// SPDX-License-Identifier: GPL-2.0

#define _GNU_SOURCE

#include <arpa/inet.h>
#include <errno.h>
#include <error.h>
#include <linux/in.h>
#include <netinet/ip.h>
#include <netinet/ip6.h>
#include <netinet/udp.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
#include <unistd.h>

static bool             cfg_do_ipv4;
static bool             cfg_do_ipv6;
static bool             cfg_verbose;
static bool             cfg_overlap;
static bool             cfg_permissive;
static unsigned short   cfg_port = 9000;

const struct in_addr addr4 = { .s_addr = __constant_htonl(INADDR_LOOPBACK + 2) };
const struct in6_addr addr6 = IN6ADDR_LOOPBACK_INIT;

#define IP4_HLEN        (sizeof(struct iphdr))
#define IP6_HLEN        (sizeof(struct ip6_hdr))
#define UDP_HLEN        (sizeof(struct udphdr))

/* IPv6 fragment header lenth. */
#define FRAG_HLEN       8

static int payload_len;
static int max_frag_len;

#define MSG_LEN_MAX     10000   /* Max UDP payload length. */

#define IP4_MF          (1u << 13)  /* IPv4 MF flag. */
#define IP6_MF          (1)  /* IPv6 MF flag. */

#define CSUM_MANGLED_0 (0xffff)

static uint8_t udp_payload[MSG_LEN_MAX];
static uint8_t ip_frame[IP_MAXPACKET];
static uint32_t ip_id = 0xabcd;
static int msg_counter;
static int frag_counter;
static unsigned int seed;

/* Receive a UDP packet. Validate it matches udp_payload. */
static void recv_validate_udp(int fd_udp)
{
        ssize_t ret;
        static uint8_t recv_buff[MSG_LEN_MAX];

        ret = recv(fd_udp, recv_buff, payload_len, 0);
        msg_counter++;

        if (cfg_overlap) {
                if (ret == -1 && (errno == ETIMEDOUT || errno == EAGAIN))
                        return;  /* OK */
                if (!cfg_permissive) {
                        if (ret != -1)
                                error(1, 0, "recv: expected timeout; got %d",
                                        (int)ret);
                        error(1, errno, "recv: expected timeout: %d", errno);
                }
        }

        if (ret == -1)
                error(1, errno, "recv: payload_len = %d max_frag_len = %d",
                        payload_len, max_frag_len);
        if (ret != payload_len)
                error(1, 0, "recv: wrong size: %d vs %d", (int)ret, payload_len);
        if (memcmp(udp_payload, recv_buff, payload_len))
                error(1, 0, "recv: wrong data");
}

static uint32_t raw_checksum(uint8_t *buf, int len, uint32_t sum)
{
        int i;

        for (i = 0; i < (len & ~1U); i += 2) {
                sum += (u_int16_t)ntohs(*((u_int16_t *)(buf + i)));
                if (sum > 0xffff)
                        sum -= 0xffff;
        }

        if (i < len) {
                sum += buf[i] << 8;
                if (sum > 0xffff)
                        sum -= 0xffff;
        }

        return sum;
}

static uint16_t udp_checksum(struct ip *iphdr, struct udphdr *udphdr)
{
        uint32_t sum = 0;
        uint16_t res;

        sum = raw_checksum((uint8_t *)&iphdr->ip_src, 2 * sizeof(iphdr->ip_src),
                                IPPROTO_UDP + (uint32_t)(UDP_HLEN + payload_len));
        sum = raw_checksum((uint8_t *)udphdr, UDP_HLEN, sum);
        sum = raw_checksum((uint8_t *)udp_payload, payload_len, sum);
        res = 0xffff & ~sum;
        if (res)
                return htons(res);
        else
                return CSUM_MANGLED_0;
}

static uint16_t udp6_checksum(struct ip6_hdr *iphdr, struct udphdr *udphdr)
{
        uint32_t sum = 0;
        uint16_t res;

        sum = raw_checksum((uint8_t *)&iphdr->ip6_src, 2 * sizeof(iphdr->ip6_src),
                                IPPROTO_UDP);
        sum = raw_checksum((uint8_t *)&udphdr->len, sizeof(udphdr->len), sum);
        sum = raw_checksum((uint8_t *)udphdr, UDP_HLEN, sum);
        sum = raw_checksum((uint8_t *)udp_payload, payload_len, sum);
        res = 0xffff & ~sum;
        if (res)
                return htons(res);
        else
                return CSUM_MANGLED_0;
}

