Sending an ICMP packet with ip_local_out

[Rami Rosen]

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 at gmail.com> 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 = skb_put(newPacket, 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
>
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>
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