段错误...位置很奇怪...

[Armeng]

linux下用gdb调试
错误地点竟然是
int size_udp=8;


达人帮忙看下这段代码 = =

void
got_packet(u_char *args, const struct pcap_pkthdr *header, const u_char *packet)
{
	static int count = 1;                   /* packet counter */
	
	/* declare pointers to packet headers */
	const struct sniff_ethernet *ethernet;  /* The ethernet header [1] */
	const struct sniff_ip *ip;              /* The IP header */
	const struct sniff_tcp *tcp;            /* The TCP header */
	const struct sniff_udp *udp;		/* The UDP header */
	const char *payload;                    /* Packet payload */

	int size_ip;
	int size_tcp;
	int size_udp = 8;
	int size_payload;
	
	printf("\nPacket number %d:\n", count);
	count++;
	
	/* define ethernet header */
	ethernet = (struct sniff_ethernet*)(packet);
	
	/* define/compute ip header offset */
	ip = (struct sniff_ip*)(packet + SIZE_ETHERNET);
	size_ip = IP_HL(ip)*4;
	printf("IP header length:%u bytes\n",size_ip);
	if (size_ip < 20) {
		printf("   * Invalid IP header length: %u bytes\n", size_ip);
		return;
	}

	/* print source and destination IP addresses */
	printf("       From: %s\n", inet_ntoa(ip->ip_src));
	printf("         To: %s\n", inet_ntoa(ip->ip_dst));
	
	/* determine protocol */	
	switch(ip->ip_p) {
		case IPPROTO_TCP:
			printf("   Protocol: TCP\n");
			break;
		case IPPROTO_UDP:
			printf("   Protocol: UDP\n");
			break;
		case IPPROTO_ICMP:
			printf("   Protocol: ICMP\n");
			return;
		case IPPROTO_IP:
			printf("   Protocol: IP\n");
			return;
		default:
			printf("   Protocol: unknown\n");
			return;
	}
	
	/*
	 *  OK, this packet is udp.
	 */
	
	/* define/compute tcp header offset */
	udp = (struct sniff_udp*)(packet + SIZE_ETHERNET + size_ip);
	if (size_udp < 8) {
		printf("   * Invalid udp header length: %u bytes\n", size_tcp);
		return;
	}
	
	printf("   Src port: %d\n", ntohs(udp->uh_sport));
	printf("   Dst port: %d\n", ntohs(udp->uh_dport));
	
	/* define/compute udp payload (segment) offset */
	payload = (u_char *)(packet + SIZE_ETHERNET + size_ip + size_udp);
	
	/* compute udp payload (segment) size */
	size_payload = ntohs(ip->ip_len) - (size_ip + size_udp);

	int seclen;
	seclen= ntohs(ip->ip_len)+16;
	//char *data = new char[seclen];
	char *data = (char *)malloc(seclen*sizeof(char));
	data[0] = (char)0x3E;
	data[1] = (char)0xB | (char)((seclen-3)>>8);
	data[2] = (char)(seclen-3);
	data[3] = (char)0x70;
	data[4] = (char)0x25;
	data[5] = (char)0xB1;
	data[6] = (char)0x00;
	data[7] = (char)0x00;
	data[8] = (char)0x40;
	data[9] = (char)0x5E;
	data[10] = (char)0x00;
	data[11] = (char)0x01;
	memcpy(data+12,*packet,ntohs(ip->ip_len));
	//for(int i=0;i<s)
	printf("%s\n",data);	

return;
}

[mosaic]

估计got_packet之前的代码就出问题了。

[jackyjkchen]

[Quote=引用 5 楼 morris88 的回复:]
C/C++ code /* define/compute udp payload (segment) offset */
payload = (u_char *)(packet + SIZE_ETHERNET + size_ip + size_udp);

/* compute udp payload (segment) size */
size_payload = ntohs(ip->ip_len) - (size_ip + size_udp);

int seclen;
seclen= ntohs(ip->ip_len)+16;
//char *data = new char[seclen];
char *data = (char *)malloc(seclen*sizeof(char));
…
[/Quote]

正解，地址应该向地址赋值，加了*就变成元素了

[Armeng]

哦 那个是笔误...
*packet 已经改成packet了,不过问题依旧...

[yashuwa0622]

udp = (struct sniff_udp*)(packet + SIZE_ETHERNET + size_ip);
if (size_udp < 8) {
printf(" * Invalid udp header length: %u bytes\n", size_tcp);
return;
}

这个中间是不是漏了什么。。

[dongpy]

不太可能吧，除非栈帧寄存器的值被破坏了。调试能看到ebp的值吗

[猫已经找不回了]

memcpy(data+12,*packet,ntohs(ip->ip_len));

这里没越界吧？

int size_udp = 8;
这么神奇？难道机器出问题了。

[zbing0203]

函数在这之前做了什么 有内存泄漏吗

[WOBUGUAN]

我也觉得这行有问题，
memcpy(data+12,*packet,ntohs(ip->ip_len));
我总觉得不该有那个星号

[morris88]

    /* define/compute udp payload (segment) offset */
    payload = (u_char *)(packet + SIZE_ETHERNET + size_ip + size_udp);
    
    /* compute udp payload (segment) size */
    size_payload = ntohs(ip->ip_len) - (size_ip + size_udp);

    int seclen;
    seclen= ntohs(ip->ip_len)+16;
    //char *data = new char[seclen];
    char *data = (char *)malloc(seclen*sizeof(char));
    data[0] = (char)0x3E;
    data[1] = (char)0xB | (char)((seclen-3)>>8);
    data[2] = (char)(seclen-3);
    data[3] = (char)0x70;
    data[4] = (char)0x25;
    data[5] = (char)0xB1;
    data[6] = (char)0x00;
    data[7] = (char)0x00;
    data[8] = (char)0x40;
    data[9] = (char)0x5E;
    data[10] = (char)0x00;
    data[11] = (char)0x01;
    memcpy(data+12,*packet,ntohs(ip->ip_len));
    //for(int i=0;i<s)
    printf("%s\n",data);    

其中：

    memcpy(data+12,*packet,ntohs(ip->ip_len));

貌似该为：

    memcpy(data+12, packet, ntohs(ip->ip_len));