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Fix use-after-free resolving reference type names in wast-parser #2805

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Merged
sbc100 merged 2 commits into from
Aug 6, 2026
+63 −0
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Fix use-after-free resolving reference type names in wast-parser #2805

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f0886ea
Fix use-after-free resolving reference type names in wast-parser
aizu-m Aug 3, 2026
13a7c66
Clean up the resolve lists inside ParseModuleField
aizu-m Aug 4, 2026
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1 change: 1 addition & 0 deletions include/wabt/wast-parser.h
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Original file line number Diff line number Diff line change
Expand Up @@ -206,6 +206,7 @@ class WastParser {
ReferenceVars*, Errors*);
Result ParseModuleFieldList(Module*);
Result ParseModuleField(Module*);
Result ParseModuleFieldImpl(Module*);
Result ParseDataModuleField(Module*);
Result ParseElemModuleField(Module*);
Result ParseTagModuleField(Module*);
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25 changes: 25 additions & 0 deletions src/wast-parser.cc
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Expand Up @@ -1494,6 +1494,31 @@ Result WastParser::ParseModuleFieldList(Module* module) {

Result WastParser::ParseModuleField(Module* module) {
WABT_TRACE(ParseModuleField);
// A field is only appended to the module once it has parsed successfully; a
// field that fails to parse is destroyed instead, so the deferred reference
// type resolutions registered while parsing it would point into freed
// memory. Remember where the resolve lists ended and drop those entries
// again if the field fails.
size_t ref_types_size = resolve_ref_types_.size();
size_t type_vectors_size = resolve_type_vectors_.size();
size_t funcs_size = resolve_funcs_.size();

Result result = ParseModuleFieldImpl(module);

if (Failed(result)) {
resolve_ref_types_.erase(resolve_ref_types_.begin() + ref_types_size,
resolve_ref_types_.end());
resolve_type_vectors_.erase(
resolve_type_vectors_.begin() + type_vectors_size,
resolve_type_vectors_.end());
resolve_funcs_.erase(resolve_funcs_.begin() + funcs_size,
resolve_funcs_.end());

@sbc100 sbc100 Aug 4, 2026

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I'm still a little confused, if we are returning failure, when why does it matter about the state of these members? If we fail to parse why is anybody accessing these after this point?

@aizu-m aizu-m Aug 6, 2026

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The failure doesn't propagate. ParseModuleFieldList swallows it:

if (Failed(ParseModuleField(module))) {
  CHECK_RESULT(Synchronize(IsModuleField));
}

It resynchronises to the next module field and carries on parsing, so wat2wasm reports every parse error in one pass rather than stopping at the first. The failed field's result is dropped right there.

So control still reaches the three resolve loops at the bottom of that same function, which walk resolve_ref_types_ / resolve_type_vectors_ / resolve_funcs_ and dereference the pointers recorded while the field was being parsed. Those point into the field's local unique_ptr, which was destroyed on the error path instead of being handed to AppendField. That's the freed read, and a freed write via local_types.Set() in the func-local case.

The one case where nobody touches them is when Synchronize fails too, i.e. the bad field is the last thing in the file, since then we return early and never reach the loops. That's why the test has a (memory 1) after the broken fields: it gives Synchronize somewhere to land so the loops are actually reached.

}

return result;
}

Result WastParser::ParseModuleFieldImpl(Module* module) {
switch (Peek(1)) {
case TokenType::Data: return ParseDataModuleField(module);
case TokenType::Elem: return ParseElemModuleField(module);
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37 changes: 37 additions & 0 deletions test/parse/bad-ref-type-in-failed-field.txt
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@@ -0,0 +1,37 @@
;;; TOOL: wat2wasm
;;; ARGS: --enable-function-references
;;; ERROR: 1
(module
(type $t (func))

;; Each field below names a reference type, which defers its resolution to
;; the end of the module, and then fails to parse.
(func (param (ref $t)) (foo))
(func (result (ref null $t)) (foo))
(func (local (ref $t)) (foo))
(table 0 (ref null $t) (foo))
(elem declare (ref null $t) (item ref.null $t) foo)
(import "a" "b" (func (param (ref $t)) foo))

(memory 1)
)
(;; STDERR ;;;
out/test/parse/bad-ref-type-in-failed-field.txt:9:27: error: unexpected token "foo", expected an instr.
(func (param (ref $t)) (foo))
^^^
out/test/parse/bad-ref-type-in-failed-field.txt:10:33: error: unexpected token "foo", expected an instr.
(func (result (ref null $t)) (foo))
^^^
out/test/parse/bad-ref-type-in-failed-field.txt:11:27: error: unexpected token "foo", expected an instr.
(func (local (ref $t)) (foo))
^^^
out/test/parse/bad-ref-type-in-failed-field.txt:12:27: error: unexpected token "foo", expected an instr.
(table 0 (ref null $t) (foo))
^^^
out/test/parse/bad-ref-type-in-failed-field.txt:13:50: error: unexpected token foo, expected ).
(elem declare (ref null $t) (item ref.null $t) foo)
^^^
out/test/parse/bad-ref-type-in-failed-field.txt:14:42: error: unexpected token foo, expected ).
(import "a" "b" (func (param (ref $t)) foo))
^^^
;;; STDERR ;;)
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