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
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
|
// Copyright (C) 2013, 2015 Internet Systems Consortium, Inc. ("ISC")
//
// Permission to use, copy, modify, and/or distribute this software for any
// purpose with or without fee is hereby granted, provided that the above
// copyright notice and this permission notice appear in all copies.
//
// THE SOFTWARE IS PROVIDED "AS IS" AND ISC DISCLAIMS ALL WARRANTIES WITH
// REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
// AND FITNESS. IN NO EVENT SHALL ISC BE LIABLE FOR ANY SPECIAL, DIRECT,
// INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
// LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE
// OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
// PERFORMANCE OF THIS SOFTWARE.
#include <config.h>
#include <asiolink/io_address.h>
#include <dhcp/dhcp6.h>
#include <dhcp/protocol_util.h>
#include <boost/static_assert.hpp>
// in_systm.h is required on some some BSD systems
// complaining that n_time is undefined but used
// in ip.h.
#include <netinet/in_systm.h>
#include <netinet/ip.h>
using namespace isc::asiolink;
using namespace isc::util;
namespace isc {
namespace dhcp {
void
decodeEthernetHeader(InputBuffer& buf, Pkt4Ptr& pkt) {
// The size of the buffer to be parsed must not be lower
// then the size of the Ethernet frame header.
if (buf.getLength() - buf.getPosition() < ETHERNET_HEADER_LEN) {
isc_throw(InvalidPacketHeader, "size of ethernet header in received "
<< "packet is invalid, expected at least "
<< ETHERNET_HEADER_LEN << " bytes, received "
<< buf.getLength() - buf.getPosition() << " bytes");
}
// Packet object must not be NULL. We want to output some values
// to this object.
if (!pkt) {
isc_throw(BadValue, "NULL packet object provided when parsing ethernet"
" frame header");
}
// The size of the single address is always lower then the size of
// the header that holds this address. Otherwise, it is a programming
// error that we want to detect in the compilation time.
BOOST_STATIC_ASSERT(ETHERNET_HEADER_LEN > HWAddr::ETHERNET_HWADDR_LEN);
// Remember initial position.
size_t start_pos = buf.getPosition();
// Read the destination HW address.
std::vector<uint8_t> dest_addr;
buf.readVector(dest_addr, HWAddr::ETHERNET_HWADDR_LEN);
pkt->setLocalHWAddr(HWTYPE_ETHERNET, HWAddr::ETHERNET_HWADDR_LEN, dest_addr);
// Read the source HW address.
std::vector<uint8_t> src_addr;
buf.readVector(src_addr, HWAddr::ETHERNET_HWADDR_LEN);
pkt->setRemoteHWAddr(HWTYPE_ETHERNET, HWAddr::ETHERNET_HWADDR_LEN, src_addr);
// Move the buffer read pointer to the end of the Ethernet frame header.
buf.setPosition(start_pos + ETHERNET_HEADER_LEN);
}
void
decodeIpUdpHeader(InputBuffer& buf, Pkt4Ptr& pkt) {
// The size of the buffer must be at least equal to the minimal size of
// the IPv4 packet header plus UDP header length.
if (buf.getLength() - buf.getPosition() < MIN_IP_HEADER_LEN + UDP_HEADER_LEN) {
isc_throw(InvalidPacketHeader, "the total size of the IP and UDP headers in "
<< "received packet is invalid, expected at least "
<< MIN_IP_HEADER_LEN + UDP_HEADER_LEN
<< " bytes, received " << buf.getLength() - buf.getPosition()
<< " bytes");
}
// Packet object must not be NULL.
if (!pkt) {
isc_throw(BadValue, "NULL packet object provided when parsing IP and UDP"
" packet headers");
}
BOOST_STATIC_ASSERT(IP_SRC_ADDR_OFFSET < MIN_IP_HEADER_LEN);
// Remember initial position of the read pointer.
size_t start_pos = buf.getPosition();
// Read IP header length (mask most significant bits as they indicate IP version).
uint8_t ip_len = buf.readUint8() & 0xF;
// IP length is the number of 4 byte chunks that construct IPv4 header.
// It must not be lower than 5 because first 20 bytes are fixed.
if (ip_len < 5) {
isc_throw(InvalidPacketHeader, "Value of the length of the IP header must not be"
<< " lower than 5 words. The length of the received header is "
<< ip_len << ".");
}
// Seek to the position of source IP address.
buf.setPosition(start_pos + IP_SRC_ADDR_OFFSET);
// Read source address.
pkt->setRemoteAddr(IOAddress(buf.readUint32()));
// Read destination address.
pkt->setLocalAddr(IOAddress(buf.readUint32()));
// Skip IP header options (if any) to start of the
// UDP header.
buf.setPosition(start_pos + ip_len * 4);
// Read source port from UDP header.
pkt->setRemotePort(buf.readUint16());
// Read destination port from UDP header.
pkt->setLocalPort(buf.readUint16());
// Set the pointer position to the first byte o the
// UDP payload (DHCP packet).
buf.setPosition(start_pos + ip_len * 4 + UDP_HEADER_LEN);
}
void
writeEthernetHeader(const Pkt4Ptr& pkt, OutputBuffer& out_buf) {
// Set destination HW address.
