Add regression test and fuzz coverage for zero first offset in lists#29
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MegaRedHand wants to merge 1 commit into
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Add regression test and fuzz coverage for zero first offset in lists#29MegaRedHand wants to merge 1 commit into
MegaRedHand wants to merge 1 commit into
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leanEthereum/leanSpec#1175 reports that leanSpec's SSZ list decoder accepts first_offset == 0, deriving a zero element count while the offset/scope boundary describes one element spanning the whole input. libssz already rejects this up front (the num_items == 0 check in decode_variable_length_items_with_max), but nothing pinned that behavior. Pin it with a regression test using the issue's exact payload, and extend the offset_adversarial fuzz target with list-of-variable-length items types: it previously only exercised ContainerDecoder, never the list offset-table path where this class of bug lives.
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Context
leanEthereum/leanSpec#1175 reports that leanSpec's SSZ variable-length list decoder accepts
first_offset == 0: the element count computes to 0 while the offset/scope boundary describes one element spanning the whole input. It fails there only by accident, at the wrong layer.libssz is not affected
decode_variable_length_items_with_maxalready rejects this up front via thenum_items == 0check (crates/ssz/src/decode.rs), returningInvalidFirstOffsetbefore any offsets or element bodies are parsed.ContainerDecoderis stricter still: the first offset must equal the fixed-part length exactly.Changes
vec_of_vecs_zero_first_offset): pins the rejection using the issue's exact payload00000000aabbccdd, plus the bare00000000case.offset_adversarialonly exercisedContainerDecoder(its fields areVec<u8>, which decodes as raw bytes with no inner offset table), so the list offset-table path had no raw-bytes fuzz coverage anywhere. AddedVec<Vec<u8>>and a container holding one, matching the target's documented intent of covering zero-offset patterns.