Question

我正在研究类似netcat的工具（主要用于自学）。我想通过SOCK_RAW套接字发送带有IP和UDP头的数据包。我在Debian VM上运行以下代码，通过套接字发送数据包。

/* header must already have source IP, destination IP, and protocol number filled in */
int send_ip_packet(ipheader_t *header, char *buf, int numbytes)
{
    int sizeofpacket = sizeof(ipheader_t) + numbytes;
    if(sizeofpacket > MAX_PCKT_LEN)
    {
        printf("Cannot send ip packet of len %i. Too large. - FAIL\n", sizeofpacket);
        return -1;
    }

    /* open a raw socket */
    int sd;
    sd = socket(PF_INET, SOCK_RAW, header->ip_p);
    if(sd < 0)
    {
        perror("socket()");
        printf("socket() call - FAIL\n");
        return -1;
    }
    else
    {
        printf("socket() call - SUCCESS\n");
    }

    char packet[sizeofpacket];
    memset(packet, 0, sizeofpacket);

    /* set remaining ip header */
    header->ip_hl = 5; /* header length is 5 32-bit octets */
    header->ip_v = 4; /* IPv4 */
    header->ip_tos = 16; /* low delay */
    header->ip_len = sizeofpacket;
    header->ip_id = htons(54321); /* identifier used for fragmentation */
    header->ip_off = 0; /* fragmentation options */
    header->ip_ttl = 64; /* max num hops */
    header->ip_sum = csum((unsigned short*)packet, sizeofpacket);

    /* fill packet */
    memcpy(packet, (char*) header, sizeof(ipheader_t));
    memcpy(packet + sizeof(ipheader_t), (char*) buf, numbytes);

    /* setup socket addresses */
    struct sockaddr_in sin, din;
    sin.sin_family = AF_INET;
    din.sin_family = AF_INET;
    memcpy(&sin.sin_addr.s_addr, &header->ip_src, sizeof(in_addr_t));
    memcpy(&din.sin_addr.s_addr, &header->ip_dst, sizeof(in_addr_t));

    /* send out the packet */
    int one = 1;
    int *val = &one;
    if(setsockopt(sd, IPPROTO_IP, IP_HDRINCL, val, sizeof(one)))
    {
        perror("setsockopt()");
        printf("setsockopt() call - FAIL\n");
        return -1;
    }
    else
    {
        printf("setsockopt() call - SUCCESS\n");
    }

    if(sendto(sd, packet, header->ip_len, 0, (struct sockaddr *) &sin, sizeof(sin)) < 0)
    {
        perror("sendto()");
        printf("sendto() call - FAIL\n");
        return -1;
    }
    else
    {
        printf("Message sent! - SUCCESS\n");
    }

    return 0;
}

当我运行ifconfig时，只要源IP I提供的不是我的“真实”IP列表，代码就会成功发送wireshark中可见的数据包。任何人都可以告诉我为什么会这样或我如何解决它（除了不使用SOCK_RAW）？我会假设操作系统专门处理数据包，但为什么呢？

Answer 1

sendto()期望目标地址为第5个参数。

从OP中给出的变量命名我强烈假设源地址被传入，这将完美地解释所描述的行为。

SOCK_RAW数据包不发送某些源地址

1 个答案: