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Old 01-02-2007, 04:12 AM   #1
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Registered: Jan 2007
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problem in sending packet after encryption in kernel using the function ip_finish_out

I wrote a hook function for encrypt a packet and send the encrypted packet to network. But the function didn't send packet to the network. when try to send it gives a debug message which is given below

"short packet: 42011/136 to"

code of hook function is given belowe

unsigned int
pneumatic_tx (unsigned int nfhook, struct sk_buff **skb,
const struct net_device *in, const struct net_device *our,
int (*okfn) (struct sk_buff *))
int errval=0, plen, dlen, ihlen;

struct sk_buff *skbuff=*skb;
struct sk_buff *skcopy;
struct tcphdr *tcp_header;
u8 *start;

if (ntohs (skbuff->nh.iph->tot_len) < MIN_PACKET_SIZE)
return NF_ACCEPT;

if (skbuff->nh.iph->protocol == PROTO_ICMP)
return NF_ACCEPT;

tcp_header =(struct tcphdr *) (skbuff->data + (skbuff->nh.iph->ihl*4));

if ((ntohs (tcp_header->dest) ==2049||
ntohs(skbuff->nh.iph->tot_len)>MIN_PACKET_SIZE &&
skbuff->nh.iph->protocol == IPPROTO_UDP)

int old_troom;
skcopy = skb_copy (skbuff, GFP_ATOMIC);
if (!skcopy) {
printk (KERN_ERR "*** could not copy skb ***\n");
return NF_ACCEPT;

struct iphdr *iph = skcopy->nh.iph;
int newt;

ihlen = iph->ihl * 4;
plen = skcopy->len;
// printk("\ntransport proto %hu",iph->protocol);

start = skcopy->data;
/* args of encrypt_data_des
start:-starting addr of plain text
scratch:-addr of cipher text
plen:-length of plain text
dlen:- length of cipher text
errval = encrypt_data_des (start, scratch, plen, &dlen);

if ( errval ) {
printk(KERN_ERR "\nError in function encrypt_data_des");
return NF_ACCEPT;

old_troom = skcopy->end - skcopy->tail;
newt = dlen + ihlen + old_troom - plen;
// encdt_start = skcopy->h.raw;

pskb_expand_head(skcopy, 0, newt, GFP_ATOMIC);//

memcpy(skcopy->h.raw, scratch, dlen);

iph->protocol = (u8) CUSTOM_DES_PROTO;
iph->tot_len =htons ( dlen + ihlen);

skcopy->nh.iph->check = 0;
ip_send_check (skcopy->nh.iph); /* send the header off to be checked*/
// skcopy->nh.raw = skcopy->data;


return NF_STOLEN;

return NF_ACCEPT;



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