Я пытаюсь отправить необработанный пакет с использованием UDP с заголовками IP и UDP, которые я создал в своем коде.Необработанный пакет успешно инициализирован с помощью socket(PF_INET, SOCK_RAW, IPPROTO_UDP), а параметр сокета установлен с помощью setsockopt(sd, IPPROTO_IP, IP_HDRINCL, val, sizeof(int)).
. Проблема заключается в том, что при отправке пакета с использованием sendto() появляется сообщение об ошибке «Слишком длинное сообщение».
Мой заголовок IP составляет 20 байтов, а заголовок UDP - 8 байтов, а мои данные - 12 байтов.Таким образом, всего 40 байтов.Это не может быть слишком длинным для одного пакета UDP.Может кто-нибудь помочь?
Тип val - это указатель на int
Вот мой код:
#include <unistd.h>
#include <stdio.h>
#include <sys/socket.h>
#include <netinet/ip.h>
#include <netinet/udp.h>
#include <string.h>
#include <stdlib.h>
#include <arpa/inet.h>
#include <netinet/in.h>
//The packet length in byes
#define PCKT_LEN 50
//Date size in bytes
#define DATA_SIZE 12
//PseudoHeader struct used to calculate UDP checksum.
typedef struct PseudoHeader{
unsigned long int source_ip;
unsigned long int dest_ip;
unsigned char reserved;
unsigned char protocol;
unsigned short int udp_length;
}PseudoHeader;
// Ripped from Richard Stevans Book
unsigned short ComputeChecksum(unsigned char *data, int len)
{
long sum = 0; /* assume 32 bit long, 16 bit short */
unsigned short *temp = (unsigned short *)data;
while(len > 1){
sum += *temp++;
if(sum & 0x80000000) /* if high order bit set, fold */
sum = (sum & 0xFFFF) + (sum >> 16);
len -= 2;
}
if(len) /* take care of left over byte */
sum += (unsigned short) *((unsigned char *)temp);
while(sum>>16)
sum = (sum & 0xFFFF) + (sum >> 16);
return ~sum;
}
int BindRawSocketToInterface(int rawsock, char *addr, short int port)
{
struct sockaddr_in s_addr;
s_addr.sin_family = AF_INET;
s_addr.sin_addr.s_addr = inet_addr(addr);
s_addr.sin_port = htons(port);
if((bind(rawsock, (struct sockaddr *)&s_addr, sizeof(s_addr)))== -1)
{
perror("Error binding raw socket to interface\n");
exit(-1);
}
return 1;
}
// Fabricate the IP header or we can use the
// standard header structures but assign our own values.
struct ip *CreateIPHeader(char *srcip, char *destip)
{
struct ip *ip_header;
ip_header = (struct ip *)malloc(sizeof(struct ip));
ip_header->ip_v = 4;
ip_header->ip_hl = 5;
ip_header->ip_tos = 0;
ip_header->ip_len = htons(sizeof(struct ip) + sizeof(struct udphdr) + DATA_SIZE);
ip_header->ip_id = htons(111);
ip_header->ip_off = 0;
ip_header->ip_ttl = 111;
ip_header->ip_p = IPPROTO_TCP;
ip_header->ip_sum = 0; /* We will calculate the checksum later */
inet_pton(AF_INET, srcip, &ip_header->ip_src);
inet_pton(AF_INET, destip, &ip_header->ip_dst);
/* Calculate the IP checksum now :
The IP Checksum is only over the IP header */
ip_header->ip_sum = ComputeChecksum((unsigned char *)ip_header, ip_header->ip_hl*4);
return (ip_header);
}
// Creates a the UDP header.
