Userspace: Implement super simple DHCP client

This commit is contained in:
Bananymous 2024-02-03 02:41:06 +02:00
parent 102aa50a41
commit 2138eeb87f
4 changed files with 403 additions and 0 deletions

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@ -8,6 +8,7 @@ set(USERSPACE_PROJECTS
chmod chmod
cp cp
dd dd
dhcp-client
echo echo
id id
init init

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@ -0,0 +1,16 @@
cmake_minimum_required(VERSION 3.26)
project(dhcp-client CXX)
set(SOURCES
main.cpp
)
add_executable(dhcp-client ${SOURCES})
target_compile_options(dhcp-client PUBLIC -O2 -g)
target_link_libraries(dhcp-client PUBLIC libc)
add_custom_target(dhcp-client-install
COMMAND ${CMAKE_COMMAND} -E copy ${CMAKE_CURRENT_BINARY_DIR}/dhcp-client ${BANAN_BIN}/
DEPENDS dhcp-client
)

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@ -0,0 +1,380 @@
#include <BAN/Endianness.h>
#include <BAN/IPv4.h>
#include <BAN/MAC.h>
#include <BAN/Vector.h>
#include <fcntl.h>
#include <net/if.h>
#include <netinet/in.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stropts.h>
#include <sys/socket.h>
#define DEBUG_DHCP 0
struct DHCPPacket
{
uint8_t op;
uint8_t htype { 0x01 };
uint8_t hlen { 0x06 };
uint8_t hops { 0x00 };
BAN::NetworkEndian<uint32_t> xid { 0x3903F326 };
BAN::NetworkEndian<uint16_t> secs { 0x0000 };
BAN::NetworkEndian<uint16_t> flags { 0x0000 };
BAN::NetworkEndian<uint32_t> ciaddr { 0 };
BAN::NetworkEndian<uint32_t> yiaddr { 0 };
BAN::NetworkEndian<uint32_t> siaddr { 0 };
BAN::NetworkEndian<uint32_t> giaddr { 0 };
BAN::MACAddress chaddr;
uint8_t padding[10] {};
uint8_t legacy[192] {};
BAN::NetworkEndian<uint32_t> magic_cookie { 0x63825363 };
uint8_t options[0x100];
};
static_assert(offsetof(DHCPPacket, options) == 240);
enum DHCPType
{
SubnetMask = 1,
Router = 3,
DomainNameServer = 6,
RequestedIPv4Address= 50,
DHCPMessageType = 53,
ServerIdentifier = 54,
ParameterRequestList = 55,
End = 255,
};
enum DHCPMessageType
{
INVALID = 0,
DHCPDISCOVER = 1,
DHCPOFFER = 2,
DHCPREQUEST = 3,
DHCPDECLINE = 4,
DHCPACK = 5,
};
BAN::MACAddress get_mac_address(int socket)
{
ifreq ifreq;
if (ioctl(socket, SIOCGIFHWADDR, &ifreq) == -1)
{
perror("ioctl");
exit(1);
}
BAN::MACAddress mac_address;
memcpy(&mac_address, ifreq.ifr_ifru.ifru_hwaddr.sa_data, sizeof(mac_address));
return mac_address;
}
void update_ipv4_info(int socket, BAN::IPv4Address address, BAN::IPv4Address subnet)
{
{
ifreq ifreq;
ifreq.ifr_ifru.ifru_addr.sa_family = AF_INET;
*(uint32_t*)ifreq.ifr_ifru.ifru_addr.sa_data = address.as_u32();
if (ioctl(socket, SIOCSIFADDR, &ifreq) == -1)
{
perror("ioctl");
exit(1);
}
}
{
ifreq ifreq;
ifreq.ifr_ifru.ifru_netmask.sa_family = AF_INET;
*(uint32_t*)ifreq.ifr_ifru.ifru_netmask.sa_data = subnet.as_u32();
if (ioctl(socket, SIOCSIFNETMASK, &ifreq) == -1)
{
perror("ioctl");
exit(1);
}
}
}
void send_dhcp_packet(int socket, const DHCPPacket& dhcp_packet, BAN::IPv4Address server_ipv4)
{
sockaddr_in server_addr;
server_addr.sin_family = AF_INET;
server_addr.sin_port = 67;
server_addr.sin_addr.s_addr = server_ipv4.as_u32();;
if (sendto(socket, &dhcp_packet, sizeof(DHCPPacket), 0, (sockaddr*)&server_addr, sizeof(server_addr)) == -1)
{
perror("sendto");
exit(1);
}
}
void send_dhcp_discover(int socket, BAN::MACAddress mac_address)
{
