src/connectivity/lib/packet-formats/src/arp.rs

// Copyright 2018 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

//! Parsing and serialization of ARP packets.

#[cfg(test)]
use core::fmt::{self, Debug, Formatter};
use core::hash::Hash;
use core::mem;

use net_types::ethernet::Mac;
use net_types::ip::{IpAddress, Ipv4Addr};
use packet::{BufferView, BufferViewMut, InnerPacketBuilder, ParsablePacket, ParseMetadata};
use zerocopy::byteorder::network_endian::U16;
use zerocopy::{AsBytes, ByteSlice, FromBytes, FromZeros, NoCell, Ref, Unaligned};

use crate::error::{ParseError, ParseResult};

#[cfg(test)]
pub(crate) const ARP_HDR_LEN: usize = 8;
#[cfg(test)]
pub(crate) const ARP_ETHERNET_IPV4_PACKET_LEN: usize = 28;

create_protocol_enum!(
    /// The type of an ARP operation.
    #[derive(Copy, Clone, Eq, PartialEq)]
    #[allow(missing_docs)]
    pub enum ArpOp : u16 {
        Request, 0x0001, "Request";
        Response, 0x0002, "Response";
        _, "ArpOp {}";
    }
);

/// A trait to represent an ARP hardware type.
pub trait HType: FromBytes + AsBytes + NoCell + Unaligned + Copy + Clone + Hash + Eq {
    /// The hardware type.
    const HTYPE: ArpHardwareType;
    /// The in-memory size of an instance of the type.
    const HLEN: u8;
    /// The broadcast address for this type.
    const BROADCAST: Self;
}

/// A trait to represent an ARP protocol type.
pub trait PType: FromBytes + AsBytes + NoCell + Unaligned + Copy + Clone + Hash + Eq {
    /// The protocol type.
    const PTYPE: ArpNetworkType;
    /// The in-memory size of an instance of the type.
    const PLEN: u8;
}

impl HType for Mac {
    const HTYPE: ArpHardwareType = ArpHardwareType::Ethernet;
    const HLEN: u8 = mem::size_of::<Mac>() as u8;
    const BROADCAST: Mac = Mac::BROADCAST;
}

impl PType for Ipv4Addr {
    const PTYPE: ArpNetworkType = ArpNetworkType::Ipv4;
    const PLEN: u8 = Ipv4Addr::BYTES;
}

create_protocol_enum!(
    /// An ARP hardware protocol.
    #[derive(PartialEq)]
    #[allow(missing_docs)]
    pub enum ArpHardwareType : u16 {
        Ethernet, 0x0001, "Ethernet";
    }
);

create_protocol_enum!(
    /// An ARP network protocol.
    #[derive(PartialEq)]
    #[allow(missing_docs)]
    pub enum ArpNetworkType : u16 {
        Ipv4, 0x0800, "IPv4";
    }
);

#[derive(Default, FromZeros, FromBytes, AsBytes, NoCell, Unaligned)]
#[repr(C)]
struct Header {
    htype: U16, // Hardware (e.g. Ethernet)
    ptype: U16, // Protocol (e.g. IPv4)
    hlen: u8,   // Length (in octets) of hardware address
    plen: u8,   // Length (in octets) of protocol address
    oper: U16,  // Operation: 1 for Req, 2 for Reply
}

impl Header {
    fn new<HwAddr: HType, ProtoAddr: PType>(op: ArpOp) -> Header {
        Header {
            htype: U16::new(<HwAddr as HType>::HTYPE.into()),
            hlen: <HwAddr as HType>::HLEN,
            ptype: U16::new(<ProtoAddr as PType>::PTYPE.into()),
            plen: <ProtoAddr as PType>::PLEN,
            oper: U16::new(op.into()),
        }
    }
}

