fix(sandbox): add managed loopback proxy

Author: ericksoa

crates/openshell-core/src/sandbox_env.rs

@@ -26,6 +26,12 @@ pub const LOG_LEVEL: &str = "OPENSHELL_LOG_LEVEL";
 /// Shell command to run inside the sandbox.
 pub const SANDBOX_COMMAND: &str = "OPENSHELL_SANDBOX_COMMAND";
 
+/// Sandbox-local loopback HTTP proxy URL managed by the supervisor.
+///
+/// This is distinct from HTTP_PROXY/HTTPS_PROXY, which continue to point at the
+/// gateway-side proxy address for ordinary proxy-aware clients.
+pub const LOOPBACK_PROXY_URL: &str = "OPENSHELL_LOOPBACK_PROXY_URL";
+
 /// Path to the CA certificate for mTLS communication with the gateway.
 pub const TLS_CA: &str = "OPENSHELL_TLS_CA";
 

crates/openshell-sandbox/src/child_env.rs

@@ -21,6 +21,13 @@ pub fn proxy_env_vars(proxy_url: &str) -> [(&'static str, String); 9] {
     ]
 }
 
+pub fn loopback_proxy_env_vars(proxy_url: &str) -> [(&'static str, String); 1] {
+    [(
+        openshell_core::sandbox_env::LOOPBACK_PROXY_URL,
+        proxy_url.to_owned(),
+    )]
+}
+
 pub fn tls_env_vars(
     ca_cert_path: &Path,
     combined_bundle_path: &Path,
@@ -65,6 +72,27 @@ mod tests {
         assert!(stdout.contains("no_proxy=127.0.0.1,localhost,::1"));
     }
 
+    #[test]
+    fn apply_loopback_proxy_env_exposes_managed_url_without_changing_proxy_vars() {
+        let mut cmd = Command::new("/usr/bin/env");
+        cmd.stdin(Stdio::null())
+            .stdout(Stdio::piped())
+            .stderr(Stdio::null());
+
+        for (key, value) in proxy_env_vars("http://10.200.0.1:3128") {
+            cmd.env(key, value);
+        }
+        for (key, value) in loopback_proxy_env_vars("http://127.0.0.1:3128") {
+            cmd.env(key, value);
+        }
+
+        let output = cmd.output().expect("spawn env");
+        let stdout = String::from_utf8(output.stdout).expect("utf8");
+
+        assert!(stdout.contains("HTTP_PROXY=http://10.200.0.1:3128"));
+        assert!(stdout.contains("OPENSHELL_LOOPBACK_PROXY_URL=http://127.0.0.1:3128"));
+    }
+
     #[test]
     fn apply_tls_env_sets_node_and_bundle_paths() {
         let mut cmd = Command::new("/usr/bin/env");

crates/openshell-sandbox/src/lib.rs

@@ -174,6 +174,8 @@ use crate::l7::tls::{
 };
 use crate::opa::OpaEngine;
 use crate::policy::{NetworkMode, NetworkPolicy, ProxyPolicy, SandboxPolicy};
+#[cfg(target_os = "linux")]
+use crate::proxy::LoopbackProxyHandle;
 use crate::proxy::ProxyHandle;
 #[cfg(target_os = "linux")]
 use crate::sandbox::linux::netns::NetworkNamespace;
@@ -571,8 +573,10 @@ pub async fn run_sandbox(
     // the entrypoint process's /proc/net/tcp for identity binding.
     let entrypoint_pid = Arc::new(AtomicU32::new(0));
 
-    let (_proxy, denial_rx, bypass_denial_tx) = if matches!(policy.network.mode, NetworkMode::Proxy)
-    {
+    let (_proxy, loopback_proxy, denial_rx, bypass_denial_tx) = if matches!(
+        policy.network.mode,
+        NetworkMode::Proxy
+    ) {
         let proxy_policy = policy.network.proxy.as_ref().ok_or_else(|| {
             miette::miette!("Network mode is set to proxy but no proxy configuration was provided")
         })?;
@@ -617,21 +621,66 @@ pub async fn run_sandbox(
         let proxy_handle = ProxyHandle::start_with_bind_addr(
             proxy_policy,
             bind_addr,
-            engine,
-            cache,
+            engine.clone(),
+            cache.clone(),
             entrypoint_pid.clone(),
-            tls_state,
-            inference_ctx,
+            tls_state.clone(),
+            inference_ctx.clone(),
             Some(provider_credentials.clone()),
             Some(policy_local_ctx.clone()),
-            denial_tx,
+            denial_tx.clone(),
         )
         .await?;
-        (Some(proxy_handle), denial_rx, bypass_denial_tx)
+
+        #[cfg(target_os = "linux")]
+        let loopback_proxy_handle = if let (Some(ns), Some(_upstream_addr)) =
+            (netns.as_ref(), bind_addr)
+        {
+            let Some(netns_fd) = ns.ns_fd() else {
+                return Err(miette::miette!(
+                    "Managed loopback proxy requires a sandbox network namespace file descriptor"
+                ));
+            };
+            let port = proxy_policy.http_addr.map_or(3128, |addr| addr.port());
+            let listen_addr: SocketAddr = ([127, 0, 0, 1], port).into();
+            Some(LoopbackProxyHandle::start_in_netns(
+                netns_fd,
+                listen_addr,
+                engine,
+                cache,
+                entrypoint_pid.clone(),
+                tls_state,
+                inference_ctx,
+                Some(provider_credentials.clone()),
+                Some(policy_local_ctx.clone()),
+                denial_tx,
+            )?)
+        } else {
+            None
+        };
+
+        #[cfg(not(target_os = "linux"))]
+        let loopback_proxy_handle: Option<()> = None;
+
+        (
+            Some(proxy_handle),
+            loopback_proxy_handle,
+            denial_rx,
+            bypass_denial_tx,
+        )
     } else {
-        (None, None, None)
+        (None, None, None, None)
     };
 
