(tcpedit, "%s", "Unable to checksum UDP with insufficient L4 data");
            return TCPEDIT_WARN;
        }
        udp = (udp_hdr_t *)(data + ip_hl);
        /* No need to recalculate UDP checksums if already 0 */
        if (udp->uh_sum == 0)
            break;
        udp->uh_sum = 0;
        if (ipv6 != NULL) {
            sum = do_checksum_math((uint16_t *)&ipv6->ip_src, 32);
        } else {
            sum = do_checksum_math((uint16_t *)&ipv4->ip_src, 8);
        }
        sum += ntohs(IPPROTO_UDP + len);
        sum += do_checksum_math((uint16_t *)udp, len);
        udp->uh_sum = CHECKSUM_CARRY(sum);
        break;

    case IPPROTO_ICMP:
        if (len < (int)sizeof(icmpv4_hdr_t)) {
            tcpedit_setwarn(tcpedit, "%s", "Unable to checksum ICMP with insufficient L4 data");
            return TCPEDIT_WARN;
        }
        icmp = (icmpv4_hdr_t *)(data + ip_hl);
        icmp->icmp_sum = 0;
        if (ipv6 != NULL) {
            sum = do_checksum_math((uint16_t *)&ipv6->ip_src, 32);
            icmp->icmp_sum = CHECKSUM_CARRY(sum);
        }
        sum += do_checksum_math((uint16_t *)icmp, len);
        icmp->icmp_sum = CHECKSUM_CARRY(sum);
        break;

    case IPPROTO_ICMP6:
        if (len < (int)sizeof(icmpv6_hdr_t)) {
            tcpedit_setwarn(tcpedit, "%s", "Unable to checksum ICMP6 with insufficient L4 data");
            return TCPEDIT_WARN;
        }
        icmp6 = (icmpv6_hdr_t *)(data + ip_hl);
        icmp6->icmp_sum = 0;
        if (ipv6 != NULL) {
            sum = do_checksum_math((u_int16_t *)&ipv6->ip_src, 32);
        }
        sum += ntohs(IPPROTO_ICMP6 + len);
        sum += do_checksum_math((u_int16_t *)icmp6, len);
        icmp6->icmp_sum = CHECKSUM_CARRY(sum);
        break;

    default:
        if (ipv4) {
            ipv4->ip_sum = 0;
            sum = do_checksum_math((uint16_t *)data, ip_hl);
            ipv4->ip_sum = CHECKSUM_CARRY(sum);
        } else {
            tcpedit_setwarn(tcpedit, "Unsupported protocol for checksum: 0x%x", proto);
            return TCPEDIT_WARN;
        }
    }

    return TCPEDIT_OK;
}

/**
 * code to do a ones-compliment checksum
 */
static int
do_checksum_math(uint16_t *data, int len)
{
    int sum = 0;
    union {
        uint16_t s;
        uint8_t b[2];
    } pad;

    while (len > 1) {
        sum += *data++;
        len -= 2;
    }

    if (len == 1) {
        pad.b[0] = *(uint8_t *)data;
        pad.b[1] = 0;
        sum += pad.s;
    }

    return (sum);
}