Linux内核：为特定的UDP端口流量注册处理程序？

Question

我正在写一个隧道内核模块，我想为自己的处理程序注册一个特定的UDP端口。什么是最好的方式来做到这一点？这个想法是注册该处理程序，以便当该端口上的流量到达时，linux堆栈将调用我的处理程序。

[EDIT1]

通过套接字API的方法是结合于插座这样

sin.sin_family = AF_INET; 
sin.sin_addr.s_addr = htonl(INADDR_ANY); 
sin.sin_port = htons(my_port); 

err = kernel_bind(rcv_socket, (struct sockaddr *)&sin, 
     sizeof(struct sockaddr_in)); 

udp_sk(rcv_socket->sk)->encap_rcv = my_handler; 

的问题是，该插座与INADDR_ANY相关联，其对应于任何主机IP的在机器上。我想为数据包中的任何IP执行此操作？这怎么能实现？

插座不能在这种情况下使用我认为，因为任何IP意味着在堆栈中数据包通过ip_forward路径而不是ip_local_delivery。将不会有这样的数据包套接字。如何在这种情况下实现它？

Answer 1

我不知道相关的内核级别的功能，但我建议绑定到侦听第2层帧的RAW SOCKET，并使用ip包的进一步过滤器。

像这样：

fd = socket(PF_PACKET, SOCK_RAW, htons(ETH_P_IP));

那么它是由你来剖析框架和提取您只需要UDP数据包。

在第2层工作应该会授予您100％通过主机传输的IP数据包。

Answer 2

向下投票：请评论为什么你投下了这个经过测试的答案？

以下示例很有帮助。根据需要，您可以通过添加过滤器来修改示例。

对于UDP以下变化需要存在在下面的例子中

sock_raw = socket(AF_INET , SOCK_RAW , IPPROTO_UDP);

http://www.binarytides.com/packet-sniffer-code-in-c-using-linux-sockets-bsd/ http://www.binarytides.com/packet-sniffer-code-in-c-using-linux-sockets-bsd-part-2/ [相关性]

我列出的代码FYI

#include<netinet/in.h> 
#include<errno.h> 
#include<netdb.h> 
#include<stdio.h> //For standard things 
#include<stdlib.h> //malloc 
#include<string.h> //strlen 

#include<netinet/ip_icmp.h> //Provides declarations for icmp header 
#include<netinet/udp.h> //Provides declarations for udp header 
#include<netinet/tcp.h> //Provides declarations for tcp header 
#include<netinet/ip.h> //Provides declarations for ip header 
#include<netinet/if_ether.h> //For ETH_P_ALL 
#include<net/ethernet.h> //For ether_header 
#include<sys/socket.h> 
#include<arpa/inet.h> 
#include<sys/ioctl.h> 
#include<sys/time.h> 
#include<sys/types.h> 
#include<unistd.h> 

void ProcessPacket(unsigned char* , int); 
void print_ip_header(unsigned char* , int); 
void print_tcp_packet(unsigned char * , int); 
void print_udp_packet(unsigned char * , int); 
void print_icmp_packet(unsigned char* , int); 
void PrintData (unsigned char* , int); 

FILE *logfile; 
struct sockaddr_in source,dest; 
int tcp=0,udp=0,icmp=0,others=0,igmp=0,total=0,i,j; 

int main() 
{ 
    int saddr_size , data_size; 
    struct sockaddr saddr; 

    unsigned char *buffer = (unsigned char *) malloc(65536); //Its Big! 

    logfile=fopen("log.txt","w"); 
    if(logfile==NULL) 
    { 
     printf("Unable to create log.txt file."); 
    } 
    printf("Starting...\n"); 

    int sock_raw = socket(AF_PACKET , SOCK_RAW , htons(ETH_P_ALL)) ; 
    //setsockopt(sock_raw , SOL_SOCKET , SO_BINDTODEVICE , "eth0" , strlen("eth0")+ 1); 

