(usagi-users 02061) Re: ICMP_ECHO raw socket

[David Lamparter <david.lamparter@xxxxxxxxxxx>]

Abdul Basit wrote:
> // -- code snipped
>
>        buf = (char*) malloc(sizeof(struct ip)+sizeof(struct icmp));
>
>         sockfd = socket(AF_INET, SOCK_RAW, IPPROTO_ICMP);
>
>         for (;;) {
>                 n = recv(sockfd, buf, sizeof(buf),0);

you can't use sizeof() for dynamically allocated buffers. sizeof will 
give you 4, the size of the pointer, not the size of the buffer behind 
the pointer ...

>                 ip = (struct ip *) buf;
>                 ip_len = ip->ip_hl << 2; // ip header length
>
>                 icmp = (struct icmp *) (buf + ip_len);
>
>                 printf("n= %d\n",n);
>                 if (icmp->icmp_type == ICMP_ECHO) {
>                         printf("ping request arrived\n");
>                 }
>         }
>
>
> It seems that the kernel donot pass ICMP_ECHO to raw socket
> if i use ICMP_ECHOREPLY, it will work,
looks like the memory you allocate with malloc() is initialized to zero 
... ICMP_ECHOREPLY is zero ...

replace "sizeof(buf)" with "sizeof(struct ip)+sizeof(struct icmp)" and 
it should work

David Lamparter

-----
17yr old high school student