324 lines
12 KiB
Rust
324 lines
12 KiB
Rust
use crate::dhcp_snooper::Lease;
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use crate::proxy::conntrack::ConntrackResult;
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use crate::proxy::udp_packet_helper::UdpPacketHelper;
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use crate::proxy::{Action, Direction, Proxy, Rule, select_rules};
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use anyhow::Context;
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use anyhow::Result;
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use smoltcp::wire::{
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ArpOperation, ArpPacket, ArpRepr, EthernetFrame, EthernetProtocol, IpProtocol, Ipv4Address,
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Ipv4Packet, UdpPacket,
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};
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impl Proxy<'_> {
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pub(crate) fn process_frame_from_vm(&mut self, frame: EthernetFrame<&[u8]>) -> Result<()> {
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if self.allowed_from_vm(&frame).is_none() {
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// Block packet by not forwarding it to the host
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return Ok(());
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}
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self.host
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.write(frame.as_ref())
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.map(|_| ())
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.context("failed to write to the host")
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}
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fn allowed_from_vm(&mut self, frame: &EthernetFrame<&[u8]>) -> Option<()> {
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if frame.src_addr() != self.vm_mac_address {
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return None;
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}
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match frame.ethertype() {
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EthernetProtocol::Arp => {
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let arp_pkt = ArpPacket::new_checked(frame.payload()).ok()?;
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self.allowed_from_vm_arp(arp_pkt)
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}
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EthernetProtocol::Ipv4 => {
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let ipv4_pkt = Ipv4Packet::new_checked(frame.payload()).ok()?;
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self.allowed_from_vm_ipv4(ipv4_pkt)
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}
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_ => None,
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}
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}
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fn allowed_from_vm_arp(&self, arp_pkt: ArpPacket<&[u8]>) -> Option<()> {
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vm_arp_allowed(arp_pkt, self.vm_mac_address, self.dhcp_snooper.lease())
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}
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pub(crate) fn allowed_from_vm_ipv4(&mut self, ipv4_pkt: Ipv4Packet<&[u8]>) -> Option<()> {
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// Is this packet coming from VM's IP address that we've learned from DHCP snooping?
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if let Some(lease) = &self.dhcp_snooper.lease()
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&& lease.is_valid_for(ipv4_pkt.src_addr())
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{
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let dst_addr = ipv4_pkt.dst_addr();
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// Filter traffic based on user-specified rules first
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if let Some(rules) = select_rules(&self.rules, dst_addr, Direction::Out) {
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// DHCP is required to maintain the VM's lease and must bypass user-specified rules
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if is_allowed_dhcp_request(&ipv4_pkt, Some(self.host.gateway_ip)) {
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return Some(());
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}
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if let Some((action, _)) = rules
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.iter()
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.find(|(_, rule)| matches!(rule, Rule::Stateless(_)))
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{
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return match action {
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Action::Allow => Some(()),
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Action::Block => None,
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};
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}
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return match self.conntrack.inspect_from_vm(&ipv4_pkt) {
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ConntrackResult::Allowed => Some(()),
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ConntrackResult::Denied => None,
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ConntrackResult::New(pending) => {
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let allow_new = rules.iter().any(|(action, rule)| {
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*action == Action::Allow
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&& matches!(
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rule,
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Rule::Stateful {
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direction: Direction::Out,
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..