    if(sock_raw < 0) 
    { 
     //Print the error with proper message 
     perror("Socket Error"); 
     return 1; 
    } 
    while(1) 
    { 
     saddr_size = sizeof saddr; 
     //Receive a packet 
     data_size = recvfrom(sock_raw , buffer , 65536 , 0 , &saddr , (socklen_t*)&saddr_size); 
     if(data_size <0) 
     { 
      printf("Recvfrom error , failed to get packets\n"); 
      return 1; 
     } 
     //Now process the packet 
     ProcessPacket(buffer , data_size); 
    } 
    close(sock_raw); 
    printf("Finished"); 
    return 0; 
} 

void ProcessPacket(unsigned char* buffer, int size) 
{ 
    //Get the IP Header part of this packet , excluding the ethernet header 
    struct iphdr *iph = (struct iphdr*)(buffer + sizeof(struct ethhdr)); 
    ++total; 
    switch (iph->protocol) //Check the Protocol and do accordingly... 
    { 
     case 1: //ICMP Protocol 
      ++icmp; 
      print_icmp_packet(buffer , size); 
      break; 

     case 2: //IGMP Protocol 
      ++igmp; 
      break; 

     case 6: //TCP Protocol 
      ++tcp; 
      print_tcp_packet(buffer , size); 
      break; 

     case 17: //UDP Protocol 
      ++udp; 
      print_udp_packet(buffer , size); 
      break; 

     default: //Some Other Protocol like ARP etc. 
      ++others; 
      break; 
    } 
    printf("TCP : %d UDP : %d ICMP : %d IGMP : %d Others : %d Total : %d\r", tcp , udp , icmp , igmp , others , total); 
} 

void print_ethernet_header(unsigned char* Buffer, int Size) 
{ 
    struct ethhdr *eth = (struct ethhdr *)Buffer; 

    fprintf(logfile , "\n"); 
    fprintf(logfile , "Ethernet Header\n"); 
    fprintf(logfile , " |-Destination Address : %.2X-%.2X-%.2X-%.2X-%.2X-%.2X \n", eth->h_dest[0] , eth->h_dest[1] , eth->h_dest[2] , eth->h_dest[3] , eth->h_dest[4] , eth->h_dest[5]); 
    fprintf(logfile , " |-Source Address  : %.2X-%.2X-%.2X-%.2X-%.2X-%.2X \n", eth->h_source[0] , eth->h_source[1] , eth->h_source[2] , eth->h_source[3] , eth->h_source[4] , eth->h_source[5]); 
    fprintf(logfile , " |-Protocol   : %u \n",(unsigned short)eth->h_proto); 
} 

void print_ip_header(unsigned char* Buffer, int Size) 
{ 
    print_ethernet_header(Buffer , Size); 

    unsigned short iphdrlen; 

    struct iphdr *iph = (struct iphdr *)(Buffer + sizeof(struct ethhdr)); 
    iphdrlen =iph->ihl*4; 

    memset(&source, 0, sizeof(source)); 
    source.sin_addr.s_addr = iph->saddr; 

    memset(&dest, 0, sizeof(dest)); 
    dest.sin_addr.s_addr = iph->daddr; 

    fprintf(logfile , "\n"); 
    fprintf(logfile , "IP Header\n"); 
    fprintf(logfile , " |-IP Version  : %d\n",(unsigned int)iph->version); 
    fprintf(logfile , " |-IP Header Length : %d DWORDS or %d Bytes\n",(unsigned int)iph->ihl,((unsigned int)(iph->ihl))*4); 
    fprintf(logfile , " |-Type Of Service : %d\n",(unsigned int)iph->tos); 
    fprintf(logfile , " |-IP Total Length : %d Bytes(Size of Packet)\n",ntohs(iph->tot_len)); 
    fprintf(logfile , " |-Identification : %d\n",ntohs(iph->id)); 
    //fprintf(logfile , " |-Reserved ZERO Field : %d\n",(unsigned int)iphdr->ip_reserved_zero); 
    //fprintf(logfile , " |-Dont Fragment Field : %d\n",(unsigned int)iphdr->ip_dont_fragment); 
    //fprintf(logfile , " |-More Fragment Field : %d\n",(unsigned int)iphdr->ip_more_fragment); 
    fprintf(logfile , " |-TTL  : %d\n",(unsigned int)iph->ttl); 
    fprintf(logfile , " |-Protocol : %d\n",(unsigned int)iph->protocol); 
    fprintf(logfile , " |-Checksum : %d\n",ntohs(iph->check)); 
    fprintf(logfile , " |-Source IP  : %s\n",inet_ntoa(source.sin_addr)); 
    fprintf(logfile , " |-Destination IP : %s\n",inet_ntoa(dest.sin_addr)); 
} 

