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syscall: introduce SysProcAttr.ParentProcess on Windows
This allows users to specify which process should be used as the parent
process when creating a new process.

Note that this doesn't just trivially pass the handle onward to
PROC_THREAD_ATTRIBUTE_PARENT_PROCESS, because inherited handles must be
valid in the parent process, so if we're changing the destination
process, then we must also change the origin of the parent handles. And,
the StartProcess function must clean up these handles successfully when
exiting, regardless of where the duplication happened. So, we take care
in this commit to use DuplicateHandle for both duplicating and for
closing the inherited handles.

The test was taken originally from CL 288272 and adjusted for use here.

Fixes #44011.

Change-Id: Ib3b132028dcab1aded3dc0e65126c8abebfa35eb
Reviewed-on: https://go-review.googlesource.com/c/go/+/288300
Trust: Jason A. Donenfeld <Jason@zx2c4.com>
Trust: Alex Brainman <alex.brainman@gmail.com>
Reviewed-by: Alex Brainman <alex.brainman@gmail.com>
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zx2c4 committed Feb 26, 2021
1 parent 3146166 commit 19f96e7
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Showing 2 changed files with 87 additions and 3 deletions.
17 changes: 14 additions & 3 deletions src/syscall/exec_windows.go
Expand Up @@ -243,6 +243,7 @@ type SysProcAttr struct {
ThreadAttributes *SecurityAttributes // if set, applies these security attributes as the descriptor for the main thread of the new process
NoInheritHandles bool // if set, each inheritable handle in the calling process is not inherited by the new process
AdditionalInheritedHandles []Handle // a list of additional handles, already marked as inheritable, that will be inherited by the new process
ParentProcess Handle // if non-zero, the new process regards the process given by this handle as its parent process, and AdditionalInheritedHandles, if set, should exist in this parent process
}

var zeroProcAttr ProcAttr
Expand Down Expand Up @@ -312,18 +313,22 @@ func StartProcess(argv0 string, argv []string, attr *ProcAttr) (pid int, handle
}

p, _ := GetCurrentProcess()
parentProcess := p
if sys.ParentProcess != 0 {
parentProcess = sys.ParentProcess
}
fd := make([]Handle, len(attr.Files))
for i := range attr.Files {
if attr.Files[i] > 0 {
err := DuplicateHandle(p, Handle(attr.Files[i]), p, &fd[i], 0, true, DUPLICATE_SAME_ACCESS)
err := DuplicateHandle(p, Handle(attr.Files[i]), parentProcess, &fd[i], 0, true, DUPLICATE_SAME_ACCESS)
if err != nil {
return 0, 0, err
}
defer CloseHandle(Handle(fd[i]))
defer DuplicateHandle(parentProcess, fd[i], 0, nil, 0, false, DUPLICATE_CLOSE_SOURCE)
}
}
si := new(_STARTUPINFOEXW)
si.ProcThreadAttributeList, err = newProcThreadAttributeList(1)
si.ProcThreadAttributeList, err = newProcThreadAttributeList(2)
if err != nil {
return 0, 0, err
}
Expand All @@ -334,6 +339,12 @@ func StartProcess(argv0 string, argv []string, attr *ProcAttr) (pid int, handle
si.Flags |= STARTF_USESHOWWINDOW
si.ShowWindow = SW_HIDE
}
if sys.ParentProcess != 0 {
err = updateProcThreadAttribute(si.ProcThreadAttributeList, 0, _PROC_THREAD_ATTRIBUTE_PARENT_PROCESS, uintptr(unsafe.Pointer(&sys.ParentProcess)), unsafe.Sizeof(sys.ParentProcess), 0, nil)
if err != nil {
return 0, 0, err
}
}
si.StdInput = fd[0]
si.StdOutput = fd[1]
si.StdErr = fd[2]
Expand Down
73 changes: 73 additions & 0 deletions src/syscall/exec_windows_test.go
Expand Up @@ -5,8 +5,14 @@
package syscall_test

import (
"fmt"
"io/ioutil"
"os"
"os/exec"
"path/filepath"
"syscall"
"testing"
"time"
)

func TestEscapeArg(t *testing.T) {
Expand Down Expand Up @@ -41,3 +47,70 @@ func TestEscapeArg(t *testing.T) {
}
}
}

func TestChangingProcessParent(t *testing.T) {
if os.Getenv("GO_WANT_HELPER_PROCESS") == "parent" {
// in parent process

// Parent does nothign. It is just used as a parent of a child process.
time.Sleep(time.Minute)
os.Exit(0)
}

if os.Getenv("GO_WANT_HELPER_PROCESS") == "child" {
// in child process
dumpPath := os.Getenv("GO_WANT_HELPER_PROCESS_FILE")
if dumpPath == "" {
fmt.Fprintf(os.Stderr, "Dump file path cannot be blank.")
os.Exit(1)
}
err := os.WriteFile(dumpPath, []byte(fmt.Sprintf("%d", os.Getppid())), 0644)
if err != nil {
fmt.Fprintf(os.Stderr, "Error writing dump file: %v", err)
os.Exit(2)
}
os.Exit(0)
}

// run parent process

parent := exec.Command(os.Args[0], "-test.run=TestChangingProcessParent")
parent.Env = append(os.Environ(), "GO_WANT_HELPER_PROCESS=parent")
err := parent.Start()
if err != nil {
t.Fatal(err)
}
defer func() {
parent.Process.Kill()
parent.Wait()
}()

// run child process

const _PROCESS_CREATE_PROCESS = 0x0080
const _PROCESS_DUP_HANDLE = 0x0040
childDumpPath := filepath.Join(t.TempDir(), "ppid.txt")
ph, err := syscall.OpenProcess(_PROCESS_CREATE_PROCESS|_PROCESS_DUP_HANDLE|syscall.PROCESS_QUERY_INFORMATION,
false, uint32(parent.Process.Pid))
if err != nil {
t.Fatal(err)
}
defer syscall.CloseHandle(ph)

child := exec.Command(os.Args[0], "-test.run=TestChangingProcessParent")
child.Env = append(os.Environ(),
"GO_WANT_HELPER_PROCESS=child",
"GO_WANT_HELPER_PROCESS_FILE="+childDumpPath)
child.SysProcAttr = &syscall.SysProcAttr{ParentProcess: ph}
childOutput, err := child.CombinedOutput()
if err != nil {
t.Errorf("child failed: %v: %v", err, string(childOutput))
}
childOutput, err = ioutil.ReadFile(childDumpPath)
if err != nil {
t.Fatalf("reading child ouput failed: %v", err)
}
if got, want := string(childOutput), fmt.Sprintf("%d", parent.Process.Pid); got != want {
t.Fatalf("child output: want %q, got %q", want, got)
}
}

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