ICMP packet obsolete or malformed - sockets

Question

I'm trying to use RAW sockets to create a ping program. The program I wrote however works only for localhost(127.0.0.1) and does not work for other IP addresses. While analyzing the generated packet in Wireshark, I get a message saying "Unknown ICMP (obsolete or malformed?)". It also tells me that the ICMP checksum is incorrect. I'm posting my code here
char source[20], destination[20];
struct sockaddr_in src, dst;
int addrlen= sizeof(src), recvSize, packetSize;
char *packet;
char *buffer;
struct iphdr* ip;
struct iphdr* ip_reply;
struct icmphdr* icmp;
unsigned short csum(unsigned short *, int);
char* getip();
int main(int argc, char* argv[]){
int pingSocket, optval;
struct protoent *protocol;
if(*(argv + 1) && (!(*(argv + 2)))){
//only one argument provided,assume it is the destination server
strncpy(destination, *(argv + 1), 15);
strncpy(source, getip(), 15);
}
inet_pton(AF_INET, destination, &(dst.sin_addr));
inet_pton(AF_INET, source, &(src.sin_addr));
protocol= getprotobyname("ICMP");
printf("Protocol number for ICMP is %d\n",protocol->p_proto);
pingSocket= socket(AF_INET, SOCK_RAW, protocol->p_proto); // Create socket
if(pingSocket< 0){
perror("Error creating socket: ");
exit(3);
}
printf("Socket created with identifier %d\n", pingSocket);
packetSize= sizeof(struct iphdr) + sizeof(struct icmphdr);
packet = (char *) malloc(packetSize);
buffer = (char *) malloc(packetSize);
ip= (struct iphdr*) packet;
icmp= (struct icmphdr*) (packet+ sizeof(struct iphdr));
memset(packet, 0, packetSize);
//Fill up the IP header
ip->ihl= 5;
ip->version= 4;
ip->tos= 0;
ip->tot_len = htons(packetSize);
ip->id = htons(0);
ip->frag_off= 0;
ip->ttl = 255;
ip->protocol= protocol->p_proto;
ip->saddr= src.sin_addr.s_addr;
ip->daddr= dst.sin_addr.s_addr;
setsockopt(pingSocket, protocol->p_proto, IP_HDRINCL, &optval, sizeof(int)); //HDRINCL to tell the kernel that the header is already included
icmp->type= ICMP_ECHO;
icmp->code= 0;
icmp->un.echo.id= rand();
icmp->un.echo.sequence= rand();
icmp->checksum= 0;
icmp->checksum = csum((unsigned short *)icmp, sizeof(struct icmphdr));
dst.sin_family= AF_INET;
sendto(pingSocket, packet, packetSize, 0, (struct sockaddr *)&dst, sizeof(dst));
printf("Sent ping request with size %d to %s\n", ip->tot_len, destination);
printf("Request's IP ID: %d and IP TTL: %d\n", ip->id, ip->ttl);
printf("Packet: \n%s\n", packet);
// Wait for response
if( (recvSize= recvfrom(pingSocket, buffer, sizeof(struct iphdr)+sizeof(struct icmphdr), 0, (struct sockaddr *)&dst, &addrlen)) < 0){
perror("Receive error: ");
}
else{
printf("Received a reply from %s of size %d\n", destination, recvSize);
ip_reply= (struct iphdr*) buffer;
printf("Reply's IP ID: %d and IP TTL: %d\n", ip_reply->id, ip_reply->ttl);
}
free(packet);
free(buffer);
close(pingSocket);
return 0;
}
unsigned short csum(unsigned short *ptr, int nbytes)
{
register long sum;
u_short oddbyte;
register u_short answer;
sum = 0;
while (nbytes > 1) {
sum += *ptr++;
nbytes -= 2;
}
if (nbytes == 1) {
oddbyte = 0;
*((u_char *) & oddbyte) = *(u_char *) ptr;
sum += oddbyte;
}
sum = (sum >> 16) + (sum & 0xffff);
sum += (sum >> 16);
answer = ~sum;
return (answer);
}
char* getip()
{
char buffer[256];
struct hostent* h;
gethostname(buffer, 256);
h = gethostbyname(buffer);
return inet_ntoa(*(struct in_addr *)h->h_addr);
}
I read somewhere that someone fixed this issue by setting the ICMP checksum to Zero first and then calculating it. This however doesn't work for me. Please help me out :)