Custom IP header for ICMP packet not working - c

Question

I'm trying to make an ICMP packet with a custom IP header.
When I disable IP_HDRINCL to use the default IP header and cut out all the IP header related code, it works (I checked the checksums of the code below and the code that works with default headers, the ICMP packet is definitely valid in the code below).
The issue arrives when trying to use my own IP header, I don't receive any ICMP packets, indicating the packet didn't properly transmit or something went wrong.
I'm on Ubuntu 16.04 and compiling with GCC with the flags -std=c11 -Wall -Wextra -pedantic
#include <errno.h>
#include <sys/socket.h>
#include <netdb.h>
#include <netinet/in.h>
#include <netinet/ip.h>
#include <netinet/udp.h>
#include <netinet/ip_icmp.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <sys/time.h>
#include <arpa/inet.h>
#define PACKETSIZE 256
// Packet struct
struct packet {
struct iphdr ip; // IP Header
struct icmphdr hdr; // ICMP Header
char msg[PACKETSIZE - sizeof(struct icmphdr) - sizeof(struct iphdr)]; // Message
};
// Checksum function
unsigned short checksum(void *b, int len) {
unsigned short *buf = b;
unsigned int sum = 0;
unsigned short result;
for (sum = 0; len > 1; len -= 2) {
sum += *buf++;
}
if (len == 1) sum += *(unsigned char*)buf;
sum = (sum >> 16) + (sum & 0xFFFF);
sum += (sum >> 16);
result = ~sum;
return result;
}
int main(int argc, char* argv[])
{
// Enough arguments
if (argc < 2) {
printf("usage: ./tracert <server>\n");
return EXIT_FAILURE;
}
// Variables
struct hostent *hname;
struct sockaddr_in addr;
unsigned int i;
int sockfd, seq = 1;
struct packet pckt;
socklen_t len;
char buf[1024];
// Get host from domain
hname = gethostbyname(argv[1]);
memset(&addr, 0, sizeof(addr));
addr.sin_family = hname->h_addrtype;
addr.sin_port = htons(6969);
addr.sin_addr.s_addr = *(long *)hname->h_addr_list[0];
// Create ICMP RAW socket
sockfd = socket(AF_INET, SOCK_RAW, IPPROTO_ICMP);
if (sockfd < 0) {
printf("error on socket creation\n");
return EXIT_FAILURE;;
}
if (setsockopt(sockfd, IPPROTO_IP, IP_HDRINCL, &seq, sizeof(seq)) < 0) {
printf("error on default ip header settings\n");
return EXIT_FAILURE;
}
// Loop and receive/send packets
while (1) {
// Make packet
memset(&pckt, 0, sizeof(pckt));
// IP Header
pckt.ip.version = 4;
pckt.ip.ihl = 5;
pckt.ip.tot_len = htons(sizeof(pckt));
pckt.ip.ttl = 255;
pckt.ip.protocol = IPPROTO_ICMP;
pckt.ip.saddr = inet_addr("192.168.1.1");
pckt.ip.daddr = addr.sin_addr.s_addr;
pckt.ip.check = checksum(&pckt, sizeof(struct iphdr));
// ICMP Header
pckt.hdr.type = ICMP_ECHO;
pckt.hdr.un.echo.id = 0;
for (i = 0; i < sizeof(pckt.msg) - 1; i++) {
pckt.msg[i] = i+'0';
}
pckt.msg[i] = 0;
pckt.hdr.un.echo.sequence = seq;
pckt.hdr.checksum = checksum(&pckt.hdr, sizeof(struct icmphdr) + sizeof(pckt.msg));
// Send packet
if (sendto(sockfd, &pckt, sizeof(pckt), 0, (struct sockaddr*)&addr, sizeof(addr)) <= 0) {
printf("error on sending packet\n");
return EXIT_FAILURE;
}
// Receive packet
len = sizeof(addr);
memset(buf, 0, sizeof(buf));
if (recvfrom(sockfd, buf, sizeof(buf), 0, (struct sockaddr*)&addr, &len) > 0) {
printf("packet received\n");
// Do more stuff here later...
}
// The while is there for later, for now I just want to send one packet
return EXIT_SUCCESS;
}
close(sockfd);
return EXIT_SUCCESS;
}