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//
// Copyright (C) 2015 The Android Open Source Project
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//
#include "dhcp_client/dhcpv4.h"
#include <linux/filter.h>
#include <linux/if_packet.h>
#include <net/ethernet.h>
#include <net/if.h>
#include <net/if_arp.h>
#include <netinet/ip.h>
#include <netinet/udp.h>
#include <random>
#include <base/bind.h>
#include <base/logging.h>
#include "dhcp_client/dhcp_message.h"
using base::Bind;
using base::Unretained;
using shill::ByteString;
using shill::IOHandlerFactoryContainer;
namespace dhcp_client {
namespace {
// UDP port numbers for DHCP.
const uint16_t kDHCPServerPort = 67;
const uint16_t kDHCPClientPort = 68;
const int kInvalidSocketDescriptor = -1;
// RFC 791: the minimum value for a correct header is 20 octets.
// The maximum value is 60 octets.
const size_t kIPHeaderMinLength = 20;
const size_t kIPHeaderMaxLength = 60;
// Socket filter for dhcp packet.
const sock_filter dhcp_bpf_filter[] = {
BPF_STMT(BPF_LD + BPF_B + BPF_ABS, 23 - ETH_HLEN),
BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, IPPROTO_UDP, 0, 6),
BPF_STMT(BPF_LD + BPF_H + BPF_ABS, 20 - ETH_HLEN),
BPF_JUMP(BPF_JMP + BPF_JSET + BPF_K, 0x1fff, 4, 0),
BPF_STMT(BPF_LDX + BPF_B + BPF_MSH, 14 - ETH_HLEN),
BPF_STMT(BPF_LD + BPF_H + BPF_IND, 16 - ETH_HLEN),
BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, kDHCPClientPort, 0, 1),
BPF_STMT(BPF_RET + BPF_K, 0x0fffffff),
BPF_STMT(BPF_RET + BPF_K, 0),
};
const int dhcp_bpf_filter_len =
sizeof(dhcp_bpf_filter) / sizeof(dhcp_bpf_filter[0]);
} // namespace
DHCPV4::DHCPV4(const std::string& interface_name,
const ByteString& hardware_address,
unsigned int interface_index,
const std::string& network_id,
bool request_hostname,
bool arp_gateway,
bool unicast_arp,
EventDispatcherInterface* event_dispatcher)
: interface_name_(interface_name),
hardware_address_(hardware_address),
interface_index_(interface_index),
network_id_(network_id),
request_hostname_(request_hostname),
arp_gateway_(arp_gateway),
unicast_arp_(unicast_arp),
event_dispatcher_(event_dispatcher),
io_handler_factory_(
IOHandlerFactoryContainer::GetInstance()->GetIOHandlerFactory()),
state_(State::INIT),
from_(INADDR_ANY),
to_(INADDR_BROADCAST),
socket_(kInvalidSocketDescriptor),
sockets_(new shill::Sockets()),
random_engine_(time(nullptr)) {
}
DHCPV4::~DHCPV4() {
Stop();
}
void DHCPV4::ParseRawPacket(shill::InputData* data) {
if (data->len < sizeof(iphdr)) {
LOG(ERROR) << "Invalid packet length from buffer";
return;
}
// The socket filter has finished part the header validation.
// This function will perform the remaining part.
int header_len = ValidatePacketHeader(data->buf, data->len);
if (header_len == -1) {
return;
}
unsigned char* buffer = data->buf + header_len;
DHCPMessage msg;
if (!DHCPMessage::InitFromBuffer(buffer, data->len - header_len, &msg)) {
LOG(ERROR) << "Failed to initialize DHCP message from buffer";
return;
}
// In INIT state the client ignores all messages from server.
if (state_ == State::INIT) {
return;
}
// Check transaction id with the existing one.
if (msg.transaction_id() != transaction_id_) {
LOG(ERROR) << "Transaction id(xid) doesn't match";
return;
}
uint8_t message_type = msg.message_type();
switch (message_type) {
case kDHCPMessageTypeOffer:
HandleOffer(msg);
break;
case kDHCPMessageTypeAck:
HandleAck(msg);
break;
case kDHCPMessageTypeNak:
HandleNak(msg);
break;
default:
LOG(ERROR) << "Invalid message type: "
<< static_cast<int>(message_type);
}
}
void DHCPV4::OnReadError(const std::string& error_msg) {
LOG(INFO) << __func__;
}
bool DHCPV4::Start() {
if (!CreateRawSocket()) {
return false;
}
input_handler_.reset(io_handler_factory_->CreateIOInputHandler(
socket_,
Bind(&DHCPV4::ParseRawPacket, Unretained(this)),
Bind(&DHCPV4::OnReadError, Unretained(this))));
return true;
}
void DHCPV4::Stop() {
input_handler_.reset();
if (socket_ != kInvalidSocketDescriptor) {
sockets_->Close(socket_);
}
}
bool DHCPV4::CreateRawSocket() {
int fd = sockets_->Socket(PF_PACKET,
SOCK_DGRAM | SOCK_CLOEXEC | SOCK_NONBLOCK,
htons(ETHERTYPE_IP));
if (fd == kInvalidSocketDescriptor) {
PLOG(ERROR) << "Failed to create socket";
return false;
}
shill::ScopedSocketCloser socket_closer(sockets_.get(), fd);
// Apply the socket filter.
