從帶有MSG_ERRQUEUE的recvmsg讀取ICMP有效載荷

Question

我正在使用BSD套接字構建不需要root權限（如跟蹤路徑）的高級traceroute程序。 使用UDP和綁定套接字，我呼籲：

recvmsg(socket, header, MSG_ERRQUEUE) 

我收到關於先前發送的數據包觸發了所謂ICMP通知的信息。 你知道是否可以訪問ICMP有效載荷（應該是之前發送的數據包）？

我從recvmsg手冊頁閱讀：

[..] The payload of the original packet that caused the error 
is passed as normal data via msg_iovec. [..] 

但我無法找到任何有用的存在，它只是似乎隨機數據（我使用Wireshark的交叉檢查數據）。

Answer 1

您可以使用此示例代碼來檢查你有哪些ICMP錯誤和處理它（樣品含有一些評論和鏈接）：

#define BUFFER_MAX_SIZE 1024 
int on = 1; 
/* Set the option, so we can receive errors */ 
setsockopt(socket, SOL_IP, IP_RECVERR,(char*)&on, sizeof(on)); 
/* Other code here */ 
/* .... */ 
/* Handle receving ICMP Errors */ 
int return_status; 
char buffer[BUFFER_MAX_SIZE]; 
struct iovec iov;      /* Data array */ 
struct msghdr msg;      /* Message header */ 
struct cmsghdr *cmsg;     /* Control related data */ 
struct sock_extended_err *sock_err;  /* Struct describing the error */ 
struct icmphdr icmph;     /* ICMP header */ 
struct sockaddr_in remote;    /* Our socket */ 

for (;;) 
{ 
    iov.iov_base = &icmph; 
    iov.iov_len = sizeof(icmph); 
    msg.msg_name = (void*)&remote; 
    msg.msg_namelen = sizeof(remote); 
    msg.msg_iov = &iov; 
    msg.msg_iovlen = 1; 
    msg.msg_flags = 0; 
    msg.msg_control = buffer; 
    msg.msg_controllen = sizeof(buffer); 
    /* Receiving errors flog is set */ 
    return_status = recvmsg(socket, &msg, MSG_ERRQUEUE); 
    if (return_status < 0) 
     continue; 
    /* Control messages are always accessed via some macros 
    * http://www.kernel.org/doc/man-pages/online/pages/man3/cmsg.3.html 
    */ 
    for (cmsg = CMSG_FIRSTHDR(&msg);cmsg; cmsg = CMSG_NXTHDR(&msg, cmsg)) 
    { 
     /* Ip level */ 
     if (cmsg->cmsg_level == SOL_IP) 
     { 
      /* We received an error */ 
      if (cmsg->cmsg_type == IP_RECVERR) 
      { 
       fprintf(stderror, "We got IP_RECVERR message\n"); 
       sock_err = (struct sock_extended_err*)CMSG_DATA(cmsg); 
       if (sock_err) 
       { 
        /* We are intrested in ICMP errors */ 
        if (sock_err->ee_origin == SO_EE_ORIGIN_ICMP) 
        { 
         /* Handle ICMP errors types */ 
         switch (sock_err->ee_type) 
         { 
          case ICMP_NET_UNREACH: 
           /* Hendle this error */ 
           fprintf(stderror, "Network Unreachable Error\n"); 
           break; 
          case ICMP_HOST_UNREACH: 
           /* Hendle this error */ 
           fprintf(stderror, "Host Unreachable Error\n"); 
           break; 
          /* Handle all other cases. Find more errors : 
          * http://lxr.linux.no/linux+v3.5/include/linux/icmp.h#L39 
          */ 

         } 
        } 
       } 
      } 
     } 
    } 
}