From cbf8a7ec479cd52fbe97e13f8e733771705833fa Mon Sep 17 00:00:00 2001
From: Jack O'Connor <oconnor663@gmail.com>
Date: Fri, 11 Oct 2019 15:04:42 -0400
Subject: [PATCH] fix a bug where cloned pipes were inheritable on Windows

There is a bug (I think it's a bug?) in libstd which makes
File::try_clone return inheritable handles. We need to work around that
by making the same system calls explictly, but with the inheritable flag
set to false. I've filed a fix against libstd
(https://github.com/rust-lang/rust/pull/65316), but even if that lands
we'll need to retain this workaround for all the past versions of Rust
that have the bug.
---
 Cargo.toml     |  2 +-
 src/windows.rs | 40 ++++++++++++++++++++++++++++++++++++----
 2 files changed, 37 insertions(+), 5 deletions(-)

diff --git a/Cargo.toml b/Cargo.toml
index 7d99d76..f703343 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -13,4 +13,4 @@ edition = "2018"
 libc = "0.2.62"
 
 [target.'cfg(windows)'.dependencies]
-winapi = { version = "0.3.5", features = ["namedpipeapi"] }
+winapi = { version = "0.3.5", features = ["handleapi", "namedpipeapi", "processthreadsapi", "winnt"] }
diff --git a/src/windows.rs b/src/windows.rs
index 45dd1b1..c931d39 100644
--- a/src/windows.rs
+++ b/src/windows.rs
@@ -2,11 +2,14 @@ use crate::PipeReader;
 use crate::PipeWriter;
 use std::fs::File;
 use std::io;
-use std::mem::ManuallyDrop;
 use std::os::windows::prelude::*;
 use std::ptr;
+use winapi::shared::minwindef::BOOL;
 use winapi::shared::ntdef::{HANDLE, PHANDLE};
+use winapi::um::handleapi::DuplicateHandle;
 use winapi::um::namedpipeapi;
+use winapi::um::processthreadsapi::GetCurrentProcess;
+use winapi::um::winnt::DUPLICATE_SAME_ACCESS;
 
 pub(crate) fn pipe() -> io::Result<(PipeReader, PipeWriter)> {
     let mut read_pipe: HANDLE = ptr::null_mut();
@@ -36,9 +39,38 @@ pub(crate) fn pipe() -> io::Result<(PipeReader, PipeWriter)> {
 }
 
 pub(crate) fn dup<T: AsRawHandle>(wrapper: T) -> io::Result<File> {
-    let handle = wrapper.as_raw_handle();
-    let temp_file = ManuallyDrop::new(unsafe { File::from_raw_handle(handle) });
-    temp_file.try_clone()
+    // We rely on ("abuse") std::fs::File for a lot of descriptor/handle
+    // operations. (For example, setting F_DUPFD_CLOEXEC on Unix is a
+    // compatibility mess.) However, in the particular case of try_clone on
+    // Windows, the standard library has a bug where duplicated handles end up
+    // inheritable when they shouldn't be. See
+    // https://github.com/rust-lang/rust/pull/65316. This leads to races where
+    // child processes can inherit each other's handles, which tends to cause
+    // deadlocks when the handle in question is a stdout pipe. To get that
+    // right, we explicitly make the necessary system calls here, just like
+    // libstd apart from that one flag.
+    let source_handle = wrapper.as_raw_handle() as HANDLE;
+    let desired_access = 0; // Ignored because of DUPLICATE_SAME_ACCESS.
+    let inherit_handle = false as BOOL; // <-- Libstd sets this to true!
+    let options = DUPLICATE_SAME_ACCESS;
+    let mut duplicated_handle = 0 as HANDLE;
+    let ret = unsafe {
+        let current_process = GetCurrentProcess();
+        DuplicateHandle(
+            current_process,
+            source_handle,
+            current_process,
+            &mut duplicated_handle,
+            desired_access,
+            inherit_handle,
+            options,
+        )
+    };
+    if ret == 0 {
+        Err(io::Error::last_os_error())
+    } else {
+        unsafe { Ok(File::from_raw_handle(duplicated_handle as RawHandle)) }
+    }
 }
 
 impl IntoRawHandle for PipeReader {