feat: First version of broker based WireGuard PSK interface

This allows us to run with minimal priviledges in the Rosenpass process itself

wireguard-broker/src/bin/socket_handler.rs

@@ -0,0 +1,191 @@
+use std::process::Stdio;
+
+use tokio::io::{AsyncReadExt, AsyncWriteExt};
+use tokio::net::{UnixListener, UnixStream};
+use tokio::process::Command;
+use tokio::sync::{mpsc, oneshot};
+use tokio::task;
+
+use anyhow::{bail, ensure, Result};
+use clap::{ArgGroup, Parser};
+
+use rosenpass_util::fd::claim_fd;
+use rosenpass_wireguard_broker::api::msgs;
+
+#[derive(Parser, Debug)]
+#[command(author, version, about, long_about = None)]
+#[clap(group(
+            ArgGroup::new("socket")
+                .required(true)
+                .args(&["listen_path", "listen_fd", "stream_fd"]),
+        ))]
+struct Args {
+    /// Where in the file-system to create the unix socket this broker will be listening for
+    /// connections on
+    #[arg(long)]
+    listen_path: Option<String>,
+
+    /// When this broker is called from another process, the other process can open and bind the
+    /// unix socket to use themselves, passing it to this process. In Rust this can be achieved
+    /// using the [command-fds](https://docs.rs/command-fds/latest/command_fds/) crate.
+    #[arg(long)]
+    listen_fd: Option<i32>,
+
+    /// When this broker is called from another process, the other process can connect the unix socket
+    /// themselves, for instance using the `socketpair(2)` system call.
+    #[arg(long)]
+    stream_fd: Option<i32>,
+
+    /// The underlying broker, accepting commands through stdin and sending results through stdout.
+    #[arg(
+        last = true,
+        allow_hyphen_values = true,
+        default_value = "rosenpass-wireguard-broker-privileged"
+    )]
+    command: Vec<String>,
+}
+
+struct BrokerRequest {
+    reply_to: oneshot::Sender<BrokerResponse>,
+    request: Vec<u8>,
+}
+
+struct BrokerResponse {
+    response: Vec<u8>,
+}
+
+#[tokio::main]
+async fn main() -> Result<()> {
+    env_logger::init();
+
+    let args = Args::parse();
+
+    let (proc_tx, proc_rx) = mpsc::channel(100);
+
+    // Start the inner broker handler
+    task::spawn(async move {
+        if let Err(e) = direct_broker_process(proc_rx, args.command).await {
+            log::error!("Error in broker command handler: {e}");
+            panic!("Can not proceed without underlying broker process");
+        }
+    });
+
+    // Listen for incoming requests
+    if let Some(path) = args.listen_path {
+        let sock = UnixListener::bind(path)?;
+        listen_for_clients(proc_tx, sock).await
+    } else if let Some(fd) = args.listen_fd {
+        let sock = std::os::unix::net::UnixListener::from(claim_fd(fd)?);
+        sock.set_nonblocking(true)?;
+        listen_for_clients(proc_tx, UnixListener::from_std(sock)?).await
+    } else if let Some(fd) = args.stream_fd {
+        let stream = std::os::unix::net::UnixStream::from(claim_fd(fd)?);
+        stream.set_nonblocking(true)?;
+        on_accept(proc_tx, UnixStream::from_std(stream)?).await
+    } else {
+        unreachable!();
+    }
+}
+
+async fn direct_broker_process(
+    mut queue: mpsc::Receiver<BrokerRequest>,
+    cmd: Vec<String>,
+) -> Result<()> {
+    let proc = Command::new(&cmd[0])
+        .args(&cmd[1..])
+        .stdin(Stdio::piped())
+        .stdout(Stdio::piped())
+        .spawn()?;
+
+    let mut stdin = proc.stdin.unwrap();
+    let mut stdout = proc.stdout.unwrap();
+
+    loop {
+        let BrokerRequest { reply_to, request } = queue.recv().await.unwrap();
+
+        stdin
+            .write_all(&(request.len() as u64).to_le_bytes())
+            .await?;
+        stdin.write_all(&request[..]).await?;
+
+        // Read the response length
+        let mut len = [0u8; 8];
+        stdout.read_exact(&mut len).await?;
+
+        // Parse the response length
+        let len = u64::from_le_bytes(len) as usize;
+        ensure!(
+            len <= msgs::RESPONSE_MSG_BUFFER_SIZE,
+            "Oversized buffer ({len}) in broker stdout."
+        );
+
+        // Read the message itself
+        let mut res_buf = request; // Avoid allocating memory if we don't have to
+        res_buf.resize(len as usize, 0);
+        stdout.read_exact(&mut res_buf[..len]).await?;
+
+        // Return to the unix socket connection worker
+        reply_to
+            .send(BrokerResponse { response: res_buf })
+            .or_else(|_| bail!("Unable to send respnse to unix socket worker."))?;
+    }
+}
+
+async fn listen_for_clients(queue: mpsc::Sender<BrokerRequest>, sock: UnixListener) -> Result<()> {
+    loop {
+        let (stream, _addr) = sock.accept().await?;
+        let queue = queue.clone();
+        task::spawn(async move {
+            if let Err(e) = on_accept(queue, stream).await {
+                log::error!("Error during connection processing: {e}");
+            }
+        });
+    }
+
+    // NOTE: If loop can ever terminate we need to join the spawned tasks
+}
+
+async fn on_accept(queue: mpsc::Sender<BrokerRequest>, mut stream: UnixStream) -> Result<()> {
+    let mut req_buf = Vec::new();
+
+    loop {
+        stream.readable().await?;
+
+        // Read the message length
+        let mut len = [0u8; 8];
+        stream.read_exact(&mut len).await?;
+
+        // Parse the message length
+        let len = u64::from_le_bytes(len) as usize;
+        ensure!(
+            len <= msgs::REQUEST_MSG_BUFFER_SIZE,
+            "Oversized buffer ({len}) in unix socket input."
+        );
+
+        // Read the message itself
+        req_buf.resize(len as usize, 0);
+        stream.read_exact(&mut req_buf[..len]).await?;
+
+        // Handle the message
+        let (reply_tx, reply_rx) = oneshot::channel();
+        queue
+            .send(BrokerRequest {
+                reply_to: reply_tx,
+                request: req_buf,
+            })
+            .await?;
+
+        // Wait for the reply
+        let BrokerResponse { response } = reply_rx.await.unwrap();
+
+        // Write reply back to unix socket
+        stream
+            .write_all(&(response.len() as u64).to_le_bytes())
+            .await?;
+        stream.write_all(&response[..]).await?;
+        stream.flush().await?;
+
+        // Reuse the same memory for the next message
+        req_buf = response;
+    }
+}