SCardEstablishContext memory leak

Question

We suddenly have problems with the smart card api on some windows installations. There seem to be a memory leak while calling the SCardEstablishContext function. The problem can be reproduced in a console application with the code sample available at http://www.pinvoke.net/default.aspx/winscard.scardestablishcontext

class Program
{
    #region Win32
    // WinSCard APIs to be imported.
    [DllImport("WinScard.dll")]
    static extern int SCardEstablishContext(uint dwScope,
        IntPtr notUsed1,
        IntPtr notUsed2,
        out IntPtr phContext);

    [DllImport("WinScard.dll")]
    static extern int SCardReleaseContext(IntPtr phContext);

    [DllImport("WinScard.dll")]
    static extern int SCardConnect(IntPtr hContext,
        string cReaderName,
        uint dwShareMode,
        uint dwPrefProtocol,
        ref IntPtr phCard,
        ref IntPtr ActiveProtocol);

    [DllImport("WinScard.dll")]
    static extern int SCardDisconnect(IntPtr hCard, int Disposition);

    [DllImport("WinScard.dll", EntryPoint = "SCardListReadersA", CharSet = CharSet.Ansi)]
    static extern int SCardListReaders(
      IntPtr hContext,
      byte[] mszGroups,
      byte[] mszReaders,
      ref UInt32 pcchReaders);
    #endregion

    static void Main(string[] args)
    {
        while (true)
        {
            SmartCardInserted();
            System.Threading.Thread.Sleep(10);
        }
    }

    internal static bool SmartCardInserted()
    {
        bool cardInserted = false;
        IntPtr hContext = IntPtr.Zero;

        try
        {
            List<string> readersList = new List<string>();

            int ret = 0;
            uint pcchReaders = 0;
            int nullindex = -1;
            char nullchar = (char)0;

            // Establish context.
            ret = SCardEstablishContext(2, IntPtr.Zero, IntPtr.Zero, out hContext);

            // First call with 3rd parameter set to null gets readers buffer length.
            ret = SCardListReaders(hContext, null, null, ref pcchReaders);

            byte[] mszReaders = new byte[pcchReaders];

            // Fill readers buffer with second call.
            ret = SCardListReaders(hContext, null, mszReaders, ref pcchReaders);

            // Populate List with readers.
            ASCIIEncoding ascii = new ASCIIEncoding();

            string currbuff = ascii.GetString(mszReaders);

            int len = (int)pcchReaders;

            if (len > 0)
            {
                while (currbuff[0] != nullchar)
                {
                    nullindex = currbuff.IndexOf(nullchar);   // Get null end character.
                    string reader = currbuff.Substring(0, nullindex);
                    readersList.Add(reader);
                    len = len - (reader.Length + 1);
                    currbuff = currbuff.Substring(nullindex + 1, len);
                }
            }

            // We have list of readers, check for cards.
            IntPtr phCard = IntPtr.Zero;
            IntPtr ActiveProtocol = IntPtr.Zero;
            int result = 0;

            foreach (string readerName in readersList)
            {
                try
                {
                    result = SCardConnect(hContext, readerName, 2, 3, ref phCard, ref ActiveProtocol);
                    if (result == 0)
                    {
                        cardInserted = true;
                        break;
                    }
                }
                finally
                {
                    SCardDisconnect(phCard, 0);
                }
            }
        }
        finally
        {
            SCardReleaseContext(hContext);
        }

        return cardInserted;

    }
}

To test, we call the method SmartCardInserted() in an infinite loop with a small delay => the memory grows constantly and new hadles are allocated.

We see this problem on systems runing Windows 10 or Windows Server 2012, but not on Windows Server 2008.

Any ideas are greatly appreciated!

Sisera

The policy of this site is to post the code on this site. – Engeddi

Cannot reproduce your problem (see github.com/danm-de/pcsc-sharp/issues/66) – Lakeesha

Answer 1

The problem seems to have been released with v1709 of Windows 10. The shortest amount of code to reproduce the bug is

while(true) {
    ret = SCardEstablishContext(2, IntPtr.Zero, IntPtr.Zero, out hContext);
    SCardReleaseContext(hContext);
}

It leaks ~264 bytes of memory each time a context is established and released.

