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zstd: Fix corrupted output in "best" #876

Merged
merged 3 commits into from
Oct 22, 2023
Merged

zstd: Fix corrupted output in "best" #876

merged 3 commits into from
Oct 22, 2023

Commits on Oct 22, 2023

  1. zstd: Fix corrupted output in "best" 

    Regression from #784 and followup #793

Fixes #875

A 0 offset backreference was possible when "improve" was successful twice in a row in the "skipBeginning" part, only finding 2 (previously unmatches) length 4 matches, but where start offset decreased by 2 in both cases.

This would result in output where the end offset would equal to the next 's', thereby doing a self-reference.

Add a general check in "improve" and just reject these. Will also guard against similar issues in the future.

This also hints at some potentially suboptimal hash indexing - but I will take that improvement separately.

Fuzz test set updated.
    @klauspost
    klauspost committed Oct 22, 2023
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  2. Merge branch 'master' into zstd-fix-best-corruption

    @klauspost
    klauspost committed Oct 22, 2023
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  3. Update error text.

    @klauspost
    klauspost committed Oct 22, 2023
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