Hi.
I am developping an application where I need to patch
data coming from Ethernet. ( changgin IP @ for example )
I have patched the kernel in order to add a hook when a packet is received.
When netif_receive_skb is called and if the Hook is non null I call it with
the skb as argument.
int netif_receive_skb(struct sk_buff *skb)
{
struct packet_type *ptype, *pt_prev;
int ret = NET_RX_DROP;
unsigned short type = skb->protocol;
/* Patch C.Lindheimer */
if ( Lindheimer_Hook_RX != NULL )
(*((void (*)(struct sk_buff
*))Lindheimer_Hook_RX))(skb);
if (skb->stamp.tv_sec == 0)
do_gettimeofday(&skb->stamp);
...
}
Then here is the Hook I wrote :
void Hook_RX(struct sk_buff *skb)
{
unsigned char *i;
unsigned char num;
num = (skb->dev)->name[3] - '0';
printk("Hook RX device %s -> %d\n",((skb->dev))->name, num);
printk("h : %x\n", skb->h.raw);
printk("nh : %x\n", skb->nh.raw);
printk("mac : %x\n", skb->mac.raw);
printk("len : %x\n", skb->len);
printk("da len: %x\n", skb->data_len);
printk("head : %x\n", skb->head);
printk("data : %x\n", skb->data);
printk("tail : %x\n", skb->tail);
printk("end : %x\n", skb->end);
for ( i = skb->head; i < skb->end; i++ )
{
if ( i == skb->data ) printk("** ");
printk("%x ", *i);
}
....
}
I have two Ethernet devices.
The trace just shows received packets : ARP Packets due to a ping done on
each interface.
Mac eth1 : 0 9 5b 8e ee d3
Mac machine 1 : 0 10 cd 32 50 8
Mac eth2 : 0 e 7f 64 10 fd
Mac machein 2 : 0 10 cd 32 4f e0
I don't understand how skb->head works.
On eth1 I have 16 bytes before reaching the beginning of the paquet ( @ MAC
eth1 )
On eth0 I have 18 bytes.
eth0 & eth1 are two hardware differents cards.
what is the right way to find the start of the data in the buffer ?
what is the meaning of skb->data ?
Thanks
Chris
.....
Hook RX device eth1 -> 1
h : c7805980
nh : cad65010
mac : c328a010
len : 2e
da len: 0
head : c328a000
data : c328a01e
tail : c328a04c
end : c328a680
12 0 ef 0 f 0 40 1 e 1 0 0 1d 1 0 0 0 9 5b 8e ee d3 0 10 cd 32 50 8 8
6 ** 0 1 8 0 6 4 0 2 0 10 cd 32 50 8 9 f 16 3 0 9 5b 8e ee d3 9 f 16
13 ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff 94 2d 12 95
39 30 a 6d 61 63 20 20 20 3a 20 63 66 35 31 38 30 31 32 a 6c 65 6e 20
20 20 3a 20 33 36 a 64 61 20 6c 65 6e 3a 20 30 a 68 65 61 64 20 20 3a
20 63 65 31 30 33 64 38 30 a 64 61 74 61 20 20
.....
.........
Hook RX device eth0 -> 0
h : c41b1834
nh : c41b1820
mac : c9c22012
len : 54
da len: 0
head : c9c22000
data : c9c22020
tail : c9c22074
end : c9c22680
1 8 46 8d e9 0 0 0 1d 1 0 0 0 0 0 0 a1 3 0 e 7f 64 10 fd 0 10 cd 32 4f
e0 8 0 ** 45 0 0 54 0 45 40 0 40 1 fc 30 9 f 16 13 9 f 16 3 0 0 18 d
10 19 0 1 43 e9 83 40 1d ac 8 0 8 9 a b c d e f 10 11 12 13 14 15 16
17 18 19 1a 1b 1c 1d 1e 1f 20 21 22 23 24 25 26 27 28 29 2a 2b 2c 2d
2e 2f 30 31 32 33 34 35 36 37 36 7c 28 9 61 20 6c 65 6e 3a 20 30 a 68
65 61 64 20 20 3a 20 63 65 31 30 33 64 38 30 a 64 61 74 61 20 20 3a 20
63 65 31 30 33 64 38 32 a 74 61 69 6c 20 20 3a 20 63 65 31 30 33 64 62
38 a 65 6e 64 20 20 20 3a 20 63 65 31 30 33 65 30 30 a 31 63
.................
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