Trusted Helper Argv0 for Multi-call Firewall Binaries

Co-Authored-By: brekotis <93345790+brekotis@users.noreply.github.com>

src/cli/init.rs

@@ -1,9 +1,8 @@
 use std::path::{Path, PathBuf};
-use std::process::Command;
 
 use rand::RngExt;
 
-use crate::util::trusted_command::resolve_trusted_helper;
+use crate::util::trusted_command::trusted_helper_command;
 
 /// Options for the fire-and-forget init command.
 #[derive(Debug, Clone)]
@@ -167,8 +166,8 @@ pub fn run_init(opts: InitOptions) -> Result<(), Box<dyn std::error::Error>> {
                 eprintln!("[+] Service started");
 
                 std::thread::sleep(std::time::Duration::from_secs(1));
-                let status = resolve_trusted_helper("systemctl").and_then(|command_path| {
+                let status = trusted_helper_command("systemctl").and_then(|mut command| {
-                    Command::new(command_path)
+                    command
                         .args(["is-active", "telemt.service"])
                         .output()
                         .ok()
@@ -334,11 +333,11 @@ weight = 10
 }
 
 fn run_cmd(cmd: &str, args: &[&str]) {
-    let Some(command_path) = resolve_trusted_helper(cmd) else {
+    let Some(mut command) = trusted_helper_command(cmd) else {
         eprintln!("[!] Refusing unavailable or untrusted command: {}", cmd);
         return;
     };
-    match Command::new(command_path).args(args).output() {
+    match command.args(args).output() {
         Ok(output) => {
             if !output.status.success() {
                 let stderr = String::from_utf8_lossy(&output.stderr);

src/conntrack_control/firewall/command.rs

@@ -6,7 +6,7 @@ use tokio::io::AsyncWriteExt;
 use tokio::process::Command;
 
 #[cfg(unix)]
-use crate::util::trusted_command::resolve_trusted_helper;
+use crate::util::trusted_command::{resolve_trusted_helper, trusted_helper_command};
 
 const COMMAND_TIMEOUT: Duration = Duration::from_secs(30);
 
@@ -133,13 +133,13 @@ impl FirewallCommandRunner for SystemCommandRunner {
         }
         #[cfg(unix)]
         {
-            let Some(command_path) = resolve_trusted_helper(spec.binary) else {
+            let Some(command) = trusted_helper_command(spec.binary) else {
                 return Err(CommandError {
                     kind: CommandErrorKind::Missing,
                     message: format!("{} is not available", spec.binary),
                 });
             };
-            let mut command = Command::new(command_path);
+            let mut command = Command::from(command);
             command.args(&spec.args);
             command.env("LC_ALL", "C");
             if spec.stdin.is_some() {

src/synlimit_control/command.rs

@@ -1,7 +1,7 @@
 use tokio::io::AsyncWriteExt;
 use tokio::process::Command;
 
-use crate::util::trusted_command::resolve_trusted_helper;
+use crate::util::trusted_command::trusted_helper_command;
 
 const COMMAND_TIMEOUT: std::time::Duration = std::time::Duration::from_secs(30);
 
@@ -10,10 +10,10 @@ pub(super) async fn run_command(
     args: &[&str],
     stdin: Option<String>,
 ) -> Result<(), String> {
-    let Some(command_path) = resolve_trusted_helper(binary) else {
+    let Some(command) = trusted_helper_command(binary) else {
         return Err(format!("{binary} is not available"));
     };
-    let mut command = Command::new(command_path);
+    let mut command = Command::from(command);
     command.args(args);
     if stdin.is_some() {
         command.stdin(std::process::Stdio::piped());
@@ -52,10 +52,10 @@ pub(super) async fn run_command(
 }
 
 pub(super) async fn run_command_stdout(binary: &str, args: &[&str]) -> Result<String, String> {
-    let Some(command_path) = resolve_trusted_helper(binary) else {
+    let Some(command) = trusted_helper_command(binary) else {
         return Err(format!("{binary} is not available"));
     };
-    let mut command = Command::new(command_path);
+    let mut command = Command::from(command);
     command.args(args).kill_on_drop(true);
     let output = tokio::time::timeout(COMMAND_TIMEOUT, command.output())
         .await

src/util/trusted_command.rs

@@ -1,5 +1,7 @@
 use std::os::unix::fs::{MetadataExt, PermissionsExt};
+use std::os::unix::process::CommandExt;
 use std::path::{Path, PathBuf};
+use std::process::Command;
 
 const TRUSTED_HELPER_DIRS: [&str; 4] = ["/usr/sbin", "/usr/bin", "/sbin", "/bin"];
 const TRUSTED_HELPERS: [&str; 12] = [
@@ -29,6 +31,19 @@ pub(crate) fn resolve_trusted_helper(binary: &str) -> Option<PathBuf> {
         .find_map(|candidate| trusted_executable(&candidate))
 }
 
+/// Builds a trusted helper command with its allowlisted invocation name.
+pub(crate) fn trusted_helper_command(binary: &str) -> Option<Command> {
+    let command_path = resolve_trusted_helper(binary)?;
+    Some(command_for_resolved_helper(binary, command_path))
+}
+
+fn command_for_resolved_helper(binary: &str, command_path: PathBuf) -> Command {
+    let mut command = Command::new(command_path);
+    // Multi-call helpers dispatch from argv[0], which canonical path resolution discards.
+    command.arg0(binary);
+    command
+}
+
 fn trusted_executable(candidate: &Path) -> Option<PathBuf> {
     let canonical = std::fs::canonicalize(candidate).ok()?;
     let metadata = std::fs::metadata(&canonical).ok()?;
@@ -78,6 +93,27 @@ mod tests {
         assert!(!TRUSTED_HELPERS.contains(&"iptables-restore-wrapper"));
     }
 
+    #[test]
+    fn trusted_multicall_command_preserves_logical_argv0() {
+        let command_path = std::fs::canonicalize("/bin/sh").unwrap();
+        for binary in [
+            "iptables",
+            "ip6tables",
+            "iptables-restore",
+            "ip6tables-restore",
+        ] {
+            let mut command = command_for_resolved_helper(binary, command_path.clone());
+            assert_eq!(command.get_program(), command_path.as_os_str());
+
+            let output = command
+                .args(["-c", "printf '%s' \"$0\""])
+                .output()
+                .unwrap();
+            assert!(output.status.success());
+            assert_eq!(String::from_utf8(output.stdout).unwrap(), binary);
+        }
+    }
+
     #[test]
     fn writable_executable_is_not_trusted() {
         let directory = tempfile::tempdir().unwrap();