sock_fprog pf;
memset(&pf, 0, sizeof(pf));
pf.filter = const_cast<sock_filter*>(dhcp_bpf_filter);
pf.len = dhcp_bpf_filter_len;
if (sockets_->AttachFilter(fd, &pf) != 0) {
PLOG(ERROR) << "Failed to attach filter";
return false;
}
if (sockets_->ReuseAddress(fd) == -1) {
PLOG(ERROR) << "Failed to reuse socket address";
return false;
}
if (sockets_->BindToDevice(fd, interface_name_) < 0) {
PLOG(ERROR) << "Failed to bind socket to device";
return false;
}
struct sockaddr_ll local;
memset(&local, 0, sizeof(local));
local.sll_family = PF_PACKET;
local.sll_protocol = htons(ETHERTYPE_IP);
local.sll_ifindex = static_cast<int>(interface_index_);
if (sockets_->Bind(fd,
reinterpret_cast<struct sockaddr*>(&local),
sizeof(local)) < 0) {
PLOG(ERROR) << "Failed to bind to address";
return false;
}
socket_ = socket_closer.Release();
return true;
}
void DHCPV4::HandleOffer(const DHCPMessage& msg) {
return;
}
void DHCPV4::HandleAck(const DHCPMessage& msg) {
return;
}
void DHCPV4::HandleNak(const DHCPMessage& msg) {
return;
}
bool DHCPV4::MakeRawPacket(const DHCPMessage& message, ByteString* output) {
ByteString payload;
if (!message.Serialize(&payload)) {
LOG(ERROR) << "Failed to serialzie dhcp message";
return false;
}
const size_t header_len = sizeof(struct iphdr) + sizeof(struct udphdr);
const size_t payload_len = payload.GetLength();
char buffer[header_len + payload_len];
memset(buffer, 0, header_len + payload_len);
struct iphdr* ip = reinterpret_cast<struct iphdr*>(buffer);
struct udphdr* udp = reinterpret_cast<struct udphdr*>(buffer + sizeof(*ip));
if (!payload.CopyData(payload_len, buffer + header_len)) {
LOG(ERROR) << "Failed to copy data from payload";
return false;
}
udp->uh_sport = htons(kDHCPClientPort);
udp->uh_dport = htons(kDHCPServerPort);
udp->uh_ulen =
htons(static_cast<uint16_t>(sizeof(*udp) + payload.GetLength()));
// Fill pseudo header (for UDP checksum computing):
// Protocol.
ip->protocol = IPPROTO_UDP;
// Source IP address.
ip->saddr = htonl(from_);
// Destination IP address.
ip->daddr = htonl(to_);
// Total length, use udp packet length for pseudo header.
ip->tot_len = udp->uh_ulen;
// Calculate udp checksum based on:
// IPV4 pseudo header, UDP header, and payload.
udp->uh_sum = htons(DHCPMessage::ComputeChecksum(
reinterpret_cast<const uint8_t*>(buffer),
header_len + payload_len));
// IP version.
ip->version = IPVERSION;
// IP header length.
ip->ihl = sizeof(*ip) >> 2;
// Fragment offset field.
// The DHCP packet is always smaller than MTU,
// so fragmentation is not needed.
ip->frag_off = 0;
// Identification.
ip->id = static_cast<uint16_t>(
std::uniform_int_distribution<unsigned int>()(
random_engine_) % UINT16_MAX + 1);
// Time to live.
ip->ttl = IPDEFTTL;
// Total length.
ip->tot_len = htons(static_cast<uint16_t>(header_len+ payload.GetLength()));
// Calculate IP Checksum only based on IP header.
ip->check = htons(DHCPMessage::ComputeChecksum(
reinterpret_cast<const uint8_t*>(ip),
sizeof(*ip)));
*output = ByteString(buffer, header_len + payload_len);
return true;
}
bool DHCPV4::SendRawPacket(const ByteString& packet) {
struct sockaddr_ll remote;
memset(&remote, 0, sizeof(remote));
remote.sll_family = AF_PACKET;
remote.sll_protocol = htons(ETHERTYPE_IP);
remote.sll_ifindex = interface_index_;
remote.sll_hatype = htons(ARPHRD_ETHER);
// Use broadcast hardware address.
remote.sll_halen = IFHWADDRLEN;
memset(remote.sll_addr, 0xff, IFHWADDRLEN);
size_t result = sockets_->SendTo(socket_,
packet.GetConstData(),
packet.GetLength(),
0,
reinterpret_cast<struct sockaddr *>(&remote),
sizeof(remote));
if (result != packet.GetLength()) {
PLOG(ERROR) << "Socket sento failed";
return false;
}
return true;
}
int DHCPV4::ValidatePacketHeader(const unsigned char* buffer, size_t len) {
const struct iphdr* ip =
reinterpret_cast<const struct iphdr*>(buffer);
const size_t ip_header_len = static_cast<size_t>(ip->ihl) << 2;
if (ip_header_len < kIPHeaderMinLength ||
ip_header_len > kIPHeaderMaxLength) {
LOG(ERROR) << "Invalid Internet Header Length: "
<< ip_header_len << " bytes";
return -1;
}
if (ip->tot_len != len) {
LOG(ERROR) << "Invalid IP total length";
return -1;
}
// TODO(nywang): Validate other ip header fields.
const struct udphdr* udp =
reinterpret_cast<const struct udphdr*>(buffer + ip_header_len);
if (udp->uh_sport != htons(kDHCPServerPort) ||
udp->uh_dport != htons(kDHCPClientPort)) {
LOG(ERROR) << "Invlaid UDP ports";
return -1;
}
if (udp->uh_ulen != len - ip_header_len) {
LOG(ERROR) << "Invalid UDP total length";
return -1;
}
// TODO(nywang): Validate UDP checksum.
return ip_header_len + sizeof(*udp);
}
} // namespace dhcp_client