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Fix off-by-one error in Flatbuffers domain field mutation. #2065

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Merged
copybara-service merged 1 commit into from
May 26, 2026
Merged

Fix off-by-one error in Flatbuffers domain field mutation. #2065

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12 changes: 9 additions & 3 deletions fuzztest/internal/domains/flatbuffers_domain_impl.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -103,7 +103,8 @@ void FlatbuffersTableUntypedDomainImpl::Mutate(
CountNumberOfMutableFieldsVisitor{*this, field_count,
val, only_shrink});
}
auto selected_field_index = absl::Uniform(prng, 0ul, field_count);
if (field_count == 0) return;
auto selected_field_index = absl::Uniform(prng, 1ul, field_count + 1);

MutateSelectedField(val, prng, metadata, only_shrink, selected_field_index);
}
Expand All @@ -124,18 +125,23 @@ uint64_t FlatbuffersTableUntypedDomainImpl::MutateSelectedField(
const domain_implementor::MutationMetadata& metadata, bool only_shrink,
uint64_t selected_field_index) {
uint64_t field_counter = 0;
uint64_t fields_count = CountNumberOfFields(val);
if (fields_count < selected_field_index) {
return fields_count;
}

for (const auto* field : *table_object_->fields()) {
if (!IsSupportedField(field)) {
if (only_shrink && !val.contains(field->id())) continue;
}

++field_counter;
if (field_counter == selected_field_index) {
VisitFlatbufferField(
schema_, field,
MutateVisitor{*this, prng, metadata, only_shrink, val});
return field_counter;
}
field_counter++;

if (field->type()->base_type() == reflection::BaseType::Obj) {
auto sub_object = schema_->objects()->Get(field->type()->index());
Expand All @@ -148,7 +154,7 @@ uint64_t FlatbuffersTableUntypedDomainImpl::MutateSelectedField(
// TODO: Add support for structs.
}

if (field_counter > selected_field_index) {
if (field_counter >= selected_field_index) {
return field_counter;
}
}
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