DHCPPacket dhcp_packet;
dhcp_packet.op = 0x01;
dhcp_packet.chaddr = mac_address;
size_t idx = 0;
dhcp_packet.options[idx++] = DHCPMessageType;
dhcp_packet.options[idx++] = 0x01;
dhcp_packet.options[idx++] = DHCPDISCOVER;
dhcp_packet.options[idx++] = ParameterRequestList;
dhcp_packet.options[idx++] = 0x03;
dhcp_packet.options[idx++] = DomainNameServer;
dhcp_packet.options[idx++] = SubnetMask;
dhcp_packet.options[idx++] = Router;
dhcp_packet.options[idx++] = 0xFF;
send_dhcp_packet(socket, dhcp_packet, BAN::IPv4Address { 0xFFFFFFFF });
}
void send_dhcp_request(int socket, BAN::MACAddress mac_address, BAN::IPv4Address offered_ipv4, BAN::IPv4Address server_ipv4)
{
DHCPPacket dhcp_packet;
dhcp_packet.op = 0x01;
dhcp_packet.siaddr = server_ipv4.as_u32();
dhcp_packet.chaddr = mac_address;
size_t idx = 0;
dhcp_packet.options[idx++] = DHCPMessageType;
dhcp_packet.options[idx++] = 0x01;
dhcp_packet.options[idx++] = DHCPREQUEST;
dhcp_packet.options[idx++] = RequestedIPv4Address;
dhcp_packet.options[idx++] = 0x04;
dhcp_packet.options[idx++] = offered_ipv4.address[0];
dhcp_packet.options[idx++] = offered_ipv4.address[1];
dhcp_packet.options[idx++] = offered_ipv4.address[2];
dhcp_packet.options[idx++] = offered_ipv4.address[3];
dhcp_packet.options[idx++] = 0xFF;
send_dhcp_packet(socket, dhcp_packet, BAN::IPv4Address { 0xFFFFFFFF });
}
struct DHCPPacketInfo
{
enum DHCPMessageType message_type { INVALID };
BAN::IPv4Address address { 0 };
BAN::IPv4Address subnet { 0 };
BAN::IPv4Address server { 0 };
BAN::Vector<BAN::IPv4Address> routers;
BAN::Vector<BAN::IPv4Address> dns;
};
DHCPPacketInfo parse_dhcp_packet(const DHCPPacket& packet)
{
DHCPPacketInfo packet_info;
packet_info.address = BAN::IPv4Address(packet.yiaddr);
const uint8_t* options = packet.options;
while (*options != End)
{
uint8_t type = *options++;
uint8_t length = *options++;
switch (type)
{
case SubnetMask:
{
if (length != 4)
{
fprintf(stderr, "Subnet mask with invalid length %hhu\n", length);
break;
}
uint32_t raw = *reinterpret_cast<const BAN::NetworkEndian<uint32_t>*>(options);
packet_info.subnet = BAN::IPv4Address(raw);
break;
}
case Router:
{
if (length % 4 != 0)
{
fprintf(stderr, "Router with invalid length %hhu\n", length);
break;
}
for (int i = 0; i < length; i += 4)
{
uint32_t raw = *reinterpret_cast<const BAN::NetworkEndian<uint32_t>*>(options + i);
MUST(packet_info.routers.emplace_back(raw));
}
break;
}
case DomainNameServer:
{
if (length % 4 != 0)
{
fprintf(stderr, "DNS with invalid length %hhu\n", length);
break;
}
for (int i = 0; i < length; i += 4)
{
uint32_t raw = *reinterpret_cast<const BAN::NetworkEndian<uint32_t>*>(options + i);
MUST(packet_info.dns.emplace_back(raw));
}
break;
}
case DHCPMessageType:
{
if (length != 1)
{
fprintf(stderr, "DHCP Message Type with invalid length %hhu\n", length);
break;
}
switch (*options)
{
case DHCPDISCOVER: packet_info.message_type = DHCPDISCOVER; break;
case DHCPOFFER: packet_info.message_type = DHCPOFFER; break;
case DHCPREQUEST: packet_info.message_type = DHCPREQUEST; break;
case DHCPDECLINE: packet_info.message_type = DHCPDECLINE; break;
case DHCPACK: packet_info.message_type = DHCPACK; break;
}
break;
}
case ServerIdentifier:
{
if (length != 4)
{
fprintf(stderr, "Server identifier with invalid length %hhu\n", length);
break;
}
