Re: Sending an ICMP packet with ip_local_out

Rami Rosen <roszenrami@xxxxxxxxx> · Mon, 17 Jun 2013 07:32:59 +0300

Adel,You say you have a  NULL pointer but you do not specify where.

can you please send the  log of the panic ? 

Can you send the kernel module full code ? 

Regards,
Rami Rosen
http://ramirose.wix.com/ramirosen

On Mon, Jun 17, 2013 at 6:18 AM, Adel Qodmani <mpcadel@xxxxxxxxx> wrote:

Hello everyone, 

I am trying to send an ICMP message in a kernel module; typically I'd build the skb, set up the net_device, the ethernet header and then use dev_queue_xmit.

But right now I want my packet to follow the IP routing rules set in the system, so I thought I'll use ip_local_out function and let it handle the routing and setting the rest of the parameters in the skb.

Yet, my code causes the kernel to panic due to a NULL pointer.

The code is as follows:
/* This function assumes source and dest are in NETWORK byte order */
int sendICMPEcho(char *msg, unsigned int length, __be32 source, __be32 dest)

{
	struct iphdr *iph;
	struct icmphdr *icmph;
	struct sk_buff *newPacket;

	unsigned char *data;
	unsigned int skbSize = length + sizeof(struct icmphdr) * 2
				+ sizeof(struct iphdr) * 2

				+ sizeof(struct ethhdr) * 2;

	/* Allocate the skb */
	newPacket = alloc_skb(skbSize, GFP_ATOMIC);

	if(newPacket == NULL)
		return SEND_FAIL_MEMORY;

	/* Reserve the headers area */

	skb_reserve(newPacket, sizeof(struct icmphdr)
				 + sizeof(struct iphdr) 
				+ sizeof(struct ethhdr));	

	/* Extend the data area from 0 to the message length */
	data = "" length);

	/* Copy the data from the message buffer to the newPacket */
	memcpy(data, msg, length);

	/************** ICMP HEADER***************/	

	/* skb_push - pushing the icmp header in the packet data */
	icmph = (struct icmphdr *) skb_push(newPacket,

						sizeof(struct icmphdr));
	/*set ICMP header here */
	icmph->type = ICMP_ECHO;

	icmph->code = 0;
	icmph->un.echo.id = 0;
	icmph->un.echo.sequence = htons(sendCounter);

	icmph->checksum= 0;
	icmph->checksum = in_cksum((unsigned short *)icmph, 
				sizeof(struct icmphdr) + length);

	/************** END ICMP HEADER**************/

	/************** IP HEADER ***************/

	iph = (struct iphdr *) skb_push(newPacket,
						sizeof(struct iphdr));
	/* set IP header here */

	iph->ihl = 5;/* 5 * 32(bits) */
	iph->version = 4;
	iph->tos = 0; /* The recommended value by IANA for ICMP request */

	iph->tot_len = htons( sizeof(struct iphdr) 
				+ sizeof(struct icmphdr)
				+ length);

	iph->id = 0;
	iph->frag_off = 0; /* No fragementation */
	iph->ttl = 65;

	iph->protocol =  IPPROTO_ICMP;
	iph->saddr = source;
	iph->daddr = dest;

	iph->check = 0;
	iph->check = in_cksum((unsigned short *)iph, sizeof(struct iphdr));
	/************** END IP HEADER ***************/

//	if(ip_local_out(newPacket) < 0) THIS CRASHES WITH A NULL POINTER
//		return SEND_FAIL_SEND;

	++sendCounter;
	return SEND_SUCCESS;
}
/* end sendICMPEcho */

In my attempts when trying to solve this, I've tried to manually set the net_device in the skb and that didn't work either; I still had the same kernel panic.

So I am sorry for the trouble, any hint where the error can be?

Regards,
Adel

_______________________________________________

Kernelnewbies mailing list

Kernelnewbies@xxxxxxxxxxxxxxxxx

http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies

_______________________________________________
Kernelnewbies mailing list
Kernelnewbies@xxxxxxxxxxxxxxxxx
http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies