python: handling stderr stream when using createprocessasuser api in windows

Question

Need some help debugging this issue. I tried searching online and stackoverflow but could not find a solution for this. I am fairly new to the windows api so please pardon my ignorance.

Basically, I am trying to run a c++ application that outputs to stdout and stderr from python using a specific user. For this purpose, I am invoking the binary using the LogonUser API and CreateProcessAsUser apis and using Pipes for capturing the output and error streams. Have picked up the code mostly from a demo code in python win32 module. However, for some reason when my process is dumping to error stream it gets hung at WriteFile. Looking into the crash dump I see that the filehandle is 2 (stderr). Can someone help me with the issue?

Thanks in advance

Here is the code snippet --

userToken = win32security.LogonUser(user, domain, password,
                                    win32con.LOGON32_LOGON_BATCH,
                                    win32con.LOGON32_PROVIDER_DEFAULT)

secAttrs = win32security.SECURITY_ATTRIBUTES()
secAttrs.bInheritHandle = 1
stdout_r, stdout_w = win32pipe.CreatePipe(secAttrs, 0)
stderr_r, stderr_w = win32pipe.CreatePipe(secAttrs, 0)

startupInfo = win32process.STARTUPINFO()
startupInfo.dwFlags = win32con.STARTF_USESTDHANDLES
startupInfo.hStdOutput = stdout_w
startupInfo.hStdError = stderr_w

ppid = win32api.GetCurrentProcess()
tmp = win32api.DuplicateHandle(ppid, stdout_r, ppid, 0, 0,
                               win32con.DUPLICATE_SAME_ACCESS)
win32file.CloseHandle(stdout_r)
stdout_r = tmp

procArgs = (None,       # appName
            cmd_line,   # commandLine
            None,       # processAttributes
            None,       # threadAttributes
            1,          # bInheritHandles
            win32process.CREATE_NEW_CONSOLE, # dwCreationFlags
            None,       # newEnvironment
            None,       # currentDirectory
            startupInfo)

procHandles = win32process.CreateProcessAsUser(userToken, *procArgs)

win32file.CloseHandle(stderr_w)
win32file.CloseHandle(stdout_w)
win32security.RevertToSelf()

# Wait for process to complete
hProcess, hThread, pid, tid = procHandles

stdout_buf = os.fdopen(msvcrt.open_osfhandle(stdout_r, 0), "rb")
stdout = stdout_buf.read()
stderr_buf = os.fdopen(msvcrt.open_osfhandle(stderr_r, 0), "rb")
stderr = stderr_buf.read()

win32event.WaitForSingleObject(hProcess, 3600*1000)
rc = win32process.GetExitCodeProcess(hProcess)