+    #[cfg(target_os = "linux")]
+    let loopback_proxy_url = loopback_proxy.as_ref().map(LoopbackProxyHandle::proxy_url);
+
+    #[cfg(not(target_os = "linux"))]
+    let _ = &loopback_proxy;
+
+    #[cfg(not(target_os = "linux"))]
+    let loopback_proxy_url: Option<String> = None;
+
     // Spawn bypass detection monitor (Linux only, proxy mode only).
     // Reads /dev/kmsg for nftables log entries and emits structured
     // tracing events for direct connection attempts that bypass the proxy.
@@ -758,6 +807,7 @@ pub async fn run_sandbox(
         let policy_clone = policy.clone();
         let workdir_clone = workdir.clone();
         let proxy_url = ssh_proxy_url;
+        let loopback_proxy_url = loopback_proxy_url.clone();
         let netns_fd = ssh_netns_fd;
         let ca_paths = ca_file_paths.clone();
         let provider_credentials_clone = provider_credentials.clone();
@@ -772,6 +822,7 @@ pub async fn run_sandbox(
                 workdir_clone,
                 netns_fd,
                 proxy_url,
+                loopback_proxy_url,
                 ca_paths,
                 provider_credentials_clone,
             )
@@ -838,6 +889,7 @@ pub async fn run_sandbox(
         interactive,
         &policy,
         netns.as_ref(),
+        loopback_proxy_url.as_deref(),
         ca_file_paths.as_ref(),
         &provider_env,
     )?;
@@ -849,6 +901,7 @@ pub async fn run_sandbox(
         workdir.as_deref(),
         interactive,
         &policy,
+        loopback_proxy_url.as_deref(),
         ca_file_paths.as_ref(),
         &provider_env,
     )?;

crates/openshell-sandbox/src/process.rs

@@ -94,6 +94,7 @@ impl ProcessHandle {
         interactive: bool,
         policy: &SandboxPolicy,
         netns: Option<&NetworkNamespace>,
+        loopback_proxy_url: Option<&str>,
         ca_paths: Option<&(PathBuf, PathBuf)>,
         provider_env: &HashMap<String, String>,
     ) -> Result<Self> {
@@ -104,6 +105,7 @@ impl ProcessHandle {
             interactive,
             policy,
             netns.and_then(NetworkNamespace::ns_fd),
+            loopback_proxy_url,
             ca_paths,
             provider_env,
         )
@@ -121,6 +123,7 @@ impl ProcessHandle {
         workdir: Option<&str>,
         interactive: bool,
         policy: &SandboxPolicy,
+        loopback_proxy_url: Option<&str>,
         ca_paths: Option<&(PathBuf, PathBuf)>,
         provider_env: &HashMap<String, String>,
     ) -> Result<Self> {
@@ -130,6 +133,7 @@ impl ProcessHandle {
             workdir,
             interactive,
             policy,
+            loopback_proxy_url,
             ca_paths,
             provider_env,
         )
@@ -144,6 +148,7 @@ impl ProcessHandle {
         interactive: bool,
         policy: &SandboxPolicy,
         netns_fd: Option<RawFd>,
+        loopback_proxy_url: Option<&str>,
         ca_paths: Option<&(PathBuf, PathBuf)>,
         provider_env: &HashMap<String, String>,
     ) -> Result<Self> {
@@ -185,6 +190,12 @@ impl ProcessHandle {
             }
         }
 
+        if let Some(url) = loopback_proxy_url {
+            for (key, value) in child_env::loopback_proxy_env_vars(url) {
+                cmd.env(key, value);
+            }
+        }
+
         // Set TLS trust store env vars so sandbox processes trust the ephemeral CA
         if let Some((ca_cert_path, combined_bundle_path)) = ca_paths {
             for (key, value) in child_env::tls_env_vars(ca_cert_path, combined_bundle_path) {
@@ -270,6 +281,7 @@ impl ProcessHandle {
         workdir: Option<&str>,
         interactive: bool,
         policy: &SandboxPolicy,
+        loopback_proxy_url: Option<&str>,
         ca_paths: Option<&(PathBuf, PathBuf)>,
         provider_env: &HashMap<String, String>,
     ) -> Result<Self> {
@@ -301,6 +313,12 @@ impl ProcessHandle {
             }
         }
 
+        if let Some(url) = loopback_proxy_url {
+            for (key, value) in child_env::loopback_proxy_env_vars(url) {
+                cmd.env(key, value);
+            }
+        }
+
         // Set TLS trust store env vars so sandbox processes trust the ephemeral CA
         if let Some((ca_cert_path, combined_bundle_path)) = ca_paths {
             for (key, value) in child_env::tls_env_vars(ca_cert_path, combined_bundle_path) {