OutOfMemoryException when parsing Excel document / endless while-loop

I’m trying to parse an Excel document (xls) using the OpenMcdf.Extensions package.

We call AsOLEProperties extension method and eventually, the execution gets stuck in this while loop (https://github.com/ironfede/openmcdf/blob/master/sources/OpenMcdf/CompoundFile.cs#L1493-L1514) :

while (true)
{
    if (nextSecID == Sector.ENDOFCHAIN)
        break;

    Sector ms = new Sector(Sector.MINISECTOR_SIZE, sourceStream);
    byte[] temp = new byte[Sector.MINISECTOR_SIZE];

    ms.Id = nextSecID;
    ms.Type = SectorType.Mini;

    miniStreamView.Seek(nextSecID * Sector.MINISECTOR_SIZE, SeekOrigin.Begin);
    miniStreamView.Read(ms.GetData(), 0, Sector.MINISECTOR_SIZE);

    result.Add(ms);

    miniFATView.Seek(nextSecID * 4, SeekOrigin.Begin);
    nextSecID = miniFATReader.ReadInt32();
}

When the loop is entered, the nextSecID is 27. At the end of the loop the nextSecID is set to 0. And the nextSecID keeps being null as the same data is read on each loop.

Is 0 even a valid value for nextSecID?

Any idea, what to do about this?

The document in question can be opened fine in Excel. Unfortunately, we got it from a customer of ours, so we can’t share it.

[henning-krause]

@ironfede Of course, this doesn’t fix the underlying problem, but at least the load operation fails fast and does not cause an OutOfMemoryException. So it’s a quick fix.

That being said, I don’t even think that this PR fixed all problems - only the simple ones. In multiple places, the following check is performed:

if (next != nextSecID)
    nextSecID = next;
else
    throw new CFCorruptedFileException("Cyclic sector chain found. File is corrupted");

This certainly helps when you have a corrupt file where one sector points to itself. But what if you have something like a cyclic chain?

1 -> 2 -> 3 -> 1

This wouldn’t be catched and we would be in the same mess as before. I would propose a change in that check that we keep a list of all processed ids and if we hit one we had before, we’ll throw the CFCorruptedFileException.

As for the source file: It was created by one of our customers. I’ll try to strip out all the content and to reproduce the error. If it still happens, I might be able to share it with you.

[Numpsy]

Yes, there are potentially issues in multiple places (there is a file attached to #40 that makes it blow up in GetDifatSectorChain).