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Prevent over-deep type hierarchies in wasm-smith #2143

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Merged
fitzgen merged 2 commits into from
Apr 15, 2025
Merged

Prevent over-deep type hierarchies in wasm-smith #2143

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Prevent over-deep type hierarchies in wasm-smith
alexcrichton Apr 15, 2025
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alexcrichton Apr 15, 2025
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18 changes: 17 additions & 1 deletion crates/wasm-smith/src/core.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -260,6 +260,9 @@ pub(crate) struct SubType {
pub(crate) is_final: bool,
pub(crate) supertype: Option<u32>,
pub(crate) composite_type: CompositeType,
/// How "deep" this subtype's supertype hierarchy is. The base case is 1 and
/// if `supertype` is present it's `1 + supertype.depth`.
depth: u32,
}

impl SubType {
Expand Down Expand Up @@ -591,7 +594,15 @@ impl Module {
};
list.push(index);

if !ty.is_final {
// Calculate the recursive depth of this type, and if it's beneath a
// threshold then allow future types to subtype this one. Otherwise this
// can no longer be subtyped so despite this not being final don't add
// it to the `can_subtype` list.
//
// Note that this limit is intentinally a bit less than the wasm-defined
// maximum of 63.
const MAX_SUBTYPING_DEPTH: u32 = 60;
if !ty.is_final && ty.depth < MAX_SUBTYPING_DEPTH {
self.can_subtype.push(index);
}

Expand Down Expand Up @@ -682,6 +693,7 @@ impl Module {
is_final: true,
supertype: None,
composite_type,
depth: 1,
});
}

Expand All @@ -692,6 +704,7 @@ impl Module {
is_final: u.arbitrary()?,
supertype: None,
composite_type: self.arbitrary_composite_type(u)?,
depth: 1,
})
}
}
Expand All @@ -718,6 +731,7 @@ impl Module {
is_final: u.arbitrary()?,
supertype: Some(supertype),
composite_type,
depth: 1 + self.types[supertype as usize].depth,
})
}

Expand Down Expand Up @@ -1364,6 +1378,7 @@ impl Module {
is_final: true,
supertype: None,
composite_type: CompositeType::new_func(Rc::clone(&func_type), shared),
depth: 1,
});
new_index
}
Expand Down Expand Up @@ -1948,6 +1963,7 @@ impl Module {
let type_index = self.add_type(SubType {
is_final: true,
supertype: None,
depth: 1,
composite_type: CompositeType::new_func(
Rc::clone(&new_type),
subtype.composite_type.shared,
Expand Down