Re: LocalFree fails - HELP! (Again)

From:
"David Ching" <dc@remove-this.dcsoft.com>
Newsgroups:
microsoft.public.vc.mfc
Date:
Fri, 28 Dec 2007 03:25:30 GMT
Message-ID:
<K0_cj.11$jJ5.0@newssvr11.news.prodigy.net>
"billyard" <dmetcalf@columbus.rr.com> wrote in message
news:47745a84$0$7206$4c368faf@roadrunner.com...

If I don't execute the LocalFree functions - memory leak.

If I do execute ALL the LocalFree functions - program dies.

Without my "LocalFree" problems - the program works perfectly.

I know I'm doing something stupid. There is some extraneous code in here
that is due to my testing. I left it in. Once again, Thank you in advance!

Here's the code.

CString CChildView::DecryptPOP3Password(BYTE* ppData, DWORD pBytes)
{
   // Get the hard drive's serial number - used for encryption purposes.
   CHardDriveInfo hardDriveInfo;
   hardDriveInfo.InitDriveInfo();
   CString strPassword;

   DATA_BLOB DataEntropy;
   DATA_BLOB DataOut;
   DATA_BLOB EncData;

   LPWSTR description;

   DataEntropy.pbData = (BYTE*)hardDriveInfo.HardDriveSerialNumber;
   DataEntropy.cbData = (DWORD)strlen((char*)
hardDriveInfo.HardDriveSerialNumber);

   EncData.cbData = pBytes;
   EncData.pbData = ppData;

   if(CryptUnprotectData(
&EncData,
&description,
&DataEntropy,
NULL,
NULL,
CRYPTPROTECT_LOCAL_MACHINE,
&DataOut))
   {
      TRACE0("Successful\n");

   }
   else
   {
      TRACE0("Failed\n");
   }
   strPassword = DataOut.pbData;

   HLOCAL MyLocalMemory;
   DWORD LastError;
   MyLocalMemory = LocalFree(description); // This works fine
   if (NULL != MyLocalMemory)
      LastError = GetLastError();

   MyLocalMemory = LocalFree(DataOut.pbData); // This works fine
   if (NULL != MyLocalMemory)
      LastError = GetLastError();

   MyLocalMemory = LocalFree(&hardDriveInfo); // DOESN'T WORK
   if (NULL != MyLocalMemory)
   {
      LastError = GetLastError();
      TRACE1("failed with error %d", LastError);
   }


Don't call LocalFree() for hardDriveInfo; it is a stack variable and will be
cleaned up when the function exits.

   MyLocalMemory = LocalFree(EncData.pbData); // THIS FAILS - CORRUPT
                                                 // HEAP - STOPS PROGRAM


Don't call LocalFree() for this either...

   MyLocalMemory = LocalFree(DataEntropy.pbData);
   if (NULL != MyLocalMemory)
   {
      LastError = GetLastError();
      TRACE1("failed with error %d", LastError);
   }
   return strPassword;
}


Don't call LocalFree() for this either...

The rule that you are missing is that you call LocalFree() for any memory
allocated by CryptUnprotectData() to return data to you. As the doc at
http://msdn2.microsoft.com/en-us/library/aa380882.aspx says, you are only
supposed to call LocalFree() for the description and for DataOut.pbData, and
not anything else.

-- David

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