struct udphdr *CreateUdpHeader(char *srcport, char *destport )
{
struct udphdr *udp_header;
/* Check netinet/udp.h for header definiation */
udp_header = (struct udphdr *)malloc(sizeof(struct udphdr));
udp_header->source = htons(atoi(srcport));
udp_header->dest = htons(atoi(destport));
udp_header->len = htons(sizeof(struct udphdr) + DATA_SIZE); //TODO: need to specify this
udp_header->check = htons(0);
return (udp_header);
}
void CreatePseudoHeaderAndComputeUdpChecksum(struct udphdr *udp_header, struct ip *ip_header, unsigned char *data)
{
/*The TCP Checksum is calculated over the PseudoHeader + TCP header +Data*/
/* Find the size of the TCP Header + Data */
int segment_len = ntohs(ip_header->ip_len) - ip_header->ip_hl*4;
/* Total length over which TCP checksum will be computed */
int header_len = sizeof(PseudoHeader) + segment_len;
/* Allocate the memory */
unsigned char *hdr = (unsigned char *)malloc(header_len);
/* Fill in the pseudo header first */
PseudoHeader *pseudo_header = (PseudoHeader *)hdr;
pseudo_header->source_ip = ip_header->ip_src.s_addr;
pseudo_header->dest_ip = ip_header->ip_dst.s_addr;
pseudo_header->reserved = 0;
pseudo_header->protocol = ip_header->ip_p;
pseudo_header->udp_length = htons(segment_len);
/* Now copy TCP */
memcpy((hdr + sizeof(PseudoHeader)), (void *)udp_header, 8);
/* Now copy the Data */
memcpy((hdr + sizeof(PseudoHeader) + 8), data, DATA_SIZE);
/* Calculate the Checksum */
udp_header->check = ComputeChecksum(hdr, header_len);
/* Free the PseudoHeader */
free(hdr);
}
// Source IP, source port, target IP, target port from the command line arguments
int main(int argc, char *argv[])
{
int sd;
char buffer[PCKT_LEN];
char *data = "Hello World!";
// Source and destination addresses: IP and port
struct sockaddr_in to_addr;
int one = 1;
const int *val = &one;
printf("IP Header Size: %lu \n", sizeof(struct ip));
printf("UDP Header Size: %lu \n", sizeof(struct udphdr));
printf("Data Size: %d\n", DATA_SIZE);
printf("IP Total: %lu \n", sizeof(struct ip) + sizeof(struct udphdr) + DATA_SIZE);
memset(buffer, 0, PCKT_LEN);
if(argc != 5)
{
printf("- Invalid parameters!!!\n");
printf("- Usage %s <source hostname/IP> <source port> <target hostname/IP> <target port>\n", argv[0]);
exit(-1);
}
// Create a raw socket with UDP protocol
sd = socket(PF_INET, SOCK_RAW, IPPROTO_UDP);
if(sd < 0)
{
perror("socket() error");
exit(-1);
}
else
printf("socket() - Using SOCK_RAW socket and UDP protocol is OK.\n");
//Bind the socket to the source address and port.
BindRawSocketToInterface(sd, argv[1], atoi(argv[2]));
// Inform the kernel do not fill up the packet structure. we will build our own...
if(setsockopt(sd, IPPROTO_IP, IP_HDRINCL, val, sizeof(int)) < 0)
{
perror("setsockopt() error");
close(sd);
exit(-1);
}
else
printf("setsockopt() is OK.\n");
// The source is redundant, may be used later if needed
// The address family
to_addr.sin_family = AF_INET;
to_addr.sin_addr.s_addr = inet_addr(argv[3]);
to_addr.sin_port = htons(atoi(argv[4]));
//Create the IP header.
struct ip *ip_header = CreateIPHeader(argv[1], argv[3]);
//Create the UDP header.
struct udphdr *udp_header = CreateUdpHeader(argv[2], argv[4]);
//Compute UDP checksum
CreatePseudoHeaderAndComputeUdpChecksum(udp_header, ip_header, (unsigned char*)data);
//Copy IP header, UDP header, and data to the packet buffer.
memcpy(buffer, ip_header, sizeof(struct ip));
memcpy(buffer + sizeof(struct ip), udp_header, 8 /*sizeof(struct udphdr)*/);
memcpy(buffer + sizeof(struct ip) + 8, data, DATA_SIZE);
printf("Using raw socket and UDP protocol\n");
printf("Using Source IP: %s port: %u, Target IP: %s port: %u.\n", argv[1], atoi(argv[2]), argv[3], atoi(argv[4]));
if(sendto(sd, buffer, htons(20)/*ip_header->ip_len*/, 0, (struct sockaddr *)&to_addr, sizeof(to_addr)) < 0)
{
perror("sendto() error");
}
else
{
printf("sendto() is OK.\n");
}
free(ip_header);
free(udp_header);
close(sd);
return 0;
}