static void send_fragment(int fd_raw, struct sockaddr *addr, socklen_t alen,
                                int offset, bool ipv6)
{
        int frag_len;
        int res;
        int payload_offset = offset > 0 ? offset - UDP_HLEN : 0;
        uint8_t *frag_start = ipv6 ? ip_frame + IP6_HLEN + FRAG_HLEN :
                                        ip_frame + IP4_HLEN;

        if (offset == 0) {
                struct udphdr udphdr;
                udphdr.source = htons(cfg_port + 1);
                udphdr.dest = htons(cfg_port);
                udphdr.len = htons(UDP_HLEN + payload_len);
                udphdr.check = 0;
                if (ipv6)
                        udphdr.check = udp6_checksum((struct ip6_hdr *)ip_frame, &udphdr);
                else
                        udphdr.check = udp_checksum((struct ip *)ip_frame, &udphdr);
                memcpy(frag_start, &udphdr, UDP_HLEN);
        }

        if (ipv6) {
                struct ip6_hdr *ip6hdr = (struct ip6_hdr *)ip_frame;
                struct ip6_frag *fraghdr = (struct ip6_frag *)(ip_frame + IP6_HLEN);
                if (payload_len - payload_offset <= max_frag_len && offset > 0) {
                        /* This is the last fragment. */
                        frag_len = FRAG_HLEN + payload_len - payload_offset;
                        fraghdr->ip6f_offlg = htons(offset);
                } else {
                        frag_len = FRAG_HLEN + max_frag_len;
                        fraghdr->ip6f_offlg = htons(offset | IP6_MF);
                }
                ip6hdr->ip6_plen = htons(frag_len);
                if (offset == 0)
                        memcpy(frag_start + UDP_HLEN, udp_payload,
                                frag_len - FRAG_HLEN - UDP_HLEN);
                else
                        memcpy(frag_start, udp_payload + payload_offset,
                                frag_len - FRAG_HLEN);
                frag_len += IP6_HLEN;
        } else {
                struct ip *iphdr = (struct ip *)ip_frame;
                if (payload_len - payload_offset <= max_frag_len && offset > 0) {
                        /* This is the last fragment. */
                        frag_len = IP4_HLEN + payload_len - payload_offset;
                        iphdr->ip_off = htons(offset / 8);
                } else {
                        frag_len = IP4_HLEN + max_frag_len;
                        iphdr->ip_off = htons(offset / 8 | IP4_MF);
                }
                iphdr->ip_len = htons(frag_len);
                if (offset == 0)
                        memcpy(frag_start + UDP_HLEN, udp_payload,
                                frag_len - IP4_HLEN - UDP_HLEN);
                else
                        memcpy(frag_start, udp_payload + payload_offset,
                                frag_len - IP4_HLEN);
        }

        res = sendto(fd_raw, ip_frame, frag_len, 0, addr, alen);
        if (res < 0 && errno != EPERM)
                error(1, errno, "send_fragment");
        if (res >= 0 && res != frag_len)
                error(1, 0, "send_fragment: %d vs %d", res, frag_len);

        frag_counter++;
}

static void send_udp_frags(int fd_raw, struct sockaddr *addr,
                                socklen_t alen, bool ipv6)
{
        struct ip *iphdr = (struct ip *)ip_frame;
        struct ip6_hdr *ip6hdr = (struct ip6_hdr *)ip_frame;
        int res;
        int offset;
        int frag_len;

        /* Send the UDP datagram using raw IP fragments: the 0th fragment
         * has the UDP header; other fragments are pieces of udp_payload
         * split in chunks of frag_len size.
         *
         * Odd fragments (1st, 3rd, 5th, etc.) are sent out first, then
         * even fragments (0th, 2nd, etc.) are sent out.
         */
        if (ipv6) {
                struct ip6_frag *fraghdr = (struct ip6_frag *)(ip_frame + IP6_HLEN);
                ((struct sockaddr_in6 *)addr)->sin6_port = 0;
                memset(ip6hdr, 0, sizeof(*ip6hdr));
                ip6hdr->ip6_flow = htonl(6<<28);  /* Version. */
                ip6hdr->ip6_nxt = IPPROTO_FRAGMENT;
                ip6hdr->ip6_hops = 255;
                ip6hdr->ip6_src = addr6;
                ip6hdr->ip6_dst = addr6;
                fraghdr->ip6f_nxt = IPPROTO_UDP;
                fraghdr->ip6f_reserved = 0;
                fraghdr->ip6f_ident = htonl(ip_id++);
        } else {
                memset(iphdr, 0, sizeof(*iphdr));
                iphdr->ip_hl = 5;
                iphdr->ip_v = 4;
                iphdr->ip_tos = 0;
                iphdr->ip_id = htons(ip_id++);
                iphdr->ip_ttl = 0x40;
                iphdr->ip_p = IPPROTO_UDP;
                iphdr->ip_src.s_addr = htonl(INADDR_LOOPBACK);
                iphdr->ip_dst = addr4;
                iphdr->ip_sum = 0;
        }

