linux: add namespace egress filter to block non-HTTP traffic (#11)

Author: ammario

src/jail/linux/nftables.rs

@@ -121,7 +121,7 @@ table ip {} {{
         })
     }
 
-    /// Create namespace-side nftables rules for traffic redirection
+    /// Create namespace-side nftables rules for traffic redirection and egress filtering
     pub fn new_namespace_table(
         namespace: &str,
         host_ip: &str,
@@ -130,26 +130,45 @@ table ip {} {{
     ) -> Result<Self> {
         let table_name = "httpjail".to_string();
 
-        // Generate the ruleset for namespace-side DNAT
+        // Generate the ruleset for namespace-side DNAT + FILTER
         let ruleset = format!(
             r#"
 table ip {} {{
+    # NAT output chain: redirect HTTP/HTTPS to host proxy
     chain output {{
         type nat hook output priority -100; policy accept;
-        
-        # Skip DNS traffic
+
+        # Skip DNS traffic from NAT processing
         udp dport 53 return
         tcp dport 53 return
-        
-        # Redirect HTTP to proxy
+
+        # Redirect HTTP to proxy running on host
         tcp dport 80 dnat to {}:{}
-        
-        # Redirect HTTPS to proxy
+
+        # Redirect HTTPS to proxy running on host
         tcp dport 443 dnat to {}:{}
     }}
+
+    # FILTER output chain: block non-HTTP/HTTPS egress
+    chain outfilter {{
+        type filter hook output priority 0; policy drop;
+
+        # Always allow established/related traffic
+        ct state established,related accept
+
+        # Allow DNS to anywhere
+        udp dport 53 accept
+        tcp dport 53 accept
+
+        # Explicitly block all other UDP (e.g., QUIC on 443)
+        ip protocol udp drop
+
+        # Allow traffic to the host proxy ports after DNAT
+        ip daddr {} tcp dport {{ {}, {} }} accept
+    }}
 }}
 "#,
-            table_name, host_ip, http_port, host_ip, https_port
+            table_name, host_ip, http_port, host_ip, https_port, host_ip, http_port, https_port
         );
 
         debug!(

tests/linux_integration.rs

@@ -280,4 +280,38 @@ mod tests {
             initial_ns_count, final_ns_count
         );
     }
+
+    /// Verify outbound TCP connections to non-HTTP ports are blocked inside the jail
+    ///
+    /// Uses portquiz.net which listens on all TCP ports and returns an HTTP response,
+    /// allowing us to test egress on non-standard ports reliably.
+    #[test]
+    fn test_outbound_tcp_non_http_blocked() {
+        LinuxPlatform::require_privileges();
+
+        // Attempt to connect to portquiz.net on port 81 (non-standard HTTP port)
+        // Expectation: connection is blocked by namespace egress filter
+        let mut cmd = httpjail_cmd();
+        cmd.arg("-r").arg("allow: .*") // proxy allows HTTP/HTTPS, but port 81 should be blocked
+            .arg("--")
+            .arg("sh")
+            .arg("-c")
+            .arg("curl -s -o /dev/null -w '%{http_code}' --connect-timeout 5 --max-time 8 http://portquiz.net:81 && echo CONNECTED || echo BLOCKED");
+
+        let output = cmd.output().expect("Failed to execute httpjail");
+        let stdout = String::from_utf8_lossy(&output.stdout);
+        let stderr = String::from_utf8_lossy(&output.stderr);
+
+        eprintln!("[Linux] outbound TCP test stdout: {}", stdout);
+        if !stderr.is_empty() {
+            eprintln!("[Linux] outbound TCP test stderr: {}", stderr);
+        }
+
+        assert!(
+            stdout.contains("BLOCKED"),
+            "Non-HTTP outbound TCP should be blocked. stdout: {}, stderr: {}",
+            stdout.trim(),
+            stderr.trim()
+        );
+    }
 }