If you maintain hContext outside of the loop and only create a context if it's IntPtr.Zero you should be able to avoid the leak. Then when you call SCardListReaders, check to see if you get SCARD_E_INVALID_HANDLE back and invalidate your hContext.

class Program
{
    #region Win32
    // WinSCard APIs to be imported.
    [DllImport("WinScard.dll")]
    static extern int SCardEstablishContext(uint dwScope,
        IntPtr notUsed1,
        IntPtr notUsed2,
        out IntPtr phContext);

    [DllImport("WinScard.dll")]
    static extern int SCardReleaseContext(IntPtr phContext);

    [DllImport("WinScard.dll")]
    static extern int SCardConnect(IntPtr hContext,
        string cReaderName,
        uint dwShareMode,
        uint dwPrefProtocol,
        ref IntPtr phCard,
        ref IntPtr ActiveProtocol);

    [DllImport("WinScard.dll")]
    static extern int SCardDisconnect(IntPtr hCard, int Disposition);

    [DllImport("WinScard.dll", EntryPoint = "SCardListReadersA", CharSet = CharSet.Ansi)]
    static extern int SCardListReaders(
      IntPtr hContext,
      byte[] mszGroups,
      byte[] mszReaders,
      ref UInt32 pcchReaders);
    #endregion

    static void Main(string[] args)
    {
        IntPtr hContext = IntPtr.Zero;
        while (true)
        {
            SmartCardInserted(hContext);
            System.Threading.Thread.Sleep(10);
        }
        SCardReleaseContext(hContext);
    }

    internal static bool SmartCardInserted(IntPtr hContext)
    {
        bool cardInserted = false;

        try
        {
            List<string> readersList = new List<string>();

            int ret = 0;
            uint pcchReaders = 0;
            int nullindex = -1;
            char nullchar = (char)0;

            // Establish context.
            if(hContext == IntPtr.Zero)
                ret = SCardEstablishContext(2, IntPtr.Zero, IntPtr.Zero, out hContext);

            // First call with 3rd parameter set to null gets readers buffer length.
            ret = SCardListReaders(hContext, null, null, ref pcchReaders);

            if(ret == 0x80100003) // SCARD_E_INVALID_HANDLE = 0x80100003, // The supplied handle was invalid
            {
                try
                {
                    SCardReleaseContext(hContext);
                }
                catch {}
                finally
                {
                    hContext = IntPtr.Zero;
                }
                return false;
            }

            byte[] mszReaders = new byte[pcchReaders];

            // Fill readers buffer with second call.
            ret = SCardListReaders(hContext, null, mszReaders, ref pcchReaders);

            // Populate List with readers.
            ASCIIEncoding ascii = new ASCIIEncoding();

            string currbuff = ascii.GetString(mszReaders);

            int len = (int)pcchReaders;

            if (len > 0)
            {
                while (currbuff[0] != nullchar)
                {
                    nullindex = currbuff.IndexOf(nullchar);   // Get null end character.
                    string reader = currbuff.Substring(0, nullindex);
                    readersList.Add(reader);
                    len = len - (reader.Length + 1);
                    currbuff = currbuff.Substring(nullindex + 1, len);
                }
            }

            // We have list of readers, check for cards.
            IntPtr phCard = IntPtr.Zero;
            IntPtr ActiveProtocol = IntPtr.Zero;
            int result = 0;

            foreach (string readerName in readersList)
            {
                try
                {
                    result = SCardConnect(hContext, readerName, 2, 3, ref phCard, ref ActiveProtocol);
                    if (result == 0)
                    {
                        cardInserted = true;
                        break;
                    }
                }
                finally
                {
                    SCardDisconnect(phCard, 0);
                }
            }
        }

        return cardInserted;
    }
}

It's a workaround until the Winscard.dll API is fixed.

Despicable

Thank you for confirming that this is a Windows issue (as we also suspected). We already changed our codebase and maintain the hContext outside the loop. That fixed our problem. Regards. – Sisera

But the leak is still present. Each time you get 0x80100003 two handles are lost. I thing it happens somewhere inside stopping smartcard service. – Whitish