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wasmparser: reject function bodies larger than implementation limit. #2302

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Merged
alexcrichton merged 1 commit into from
Sep 12, 2025
Merged

wasmparser: reject function bodies larger than implementation limit. #2302

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4 changes: 3 additions & 1 deletion crates/wasmparser/src/limits.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -17,6 +17,8 @@

// The following limits are imposed by wasmparser on WebAssembly modules.
// The limits are agreed upon with other engines for consistency.
//
// See https://webassembly.github.io/spec/js-api/#limits for details.
pub const MAX_WASM_TYPES: usize = 1_000_000;
pub const MAX_WASM_SUPERTYPES: usize = 1;
pub const MAX_WASM_FUNCTIONS: usize = 1_000_000;
Expand All @@ -26,7 +28,7 @@ pub const MAX_WASM_GLOBALS: usize = 1_000_000;
pub const MAX_WASM_ELEMENT_SEGMENTS: usize = 100_000;
pub const MAX_WASM_DATA_SEGMENTS: usize = 100_000;
pub const MAX_WASM_STRING_SIZE: usize = 100_000;
pub const MAX_WASM_FUNCTION_SIZE: usize = 128 * 1024;
pub const MAX_WASM_FUNCTION_SIZE: usize = 7_654_321;
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@cfallin cfallin Sep 12, 2025

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I'll note that I'm not entirely sure what was going on with the previous limit of 128K here -- it wasn't actually used to enforce function-size limits (despite the name of the constant), only the number of branch-table targets. Given the name it seems reasonable to use it for what it says on the tin.

pub const MAX_WASM_FUNCTION_LOCALS: u32 = 50000;
pub const MAX_WASM_FUNCTION_PARAMS: usize = 1000;
pub const MAX_WASM_FUNCTION_RETURNS: usize = 1000;
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8 changes: 8 additions & 0 deletions crates/wasmparser/src/validator.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1006,6 +1006,14 @@ impl Validator {
) -> Result<FuncToValidate<ValidatorResources>> {
let offset = body.range().start;
self.state.ensure_module("code", offset)?;
check_max(
0,
u32::try_from(body.range().len())
.expect("usize already validated to u32 during section-length decoding"),
MAX_WASM_FUNCTION_SIZE,
"function body size",
offset,
)?;

let state = self.module.as_mut().unwrap();

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28 changes: 28 additions & 0 deletions crates/wasmparser/tests/big-module.rs
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Expand Up @@ -32,3 +32,31 @@ fn big_type_indices() {
.validate_all(&wasm)
.unwrap();
}

#[test]
fn big_function_body() {
let mut module = Module::new();

let mut types = TypeSection::new();
types.ty().function([], []);
module.section(&types);
let mut funcs = FunctionSection::new();
funcs.function(0);
module.section(&funcs);

let mut code = CodeSection::new();
let mut body = Function::new([]);
// Function body larger than the 7_654_321-byte implementation
// limit.
for _ in 0..8_000_000 {
body.instructions().unreachable();
}
body.instructions().end();
code.function(&body);
module.section(&code);

let wasm = module.finish();

let result = wasmparser::Validator::default().validate_all(&wasm);
assert!(result.is_err());
}
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