3 files changed, 58 insertions, 7 deletions

diff --git a/src/error.rs b/src/error.rs
index 43378a8..d97212b 100644
--- a/src/error.rs
+++ b/src/error.rs
@@ -1,4 +1,6 @@
+use std::ffi;
 use std::io;
+use std::net;
 
 use dhcproto::v4::{MessageType, Opcode};
 use thiserror::Error;
@@ -31,6 +33,10 @@ pub enum Error {
     LinkAddrs(#[from] linkaddrs::Error),
     #[error("serde_json error")]
     SerdeJson(#[from] serde_json::Error),
+    #[error("error parsing IP address")]
+    AddrParseError(#[from] net::AddrParseError),
+    #[error("ffi nul error (string contains nul bytes)")]
+    FfiNulError(#[from] ffi::NulError),
 }
 
 pub type Result<T> = std::result::Result<T, Error>;
diff --git a/src/main.rs b/src/main.rs
index 4ef4b23..1ef444c 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,11 +1,14 @@
 use dhcp4d::error::{Error, Result};
 use dhcp4d::lease::{LeaseFileManager, LeaseFileManagerConfig, LeaseManager};
-use dhcp4d::util::{format_client_id, local_ip};
+use dhcp4d::util::{format_client_id, local_ip, setsockopt};
 
+use std::ffi::CString;
 use std::fs::{self, OpenOptions};
 use std::io::Write;
 use std::mem::MaybeUninit;
-use std::net::{IpAddr, SocketAddr, SocketAddrV4};
+use std::net::{SocketAddr, SocketAddrV4};
+use std::os::fd::AsRawFd;
+use std::str::FromStr;
 use std::sync::{Arc, Mutex};
 use std::thread;
 use std::time::Duration;
@@ -60,13 +63,23 @@ fn main() -> Result<()> {
 fn run<T: LeaseManager>(link: String, lease_mgr: Arc<Mutex<T>>) -> Result<()> {
     let sock = Socket::new(Domain::IPV4, Type::DGRAM, None)?;
 
-    let addresses = linkaddrs::ipv4_addresses(link)?;
-    let address = addresses.first().expect("interface has no IPv4 addresses");
-
-    let address = SocketAddr::new(IpAddr::V4(address.addr()), 67);
+    let address = SocketAddr::from_str("0.0.0.0:67")?;
     sock.bind(&address.into())?;
 
     sock.set_broadcast(true)?;
+    sock.set_reuse_port(true)?;
+
+    // Bind socket to interface.
+    unsafe {
+        let link_index = libc::if_nametoindex(CString::new(link)?.into_raw());
+
+        setsockopt(
+            sock.as_raw_fd(),
+            libc::IPPROTO_IP,
+            libc::SO_BINDTODEVICE,
+            link_index,
+        )?;
+    }
 
     loop {
         let mut buf = [MaybeUninit::new(0); 1024];
diff --git a/src/util.rs b/src/util.rs
index 81e4fce..dfacaad 100644
--- a/src/util.rs
+++ b/src/util.rs
@@ -1,6 +1,25 @@
 use crate::error::{Error, Result};
-use socket2::Socket;
+
+use std::ffi::c_int;
+use std::io;
+use std::mem;
 use std::net::Ipv4Addr;
+use std::ptr;
+
+use socket2::Socket;
+
+/// Helper macro to execute a system call that returns an `io::Result`.
+macro_rules! syscall {
+    ($fn: ident ( $($arg: expr),* $(,)* ) ) => {{
+        #[allow(unused_unsafe)]
+        let res = unsafe { libc::$fn($($arg, )*) };
+        if res == -1 {
+            Err(io::Error::last_os_error())
+        } else {
+            Ok(res)
+        }
+    }};
+}
 
 pub fn format_client_id(client_id: &[u8]) -> Result<String> {
     client_id
@@ -14,3 +33,16 @@ pub fn local_ip(sock: &Socket) -> Ipv4Addr {
     let local_addr = sock.local_addr().unwrap().as_socket_ipv4().unwrap();
     *local_addr.ip()
 }
+
+#[allow(clippy::missing_safety_doc)]
+pub unsafe fn setsockopt<T>(fd: c_int, opt: c_int, val: c_int, payload: T) -> io::Result<()> {
+    let payload = ptr::addr_of!(payload).cast();
+    syscall!(setsockopt(
+        fd,
+        opt,
+        val,
+        payload,
+        mem::size_of::<T>() as libc::socklen_t
+    ))
+    .map(|_| ())
+}