/// Peek at an ARP header to see what hardware and protocol address types are
/// used.
///
/// Since `ArpPacket` is statically typed with the hardware and protocol address
/// types expected in the header and body, these types must be known ahead of
/// time before calling `parse`. If multiple different types are valid in a
/// given parsing context, and so the caller cannot know ahead of time which
/// types to use, `peek_arp_types` can be used to peek at the header first to
/// figure out which static types should be used in a subsequent call to
/// `parse`.
///
/// Note that `peek_arp_types` only inspects certain fields in the header, and
/// so `peek_arp_types` succeeding does not guarantee that a subsequent call to
/// `parse` will also succeed.
pub fn peek_arp_types<B: ByteSlice>(bytes: B) -> ParseResult<(ArpHardwareType, ArpNetworkType)> {
    let (header, _) = Ref::<B, Header>::new_unaligned_from_prefix(bytes)
        .ok_or_else(debug_err_fn!(ParseError::Format, "too few bytes for header"))?;

    let hw = ArpHardwareType::try_from(header.htype.get()).ok().ok_or_else(debug_err_fn!(
        ParseError::NotSupported,
        "unrecognized hardware protocol: {:x}",
        header.htype.get()
    ))?;
    let proto = ArpNetworkType::try_from(header.ptype.get()).ok().ok_or_else(debug_err_fn!(
        ParseError::NotSupported,
        "unrecognized network protocol: {:x}",
        header.ptype.get()
    ))?;
    let hlen = match hw {
        ArpHardwareType::Ethernet => <Mac as HType>::HLEN,
    };
    let plen = match proto {
        ArpNetworkType::Ipv4 => <Ipv4Addr as PType>::PLEN,
    };
    if header.hlen != hlen || header.plen != plen {
        return debug_err!(
            Err(ParseError::Format),
            "unexpected hardware or protocol address length for protocol {:?}",
            proto
        );
    }
    Ok((hw, proto))
}

// Body has the same memory layout (thanks to repr(C)) as an ARP body. Thus, we
// can simply reinterpret the bytes of the ARP body as a Body and then safely
// access its fields.
#[derive(FromZeros, FromBytes, AsBytes, NoCell, Unaligned)]
#[repr(C)]
struct Body<HwAddr, ProtoAddr> {
    sha: HwAddr,
    spa: ProtoAddr,
    tha: HwAddr,
    tpa: ProtoAddr,
}

/// An ARP packet.
///
/// A `ArpPacket` shares its underlying memory with the byte slice it was parsed
/// from or serialized to, meaning that no copying or extra allocation is
/// necessary.
pub struct ArpPacket<B, HwAddr, ProtoAddr> {
    header: Ref<B, Header>,
    body: Ref<B, Body<HwAddr, ProtoAddr>>,
}

impl<B: ByteSlice, HwAddr, ProtoAddr> ParsablePacket<B, ()> for ArpPacket<B, HwAddr, ProtoAddr>
where
    HwAddr: Copy + HType + FromBytes + Unaligned,
    ProtoAddr: Copy + PType + FromBytes + Unaligned,
{
    type Error = ParseError;

    fn parse_metadata(&self) -> ParseMetadata {
        ParseMetadata::from_inner_packet(self.header.bytes().len() + self.body.bytes().len())
    }

    fn parse<BV: BufferView<B>>(mut buffer: BV, _args: ()) -> ParseResult<Self> {
        let header = buffer
            .take_obj_front::<Header>()
            .ok_or_else(debug_err_fn!(ParseError::Format, "too few bytes for header"))?;
        let body = buffer
            .take_obj_front::<Body<HwAddr, ProtoAddr>>()
            .ok_or_else(debug_err_fn!(ParseError::Format, "too few bytes for body"))?;
        // Consume any padding bytes added by the previous layer.
        let _: B = buffer.take_rest_front();

        if header.htype.get() != <HwAddr as HType>::HTYPE.into()
            || header.ptype.get() != <ProtoAddr as PType>::PTYPE.into()
        {
            return debug_err!(
                Err(ParseError::NotExpected),
                "unexpected hardware or network protocols"
            );
        }
        if header.hlen != <HwAddr as HType>::HLEN || header.plen != <ProtoAddr as PType>::PLEN {
            return debug_err!(
                Err(ParseError::Format),
                "unexpected hardware or protocol address length"
            );
        }

        if let ArpOp::Other(x) = header.oper.get().into() {
            return debug_err!(Err(ParseError::Format), "unrecognized op code: {:x}", x);
        }

        Ok(ArpPacket { header, body })
    }
}

impl<B: ByteSlice, HwAddr, ProtoAddr> ArpPacket<B, HwAddr, ProtoAddr>
where
    HwAddr: Copy + HType + FromBytes + NoCell + Unaligned,
    ProtoAddr: Copy + PType + FromBytes + NoCell + Unaligned,
{
    /// The type of ARP packet
    pub fn operation(&self) -> ArpOp {
        self.header.oper.get().into()
    }

