1 files changed, 91 insertions, 0 deletions
diff --git a/src/os/exec/read3.go b/src/os/exec/read3.go
new file mode 100644
index 0000000..8327d73
--- /dev/null
+++ b/src/os/exec/read3.go
@@ -0,0 +1,91 @@
+// Copyright 2020 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.
+
+//go:build ignore
+
+// This is a test program that verifies that it can read from
+// descriptor 3 and that no other descriptors are open.
+// This is not done via TestHelperProcess and GO_EXEC_TEST_PID
+// because we want to ensure that this program does not use cgo,
+// because C libraries can open file descriptors behind our backs
+// and confuse the test. See issue 25628.
+package main
+
+import (
+	"fmt"
+	"internal/poll"
+	"io"
+	"os"
+	"os/exec"
+	"os/exec/internal/fdtest"
+	"runtime"
+	"strings"
+)
+
+func main() {
+	fd3 := os.NewFile(3, "fd3")
+	defer fd3.Close()
+
+	bs, err := io.ReadAll(fd3)
+	if err != nil {
+		fmt.Printf("ReadAll from fd 3: %v\n", err)
+		os.Exit(1)
+	}
+
+	// Now verify that there are no other open fds.
+	// stdin == 0
+	// stdout == 1
+	// stderr == 2
+	// descriptor from parent == 3
+	// All descriptors 4 and up should be available,
+	// except for any used by the network poller.
+	for fd := uintptr(4); fd <= 100; fd++ {
+		if poll.IsPollDescriptor(fd) {
+			continue
+		}
+
+		if !fdtest.Exists(fd) {
+			continue
+		}
+
+		fmt.Printf("leaked parent file. fdtest.Exists(%d) got true want false\n", fd)
+
+		fdfile := fmt.Sprintf("/proc/self/fd/%d", fd)
+		link, err := os.Readlink(fdfile)
+		fmt.Printf("readlink(%q) = %q, %v\n", fdfile, link, err)
+
+		var args []string
+		switch runtime.GOOS {
+		case "plan9":
+			args = []string{fmt.Sprintf("/proc/%d/fd", os.Getpid())}
+		case "aix", "solaris", "illumos":
+			args = []string{fmt.Sprint(os.Getpid())}
+		default:
+			args = []string{"-p", fmt.Sprint(os.Getpid())}
+		}
+
+		// Determine which command to use to display open files.
+		ofcmd := "lsof"
+		switch runtime.GOOS {
+		case "dragonfly", "freebsd", "netbsd", "openbsd":
+			ofcmd = "fstat"
+		case "plan9":
+			ofcmd = "/bin/cat"
+		case "aix":
+			ofcmd = "procfiles"
+		case "solaris", "illumos":
+			ofcmd = "pfiles"
+		}
+
+		cmd := exec.Command(ofcmd, args...)
+		out, err := cmd.CombinedOutput()
+		if err != nil {
+			fmt.Fprintf(os.Stderr, "%s failed: %v\n", strings.Join(cmd.Args, " "), err)
+		}
+		fmt.Printf("%s", out)
+		os.Exit(1)
+	}
+
+	os.Stdout.Write(bs)
+}