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}
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)
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});
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if !allow_new {
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return None;
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}
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self.conntrack.commit(pending).then_some(())
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}
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};
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}
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// When no user-specified rules matched, simply allow all global traffic
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if ip_network::IpNetwork::from(dst_addr).is_global() {
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return Some(());
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}
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// Additionally, allow communication with the host,
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// otherwise things like SSH to a VM won't work
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if ipv4_pkt.dst_addr() == self.host.gateway_ip {
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return Some(());
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}
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// Additionally, allow DNS requests to DNS-servers
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// provided to a VM by the host's DHCP server
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if ipv4_pkt.next_header() == IpProtocol::Udp {
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let udp_pkt = UdpPacket::new_checked(ipv4_pkt.payload()).ok()?;
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if udp_pkt.is_dns_request()
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&& self.dhcp_snooper.valid_dns_target(&ipv4_pkt.dst_addr())
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{
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return Some(());
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}
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}
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}
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// Allow outgoing DHCP requests to the bootpd(8) broadcast address,
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// otherwise DHCP snooper will never be populated
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if is_allowed_dhcp_request(&ipv4_pkt, None) {
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return Some(());
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}
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None
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}
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}
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fn is_allowed_dhcp_request(
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ipv4_pkt: &Ipv4Packet<&[u8]>,
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unicast_target: Option<Ipv4Address>,
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) -> bool {
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let dst_addr = ipv4_pkt.dst_addr();
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// Keep the common path cheap and inspect UDP only for a permitted DHCP target
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if !dst_addr.is_broadcast() && unicast_target != Some(dst_addr) {
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return false;
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}
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if ipv4_pkt.next_header() != IpProtocol::Udp {
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return false;
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}
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let Ok(udp_pkt) = UdpPacket::new_checked(ipv4_pkt.payload()) else {
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return false;
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};
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udp_pkt.is_dhcp_request()
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}
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fn vm_arp_allowed(
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arp_pkt: ArpPacket<&[u8]>,
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vm_mac_address: smoltcp::wire::EthernetAddress,
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lease: &Option<Lease>,
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) -> Option<()> {
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let (operation, source_hardware_addr, source_protocol_addr) =
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match ArpRepr::parse(&arp_pkt).ok()? {
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ArpRepr::EthernetIpv4 {
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operation,
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source_hardware_addr,
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source_protocol_addr,
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..
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} => (operation, source_hardware_addr, source_protocol_addr),
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_ => return None,
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};
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if !matches!(operation, ArpOperation::Request | ArpOperation::Reply) {
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return None;
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}
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if source_hardware_addr != vm_mac_address {
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return None;
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}
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if let Some(lease) = lease {
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if lease.is_valid_for(source_protocol_addr) {
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return Some(());
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}
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} else if source_protocol_addr.is_unspecified() {
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return Some(());
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}
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None
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}
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#[cfg(test)]
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mod tests {
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use crate::dhcp_snooper::Lease;
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use smoltcp::wire::{
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ArpHardware, ArpOperation, ArpPacket, EthernetAddress, EthernetProtocol, IpProtocol,
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Ipv4Address, Ipv4Packet, UdpPacket,
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};
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use std::collections::HashSet;
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use std::time::Duration;
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#[test]
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fn test_allowed_dhcp_request_targets() {
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let gateway = Ipv4Address::new(192, 168, 64, 1);
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let other = Ipv4Address::new(192, 168, 64, 2);
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assert!(allowed_dhcp_request(Ipv4Address::BROADCAST, None));
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assert!(allowed_dhcp_request(gateway, Some(gateway)));
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assert!(!allowed_dhcp_request(gateway, None));
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assert!(!allowed_dhcp_request(other, Some(gateway)));
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}
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#[test]
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fn test_allowed_from_vm_arp_allows_unspecified_request_without_lease() {
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let vm_mac_address = EthernetAddress([0x02, 0x00, 0x00, 0x00, 0x00, 0x01]);
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let buf = arp_packet(vm_mac_address.0, [0, 0, 0, 0], ArpOperation::Request, 6, 4);
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let arp_pkt = ArpPacket::new_checked(buf.as_slice()).unwrap();
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assert!(super::vm_arp_allowed(arp_pkt, vm_mac_address, &None).is_some());