    /// The hardware address of the ARP packet sender.
    pub fn sender_hardware_address(&self) -> HwAddr {
        self.body.sha
    }

    /// The protocol address of the ARP packet sender.
    pub fn sender_protocol_address(&self) -> ProtoAddr {
        self.body.spa
    }

    /// The hardware address of the ARP packet target.
    pub fn target_hardware_address(&self) -> HwAddr {
        self.body.tha
    }

    /// The protocol address of the ARP packet target.
    pub fn target_protocol_address(&self) -> ProtoAddr {
        self.body.tpa
    }

    /// Construct a builder with the same contents as this packet.
    pub fn builder(&self) -> ArpPacketBuilder<HwAddr, ProtoAddr> {
        ArpPacketBuilder {
            op: self.operation(),
            sha: self.sender_hardware_address(),
            spa: self.sender_protocol_address(),
            tha: self.target_hardware_address(),
            tpa: self.target_protocol_address(),
        }
    }
}

/// A builder for ARP packets.
#[derive(Debug)]
pub struct ArpPacketBuilder<HwAddr, ProtoAddr> {
    op: ArpOp,
    sha: HwAddr,
    spa: ProtoAddr,
    tha: HwAddr,
    tpa: ProtoAddr,
}

impl<HwAddr, ProtoAddr> ArpPacketBuilder<HwAddr, ProtoAddr> {
    /// Construct a new `ArpPacketBuilder`.
    pub fn new(
        operation: ArpOp,
        sender_hardware_addr: HwAddr,
        sender_protocol_addr: ProtoAddr,
        target_hardware_addr: HwAddr,
        target_protocol_addr: ProtoAddr,
    ) -> ArpPacketBuilder<HwAddr, ProtoAddr> {
        ArpPacketBuilder {
            op: operation,
            sha: sender_hardware_addr,
            spa: sender_protocol_addr,
            tha: target_hardware_addr,
            tpa: target_protocol_addr,
        }
    }
}

impl<HwAddr, ProtoAddr> InnerPacketBuilder for ArpPacketBuilder<HwAddr, ProtoAddr>
where
    HwAddr: Copy + HType + FromBytes + AsBytes + NoCell + Unaligned,
    ProtoAddr: Copy + PType + FromBytes + AsBytes + NoCell + Unaligned,
{
    fn bytes_len(&self) -> usize {
        mem::size_of::<Header>() + mem::size_of::<Body<HwAddr, ProtoAddr>>()
    }

    fn serialize(&self, mut buffer: &mut [u8]) {
        // implements BufferViewMut, giving us write_obj_front method
        let mut buffer = &mut buffer;
        buffer
            .write_obj_front(&Header::new::<HwAddr, ProtoAddr>(self.op))
            .expect("too few bytes for ARP packet");
        buffer
            .write_obj_front(&Body { sha: self.sha, spa: self.spa, tha: self.tha, tpa: self.tpa })
            .expect("too few bytes for ARP packet");
    }
}

#[cfg(test)]
impl<B, HwAddr, ProtoAddr> Debug for ArpPacket<B, HwAddr, ProtoAddr> {
    fn fmt(&self, fmt: &mut Formatter<'_>) -> fmt::Result {
        write!(fmt, "ArpPacket")
    }
}

#[cfg(test)]
mod tests {
    use packet::{ParseBuffer, Serializer};

    use super::*;
    use crate::ethernet::{EthernetFrame, EthernetFrameLengthCheck};
    use crate::testutil::*;

    const TEST_SENDER_IPV4: Ipv4Addr = Ipv4Addr::new([1, 2, 3, 4]);
    const TEST_TARGET_IPV4: Ipv4Addr = Ipv4Addr::new([5, 6, 7, 8]);
    const TEST_SENDER_MAC: Mac = Mac::new([0, 1, 2, 3, 4, 5]);
    const TEST_TARGET_MAC: Mac = Mac::new([6, 7, 8, 9, 10, 11]);