void print_tcp_packet(unsigned char* Buffer, int Size) 
{ 
    unsigned short iphdrlen; 

    struct iphdr *iph = (struct iphdr *)(Buffer + sizeof(struct ethhdr)); 
    iphdrlen = iph->ihl*4; 

    struct tcphdr *tcph=(struct tcphdr*)(Buffer + iphdrlen + sizeof(struct ethhdr)); 

    int header_size = sizeof(struct ethhdr) + iphdrlen + tcph->doff*4; 

    fprintf(logfile , "\n\n***********************TCP Packet*************************\n"); 

    print_ip_header(Buffer,Size); 

    fprintf(logfile , "\n"); 
    fprintf(logfile , "TCP Header\n"); 
    fprintf(logfile , " |-Source Port  : %u\n",ntohs(tcph->source)); 
    fprintf(logfile , " |-Destination Port : %u\n",ntohs(tcph->dest)); 
    fprintf(logfile , " |-Sequence Number : %u\n",ntohl(tcph->seq)); 
    fprintf(logfile , " |-Acknowledge Number : %u\n",ntohl(tcph->ack_seq)); 
    fprintf(logfile , " |-Header Length  : %d DWORDS or %d BYTES\n" ,(unsigned int)tcph->doff,(unsigned int)tcph->doff*4); 
    //fprintf(logfile , " |-CWR Flag : %d\n",(unsigned int)tcph->cwr); 
    //fprintf(logfile , " |-ECN Flag : %d\n",(unsigned int)tcph->ece); 
    fprintf(logfile , " |-Urgent Flag   : %d\n",(unsigned int)tcph->urg); 
    fprintf(logfile , " |-Acknowledgement Flag : %d\n",(unsigned int)tcph->ack); 
    fprintf(logfile , " |-Push Flag   : %d\n",(unsigned int)tcph->psh); 
    fprintf(logfile , " |-Reset Flag   : %d\n",(unsigned int)tcph->rst); 
    fprintf(logfile , " |-Synchronise Flag  : %d\n",(unsigned int)tcph->syn); 
    fprintf(logfile , " |-Finish Flag   : %d\n",(unsigned int)tcph->fin); 
    fprintf(logfile , " |-Window   : %d\n",ntohs(tcph->window)); 
    fprintf(logfile , " |-Checksum  : %d\n",ntohs(tcph->check)); 
    fprintf(logfile , " |-Urgent Pointer : %d\n",tcph->urg_ptr); 
    fprintf(logfile , "\n"); 
    fprintf(logfile , "      DATA Dump       "); 
    fprintf(logfile , "\n"); 

    fprintf(logfile , "IP Header\n"); 
    PrintData(Buffer,iphdrlen); 

    fprintf(logfile , "TCP Header\n"); 
    PrintData(Buffer+iphdrlen,tcph->doff*4); 

    fprintf(logfile , "Data Payload\n");  
    PrintData(Buffer + header_size , Size - header_size); 

    fprintf(logfile , "\n###########################################################"); 
} 

void print_udp_packet(unsigned char *Buffer , int Size) 
{ 

    unsigned short iphdrlen; 

    struct iphdr *iph = (struct iphdr *)(Buffer + sizeof(struct ethhdr)); 
    iphdrlen = iph->ihl*4; 

    struct udphdr *udph = (struct udphdr*)(Buffer + iphdrlen + sizeof(struct ethhdr)); 

    int header_size = sizeof(struct ethhdr) + iphdrlen + sizeof udph; 

    fprintf(logfile , "\n\n***********************UDP Packet*************************\n"); 

    print_ip_header(Buffer,Size);   

    fprintf(logfile , "\nUDP Header\n"); 
    fprintf(logfile , " |-Source Port  : %d\n" , ntohs(udph->source)); 
    fprintf(logfile , " |-Destination Port : %d\n" , ntohs(udph->dest)); 
    fprintf(logfile , " |-UDP Length  : %d\n" , ntohs(udph->len)); 
    fprintf(logfile , " |-UDP Checksum  : %d\n" , ntohs(udph->check)); 

    fprintf(logfile , "\n"); 
    fprintf(logfile , "IP Header\n"); 
    PrintData(Buffer , iphdrlen); 

    fprintf(logfile , "UDP Header\n"); 
    PrintData(Buffer+iphdrlen , sizeof udph); 

    fprintf(logfile , "Data Payload\n");  

