memmod: do not use IsBadReadPtr

It should be enough to check for the trailing zero name.

Signed-off-by: Jason A. Donenfeld <[email protected]>

Author: zx2c4

tun/wintun/memmod/memmod_windows.go

@@ -304,6 +304,16 @@ func (module *Module) performBaseRelocation(delta uintptr) (relocated bool, err
 	return true, nil
 }
 
+func isBadPtr(p, l uintptr) bool {
+	if l == 0 {
+		return false
+	}
+	if p == 0 {
+		return true
+	}
+	return p + l - 1 >= p //TODO: maybe compare signed?
+}
+
 func (module *Module) buildImportTable() error {
 	directory := module.headerDirectory(IMAGE_DIRECTORY_ENTRY_IMPORT)
 	if directory.Size == 0 {
@@ -312,7 +322,7 @@ func (module *Module) buildImportTable() error {
 
 	module.modules = make([]windows.Handle, 0, 16)
 	importDesc := (*IMAGE_IMPORT_DESCRIPTOR)(a2p(module.codeBase + uintptr(directory.VirtualAddress)))
-	for !isBadReadPtr(uintptr(unsafe.Pointer(importDesc)), unsafe.Sizeof(*importDesc)) && importDesc.Name != 0 {
+	for importDesc.Name != 0 {
 		handle, err := windows.LoadLibraryEx(windows.BytePtrToString((*byte)(a2p(module.codeBase+uintptr(importDesc.Name)))), 0, windows.LOAD_LIBRARY_SEARCH_SYSTEM32)
 		if err != nil {
 			return fmt.Errorf("Error loading module: %w", err)

tun/wintun/memmod/mksyscall.go

@@ -324,8 +324,6 @@ const (
 	DLL_PROCESS_DETACH = 0
 )
 
-//sys	isBadReadPtr(addr uintptr, ucb uintptr) (ret bool) = kernel32.IsBadReadPtr
-
 type SYSTEM_INFO struct {
 	ProcessorArchitecture     uint16
 	Reserved                  uint16