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Alex ChambersandClaude Opus 5.5
8feda7a997
Pre-existing on main. The reader computed the position of a directory's next-IFD pointer before it checked that every declared entry had been read: a saturating multiplication of the declared count, then an unchecked addition. A 44-byte BigTIFF declaring u64::MAX entries therefore panicked with overflow checks on. The position is now computed only for a directory read whole, with checked arithmetic. 32-bit note: the same guard compared the counts after narrowing the declared one to usize, so on wasm32 a BigTIFF declaring 4,294,967,297 entries but holding one passed for a whole directory and its next pointer was followed. The counts now compare as 64-bit numbers (reads_every_entry). On wasm32 the old comparison followed all six malformed test chains and the new one follows none; 64-bit results are unchanged for every directory whose count is read whole. Regression tests (crates/tiff/src/reader.rs): a_bigtiff_directory_declaring_u64_max_entries_parses_without_overflow, which panicked before; a_bigtiff_count_past_u32_max_never_follows_the_next_pointer (the whole chain, on every target); and only_a_directory_read_whole_has_a_next_pointer (the comparison itself, on every target). Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>