    //Move the pointer ahead and reduce the size of string 
    PrintData(Buffer + header_size , Size - header_size); 

    fprintf(logfile , "\n###########################################################"); 
} 

void print_icmp_packet(unsigned char* Buffer , int Size) 
{ 
    unsigned short iphdrlen; 

    struct iphdr *iph = (struct iphdr *)(Buffer + sizeof(struct ethhdr)); 
    iphdrlen = iph->ihl * 4; 

    struct icmphdr *icmph = (struct icmphdr *)(Buffer + iphdrlen + sizeof(struct ethhdr)); 

    int header_size = sizeof(struct ethhdr) + iphdrlen + sizeof icmph; 

    fprintf(logfile , "\n\n***********************ICMP Packet*************************\n"); 

    print_ip_header(Buffer , Size); 

    fprintf(logfile , "\n"); 

    fprintf(logfile , "ICMP Header\n"); 
    fprintf(logfile , " |-Type : %d",(unsigned int)(icmph->type)); 

    if((unsigned int)(icmph->type) == 11) 
    { 
     fprintf(logfile , " (TTL Expired)\n"); 
    } 
    else if((unsigned int)(icmph->type) == ICMP_ECHOREPLY) 
    { 
     fprintf(logfile , " (ICMP Echo Reply)\n"); 
    } 

    fprintf(logfile , " |-Code : %d\n",(unsigned int)(icmph->code)); 
    fprintf(logfile , " |-Checksum : %d\n",ntohs(icmph->checksum)); 
    //fprintf(logfile , " |-ID  : %d\n",ntohs(icmph->id)); 
    //fprintf(logfile , " |-Sequence : %d\n",ntohs(icmph->sequence)); 
    fprintf(logfile , "\n"); 

    fprintf(logfile , "IP Header\n"); 
    PrintData(Buffer,iphdrlen); 

    fprintf(logfile , "UDP Header\n"); 
    PrintData(Buffer + iphdrlen , sizeof icmph); 

    fprintf(logfile , "Data Payload\n");  

    //Move the pointer ahead and reduce the size of string 
    PrintData(Buffer + header_size , (Size - header_size)); 

    fprintf(logfile , "\n###########################################################"); 
} 

void PrintData (unsigned char* data , int Size) 
{ 
    int i , j; 
    for(i=0 ; i < Size ; i++) 
    { 
     if(i!=0 && i%16==0) //if one line of hex printing is complete... 
     { 
      fprintf(logfile , "   "); 
      for(j=i-16 ; j<i ; j++) 
      { 
       if(data[j]>=32 && data[j]<=128) 
        fprintf(logfile , "%c",(unsigned char)data[j]); //if its a number or alphabet 

       else fprintf(logfile , "."); //otherwise print a dot 
      } 
      fprintf(logfile , "\n"); 
     } 

     if(i%16==0) fprintf(logfile , " "); 
      fprintf(logfile , " %02X",(unsigned int)data[i]); 

     if(i==Size-1) //print the last spaces 
     { 
      for(j=0;j<15-i%16;j++) 
      { 
       fprintf(logfile , " "); //extra spaces 
      } 

      fprintf(logfile , "   "); 

      for(j=i-i%16 ; j<=i ; j++) 
      { 
       if(data[j]>=32 && data[j]<=128) 
       { 
        fprintf(logfile , "%c",(unsigned char)data[j]); 
       } 
       else 
       { 
        fprintf(logfile , "."); 
       } 
      } 

      fprintf(logfile , "\n"); 
     } 
    } 
} 

在Linux运行带有前缀“sudo”的代码。 :)