    #[test]
    fn test_parse_serialize_full() {
        use crate::testdata::arp_request::*;

        let mut buf = ETHERNET_FRAME.bytes;
        let frame = buf.parse_with::<_, EthernetFrame<_>>(EthernetFrameLengthCheck::Check).unwrap();
        verify_ethernet_frame(&frame, ETHERNET_FRAME);

        let (hw, proto) = peek_arp_types(frame.body()).unwrap();
        assert_eq!(hw, ArpHardwareType::Ethernet);
        assert_eq!(proto, ArpNetworkType::Ipv4);

        let mut body = frame.body();
        let arp = body.parse::<ArpPacket<_, Mac, Ipv4Addr>>().unwrap();
        assert_eq!(arp.operation(), ARP_OPERATION);
        assert_eq!(frame.src_mac(), arp.sender_hardware_address());

        let frame_bytes = arp
            .builder()
            .into_serializer()
            .encapsulate(frame.builder())
            .serialize_vec_outer()
            .unwrap();
        assert_eq!(frame_bytes.as_ref(), ETHERNET_FRAME.bytes);
    }

    fn header_to_bytes(header: Header) -> [u8; ARP_HDR_LEN] {
        zerocopy::transmute!(header)
    }

    // Return a new Header for an Ethernet/IPv4 ARP request.
    fn new_header() -> Header {
        Header::new::<Mac, Ipv4Addr>(ArpOp::Request)
    }

    #[test]
    fn test_peek() {
        let header = new_header();
        let (hw, proto) = peek_arp_types(&header_to_bytes(header)[..]).unwrap();
        assert_eq!(hw, ArpHardwareType::Ethernet);
        assert_eq!(proto, ArpNetworkType::Ipv4);

        // Test that an invalid operation is not rejected; peek_arp_types does
        // not inspect the operation.
        let mut header = new_header();
        header.oper = U16::new(3);
        let (hw, proto) = peek_arp_types(&header_to_bytes(header)[..]).unwrap();
        assert_eq!(hw, ArpHardwareType::Ethernet);
        assert_eq!(proto, ArpNetworkType::Ipv4);
    }

    #[test]
    fn test_parse() {
        let mut buf = &mut [
            0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 2, 3, 4, 5, 1, 2, 3, 4, 6, 7, 8, 9, 10, 11, 5, 6, 7, 8,
        ][..];
        (&mut buf[..ARP_HDR_LEN]).copy_from_slice(&header_to_bytes(new_header()));
        let (hw, proto) = peek_arp_types(&buf[..]).unwrap();
        assert_eq!(hw, ArpHardwareType::Ethernet);
        assert_eq!(proto, ArpNetworkType::Ipv4);

        let buf = &mut buf;
        let packet = buf.parse::<ArpPacket<_, Mac, Ipv4Addr>>().unwrap();
        assert_eq!(packet.sender_hardware_address(), TEST_SENDER_MAC);
        assert_eq!(packet.sender_protocol_address(), TEST_SENDER_IPV4);
        assert_eq!(packet.target_hardware_address(), TEST_TARGET_MAC);
        assert_eq!(packet.target_protocol_address(), TEST_TARGET_IPV4);
        assert_eq!(packet.operation(), ArpOp::Request);
    }

    #[test]
    fn test_serialize() {
        let mut buf = ArpPacketBuilder::new(
            ArpOp::Request,
            TEST_SENDER_MAC,
            TEST_SENDER_IPV4,
            TEST_TARGET_MAC,
            TEST_TARGET_IPV4,
        )
        .into_serializer()
        .serialize_vec_outer()
        .unwrap();
        assert_eq!(
            AsRef::<[u8]>::as_ref(&buf),
            &[0, 1, 8, 0, 6, 4, 0, 1, 0, 1, 2, 3, 4, 5, 1, 2, 3, 4, 6, 7, 8, 9, 10, 11, 5, 6, 7, 8,]
        );
        let packet = buf.parse::<ArpPacket<_, Mac, Ipv4Addr>>().unwrap();
        assert_eq!(packet.sender_hardware_address(), TEST_SENDER_MAC);
        assert_eq!(packet.sender_protocol_address(), TEST_SENDER_IPV4);
        assert_eq!(packet.target_hardware_address(), TEST_TARGET_MAC);
        assert_eq!(packet.target_protocol_address(), TEST_TARGET_IPV4);
        assert_eq!(packet.operation(), ArpOp::Request);
    }