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}
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#[test]
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fn test_allowed_from_vm_arp_allows_reply_for_leased_ip() {
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let vm_mac_address = EthernetAddress([0x02, 0x00, 0x00, 0x00, 0x00, 0x01]);
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let lease_ip = Ipv4Address::new(192, 168, 0, 2);
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let lease = Some(Lease::new(
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lease_ip,
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Duration::from_secs(600),
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HashSet::new(),
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));
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let buf = arp_packet(
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vm_mac_address.0,
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lease_ip.octets(),
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ArpOperation::Reply,
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6,
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4,
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);
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let arp_pkt = ArpPacket::new_checked(buf.as_slice()).unwrap();
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assert!(super::vm_arp_allowed(arp_pkt, vm_mac_address, &lease).is_some());
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}
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#[test]
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fn test_allowed_from_vm_arp_rejects_unknown_operation() {
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let vm_mac_address = EthernetAddress([0x02, 0x00, 0x00, 0x00, 0x00, 0x01]);
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let buf = arp_packet(
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vm_mac_address.0,
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[0, 0, 0, 0],
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ArpOperation::Unknown(3),
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6,
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4,
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);
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let arp_pkt = ArpPacket::new_checked(buf.as_slice()).unwrap();
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assert!(super::vm_arp_allowed(arp_pkt, vm_mac_address, &None).is_none());
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}
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#[test]
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fn test_allowed_from_vm_arp_rejects_non_ethernet_hardware_type() {
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let vm_mac_address = EthernetAddress([0x02, 0x00, 0x00, 0x00, 0x00, 0x01]);
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let mut buf = arp_packet(vm_mac_address.0, [0, 0, 0, 0], ArpOperation::Request, 6, 4);
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let mut arp_pkt = ArpPacket::new_unchecked(buf.as_mut_slice());
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arp_pkt.set_hardware_type(ArpHardware::Unknown(2));
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let arp_pkt = ArpPacket::new_checked(buf.as_slice()).unwrap();
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assert!(super::vm_arp_allowed(arp_pkt, vm_mac_address, &None).is_none());
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}
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#[test]
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fn test_allowed_from_vm_arp_rejects_non_ipv4_protocol_type() {
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let vm_mac_address = EthernetAddress([0x02, 0x00, 0x00, 0x00, 0x00, 0x01]);
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let mut buf = arp_packet(vm_mac_address.0, [0, 0, 0, 0], ArpOperation::Request, 6, 4);
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let mut arp_pkt = ArpPacket::new_unchecked(buf.as_mut_slice());
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arp_pkt.set_protocol_type(EthernetProtocol::Ipv6);
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let arp_pkt = ArpPacket::new_checked(buf.as_slice()).unwrap();
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assert!(super::vm_arp_allowed(arp_pkt, vm_mac_address, &None).is_none());
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}
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#[test]
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fn test_allowed_from_vm_arp_rejects_non_ipv4_protocol_length() {
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let vm_mac_address = EthernetAddress([0x02, 0x00, 0x00, 0x00, 0x00, 0x01]);
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let buf = arp_packet(vm_mac_address.0, [0, 0, 0], ArpOperation::Request, 6, 3);
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let arp_pkt = ArpPacket::new_checked(buf.as_slice()).unwrap();
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assert!(super::vm_arp_allowed(arp_pkt, vm_mac_address, &None).is_none());
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}
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fn arp_packet(
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source_hardware_addr: [u8; 6],
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source_protocol_addr: impl AsRef<[u8]>,
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operation: ArpOperation,
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hardware_len: u8,
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protocol_len: u8,
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) -> Vec<u8> {
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let source_protocol_addr = source_protocol_addr.as_ref();
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let payload_len = 8 + 2 * (hardware_len as usize + protocol_len as usize);
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let mut buf = vec![0; payload_len];
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let mut arp_pkt = ArpPacket::new_unchecked(buf.as_mut_slice());
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arp_pkt.set_hardware_type(ArpHardware::Ethernet);
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arp_pkt.set_protocol_type(EthernetProtocol::Ipv4);
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arp_pkt.set_hardware_len(hardware_len);
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arp_pkt.set_protocol_len(protocol_len);
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arp_pkt.set_operation(operation);
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arp_pkt.set_source_hardware_addr(&source_hardware_addr[..hardware_len as usize]);
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arp_pkt.set_source_protocol_addr(source_protocol_addr);
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arp_pkt.set_target_hardware_addr(&[0; 6][..hardware_len as usize]);
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arp_pkt.set_target_protocol_addr(&vec![0; protocol_len as usize]);
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buf
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}
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fn allowed_dhcp_request(dst_addr: Ipv4Address, unicast_target: Option<Ipv4Address>) -> bool {
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let mut buf = vec![0; 28];
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let mut ipv4_pkt = Ipv4Packet::new_unchecked(buf.as_mut_slice());
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ipv4_pkt.set_version(4);
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ipv4_pkt.set_header_len(20);
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ipv4_pkt.set_total_len(28);
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ipv4_pkt.set_next_header(IpProtocol::Udp);
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ipv4_pkt.set_dst_addr(dst_addr);
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let mut udp_pkt = UdpPacket::new_unchecked(ipv4_pkt.payload_mut());
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udp_pkt.set_src_port(68);
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udp_pkt.set_dst_port(67);
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udp_pkt.set_len(8);
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let ipv4_pkt = Ipv4Packet::new_checked(buf.as_slice()).unwrap();
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super::is_allowed_dhcp_request(&ipv4_pkt, unicast_target)
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}
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}
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