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https://issues.apache.org/jira/browse/LOG4NET-360?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Michael Cessna updated LOG4NET-360:
-----------------------------------
Attachment: Event Log Corruption.txt
This file shows the stack from an exception that was the result of a
System.ComponentModel.Win32Exception with the message "The event log file is
corrupted" after calling EventLog.WriteEntry() with a string 31,876 bytes long
under Windows 7. Note: The error won't happen all of the time, but corruption
will eventually occur.
> 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
> Attachments: Event Log Corruption.txt
>
>
> 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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