        /* Occasionally test in-order fragments. */
        if (!cfg_overlap && (rand() % 100 < 15)) {
                offset = 0;
                while (offset < (UDP_HLEN + payload_len)) {
                        send_fragment(fd_raw, addr, alen, offset, ipv6);
                        offset += max_frag_len;
                }
                return;
        }

        /* Occasionally test IPv4 "runs" (see net/ipv4/ip_fragment.c) */
        if (!cfg_overlap && (rand() % 100 < 20) &&
                        (payload_len > 9 * max_frag_len)) {
                offset = 6 * max_frag_len;
                while (offset < (UDP_HLEN + payload_len)) {
                        send_fragment(fd_raw, addr, alen, offset, ipv6);
                        offset += max_frag_len;
                }
                offset = 3 * max_frag_len;
                while (offset < 6 * max_frag_len) {
                        send_fragment(fd_raw, addr, alen, offset, ipv6);
                        offset += max_frag_len;
                }
                offset = 0;
                while (offset < 3 * max_frag_len) {
                        send_fragment(fd_raw, addr, alen, offset, ipv6);
                        offset += max_frag_len;
                }
                return;
        }

        /* Odd fragments. */
        offset = max_frag_len;
        while (offset < (UDP_HLEN + payload_len)) {
                send_fragment(fd_raw, addr, alen, offset, ipv6);
                /* IPv4 ignores duplicates, so randomly send a duplicate. */
                if (rand() % 100 == 1)
                        send_fragment(fd_raw, addr, alen, offset, ipv6);
                offset += 2 * max_frag_len;
        }

        if (cfg_overlap) {
                /* Send an extra random fragment.
                 *
                 * Duplicates and some fragments completely inside
                 * previously sent fragments are dropped/ignored. So
                 * random offset and frag_len can result in a dropped
                 * fragment instead of a dropped queue/packet. Thus we
                 * hard-code offset and frag_len.
                 */
                if (max_frag_len * 4 < payload_len || max_frag_len < 16) {
                        /* not enough payload for random offset and frag_len. */
                        offset = 8;
                        frag_len = UDP_HLEN + max_frag_len;
                } else {
                        offset = rand() % (payload_len / 2);
                        frag_len = 2 * max_frag_len + 1 + rand() % 256;
                }
                if (ipv6) {
                        struct ip6_frag *fraghdr = (struct ip6_frag *)(ip_frame + IP6_HLEN);
                        /* sendto() returns EINVAL if offset + frag_len is too small. */
                        /* In IPv6 if !!(frag_len % 8), the fragment is dropped. */
                        frag_len &= ~0x7;
                        fraghdr->ip6f_offlg = htons(offset / 8 | IP6_MF);
                        ip6hdr->ip6_plen = htons(frag_len);
                        frag_len += IP6_HLEN;
                } else {
                        frag_len += IP4_HLEN;
                        iphdr->ip_off = htons(offset / 8 | IP4_MF);
                        iphdr->ip_len = htons(frag_len);
                }
                res = sendto(fd_raw, ip_frame, frag_len, 0, addr, alen);
                if (res < 0 && errno != EPERM)
                        error(1, errno, "sendto overlap: %d", frag_len);
                if (res >= 0 && res != frag_len)
                        error(1, 0, "sendto overlap: %d vs %d", (int)res, frag_len);
                frag_counter++;
        }

        /* Event fragments. */
        offset = 0;
        while (offset < (UDP_HLEN + payload_len)) {
                send_fragment(fd_raw, addr, alen, offset, ipv6);
                /* IPv4 ignores duplicates, so randomly send a duplicate. */
                if (rand() % 100 == 1)
                        send_fragment(fd_raw, addr, alen, offset, ipv6);
                offset += 2 * max_frag_len;
        }
}

static void run_test(struct sockaddr *addr, socklen_t alen, bool ipv6)
{
        int fd_tx_raw, fd_rx_udp;
        /* Frag queue timeout is set to one second in the calling script;
         * socket timeout should be just a bit longer to avoid tests interfering
         * with each other.
         */
        struct timeval tv = { .tv_sec = 1, .tv_usec = 10 };
        int idx;
        int min_frag_len = 8;

