Don't panic if LZW doesn't find an LZW end code#306
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197g merged 1 commit intoimage-rs:mainfrom Nov 4, 2025
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Currently, when getting the LZWStatus::NoProgress from the underlying weezl library, tiff checks that no input bytes were read and no output bytes were written. Although this is according to what the weezl library mentions in their doc-comment, it's not what the real result always looks like. Our fuzzer found input that triggered exactly this case, where the LZW reader is able to write some output byte before hitting the NoProgress status. This change removes the assert, as the resulting action is anyways to return an error that can be handled by the caller.
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Uff... this seems to hit a debug_assert in the underlying library: https://github.com/image-rs/weezl/blob/fa42aa42da4b611a407d1d4e0d41a72e16e3f1a7/src/decode.rs#L909-L927. What's the best way of moving this forward? Should we make the debug_assert configurable as mentioned by the doc comment? Should we run this crates fuzz-tests in release? |
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Do you have a minimal reproduction file / lzw stream data? I thought that debug assert was being fuzzed, you can definitely open it against |
197g
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Nov 4, 2025
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Currently, when getting the LZWStatus::NoProgress from the underlying weezl library, tiff checks that no input bytes were read and no output bytes were written. Although this is according to what the weezl library mentions in their doc-comment, it's not what the real result always looks like.
Our fuzzer found input that triggered exactly this case, where the LZW reader is able to write some output byte before hitting the NoProgress status.
This change removes the assert, as the resulting action is anyways to return an error that can be handled by the caller.