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From "Michael Cessna (JIRA)" <j...@apache.org>
Subject [jira] [Created] (LOG4NET-360) EventLogAppender can corrupt the event log on Windows Vista and higher if the string is longer than 31839 bytes
Date Mon, 05 Nov 2012 18:20:11 GMT
Michael Cessna created LOG4NET-360:
--------------------------------------

             Summary: EventLogAppender can corrupt the event log on Windows Vista and higher
if the string is longer than 31839 bytes
                 Key: LOG4NET-360
                 URL: https://issues.apache.org/jira/browse/LOG4NET-360
             Project: Log4net
          Issue Type: Bug
          Components: Appenders
    Affects Versions: 1.2.11
         Environment: Windows Vista or higher
            Reporter: Michael Cessna
            Priority: Blocker


private const int MaxEventLogMsgLength_PreVista = 32766;
private const int MaxEventLogMsgLength_VistaOrHigher = 31839;

/// <summary>
/// Gets the maximum allowable size of event log message for the current operating system.
/// </summary>
/// <returns></returns>
public static int GetMaxEventLogMessageSize()
{
	// http://msdn.microsoft.com/en-us/library/xzwc042w(v=vs.100).aspx            
	// The 32766 documented max size is two bytes shy of 32K (I'm assuming 32766 may leave space
for a two byte null
	// terminator of #0#0). The 32766 max length is what the .NET 4.0 source code checks for,
but this is WRONG!...
	// strings with a length > 31839 on Windows Vista or higher can CORRUPT the event log!
See:
	// System.Diagnostics.EventLogInternal.InternalWriteEvent() for the use of the 32766 max
size.
	var maxEventMsgSize = MaxEventLogMsgLength_PreVista;

	// Windows Vista and higher
	if (Environment.OSVersion.Platform == PlatformID.Win32NT && Environment.OSVersion.Version.Major
>= 6)
	{
		// See ReportEvent API: http://msdn.microsoft.com/en-us/library/aa363679(VS.85).aspx
		// ReportEvent's lpStrings parameter: "A pointer to a buffer containing an array of null-terminated
strings that are
		// merged into the message before Event Viewer displays the string to the user. This parameter
must be a valid pointer
		// (or NULL), even if wNumStrings is zero. Each string is limited to 31,839 characters."

		// Going beyond the size of 31839 will (at some point) corrupt the event log on Windows
Vista or higher! It may succeed
		// for a while...but you will eventually run into the error: "System.ComponentModel.Win32Exception
: A device attached to
		// the system is not functioning", and the event log will then be corrupt (I was able to
corrupt an event log using a 
		// length of 31877 on Windows 7).

		// The max size for Windows Vista or higher is documented here: http://msdn.microsoft.com/en-us/library/xzwc042w(v=vs.100).aspx.
		// Going over this size may succeed a few times but the buffer will overrun and eventually
corrupt the log (based on testing).
		// Log4net's own EventLogAppender will write up to 32000 bytes (0x7D00), which can corrupt
the event log.

		// The maxEventMsgSize size is based on the max buffer size of the lpStrings parameter of
the ReportEvent API.
		// The documented max size for EventLog.WriteEntry for Windows Vista and higher is 31839,
but I'm leaving room for a
		// terminator of #0#0, as we cannot see the source of ReportEvent (though we could use an
API monitor to examine the
		// buffer, given enough time).
		// TODO: Use an API monitor to examine how the ReportEvent API allocates a buffer for the
event log message strings.
		const int terminatorLength = 2; // Safety for now.
		maxEventMsgSize = MaxEventLogMsgLength_VistaOrHigher - terminatorLength;
	}
	return maxEventMsgSize;
}		

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