为什么我的程序不适用于不同的Linux发行版？

Question

I'm working on a packet sniffer. The big problem is that my code works perfectly only under Backtrack 5 R3, but it doesn't work under other distributions! In fact, on Ubuntu 12.10 and ArchLinux, when the sniffer gets the first packet, I experience a segmentation fault (I get "segmentation fault core dumped"). At first, I thought the fault lay with the libraries or the compiler, but after some tests, I think I can exclude them! This is the situation:

• Backtrack 5 R3 uses gcc 4.4.3 and libpcap 1.0.0
• Ubuntu 12.10 uses Gcc 4.7.2 and Libpcap 1.3.0
• ArchLinux the same as Ubuntu

So I tried to downgrade on Arch to gcc 4.4.3 e libpcap 1.0.0, but I get the same error. I have some warnings while compiling the code, but nothing really important, and however it works perfectly under backtrack! That's the big mystery.

Here's the code which cause the problem:

void packet_dump(unsigned char *arguments, const struct pcap_pkthdr *pcap_data, const unsigned char *packet) {
    int packet_data_len, tcp_header_size=0, total_header_size;
    unsigned char *packet_data;
    const unsigned char *ip_src_dest;
    const struct header_ip *ip_header; 

    //Calculate the value of variables
    ip_src_dest = (packet+LUNGHEZZA_INTESTAZIONE_ETH); 
    ip_header = (const struct header_ip *)ip_src_dest; 
    total_header_size = LUNGHEZZA_INTESTAZIONE_ETH+sizeof(struct header_ip)+tcp_header_size;
    packet_data = (unsigned char *)packet + total_header_size;  
    packet_data_len = pcap_data->len - total_header_size;

    //THIS CAUSE THE PROBLEM (Solved removing inet_ntoa and converting it manually)
    printf("[ %s ] ============> ", inet_ntoa(ip_header->source_addr_ip));
    printf("[ %s ]  \n", inet_ntoa(ip_header->destination_addr_ip));


}

Answer 1

I suspect your program is crashing because ip_header->source_addr_ip points to memory that you're not allowed to access. You should be able to use GDB to determine whether this is the case.