From 1c2a97ffdf069b60a696a9825b56e61c08a10147 Mon Sep 17 00:00:00 2001
From: Reiner Herrmann <reiner@reiner-h.de>
Date: Sun, 24 Feb 2019 18:15:34 +0100
Subject: Bind to real tftp port (69) and drop privileges immediately after

---
 Cargo.toml   |  1 +
 src/tftpd.rs | 44 ++++++++++++++++++++++++++++++++++++++++++--
 2 files changed, 43 insertions(+), 2 deletions(-)

diff --git a/Cargo.toml b/Cargo.toml
index ab6e99f..0262809 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -6,6 +6,7 @@ edition = "2018"
 license = "GPL-3.0-or-later"
 
 [dependencies]
+nix = "0.13.0"
 
 [[bin]]
 name = "rtftpd"
diff --git a/src/tftpd.rs b/src/tftpd.rs
index 331b27d..68e82c7 100644
--- a/src/tftpd.rs
+++ b/src/tftpd.rs
@@ -1,10 +1,14 @@
 use std::net::{SocketAddr,UdpSocket};
 use std::fs::File;
 use std::path::Path;
+use std::error::Error;
 use std::env;
 use std::io;
 use std::io::prelude::*;
 
+extern crate nix;
+use nix::unistd::{Gid,Uid,setresgid,setresuid};
+
 fn handle_wrq(_cl: &SocketAddr, _buf: &[u8]) -> Result<(), io::Error> {
     Ok(())
 }
@@ -175,12 +179,48 @@ fn handle_client(cl: &SocketAddr, buf: &[u8]) -> Result<(), io::Error> {
     Ok(())
 }
 
+fn drop_privs() -> Result<(), Box<Error>> {
+    let root_uid = Uid::from_raw(0);
+    let root_gid = Gid::from_raw(0);
+    let unpriv_uid = Uid::from_raw(65534);
+    let unpriv_gid = Gid::from_raw(65534);
+
+    if Gid::current() == root_gid || Gid::effective() == root_gid {
+        setresgid(unpriv_gid, unpriv_gid, unpriv_gid)?;
+    }
+
+    if Uid::current() == root_uid || Uid::effective() == root_uid {
+        setresuid(unpriv_uid, unpriv_uid, unpriv_uid)?;
+    }
+
+    Ok(())
+}
+
 fn main() {
-    let socket = UdpSocket::bind("127.0.0.1:12345").expect("Binding a socket failed.");
+    let socket = match UdpSocket::bind("0.0.0.0:69") {
+        Ok(s) => s,
+        Err(err) => {
+            println!("Binding a socket failed: {}", err);
+            return;
+        }
+    };
+    match drop_privs() {
+        Ok(_) => (),
+        Err(err) => {
+            println!("Dropping privileges failed: {}", err);
+            return;
+        }
+    };
 
     loop {
         let mut buf = [0; 2048];
-        let (n, src) = socket.recv_from(&mut buf).expect("Receiving from the socket failed.");
+        let (n, src) = match socket.recv_from(&mut buf) {
+            Ok(args) => args,
+            Err(err) => {
+                println!("Receiving data from socket failed: {}", err);
+                break;
+            }
+        };
 
         match handle_client(&src, &buf[0..n]) {
             /* errors intentionally ignored */
-- 
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