Title: NullReferenceException in ComInterop.ExcepInfo when GetExceptionForHR returns null

[ish-1313]

Description

If errorCode is a non-failing HRESULT, this will crash.

runtime/src/libraries/Microsoft.CSharp/src/Microsoft/CSharp/RuntimeBinder/ComInterop/ExcepInfo.cs

Lines 58 to 79 in e53094d

	int errorCode = (scode != 0) ? scode : wCode;
	Exception exception = Marshal.GetExceptionForHR(errorCode);
	string message = ConvertAndFreeBstr(ref bstrDescription);
	if (message != null)
	{
	// If we have a custom message, create a new Exception object with the message set correctly.
	// We need to create a new object because "exception.Message" is a read-only property.
	if (exception is COMException)
	{
	exception = new COMException(message, errorCode);
	}
	else
	{
	Type exceptionType = exception.GetType();
	ConstructorInfo ctor = exceptionType.GetConstructor(new Type[] { typeof(string) });
	if (ctor != null)
	{
	exception = (Exception)ctor.Invoke(new object[] { message });
	}
	}
	}

.net 9.05
windows 22h2 (19045.5965)

Reproduction Steps

Repro:

1. Call any COM method returning:
   • `HRESULT =custom code
   • bstrDescription = valid message

from GetExceptionForHR docs
"Returns
Exception
An object that represents the converted HRESULT, or null if the HRESULT value doesn't represent an error code (for example, S_OK or S_FALSE)."

Expected behavior

COMException` with the message

Actual behavior

Marshal.GetExceptionForHR() returns null (per docs, since HRESULT is unmapped)

ComInterop crashes with NullReferenceException at ex.GetType()

Regression?

No response

Known Workarounds

No response

Configuration

.NET 9.0.5

Windows 10 22H2 (19045.5965)

Other information

No response

[huoyaoyuan]

E_POINTER translates to NullReferenceException, not COMException. This is also the behavior of Marshal.GetExceptionForHR.

[ish-1313]

E_POINTER translates to NullReferenceException, not COMException. This is also the behavior of Marshal.GetExceptionForHR.

sorry. i'am attaching screenshot from debugger
errorcode = 1001
ex = null ,
text contains useful information from com target .
as far as ex = null. net will throw on ex.GetType() with nullreferenceexception

[ish-1313]

changed issue description to be more clear

[danmoseley]

Please include a complete runnable sample.

[ish-1313]

Please include a complete runnable sample.

here it is

using System.Runtime.InteropServices;

class Program
{
    static void Main() => _ = Marshal.GetExceptionForHR(1010).GetType();
}

[AaronRobinsonMSFT]

The current behavior is correct. The error code 1010 is not a failing HRESULT. An HRESULT is a 32-bit signed integer and is only an error if the high order bit is set (that is, < 0). The 1010 is a System error code, which is not the same thing as an HRESULT.

See a breakdown of the structure of HRESULTs at https://learn.microsoft.com/windows/win32/com/structure-of-com-error-codes.

System error codes are discussed at https://learn.microsoft.com/windows/win32/debug/system-error-codes.

Where is this error code coming from?

[ish-1313]

The current behavior is correct. The error code 1010 is not a failing HRESULT. An HRESULT is a 32-bit signed integer and is only an error if the high order bit is set (that is, < 0). The 1010 is a System error code, which is not the same thing as an HRESULT.

See a breakdown of the structure of HRESULTs at https://learn.microsoft.com/windows/win32/com/structure-of-com-error-codes.

System error codes are discussed at https://learn.microsoft.com/windows/win32/debug/system-error-codes.

Where is this error code coming from?

COM interface of accounting software (1C) returns custom error code 1010 with message "Duplicate key violation".
This is a valid business logic error, not a system/Win32 code.

yes, it is documented behavior that GetExceptionForHR returns null for unknown codes, but is it expected behaviour that net core Microsoft.CSharp.RuntimeBinder.ComInterop.GetException crahes with NRE because of not checking result from GetExceptionForHR for null ?

in our fork we are going to use the following workaround

   if (message != null)
   {
       // If we have a custom message, create a new Exception object with the message set correctly.
       // We need to create a new object because "exception.Message" is a read-only property.

+       if (exception == null)  //[ish]: our changes for handling 1C errors. the rest is original code and comments 
+      {
+           exception = new Exception($"{errorCode}:{message}");
+       }
       else if (exception is  COMException)
       {
           exception = new COMException(message, errorCode);
       }
       else
       {
           Type exceptionType = exception.GetType();
           ConstructorInfo ctor = exceptionType.GetConstructor(new Type[] { typeof(string) });
           if (ctor != null)
           {
               exception = (Exception)ctor.Invoke(new object[] { message });
           }
       }
   }

[ish-1313]

The current behavior is correct. The error code 1010 is not a failing HRESULT. An HRESULT is a 32-bit signed integer and is only an error if the high order bit is set (that is, < 0). The 1010 is a System error code, which is not the same thing as an HRESULT.

See a breakdown of the structure of HRESULTs at https://learn.microsoft.com/windows/win32/com/structure-of-com-error-codes.

System error codes are discussed at https://learn.microsoft.com/windows/win32/debug/system-error-codes.

Where is this error code coming from?

well, i dig a bit deeper , it is not about HRESULT structure and its correct filling

from the docs EXCEPINFO structure (oaidl.h)
private short wCode
The error code. Error codes should be greater than 1000. Either this field or the scode field must be filled in; the other must be set to 0.

and
they are mutually exclusive with scode

private int scode
A return value that describes the error. Either this field or wCode (but not both) must be filled in;

it seems that this is mistake

int errorCode = (scode != 0) ? scode : wCode;  

in our case scode = 0 , wcode = 1001;
(wCode should be larger then 1000 )

and then

Exception exception = Marshal.GetExceptionForHR(errorCode);
...
public static Exception? GetExceptionForHR(int errorCode)
{
    return GetExceptionForHR(errorCode, IntPtr.Zero);
}
public static Exception? GetExceptionForHR(int errorCode, nint errorInfo)
{
    if (errorCode >= 0)
    {
         return null;
    }
    return GetExceptionForHRInternal(errorCode, errorInfo);
}
...
Type exceptionType = exception.GetType();

so this code effectively crashes with NRE for any COM that uses wcode to return error code and has nonnull bstrDescription.
don't seems like correct behavior :)