uint32_t raw = *reinterpret_cast<const BAN::NetworkEndian<uint32_t>*>(options);
packet_info.server = BAN::IPv4Address(raw);
break;
}
}
options += length;
}
return packet_info;
}
BAN::Optional<DHCPPacketInfo> read_dhcp_packet(int socket)
{
DHCPPacket dhcp_packet;
ssize_t nrecv = recvfrom(socket, &dhcp_packet, sizeof(dhcp_packet), 0, nullptr, nullptr);
if (nrecv == -1)
{
perror("revcfrom");
return {};
}
if (nrecv <= (ssize_t)offsetof(DHCPPacket, options))
{
fprintf(stderr, "invalid DHCP offer\n");
return {};
}
if (dhcp_packet.magic_cookie != 0x63825363)
{
fprintf(stderr, "invalid DHCP offer\n");
return {};
}
return parse_dhcp_packet(dhcp_packet);
}
int main()
{
int socket = ::socket(AF_INET, SOCK_DGRAM, 0);
if (socket == -1)
{
perror("socket");
return 1;
}
sockaddr_in client_addr;
client_addr.sin_family = AF_INET;
client_addr.sin_port = 68;
client_addr.sin_addr.s_addr = 0x00000000;
if (bind(socket, (sockaddr*)&client_addr, sizeof(client_addr)) == -1)
{
perror("bind");
return 1;
}
auto mac_address = get_mac_address(socket);
#if DEBUG_DHCP
BAN::Formatter::println(putchar, "MAC: {}", mac_address);
#endif
send_dhcp_discover(socket, mac_address);
#if DEBUG_DHCP
printf("DHCPDISCOVER sent\n");
#endif
auto dhcp_offer = read_dhcp_packet(socket);
if (!dhcp_offer.has_value())
return 1;
if (dhcp_offer->message_type != DHCPOFFER)
{
fprintf(stderr, "DHCP server did not respond with DHCPOFFER\n");
return 1;
}
#if DEBUG_DHCP
BAN::Formatter::println(putchar, "DHCPOFFER");
BAN::Formatter::println(putchar, " IP {}", dhcp_offer->address);
BAN::Formatter::println(putchar, " SUBNET {}", dhcp_offer->subnet);
BAN::Formatter::println(putchar, " SERVER {}", dhcp_offer->server);
#endif
send_dhcp_request(socket, mac_address, dhcp_offer->address, dhcp_offer->server);
#if DEBUG_DHCP
printf("DHCPREQUEST sent\n");
#endif
auto dhcp_ack = read_dhcp_packet(socket);
if (!dhcp_ack.has_value())
return 1;
if (dhcp_ack->message_type != DHCPACK)
{
fprintf(stderr, "DHCP server did not respond with DHCPACK\n");
return 1;
}
#if DEBUG_DHCP
BAN::Formatter::println(putchar, "DHCPACK");
BAN::Formatter::println(putchar, " IP {}", dhcp_ack->address);
BAN::Formatter::println(putchar, " SUBNET {}", dhcp_ack->subnet);
BAN::Formatter::println(putchar, " SERVER {}", dhcp_ack->server);
#endif
if (dhcp_offer->address != dhcp_ack->address)
{
fprintf(stderr, "DHCP server OFFER and ACK ips don't match\n");
return 1;
}
update_ipv4_info(socket, dhcp_ack->address, dhcp_ack->subnet);
if (true)
{
uint32_t packet = 0x12345678;
sockaddr_in server_addr;
server_addr.sin_family = AF_INET;
server_addr.sin_port = 67;
server_addr.sin_addr.s_addr = dhcp_ack->routers.front().as_u32();
server_addr.sin_addr.s_addr = (192 << 24) | (168 << 16) | (1 << 8) | 203;
if (sendto(socket, &packet, sizeof(packet), 0, (sockaddr*)&server_addr, sizeof(server_addr)) == -1)
{
perror("sendto");
exit(1);
}
}
close(socket);
return 0;
}

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@ -29,6 +29,12 @@ int main()
if (load_keymap("/usr/share/keymaps/fi.keymap") == -1) if (load_keymap("/usr/share/keymaps/fi.keymap") == -1)
perror("load_keymap"); perror("load_keymap");
if (fork() == 0)
{
execl("/bin/dhcp-client", "dhcp-client", NULL);
exit(1);
}
bool first = true; bool first = true;
termios termios; termios termios;