Return an error instead of panicking on fixed-length-list size overflow - #2643
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alexcrichton merged 2 commits intoSep 8, 2026
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`SizeAlign::fill` (and its internal `calculate` helper) computed the
size of a `FixedLengthList` as `element_size * length` via
`checked_mul(..).unwrap()`, which panics when the multiplication
overflows `usize`. Since `list<T, N>` places no upper bound on `N` in
the WIT text format (unlike the component binary format, which bounds
it to `MAX_WASM_FIXED_LENGTH_LIST_ELEMENTS`), a WIT document with two
nested fixed-length lists of a non-trivial element type is enough to
overflow the multiplication and abort the process, in a release build
too.
This changes `SizeAlign::fill`/`calculate` to return `anyhow::Result`
and propagates that outward through `wit-dylib`'s `Adapter::encode`,
`create`, and `create_with_metadata`, and their two call sites (the
`wasm-tools wit-dylib` CLI subcommand and the wit-dylib test-programs
harness). A oversized fixed-length list now surfaces as a normal
error instead of aborting:
$ wasm-tools wit-dylib poc.wit
error: size of fixed-length list of 4294967295 elements overflows
the target architecture's address space
Adds a regression test covering both the overflow case (now returns
`Err`) and a benign nested fixed-length list (still computes
correctly).
Fixes bytecodealliance#2637
pchickey
approved these changes
Sep 8, 2026
find_signed_load's test helper still called super::create() as if it returned Vec<u8> directly; it now returns anyhow::Result<Vec<u8>>. Caught by CI's clippy job (which builds --all-targets, unlike my local clippy run that only covered the lib). Did an exhaustive grep across the whole workspace afterward for every other Adapter/SizeAlign call site to confirm this was the only one missed.
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SizeAlign::fill(and its internalcalculatehelper) computed the size of aFixedLengthListaselement_size * lengthviachecked_mul(..).unwrap(), which panics when the multiplication overflowsusize. Sincelist<T, N>places no upper bound onNin the WIT text format (unlike the component binary format, which bounds it toMAX_WASM_FIXED_LENGTH_LIST_ELEMENTS), a WIT document with two nested fixed-length lists of a non-trivial element type is enough to overflow the multiplication and abort the process, in a release build too.This changes
SizeAlign::fill/calculateto returnanyhow::Resultand propagates that outward throughwit-dylib'sAdapter::encode,create, andcreate_with_metadata, and their two call sites (thewasm-tools wit-dylibCLI subcommand and the wit-dylib test-programs harness). A oversized fixed-length list now surfaces as a normal error instead of aborting:Adds a regression test covering both the overflow case (now returns
Err) and a benign nested fixed-length list (still computes correctly).Fixes #2637