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From Konstantin Preißer <verlag.preis...@t-online.de>
Subject BufferOverflowException in Tomcat 7.0.x at AjpAprProcessor.output()
Date Fri, 20 Apr 2012 21:47:06 GMT
Hi all,

some time ago, I wrote about a BufferOverflowException which I got sporadically on my Tomcat
7.0.21 [1], when using the AJP-APR-Connector.
However, at that time I couldn't reproduce the exception.

When I looked at this again today, I was able to create a client that sends an AJP message
and aborts the connection, resulting in the BufferOverflowException in Tomcat. I was using
Tomcat 7.0.27 with Tomcat Native 1.1.23, on Oracle JDK 1.7.0_03 and Windows 7 32-bit.


To reproduce,

1. On the Server side, create a web application containing a servlet which will generate some
random data:

@WebServlet("/index.html")
public class MyTestServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;
       
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws
ServletException, IOException {
        try {
            response.setContentType("text/plain");
            response.setCharacterEncoding("utf-8");
            
            byte[] bytesToWrite = {48, 49, 50, 51, 52, 53, 54, 55, 56, 57};
            
            // Try to write 1,000,000 bytes to the client.
            try (OutputStream out = response.getOutputStream()) {
                for (int i = 0; i < 100000; i++) {
                    out.write(bytesToWrite);
                }
            }
            
        } catch (IOException ex) {
            // Ignore
        }
    }
}

Deploy the application as ROOT, so that the servlet will be reachable at "/".
Configure Tomcat to have an AJP-APR connector listening on port 8009.


2. On the client side, create a program like this:

public class AjpTester {
    public static void main(String[] args) throws IOException {

        byte[] ajpPacketBytes = { // JK_AJP13_FORWARD_REQUEST for "/"
            0x12, 0x34, 0x00, 0x54, 0x02, 0x02, 0x00, 0x08,
            0x48, 0x54, 0x54, 0x50, 0x2f, 0x31, 0x2e, 0x31,
            0x00, 0x00, 0x01, 0x2f, 0x00, 0x00, 0x07, 0x31,
            0x2e, 0x32, 0x2e, 0x33, 0x2e, 0x34, 0x00, 0x00,
            0x07, 0x31, 0x2e, 0x32, 0x2e, 0x33, 0x2e, 0x34,
            0x00, 0x00, 0x09, 0x6c, 0x6f, 0x63, 0x61, 0x6c,
            0x68, 0x6f, 0x73, 0x74, 0x00, 0x00, 0x50, 0x00,
            0x00, 0x02, (byte)0xa0, 0x06, 0x00, 0x0a, 0x4b, 0x65,
            0x65, 0x70, 0x2d, 0x41, 0x6c, 0x69, 0x76, 0x65,
            0x00, (byte)0xa0, 0x0b, 0x00, 0x09, 0x6c, 0x6f, 0x63,
            0x61, 0x6c, 0x68, 0x6f, 0x73, 0x74, 0x00, (byte)0xff
        };

        Socket s = new Socket("localhost", 8009); // connect to AJP port
        OutputStream sout = s.getOutputStream();
        InputStream sin = s.getInputStream();

        sout.write(ajpPacketBytes); // request Url "/"

        // Read between 10,000 and 11,023 bytes, then exit the JVM
        byte[] buf = new byte[1024];
        int read;
        int bytesRead = 0;
        while ((read = sin.read(buf)) > 0) {
            bytesRead += read;
            if (bytesRead >= 10000) {
                System.exit(1);
            }
        }
    }
}

The client will send an JK_AJP13_FORWARD_REQUEST message which requests URL "/" and sends
"Connection: keep-alive" and "Host: localhost" headers.


3. Tomcat will display this exception:

Apr 20, 2012 10:57:08 PM org.apache.coyote.ajp.AjpAprProcessor process
Schwerwiegend: Error processing request
java.nio.BufferOverflowException
	at java.nio.DirectByteBuffer.put(DirectByteBuffer.java:357)
	at org.apache.coyote.ajp.AjpAprProcessor.output(AjpAprProcessor.java:285)
	at org.apache.coyote.ajp.AbstractAjpProcessor$SocketOutputBuffer.doWrite(AbstractAjpProcessor.java:1119)
	at org.apache.coyote.Response.doWrite(Response.java:504)
	at org.apache.catalina.connector.OutputBuffer.realWriteBytes(OutputBuffer.java:383)
	at org.apache.tomcat.util.buf.ByteChunk.flushBuffer(ByteChunk.java:462)
	at org.apache.catalina.connector.OutputBuffer.doFlush(OutputBuffer.java:334)
	at org.apache.catalina.connector.OutputBuffer.close(OutputBuffer.java:283)
	at org.apache.catalina.connector.Response.finishResponse(Response.java:511)
	at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:434)
	at org.apache.coyote.ajp.AjpAprProcessor.process(AjpAprProcessor.java:197)
	at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:565)
	at org.apache.tomcat.util.net.AprEndpoint$SocketProcessor.run(AprEndpoint.java:1812)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1110)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:603)
	at java.lang.Thread.run(Thread.java:722)


I guess the exception itself is harmless, but it may fill up log files, if clients disconnect
frequently while receiving data.
Note that before that exception occurs, a regular "ClientAbortException:  java.io.IOException:
Failed to send AJP message" is thrown by org.apache.catalina.connector.OutputBuffer.realWriteBytes(OutputBuffer.java:388).

The exception occurs neither with AJP-BIO nor with AJP-NIO.


Regards,
Konstantin Preißer


[1] http://markmail.org/message/zogi3tfbz2kyw3jg


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