        /* Initialize the payload. */
        for (idx = 0; idx < MSG_LEN_MAX; ++idx)
                udp_payload[idx] = idx % 256;

        /* Open sockets. */
        fd_tx_raw = socket(addr->sa_family, SOCK_RAW, IPPROTO_RAW);
        if (fd_tx_raw == -1)
                error(1, errno, "socket tx_raw");

        fd_rx_udp = socket(addr->sa_family, SOCK_DGRAM, 0);
        if (fd_rx_udp == -1)
                error(1, errno, "socket rx_udp");
        if (bind(fd_rx_udp, addr, alen))
                error(1, errno, "bind");
        /* Fail fast. */
        if (setsockopt(fd_rx_udp, SOL_SOCKET, SO_RCVTIMEO, &tv, sizeof(tv)))
                error(1, errno, "setsockopt rcv timeout");

        for (payload_len = min_frag_len; payload_len < MSG_LEN_MAX;
                        payload_len += (rand() % 4096)) {
                if (cfg_verbose)
                        printf("payload_len: %d\n", payload_len);

                if (cfg_overlap) {
                        /* With overlaps, one send/receive pair below takes
                         * at least one second (== timeout) to run, so there
                         * is not enough test time to run a nested loop:
                         * the full overlap test takes 20-30 seconds.
                         */
                        max_frag_len = min_frag_len +
                                rand() % (1500 - FRAG_HLEN - min_frag_len);
                        send_udp_frags(fd_tx_raw, addr, alen, ipv6);
                        recv_validate_udp(fd_rx_udp);
                } else {
                        /* Without overlaps, each packet reassembly (== one
                         * send/receive pair below) takes very little time to
                         * run, so we can easily afford more thourough testing
                         * with a nested loop: the full non-overlap test takes
                         * less than one second).
                         */
                        max_frag_len = min_frag_len;
                        do {
                                send_udp_frags(fd_tx_raw, addr, alen, ipv6);
                                recv_validate_udp(fd_rx_udp);
                                max_frag_len += 8 * (rand() % 8);
                        } while (max_frag_len < (1500 - FRAG_HLEN) &&
                                 max_frag_len <= payload_len);
                }
        }

        /* Cleanup. */
        if (close(fd_tx_raw))
                error(1, errno, "close tx_raw");
        if (close(fd_rx_udp))
                error(1, errno, "close rx_udp");

        if (cfg_verbose)
                printf("processed %d messages, %d fragments\n",
                        msg_counter, frag_counter);

        fprintf(stderr, "PASS\n");
}


static void run_test_v4(void)
{
        struct sockaddr_in addr = {0};

        addr.sin_family = AF_INET;
        addr.sin_port = htons(cfg_port);
        addr.sin_addr = addr4;

        run_test((void *)&addr, sizeof(addr), false /* !ipv6 */);
}

static void run_test_v6(void)
{
        struct sockaddr_in6 addr = {0};

        addr.sin6_family = AF_INET6;
        addr.sin6_port = htons(cfg_port);
        addr.sin6_addr = addr6;

        run_test((void *)&addr, sizeof(addr), true /* ipv6 */);
}

static void parse_opts(int argc, char **argv)
{
        int c;

        while ((c = getopt(argc, argv, "46opv")) != -1) {
                switch (c) {
                case '4':
                        cfg_do_ipv4 = true;
                        break;
                case '6':
                        cfg_do_ipv6 = true;
                        break;
                case 'o':
                        cfg_overlap = true;
                        break;
                case 'p':
                        cfg_permissive = true;
                        break;
                case 'v':
                        cfg_verbose = true;
                        break;
                default:
                        error(1, 0, "%s: parse error", argv[0]);
                }
        }
}

int main(int argc, char **argv)
{
        parse_opts(argc, argv);
        seed = time(NULL);
        srand(seed);
        /* Print the seed to track/reproduce potential failures. */
        printf("seed = %d\n", seed);

        if (cfg_do_ipv4)
                run_test_v4();
        if (cfg_do_ipv6)
                run_test_v6();

        return 0;
}