    #[test]
    fn test_peek_error() {
        // Test that a header which is too short is rejected.
        let buf = [0; ARP_HDR_LEN - 1];
        assert_eq!(peek_arp_types(&buf[..]).unwrap_err(), ParseError::Format);

        // Test that an unexpected hardware protocol type is rejected.
        let mut header = new_header();
        header.htype = U16::ZERO;
        assert_eq!(
            peek_arp_types(&header_to_bytes(header)[..]).unwrap_err(),
            ParseError::NotSupported
        );

        // Test that an unexpected network protocol type is rejected.
        let mut header = new_header();
        header.ptype = U16::ZERO;
        assert_eq!(
            peek_arp_types(&header_to_bytes(header)[..]).unwrap_err(),
            ParseError::NotSupported
        );

        // Test that an incorrect hardware address len is rejected.
        let mut header = new_header();
        header.hlen = 7;
        assert_eq!(peek_arp_types(&header_to_bytes(header)[..]).unwrap_err(), ParseError::Format);

        // Test that an incorrect protocol address len is rejected.
        let mut header = new_header();
        header.plen = 5;
        assert_eq!(peek_arp_types(&header_to_bytes(header)[..]).unwrap_err(), ParseError::Format);
    }

    #[test]
    fn test_parse_error() {
        // Assert that parsing a buffer results in an error.
        fn assert_err(mut buf: &[u8], err: ParseError) {
            assert_eq!(buf.parse::<ArpPacket<_, Mac, Ipv4Addr>>().unwrap_err(), err);
        }

        // Assert that parsing a particular header results in an error.
        fn assert_header_err(header: Header, err: ParseError) {
            let mut buf = [0; ARP_ETHERNET_IPV4_PACKET_LEN];
            *Ref::<_, Header>::new_unaligned_from_prefix(&mut buf[..]).unwrap().0 = header;
            assert_err(&buf[..], err);
        }

        // Test that a packet which is too short is rejected.
        let buf = [0; ARP_ETHERNET_IPV4_PACKET_LEN - 1];
        assert_err(&buf[..], ParseError::Format);

        // Test that an unexpected hardware protocol type is rejected.
        let mut header = new_header();
        header.htype = U16::ZERO;
        assert_header_err(header, ParseError::NotExpected);

        // Test that an unexpected network protocol type is rejected.
        let mut header = new_header();
        header.ptype = U16::ZERO;
        assert_header_err(header, ParseError::NotExpected);

        // Test that an incorrect hardware address len is rejected.
        let mut header = new_header();
        header.hlen = 7;
        assert_header_err(header, ParseError::Format);

        // Test that an incorrect protocol address len is rejected.
        let mut header = new_header();
        header.plen = 5;
        assert_header_err(header, ParseError::Format);

        // Test that an invalid operation is rejected.
        let mut header = new_header();
        header.oper = U16::new(3);
        assert_header_err(header, ParseError::Format);
    }

    #[test]
    fn test_serialize_zeroes() {
        // Test that ArpPacket::serialize properly zeroes memory before
        // serializing the packet.
        let mut buf_0 = [0; ARP_ETHERNET_IPV4_PACKET_LEN];
        ArpPacketBuilder::new(
            ArpOp::Request,
            TEST_SENDER_MAC,
            TEST_SENDER_IPV4,
            TEST_TARGET_MAC,
            TEST_TARGET_IPV4,
        )
        .serialize(&mut buf_0[..]);
        let mut buf_1 = [0xFF; ARP_ETHERNET_IPV4_PACKET_LEN];
        ArpPacketBuilder::new(
            ArpOp::Request,
            TEST_SENDER_MAC,
            TEST_SENDER_IPV4,
            TEST_TARGET_MAC,
            TEST_TARGET_IPV4,
        )
        .serialize(&mut buf_1[..]);
        assert_eq!(buf_0, buf_1);
    }

    #[test]
    #[should_panic(expected = "too few bytes for ARP packet")]
    fn test_serialize_panic_insufficient_packet_space() {
        // Test that a buffer which doesn't leave enough room for the packet is
        // rejected.
        ArpPacketBuilder::new(
            ArpOp::Request,
            TEST_SENDER_MAC,
            TEST_SENDER_IPV4,
            TEST_TARGET_MAC,
            TEST_TARGET_IPV4,
        )
        .serialize(&mut [0; ARP_ETHERNET_IPV4_PACKET_LEN - 1]);
    }
}