Unsigned integer overflow in DiskOverflow.d

[iain-buclaw-sociomantic]

dmqnode/src/dmqnode/storage/engine/DiskOverflow.d

Lines 606 to 625 in cf7060c

	/*
	* Pushing a record means appending it to the data file. The file
	* position is always at the end.
	* If there is no record in the file then the file should be empty so we
	* have to write the data file ID string before appending the first
	* record to the file. We're also going to need the file position where
	* we append the record.
	*/
	off_t pos = this.data.seek(0, SEEK_CUR, "Unable to seek to tell the file size");
	if (this.records)
	{
	this.data.enforce(pos >= Constants.datafile_id.length, "File size less than length of ID string");
	}
	else
	{
	this.data.enforce(!pos, "File expected to be empty");
	this.data.write(Constants.datafile_id, "Unable to write the data file ID");
	pos = Constants.datafile_id.length;
	}

The records field is an unsigned 32-bit integer, it can happen that it overflows back to zero if the overflow.dat file exceeds 4 billion records. This causes the DMQ to go into a stuck state (the logs are flooded with File expected to be empty messages), which has a knock-on effect of halting all connected clients, not just those that have overflowed.