support reverse forwarding

README.md

@@ -77,4 +77,10 @@ name = "test2"
 # listening on a specific address instead of 0.0.0.0
 source = "127.0.0.1:9091"
 target = 80
+
+[[namespace.forward]]
+# forward from inside the namespace to outside instead
+reverse = true
+source = 80
+target = 80
 ```

config.sample.toml

@@ -26,3 +26,9 @@ name = "test2"
 # listening on a specific address instead of 0.0.0.0
 source = "127.0.0.1:9091"
 target = 80
+
+[[namespace.forward]]
+# forward from inside the namespace to outside instead
+reverse = true
+source = 80
+target = 80

nix/module.nix

@@ -48,6 +48,7 @@ in {
               };
             }));
             description = "ports to forward into the namespace";
+            default = [];
           };
         };
       }));

src/config/mod.rs

@@ -87,6 +87,8 @@ pub struct NamespaceConfig {
 pub struct ForwardConfig {
     pub source: ForwardSource,
     pub target: ForwardTarget,
+    #[serde(default)]
+    pub reverse: bool,
 }
 
 #[derive(Debug, Error)]

src/proxy/mod.rs

@@ -7,7 +7,7 @@ use nix::sched::{CloneFlags, setns};
 use std::fs::{File, remove_file};
 use std::io::Error as IoError;
 use std::net::SocketAddr;
-use std::path::PathBuf;
+use std::path::{Path, PathBuf};
 use std::sync::Arc;
 use std::sync::atomic::{AtomicU64, Ordering};
 use std::thread::spawn;
@@ -45,20 +45,23 @@ impl ActiveProxy {
         config: &ForwardConfig,
         namespace: &NamespaceName,
     ) -> Result<ActiveProxy, ProxyError> {
-        let proxy = Proxy::listen(config.source.clone())?;
         let stats = ProxyStats::default();
-
         let (abort, abort_reg) = AbortHandle::new_pair();
 
         let destination = config.target.clone();
         let run_stats = stats.clone();
-        let ns_path = PathBuf::from(format!("/var/run/netns/{namespace}"));
-        let ns_handle = File::open(&ns_path).map_err(|error| ProxyError::OpenNamespace {
-            error,
-            path: ns_path,
-        })?;
-        spawn(move || match setns(ns_handle, CloneFlags::CLONE_NEWNET) {
-            Ok(_) => {
+
+        let ns_handle = open_namespace(format!("/var/run/netns/{namespace}"))?;
+        let self_ns_handle = open_namespace("/proc/self/ns/net")?;
+
+        let (listen_namespace, target_namespace) = if config.reverse {
+            (Some(ns_handle), self_ns_handle)
+        } else {
+            (None, ns_handle)
+        };
+
+        let source = config.source.clone();
+        spawn(move || {
             let rt = match Builder::new_current_thread().enable_io().build() {
                 Ok(rt) => rt,
                 Err(error) => {
@@ -66,11 +69,29 @@ impl ActiveProxy {
                     return;
                 }
             };
-                rt.block_on(proxy.run(destination, abort_reg, run_stats));
+
+            rt.block_on(async {
+                if let Some(listen_namespace) = listen_namespace {
+                    if let Err(error) = setns(listen_namespace, CloneFlags::CLONE_NEWNET) {
+                        error!(%error, "Failed to join listen network namespace for proxy");
+                        return;
                     }
+                }
+
+                let proxy = match Proxy::listen(&source) {
+                    Ok(proxy) => proxy,
                     Err(error) => {
-                error!(%error, "Failed to join network namespace for proxy");
+                        error!(%error, "Failed to listen to {source}");
+                        return;
                     }
+                };
+
+                if let Err(error) = setns(target_namespace, CloneFlags::CLONE_NEWNET) {
+                    error!(%error, "Failed to join target network namespace for proxy");
+                    return;
+                }
+                proxy.run(destination, abort_reg, run_stats).await;
+            });
         });
 
         Ok(ActiveProxy {
@@ -145,3 +166,11 @@ impl ProxyStats {
         self.bytes_written.load(Ordering::Relaxed)
     }
 }
+
+fn open_namespace(path: impl AsRef<Path>) -> Result<File, ProxyError> {
+    let path = path.as_ref();
+    File::open(path).map_err(|error| ProxyError::OpenNamespace {
+        error,
+        path: path.into(),
+    })
+}

src/proxy/tcp.rs

@@ -37,8 +37,8 @@ fn bind_tcp(addr: SocketAddr) -> Result<TcpListener, IoError> {
 }
 
 impl Proxy {
-    pub fn listen(bind: ForwardSource) -> Result<Self, ProxyError> {
-        let socket = match &bind {
+    pub fn listen(bind: &ForwardSource) -> Result<Self, ProxyError> {
+        let socket = match bind {
             ForwardSource::Unix(path) => {
                 let _ = remove_file(path);
                 UnixListener::bind(path).map(|listener| {
@@ -51,7 +51,7 @@ impl Proxy {
             ForwardSource::Ip(addr) => bind_tcp(*addr).map(ProxyListener::Tcp),
         }
         .map_err(|error| ProxyError::Bind {
-            address: bind,
+            address: bind.clone(),
             error,
         })?;
         debug!("Created TCP socket");