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// SPDX-License-Identifier: GPL-2.0
/*
* Needs something like:
*
* iptables -t nat -A POSTROUTING -o nomatch -j MASQUERADE
*
* so NAT engine attaches a NAT null-binding to each connection.
*
* With unmodified kernels, child or parent will exit with
* "Port number changed" error, even though no port translation
* was requested.
*/
#include <errno.h>
#include <stdbool.h>
#include <stdint.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <time.h>
#include <unistd.h>
#include <arpa/inet.h>
#include <sys/socket.h>
#include <sys/wait.h>
#define LEN 512
#define PORT 56789
#define TEST_TIME 5
static void die(const char *e)
{
perror(e);
exit(111);
}
static void die_port(uint16_t got, uint16_t want)
{
fprintf(stderr, "Port number changed, wanted %d got %d\n", want, ntohs(got));
exit(1);
}
static int udp_socket(void)
{
static const struct timeval tv = {
.tv_sec = 1,
};
int fd = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);
if (fd < 0)
die("socket");
setsockopt(fd, SOL_SOCKET, SO_RCVTIMEO, &tv, sizeof(tv));
return fd;
}
int main(int argc, char *argv[])
{
struct sockaddr_in sa1 = {
.sin_family = AF_INET,
};
struct sockaddr_in sa2 = {
.sin_family = AF_INET,
};
int s1, s2, status;
time_t end, now;
socklen_t plen;
char buf[LEN];
bool child;
sa1.sin_port = htons(PORT);
sa2.sin_port = htons(PORT + 1);
s1 = udp_socket();
s2 = udp_socket();
inet_pton(AF_INET, "127.0.0.11", &sa1.sin_addr);
inet_pton(AF_INET, "127.0.0.12", &sa2.sin_addr);
if (bind(s1, (struct sockaddr *)&sa1, sizeof(sa1)) < 0)
die("bind 1");
if (bind(s2, (struct sockaddr *)&sa2, sizeof(sa2)) < 0)
die("bind 2");
child = fork() == 0;
now = time(NULL);
end = now + TEST_TIME;
while (now < end) {
struct sockaddr_in peer;
socklen_t plen = sizeof(peer);
now = time(NULL);
if (child) {
if (sendto(s1, buf, LEN, 0, (struct sockaddr *)&sa2, sizeof(sa2)) != LEN)
continue;
if (recvfrom(s2, buf, LEN, 0, (struct sockaddr *)&peer, &plen) < 0)
die("child recvfrom");
if (peer.sin_port != htons(PORT))
die_port(peer.sin_port, PORT);
} else {
if (sendto(s2, buf, LEN, 0, (struct sockaddr *)&sa1, sizeof(sa1)) != LEN)
continue;
if (recvfrom(s1, buf, LEN, 0, (struct sockaddr *)&peer, &plen) < 0)
die("parent recvfrom");
if (peer.sin_port != htons((PORT + 1)))
die_port(peer.sin_port, PORT + 1);
}
}
if (child)
return 0;
wait(&status);
if (WIFEXITED(status))
return WEXITSTATUS(status);
return 1;
}
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