Sending an ICMP packet with ip_local_out

[Adel Qodmani]

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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