Is possible hook EnumWindowsProc callback function?

Question

I want know if is possible hook a callback function for example like EnumWindowsProc() using inline hook approach? and if yes, could provide a code snippet (example) please?

Thank you.

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EDITION:

EnumWindowsProc is a callback implemented in other app. I not call it inside my app.

And i want hook EnumWindowsProc in this other app, by dll injection.

Answer 1

You have to handle EnumWindows at first, then you have to replace pointer to original EnumWindowsProc to yourself.

My example is valid fow win32

unit Patch;

interface

procedure PatchEnumWindows(Patch: Boolean);

implementation
uses SysUtils, SyncObjs, Windows;

const
  INSTR_SIZE = 6;

var
  OldEnumWindows: array [0..INSTR_SIZE-1] of Byte;
  EnumWindowsPatched: Boolean = False;

function PatchedEnumWindows(EnumWindowsProc: Pointer; Param: Pointer); stdcall;
begin
  // You have to replace original EnumWindowsProc to yourself
end;


procedure ApiRedirect(OrigFunction, NewFunction: Pointer; var Old);
const
  TEMP_JMP: array[0..INSTR_SIZE-1] of Byte = ($E9,$90,$90,$90,$90,$C3);
var
  JmpSize: DWORD;
  JMP: array [0..INSTR_SIZE-1] of Byte;
  OldProtect: DWORD;
begin
  Move(TEMP_JMP, JMP, INSTR_SIZE);
  JmpSize := DWORD(NewFunction) - DWORD(OrigFunction) - 5;
  if not VirtualProtect(LPVOID(OrigFunction), INSTR_SIZE, PAGE_EXECUTE_READWRITE,         OldProtect) then
    raise Exception.CreateFmt('%s', [SysErrorMessage(GetLastError)]);
  Move(OrigFunction^, Old, INSTR_SIZE);
  Move(JmpSize, JMP[1], 4);
  Move(JMP, OrigFunction^, INSTR_SIZE);
  VirtualProtect(LPVOID(OrigFunction), INSTR_SIZE, OldProtect, nil);
end;

procedure PatchEnumWindows(Patch: Boolean);
var
  OrigEnumWindows: Pointer;
begin
  if Patch <> EnumWindowsProcPatched then begin
    OrigEnumWindows := GetProcAddress(GetModuleHandle('user32.dll'), 'EnumWindows');
    if Patch then begin
      ApiRedirect(OrigEnumWindows, @PatchedEnumWindows, OldEnumWindows);
    end
    else begin
      Move(OldEnumWindows, OrigEnumWindows, INSTR_SIZE);
    end;
    EnumWindowsPatched := Patch;
  end;
end;


end.