Hi Johannes,
Thank you very much for the patch and the perfect explanation! I commited the
change as it works for me and sounds very reasonable.
Cheers,
Dominik
On Tuesday 24 August 2010 12:33:38 Dr. Johannes Bitterling wrote:
> Hi all,
>
> I've just found a bug in PdfLZWFilter, and (maybe) developed a suitable
> fix. Please verify before using it :-)
>
> Bug: parsing fails on some PDFs containing LZW-compressed streams (see
> also: "Problem with /LZWDecode filter stream" report as of of Fri, 16 Apr
> 2010 10:02:06 -0700, this might solve the problem mentioned - had the same
> problem here).
>
> Suggested solution: in file PdfFiltersPrivate.cpp, function
> PdfLZWFilter::DecodeBlockImpl, just remove the "case 4095:".
>
> Reasons: when the dictionary size reaches 4095 entries, further
> incrementing m_mask will invariably lead to an "out of bounds" array access
> in s_masks[] (which has just four entries, valid indices 0..3). - In
> addition, at least the PDF files which I used for debugging do contain an
> PdfLZWFilter::s_clear as next opcode... but with unchanged m_code_len, so
> incrementing m_code_len will lead to consumption of an additional input
> bit, which will render the rest of the stream unreadable.
>
> Regards,
> Johannes
>
>
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