runtime: enforce standard file descriptors open on init on unix

On Unix-like platforms, enforce that the standard file descriptions (0,
1, 2) are always open during initialization. If any of the FDs are
closed, we open them pointing at /dev/null, or fail.

Fixes #60641

Change-Id: Iaab6b3f3e5ca44006ae3ba3544d47da9a613f58f
Reviewed-on: https://go-review.googlesource.com/c/go/+/509020
Reviewed-by: Michael Pratt <mpratt@google.com>
Run-TryBot: Roland Shoemaker <roland@golang.org>
Auto-Submit: Roland Shoemaker <roland@golang.org>
Reviewed-by: Ian Lance Taylor <iant@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

1 files changed, 29 insertions, 0 deletions

diff --git a/src/runtime/testdata/testfds/main.go b/src/runtime/testdata/testfds/main.go
new file mode 100644
index 0000000000..238ba469a3
--- /dev/null
+++ b/src/runtime/testdata/testfds/main.go
@@ -0,0 +1,29 @@
+// Copyright 2023 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package main
+
+import (
+	"fmt"
+	"io"
+	"log"
+	"os"
+)
+
+func main() {
+	f, err := os.OpenFile(os.Getenv("TEST_OUTPUT"), os.O_CREATE|os.O_RDWR, 0600)
+	if err != nil {
+		log.Fatalf("os.Open failed: %s", err)
+	}
+	defer f.Close()
+	b, err := io.ReadAll(os.Stdin)
+	if err != nil {
+		log.Fatalf("io.ReadAll(os.Stdin) failed: %s", err)
+	}
+	if len(b) != 0 {
+		log.Fatalf("io.ReadAll(os.Stdin) returned non-nil: %x", b)
+	}
+	fmt.Fprintf(os.Stdout, "stdout\n")
+	fmt.Fprintf(os.Stderr, "stderr\n")
+}