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fix(reader): reject oversize heap vectors without panicking #179

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fix(reader): reject oversize heap vectors without panicking #179

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6 changes: 6 additions & 0 deletions src/reader.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -465,6 +465,12 @@ impl<'wasm> Reader<'wasm> {
VA: Allocator,
{
let len = self.read_u32()?;
// Reject lengths that cannot form a valid allocation layout. On 32-bit
// targets Layout::array overflows for huge declared lengths and used to
// panic inside Vec::new_in; return VecTooLong like the stack path (#158).
Comment on lines +468 to +470

@Kronos3 Kronos3 Aug 24, 2026

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Please remove these comments, I'd rather avoid superfluous comments explaining self document code. The regression test comments are good enough.

if core::alloc::Layout::array::<T>(len as usize).is_err() {
return Err(ValidationError::VecTooLong);
}
let mut out = Vec::new_in(alloc, len)?;
for _ in 0..len {
out.push(read_element(self)?);
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9 changes: 9 additions & 0 deletions tests/regression/decode-errors.wast
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Expand Up @@ -179,3 +179,12 @@
(assert_invalid
(module binary "\00asm\01\00\00\00\01\04\01\60\00\00\03\02\01\00\0a\08\01\06\01\ff\ff\03\7f\0b")
"call frame too large")

;; ---------------------------------------------------------------------------
;; A type section declaring 0xFFFFFFFF entries must not panic the heap vector
;; path on 32-bit targets (Layout::array overflow). Regression for #158.
;; ---------------------------------------------------------------------------
(assert_invalid
(module binary "\00asm\01\00\00\00\01\05\ff\ff\ff\ff\0f")
"length out of bounds")

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