HWAddrPtr remote_addr = pkt->getRemoteHWAddr();
if (remote_addr) {
if (remote_addr->hwaddr_.size() == HWAddr::ETHERNET_HWADDR_LEN) {
out_buf.writeData(&remote_addr->hwaddr_[0],
HWAddr::ETHERNET_HWADDR_LEN);
} else {
isc_throw(BadValue, "invalid size of the remote HW address "
<< remote_addr->hwaddr_.size() << " when constructing"
<< " an ethernet frame header; expected size is"
<< " " << HWAddr::ETHERNET_HWADDR_LEN);
}
} else {
// HW address has not been specified. This is possible when receiving
// packet through a logical interface (e.g. lo). In such cases, we
// don't want to fail but rather provide a default HW address, which
// consists of zeros.
out_buf.writeData(&std::vector<uint8_t>(HWAddr::ETHERNET_HWADDR_LEN)[0],
HWAddr::ETHERNET_HWADDR_LEN);
}
// Set source HW address.
HWAddrPtr local_addr = pkt->getLocalHWAddr();
if (local_addr) {
if (local_addr->hwaddr_.size() == HWAddr::ETHERNET_HWADDR_LEN) {
out_buf.writeData(&local_addr->hwaddr_[0],
HWAddr::ETHERNET_HWADDR_LEN);
} else {
isc_throw(BadValue, "invalid size of the local HW address "
<< local_addr->hwaddr_.size() << " when constructing"
<< " an ethernet frame header; expected size is"
<< " " << HWAddr::ETHERNET_HWADDR_LEN);
}
} else {
// Provide default HW address.
out_buf.writeData(&std::vector<uint8_t>(HWAddr::ETHERNET_HWADDR_LEN)[0],
HWAddr::ETHERNET_HWADDR_LEN);
}
// Type IP.
out_buf.writeUint16(ETHERNET_TYPE_IP);
}
void
writeIpUdpHeader(const Pkt4Ptr& pkt, util::OutputBuffer& out_buf) {
out_buf.writeUint8(0x45); // IP version 4, IP header length 5
out_buf.writeUint8(IPTOS_LOWDELAY); // DSCP and ECN
out_buf.writeUint16(28 + pkt->getBuffer().getLength()); // Total length.
out_buf.writeUint16(0); // Identification
out_buf.writeUint16(0x4000); // Disable fragmentation.
out_buf.writeUint8(128); // TTL
out_buf.writeUint8(IPPROTO_UDP); // Protocol UDP.
out_buf.writeUint16(0); // Temporarily set checksum to 0.
out_buf.writeUint32(pkt->getLocalAddr()); // Source address.
out_buf.writeUint32(pkt->getRemoteAddr()); // Destination address.
// Calculate pseudo header checksum. It will be necessary to compute
// UDP checksum.
// Get the UDP length. This includes udp header's and data length.
uint32_t udp_len = 8 + pkt->getBuffer().getLength();
// The magic number "8" indicates the offset where the source address
// is stored in the buffer. This offset is counted here from the
// current tail of the buffer. Starting from this offset we calculate
// the checksum using 8 following bytes of data. This will include
// 4 bytes of source address and 4 bytes of destination address.
// The IPPROTO_UDP and udp_len are also added up to the checksum.
uint16_t pseudo_hdr_checksum =
calcChecksum(static_cast<const uint8_t*>(out_buf.getData()) + out_buf.getLength() - 8,
8, IPPROTO_UDP + udp_len);
// Calculate IP header checksum.
uint16_t ip_checksum = ~calcChecksum(static_cast<const uint8_t*>(out_buf.getData())
+ out_buf.getLength() - 20, 20);
// Write checksum in the IP header. The offset of the checksum is 10 bytes
// back from the tail of the current buffer.
out_buf.writeUint16At(ip_checksum, out_buf.getLength() - 10);
// Start UDP header.
out_buf.writeUint16(pkt->getLocalPort()); // Source port.
out_buf.writeUint16(pkt->getRemotePort()); // Destination port.
out_buf.writeUint16(udp_len); // Length of the header and data.
// Checksum is calculated from the contents of UDP header, data and pseudo ip header.
// The magic number "6" indicates that the UDP header starts at offset 6 from the
// tail of the current buffer. These 6 bytes contain source and destination port
// as well as the length of the header.
uint16_t udp_checksum =
~calcChecksum(static_cast<const uint8_t*>(out_buf.getData()) + out_buf.getLength() - 6, 6,
calcChecksum(static_cast<const uint8_t*>(pkt->getBuffer().getData()),
pkt->getBuffer().getLength(),
pseudo_hdr_checksum));
// Write UDP checksum.
out_buf.writeUint16(udp_checksum);
}
uint16_t
calcChecksum(const uint8_t* buf, const uint32_t buf_size, uint32_t sum) {
uint32_t i;
for (i = 0; i < (buf_size & ~1U); i += 2) {
uint16_t chunk = buf[i] << 8 | buf[i + 1];
sum += chunk;
if (sum > 0xFFFF) {
sum -= 0xFFFF;
}
}
// If one byte has left, we also need to add it to the checksum.
if (i < buf_size) {
sum += buf[i] << 8;
if (sum > 0xFFFF) {
sum -= 0xFFFF;
}
}
return (sum);
}
}
}
|
