1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
|
#include <assert.h>
#include <drivers/pit.h>
#include <kmalloc.h>
#include <network/arp.h>
#include <network/bytes.h>
#include <network/ethernet.h>
#include <network/ipv4.h>
#include <network/tcp.h>
#include <network/udp.h>
#include <string.h>
u16 ip_checksum(void *vdata, size_t length) {
// Cast the data pointer to one that can be indexed.
char *data = (char *)vdata;
// Initialise the accumulator.
u32 acc = 0xffff;
// Handle complete 16-bit blocks.
for (size_t i = 0; i + 1 < length; i += 2) {
u16 word;
memcpy(&word, data + i, 2);
acc += ntohs(word);
if (acc > 0xffff) {
acc -= 0xffff;
}
}
// Handle any partial block at the end of the data.
if (length & 1) {
u16 word = 0;
memcpy(&word, data + length - 1, 1);
acc += ntohs(word);
if (acc > 0xffff) {
acc -= 0xffff;
}
}
// Return the checksum in network byte order.
return htons(~acc);
}
void send_ipv4_packet(ipv4_t ip, u8 protocol, const u8 *payload, u16 length) {
u8 header[20] = {0};
header[0] = (4 /*version*/ << 4) | (5 /*IHL*/);
*((u16 *)(header + 2)) = htons(length + 20);
header[8 /*TTL*/] = 0xF8;
header[9] = protocol;
memcpy(header + 12 /*src_ip*/, &ip_address, sizeof(ipv4_t));
memcpy(header + 16, &ip, sizeof(ipv4_t));
*((u16 *)(header + 10 /*checksum*/)) = ip_checksum(header, 20);
u16 packet_length = length + 20;
u8 *packet = kmalloc(packet_length);
memcpy(packet, header, 20);
memcpy(packet + 20, payload, length);
u8 mac[6];
for (; !get_mac_from_ip(ip, mac);)
;
send_ethernet_packet(mac, 0x0800, packet, packet_length);
kfree(packet);
}
void handle_ipv4(const u8 *payload, u32 packet_length) {
assert(packet_length > 4);
u16 saved_checksum = *(u16 *)(payload + 10);
*(u16 *)(payload + 10) = 0;
u16 calc_checksum = ip_checksum((u8 *)payload, 20);
*(u16 *)(payload + 10) = saved_checksum;
if (calc_checksum != saved_checksum) {
return;
}
u8 version = (*payload & 0xF0) >> 4;
u8 IHL = (*payload & 0xF);
assert(4 == version);
assert(5 == IHL);
u16 ipv4_total_length = ntohs(*(u16 *)(payload + 2));
assert(ipv4_total_length >= 20);
// Make sure the ipv4 header is not trying to get uninitalized memory
assert(ipv4_total_length <= packet_length);
ipv4_t src_ip;
memcpy(&src_ip.d, payload + 12, sizeof(u8[4]));
ipv4_t dst_ip;
memcpy(&dst_ip.d, payload + 16, sizeof(u8[4]));
u8 protocol = *(payload + 9);
switch (protocol) {
case 0x6:
handle_tcp(src_ip, dst_ip, payload + 20, ipv4_total_length - 20);
break;
case 0x11:
handle_udp(src_ip, dst_ip, payload + 20, ipv4_total_length - 20);
break;
default:
kprintf("Protocol given in IPv4 header not handeld: %x\n", protocol);
break;
}
}
|
