.NET Sockets Buffer Overflow No Error
- by Michael Covelli
I have one thread that is receiving data over a socket like this:
while (sock.Connected)
{
// Receive Data (Block if no data)
recvn = sock.Receive(recvb, 0, rlen, SocketFlags.None, out serr);
if (recvn <= 0 || sock == null || !sock.Connected)
{
OnError("Error In Receive, recvn <= 0 || sock == null || !sock.Connected");
return;
}
else if (serr != SocketError.Success)
{
OnError("Error In Receive, serr = " + serr);
return;
}
// Copy Data Into Tokenizer
tknz.Read(recvb, recvn);
// Parse Data
while (tknz.MoveToNext())
{
try
{
ParseMessageAndRaiseEvents(tknz.Buffer(), tknz.Length);
}
catch (System.Exception ex)
{
string BadMessage = ByteArrayToStringClean(tknz.Buffer(), tknz.Length);
string msg = string.Format("Exception in MDWrapper Parsing Message,
Ex = {0}, Msg = {1}", ex.Message, BadMessage);
OnError(msg);
}
}
}
And I kept seeing occasional errors in my parsing function indicating that the message wasn't valid. At first, I thought that my tokenizer class was broken. But after logging all the incoming bytes to the tokenizer, it turns out that the raw bytes in recvb weren't a valid message. I didn't think that corrupted data like this was possible with a tcp data stream.
I figured it had to be some type of buffer overflow so I set
sock.ReceiveBufferSize = 1024 * 1024 * 8;
and the parsing error never, ever occurs in testing (it happens often enough to replicate if I don't change the ReceiveBufferSize).
But my question is: why wasn't I seeing an exception or an error state or something if the socket's internal buffer was overflowing before I changed this buffer size?
