#15 Infinite loop encountered while reading Mini FAT sector chain

[Gary Hill]

Hi,

Another problem I have encountered while processing test files sourced from the internet. The attached file appears to have a blank sector in the Mini FAT sector chain that triggers an infinite loop.

I have used the refined version of GetMiniSectorChain below to address this in my application.

Gary

 private List<Sector> GetMiniSectorChain(int secID)
        {
            List<Sector> result
                  = new List<Sector>();

            if (secID != Sector.ENDOFCHAIN)
            {
                List<Sector> miniFAT = GetNormalSectorChain(header.FirstMiniFATSectorID);
                List<Sector> miniStream = GetNormalSectorChain(RootEntry.StartSetc);

                StreamView miniFATView
                    = new StreamView(miniFAT, GetSectorSize(), header.MiniFATSectorsNumber * Sector.MINISECTOR_SIZE, sourceStream);

                StreamView miniStreamView =
                    new StreamView(miniStream, GetSectorSize(), rootStorage.Size, sourceStream);

                BinaryReader miniFATReader = new BinaryReader(miniFATView);


                // list to guard against cycles in the sector list
                var visitedSectors = new List<int>();

                int nextSecID = secID;

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

                    // check we have not been here before!
                    if (visitedSectors.Contains(nextSecID))
                    {
                        throw new CFCorruptedFileException("Cyclic sector chain detected in MiniFAT");   
                    }

                    visitedSectors.Add(nextSecID);

                    Sector ms = new Sector(Sector.MINISECTOR_SIZE, sourceStream);

                    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();
                }
            }
            return result;
        }

[Federico]

Thank You very much for the accurate report.
Fix will be included in the main branch.

Best Regards,
Federico