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Re: [Full-disclosure] Defense in depth -- the Microsoft way (part 13): surprising and inconsistent behaviour, sloppy coding, sloppy QA, sloppy documentation
From: "Stefan Kanthak" <stefan.kanthak () nexgo de>
Date: Sun, 3 Nov 2013 22:07:09 +0100

"Mario Vilas" <mvilas () gmail com> wrote:

This may be a silly question, so I apologize in advance, but that would
exactly be the advantage here? Using a NULL pointer is in most (if not all)
those cases undocumented behavior to begin with. Unless I'm missing
something, the problem is not so much with Win32 as it is with the C
language in general...

For many of the Win32 functions I referenced here the behaviour of a NULL
pointer is but documented:

<http://msdn.microsoft.com/en-us/library/ms647492.aspx>

| If lpString is NULL, the function returns 0.

JFTR: I suspect that this is the reason why most of the other functions
      treat a NULL pointer as an empty string.

<http://msdn.microsoft.com/en-us/library/ms647487.aspx>
<http://msdn.microsoft.com/en-us/library/ms647490.aspx>
<http://msdn.microsoft.com/en-us/library/ms647491.aspx>

| When this function catches SEH errors, it returns NULL without null-
| terminating the string and without notifying the caller of the error.

<http://msdn.microsoft.com/en-us/library/ms682425.aspx>

| BOOL WINAPI CreateProcess(
|   _In_opt_     LPCTSTR lpApplicationName,
|   _Inout_opt_  LPTSTR lpCommandLine,

BOTH string arguments may be NULL!
Idem for the other CreateProcess*() functions.

<http://msdn.microsoft.com/en-us/library/ms645505.aspx>

| The dialog box title. If this parameter is NULL, the default title is Error.

<http://msdn.microsoft.com/en-us/library/aa364934.aspx>

| To determine the required buffer size, set this parameter to NULL and the
| nBufferLength parameter to 0.


Most of the Get*() functions return the required buffer size when the size
argument is 0 (or to small), but only
<http://msdn.microsoft.com/en-us/library/ms724301.aspx> explicitly says:

| If lpBuffer is NULL, this parameter must be zero.

and checks this contraint properly.


The problem is not the C language!
The problem is the inconsistent (and sloppy) implemenation of similar
functions of the Win32 API and their inconsistent and sloppy documentation.

regards
Stefan Kanthak


On Sun, Nov 3, 2013 at 4:30 PM, Stefan Kanthak <stefan.kanthak () nexgo de>wrote:

Hi @ll,

the Win32 API is full of idiosyncrasies resp. surprising and inconsistent,
poorly tested and documented behaviour.

Just to pick one: NULL pointer as string argument.

0. lstrlen(NULL)
   lstrcat(NULL, ...)      and  lstrcat(..., NULL)
   lstrcmp(NULL, ...)      and  lstrcmp(..., NULL)
   lstrcmpi(NULL, ...)     and  lstrcmpi(..., NULL)
   lstrcpy(NULL, ...)      and  lstrcpy(..., NULL)
   lstrcpyn(NULL, ..., 0)  and  lstrcpy(..., NULL, ...)

   do not yield an exception, but treat their NULL arguments like an
   empty string (when used as source), resp. return NULL (when used as
   destination).


1. wsprintf(NULL, ...)       and  wvsprintf(NULL, ...)
   wsprintf(..., NULL, ...)  and  wvsprintf(..., NULL, ...)

   yield an access violation in USER32.DLL.


2. CommandLineToArgvW(NULL, ...)

   yields an access violation in SHELL32.DLL.


3. CreateProcess(NULL, NULL, ...)
   CreateProcessAsUser(..., NULL, NULL, ...)
   CreateProcessWithLogonW(..., ..., ..., ..., NULL, NULL, ...)
   CreateProcessWithTokenW(..., ..., NULL, NULL, ...)

   yield an access violation in KERNEL32.DLL.


4. GetFileAttributes(NULL)

   does not yield an exception, but treats the NULL argument like an
   empty string.


5. GetBinaryType(NULL, ...)

   does not yield an exception, but treats the NULL argument like an
   empty string.


6. MessageBox(..., NULL, ...)  and  MessageBox(..., ..., NULL, ...)

   do not yield an exception, but treat the NULL argument like an
   empty string.


7. FatalAppExit(0, NULL)

   does not yield an exception, but treats the NULL argument like an
   empty string.


8. GetCurrentDirectory(..., NULL)

   returns an error if the buffer size (the argument shown as ... here)
   is sufficient to hold the result, else the required buffer size.

   GetTempPath(..., NULL)
   GetSystemDirectory(NULL, ...)
   GetSystemWindowsDirectory(NULL, ...)
   GetSystemWow64Directory(NULL, ...)
   GetWindowsDirectory(NULL, ...)
   GetComputerName(NULL, ...)

   yield an access violation in NTDLL.DLL resp. KERNEL32.DLL if the
   buffer size is sufficient to hold the result, else the required
   buffer size.

   GetUserName(NULL, ...)
   GetComputerObjectName(..., NULL, ...)

   do not yield an access violation, but return an error with
   GetLastError() == ERROR_INSUFFICIENT_BUFFER.


9. GetUserName(NULL, NULL)
   GetComputerName(NULL, NULL)

   yield an access violation in KERNEL32.DLL.

   GetComputerNameEx(..., NULL, NULL)
   GetComputerObjectName(..., NULL, NULL)

   do not yield an access violation, but return an error with
   GetLastError() == ERROR_INVALID_PARAMETER.

   JFTR: only the documentation of the last function (see
         <http://msdn.microsoft.com/en-us/library/ms724301.aspx>)
         explicitly says about the value of the third argument
         "If lpBuffer is NULL, this parameter must be zero."
         and checks this contraint properly.


The expected behavior in all cases is but to return an error with
GetLastError() == ERROR_INVALID_PARAMETER or similar.


FIX: ALL interfaces of the Win32 API should^WMUST verify (ALL) their
     arguments properly before using them and return an appropriate,
     documented error code.


stay tuned
Stefan Kanthak

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