LibGfx/JBIG2: Validate more things#26191
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nico merged 8 commits intoSerenityOS:masterfrom Sep 6, 2025
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Check that all referred-to segments exist, even for segments that aren't needed for decoding an image. This is a bit stricter than before, but it seems to be fine in practice, and it's simpler. It allows us to have each segment store pointers to all segments they refer to.
No behavior change.
Some files in the power jbig2 test set incorrectly do associate a page with EndOfFile, so don't check for that part for now.
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The extra validation in SerenityOS#26191 was added at the end of decode_segment_headers(). But in decode_embedded(), that can be called several times, once for each data chunk. We want to decode segment headers from all chunks first before we do validation, so that segments in later chunks can refer to segments in earlier chunks. Add a new complete_decoding_all_segment_headers() to house the validation code, and call it after all segment chunks have been decoded. Unbreaks rendering 0000372.pdf page 11 and 0000857.pdf pages 1-4.
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The extra validation in #26191 was added at the end of decode_segment_headers(). But in decode_embedded(), that can be called several times, once for each data chunk. We want to decode segment headers from all chunks first before we do validation, so that segments in later chunks can refer to segments in earlier chunks. Add a new complete_decoding_all_segment_headers() to house the validation code, and call it after all segment chunks have been decoded. Unbreaks rendering 0000372.pdf page 11 and 0000857.pdf pages 1-4.
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Dec 27, 2025
jbig2enc, which is used by Google Books, sometimes writes files that are technically invalid. Allow that in permissive mode. To be able to check the referred-to segment's types, switch the loop from iterating over header.referred_to_segment_numbers to iterating over referred_to_segments directly (possible after the third commit of SerenityOS#26191, 72cd151). Fixes SerenityOS#26405.
nico
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Dec 27, 2025
jbig2enc, which is used by Google Books, sometimes writes files that are technically invalid. Allow that in permissive mode. To be able to check the referred-to segment's types, switch the loop from iterating over header.referred_to_segment_numbers to iterating over referred_to_segments directly (possible after the third commit of #26191, 72cd151). Fixes #26405.
Hendiadyoin1
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jbig2enc, which is used by Google Books, sometimes writes files that are technically invalid. Allow that in permissive mode. To be able to check the referred-to segment's types, switch the loop from iterating over header.referred_to_segment_numbers to iterating over referred_to_segments directly (possible after the third commit of SerenityOS#26191, 72cd151). Fixes SerenityOS#26405.
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…and a few minor cleanups.
For writing JBIG2Writer, it's useful if the loader is pretty strict, to catch mistakes. (But not too strict to break real-world files, of course. If this does break any files in practice, we need to weaken it. I'm not aware of any files that this fires on though.)