[英]create SOCK_RAW socket just for sending data without any recvform()
如果我創建一個類型為SOCK_RAW的套接字只發送一些數據而不接收任何數據,那么當內核繼續接收網絡數據包並將其數據報復制到somebuffer(應用程序?)時是否有任何問題。 換句話說,在填充一些緩沖區后會發生什么? 錯誤或忽略?
我不知道如何防止內核將數據報副本傳遞給我的應用程序。
參考http://sock-raw.org/papers/sock_raw 0x4 raw_input
在IP層處理新的傳入IP數據報之后,它調用ip_local_deliver_finish()內核函數,該函數負責通過檢查IP頭的協議字段來調用已注冊的傳輸協議處理程序(請記住上面)。 但是,在將數據報傳遞給處理程序之前,它每次都會檢查應用程序是否創建了具有相同協議編號的原始套接字。 如果有一個或多個此類應用程序,它會復制數據報並將其傳遞給它們。
您可以使用shutdown(2)來關閉套接字的接收部分。 請參閱關閉手冊頁
編輯:我發現shutdown只適用於連接(即TCP)套接字。 使用Raw套接字,有兩種可能性:
以下是如何將接收緩沖區大小設置為0:
int opt = 0;
setsockopt(sock_fd, SOL_SOCKET, SO_RCVBUF, &opt, sizeof(opt));
測試
/**
* @file raw_print_pkt.c
* @brief
* @author Airead Fan <fgh1987168@gmail.com>
* @date 2012/08/22 12:35:22
*/
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <sys/ioctl.h>
#include <netinet/ip.h>
#include <netinet/tcp.h>
int main(int argc, char *argv[])
{
int s;
ssize_t rn; /* receive number */
struct sockaddr_in saddr;
char packet[4096];
int count;
if ((s = socket(AF_INET, SOCK_RAW, IPPROTO_TCP)) < 0) {
perror("error:");
exit(EXIT_FAILURE);
}
memset(packet, 0, sizeof(packet));
socklen_t *len = (socklen_t *)sizeof(saddr);
int fromlen = sizeof(saddr);
int opt = 0;
count = 0;
while(1) {
if ((rn = recvfrom(s, (char *)&packet, sizeof(packet), 0,
(struct sockaddr *)&saddr, &fromlen)) < 0)
perror("packet receive error:");
if (rn == 0) {
printf("the peer has performed an orderly shutdown\n");
break;
}
printf("[%d] rn = %lu \n", count++, rn);
if (count == 16) {
if (setsockopt(s, SOL_SOCKET, SO_RCVBUF, &opt, sizeof(opt)) < 0) {
perror("setsocketopt failed");
} else {
fprintf(stdout, "setsocketopt successful\n");
}
// int shutdown(int sockfd, int how);
/* if (shutdown(s, SHUT_RD) < 0) {
* perror("shutdown failed");
* } */
}
}
return 0;
}
測試2(相同包括):
int main(int argc, char *argv[])
{
int s;
ssize_t rn; /* receive number */
char packet[4096];
int count;
if ((s = socket(AF_INET, SOCK_RAW, IPPROTO_TCP)) < 0) {
perror("error:");
exit(EXIT_FAILURE);
}
memset(packet, 0, sizeof(packet));
int opt = 0;
count = 0;
//Set recv buffer size
if (setsockopt(s, SOL_SOCKET, SO_RCVBUF, &opt, sizeof(opt)) < 0) {
perror("setsocketopt failed");
} else {
fprintf(stdout, "setsocketopt successful\n");
}
//10 seconds countdown
int i = 10;
while(i > 0)
{
printf("\r%d ", i);
fflush(stdout);
i--;
sleep(1);
}
printf("\n");
while(1) {
if ((rn = recv(s, (char *)&packet, sizeof(packet), 0)) <= 0)
perror("packet receive error:");
printf("[%d] rn = %lu \n", count++, rn);
}
return 0;
}
以下是如何進行測試2:
首先,將緩沖區大小設置為4096(如果網絡上有大量流量,則將其設置為更大)。 編譯並啟動。 在開始接收數據之前的10秒內,將大量數據發送到套接字。 10秒后,程序將收到您在倒計時期間發送的所有內容。
之后,將緩沖區大小設置為0.繼續執行之前的操作。 10秒后,程序將不會收到您在倒計時期間發送的數據。 但是如果你在recvfrom中發送數據,它將正常讀取它們。
我真的不明白你想要什么! 如果你只想注入一些數據包,那很簡單:
#include<netinet/tcp.h> /* TCP header */
#include<netinet/ip.h> /* IP header */
/* Checksum compute function */
/* source : http://www.winpcap.org/pipermail/winpcap-users/2007-July/001984.html */
unsigned short checksum(unsigned short *buffer, int size)
{
unsigned long cksum=0;
while(size >1)
{
cksum+=*buffer++;
size -=sizeof(unsigned short);
}
if(size)
cksum += *(UCHAR*)buffer;
cksum = (cksum >> 16) + (cksum & 0xffff);
cksum += (cksum >>16);
return (unsigned short)(~cksum);
}
int main (int argc, char **argv)
{
char packet_buffer[BUFFER_SIZE];
struct sockaddr_in sin;
struct iphdr *ip_header; /* IP header */
struct tcphdr *tcp_header; /* TCP header */
int flag = 1;
/* Creating RAW socket */
int raw_socket = socket (PF_INET, SOCK_RAW, IPPROTO_TCP);
ip_header = (struct iphdr *) packet_buffer;
tcp_header = (struct tcphdr *) (packet_buffer + sizeof (struct ip));
sin.sin_family = AF_INET;
sin.sin_port = htons(PORT_NUMBER);
sin.sin_addr.s_addr = inet_addr (IP_ADDRESS);
/* Zeroing the bbuffer */
memset (packet_buffer, 0, BUFFER_SIZE);
/* Construct your IP Header */
ip_header->ihl = 5;
ip_header->version = 4;
ip_header->tos = 0;
ip_header->tot_len = sizeof (struct ip) + sizeof (struct tcphdr);
ip_header->id = htonl(CHOOSE_PACKET_ID);
ip_header->frag_off = 0;
ip_header->ttl = 255;
ip_header->protocol = 6; /* TCP. Change to 17 if you want UDP */
ip_header->check = 0;
ip_header->saddr = inet_addr (SOURCE_IP_ADDRESS_TO_SPOOF);
ip_header->daddr = sin.sin_addr.s_addr;
/* Construct your TCP Header */
tcp_header->source = htons (SOURCE);
tcp_header->dest = htons(DEST);
tcp_header->seq = random();
tcp_header->ack_seq = 0;
tcp_header->doff = 0;
tcp_header->syn = 1;
tcp_header->window = htonl(65535);
tcp_header->check = 0;
tcp_header->urg_ptr = 0;
/* IP Checksum */
ip_header->check = checksum((unsigned short *) packet_buffer, ip_header->tot_len >> 1);
if (setsockopt(raw_socket, IPPROTO_IP, IP_HDRINCL, &flag, sizeof(flag)) < 0)
{
/* ERROR handling */
}
while (1)
{
/* Send the packet */
if (sendto(raw_socket, packet_buffer, ip_header->tot_len, 0, (struct sockaddr *) &sin, sizeof (sin)) < 0)
{
/* ERROR handling */
}
/* The rest of your need */
}
return 0;
}
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