[英]Raw Socket Linux send/receive a packet
在接收數據包時遇到一些問題。 我可以接收和讀取傳入的數據包,但我認為我沒有與任何主機握手。 我只想在收到答案時將數據包發送到具有開放端口的遠程計算機,以查看TTL(生存時間)和窗口大小。 有誰知道錯誤在哪里?
(我對C編程沒有很深的了解)
碼:
#include <sys/types.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/socket.h>
#include <errno.h>
#include <unistd.h>
#include <arpa/inet.h>
#include <net/ethernet.h>
#include <netinet/in.h>
#include <netinet/ip.h>
#include <netinet/tcp.h>
struct pseudohdr {
u_int32_t src_addr;
u_int32_t dst_addr;
u_int8_t padding;
u_int8_t proto;
u_int16_t length;
};
struct data_4_checksum {
struct pseudohdr pshd;
struct tcphdr tcphdr;
char payload[1024];
};
unsigned short comp_chksum(unsigned short *addr, int len) {
long sum = 0;
while (len > 1) {
sum += *(addr++);
len -= 2;
}
if (len > 0)
sum += *addr;
while (sum >> 16)
sum = ((sum & 0xffff) + (sum >> 16));
sum = ~sum;
return ((u_short) sum);
}
int main(int argc, char *argv[]) {
int sock, bytes, on = 1;
char buffer[1024];
struct iphdr *ip;
struct tcphdr *tcp;
struct sockaddr_in to;
struct pseudohdr pseudoheader;
struct data_4_checksum tcp_chk_construct;
if (argc != 2) {
fprintf(stderr, "Usage: %s ", argv[0]);
fprintf(stderr, "<dest-addr>\n");
return 1;
}
sock = socket(AF_INET, SOCK_RAW, IPPROTO_TCP);
if (sock == -1) {
perror("socket() failed");
return 1;
}else{
printf("socket() ok\n");
}
if (setsockopt(sock, IPPROTO_IP, IP_HDRINCL, &on, sizeof(on)) == -1) {
perror("setsockopt() failed");
return 2;
}else{
printf("setsockopt() ok\n");
}
ip = (struct iphdr*) buffer;
tcp = (struct tcphdr*) (buffer + sizeof(struct tcphdr));
int iphdrlen = sizeof(struct iphdr);
int tcphdrlen = sizeof(struct tcphdr);
int datalen = 0;
printf("Typecasting ok\n");
ip->frag_off = 0;
ip->version = 4;
ip->ihl = 5;
ip->tot_len = htons(iphdrlen + tcphdrlen);
ip->id = 0;
ip->ttl = 40;
ip->protocol = IPPROTO_TCP;
ip->saddr = inet_addr("192.168.165.135");
ip->daddr = inet_addr(argv[1]);
ip->check = 0;
tcp->source = htons(12345);
tcp->dest = htons(80);
tcp->seq = random();
tcp->doff = 5;
tcp->ack = 0;
tcp->psh = 0;
tcp->rst = 0;
tcp->urg = 0;
tcp->syn = 1;
tcp->fin = 0;
tcp->window = htons(65535);
pseudoheader.src_addr = ip->saddr;
pseudoheader.dst_addr = ip->daddr;
pseudoheader.padding = 0;
pseudoheader.proto = ip->protocol;
pseudoheader.length = htons(tcphdrlen + datalen);
tcp_chk_construct.pshd = pseudoheader;
tcp_chk_construct.tcphdr = *tcp;
int checksum = comp_chksum((unsigned short*) &tcp_chk_construct,
sizeof(struct pseudohdr) + tcphdrlen + datalen);
tcp->check = checksum;
printf("TCP Checksum: %i\n", checksum);
printf("Destination : %i\n", ntohs(tcp->dest));
printf("Source: %i\n", ntohs(tcp->source));
to.sin_addr.s_addr = ip->daddr;
to.sin_family = AF_INET;
to.sin_port = tcp->dest;
bytes = sendto(sock, buffer, ntohs(ip->tot_len), 0, (struct sockaddr*) &to,
sizeof(to));
if (bytes == -1) {
perror("sendto() failed");
return 1;
}
recv(sock, buffer, sizeof(buffer), 0);
printf("TTL= %d\n", ip->ttl);
printf("Window= %d\n", tcp->window);
printf("ACK= %d\n", tcp->ack);
printf("%s:%d\t --> \t%s:%d \tSeq: %d \tAck: %d\n",
inet_ntoa(*(struct in_addr*) &ip->saddr), ntohs(tcp->source),
inet_ntoa(*(struct in_addr *) &ip->daddr), ntohs(tcp->dest),
ntohl(tcp->seq), ntohl(tcp->ack_seq));
return 0;
}
buffer
,但是您正在從ip
和tcp
打印數據而沒有解析該緩沖區。 您應該在接收到buffer
之后並在打印之前從buffer
解析該包。 IPPROTO_TCP
會產生誤導。 堅持IPPROTO_IP
,並為您關心的每個協議(TCP,UDP等)在代碼中添加必要條件。 因為Linux內核會驗證協議號並回IPPROTO_IP
,所以這恰好起作用。 但是,這可能在其他系統中不起作用。 tcp->seq
值可能無效,因為TCP僅接受最大65535的值,而random()
返回的值從0到RAND_MAX
(0x7fffffff)。 嘗試tcp->seq = htonl(random() % 65535);
sizeof(struct iphdr)
而不是sizeof(struct tcphdr)
。 ip = (struct iphdr*) buffer;
tcp = (struct tcphdr*) (buffer + sizeof(struct tcphdr)); //This is wrong
這里要獲取buffer
中tcp標頭的數組索引,您需要像下面提到的那樣向buffer
添加sizeof(struct iphdr)
。
ip = (struct iphdr*) buffer;
tcp = (struct tcphdr*) (buffer + sizeof(struct iphdr)); //This is correct
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