void file descriptors

src/spawner.rs

@@ -11,7 +11,6 @@ use std::fs::File;
 use std::io::Read;
 use std::os::unix::io::AsRawFd;
 
-use close_fds::CloseFdsBuilder;
 use nix::unistd;
 
 const BUFFER_SIZE: usize = 1024;
@@ -53,24 +52,17 @@ impl<'a> Spawner<'a> {
                 Trigger::Pipe(s) => {
                     let pipe = self.pipes.get_mut(s).unwrap().take_read();
 
-                    let closure = || {
-                        let mut closer = CloseFdsBuilder::new();
-                        let keep = [pipe.as_raw_fd()];
-                        closer.keep_fds(&keep);
-                        unsafe {
-                            closer.closefrom(3);
-                        }
+                    let mut builder = VoidBuilder::new();
+                    builder.keep_fd(&pipe);
 
-                        match self.pipe_trigger(pipe, entrypoint, name) {
+                    let closure = || match self.pipe_trigger(pipe, entrypoint, name) {
                         Ok(()) => std::process::exit(exitcode::OK),
                         Err(e) => {
                             error!("error in pipe_trigger: {}", e);
                             std::process::exit(1)
                         }
-                        }
                     };
 
-                    let mut builder = VoidBuilder::new();
                     builder.spawn(closure)?;
                 }
             }

src/void.rs

@@ -3,8 +3,9 @@ use log::{debug, error};
 use crate::clone::{clone3, CloneArgs, CloneFlags};
 use crate::{Error, Result};
 
-use std::collections::HashMap;
+use std::collections::{HashMap, HashSet};
 use std::fs;
+use std::os::unix::io::{AsRawFd, RawFd};
 use std::path::PathBuf;
 
 use nix::mount::{mount, umount2, MntFlags, MsFlags};
@@ -12,17 +13,20 @@ use nix::sched::unshare;
 use nix::sys::signal::Signal;
 use nix::unistd::{pivot_root, Pid};
 
+use close_fds::CloseFdsBuilder;
+
 pub struct VoidHandle {}
 
 pub struct VoidBuilder {
-    #[allow(dead_code)]
     mounts: HashMap<PathBuf, PathBuf>,
+    fds: HashSet<RawFd>,
 }
 
 impl VoidBuilder {
     pub fn new() -> VoidBuilder {
         VoidBuilder {
             mounts: HashMap::new(),
+            fds: HashSet::new(),
         }
     }
 
@@ -32,6 +36,11 @@ impl VoidBuilder {
         self
     }
 
+    pub fn keep_fd(&mut self, fd: &impl AsRawFd) -> &mut Self {
+        self.fds.insert(fd.as_raw_fd());
+        self
+    }
+
     pub fn spawn(&mut self, child_fn: impl FnOnce() -> i32) -> Result<VoidHandle> {
         let mut args = CloneArgs::new(
             CloneFlags::CLONE_NEWCGROUP
@@ -50,6 +59,7 @@ impl VoidBuilder {
 
         if child == Pid::from_raw(0) {
             let result = {
+                self.void_files()?;
                 self.void_mount_namespace()?;
                 self.void_user_namespace()?; // last to maintain permissions
 
@@ -77,6 +87,19 @@ impl VoidBuilder {
     }
 
     // per-namespace void creation
+    fn void_files(&self) -> Result<()> {
+        let mut closer = CloseFdsBuilder::new();
+
+        let keep: Box<[RawFd]> = self.fds.iter().copied().collect();
+        closer.keep_fds(&keep);
+
+        unsafe {
+            closer.closefrom(3);
+        }
+
+        Ok(())
+    }
+
     fn void_mount_namespace(&self) -> Result<()> {
         // change the propagation type of the old root to private
         mount(