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Fix wild pointer in map_key()/map_value() for malformed map_entry descriptors #27163

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Fix wild pointer in map_key()/map_value() for malformed map_entry descriptors #27163

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12 changes: 10 additions & 2 deletions src/google/protobuf/descriptor.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -2857,13 +2857,13 @@ const EnumValueDescriptor* Descriptor::FindEnumValueByName(

const FieldDescriptor* Descriptor::map_key() const {
if (!options().map_entry()) return nullptr;
ABSL_DCHECK_EQ(field_count(), 2);
ABSL_CHECK_EQ(field_count(), 2);
return field(0);
}

const FieldDescriptor* Descriptor::map_value() const {
if (!options().map_entry()) return nullptr;
ABSL_DCHECK_EQ(field_count(), 2);
ABSL_CHECK_EQ(field_count(), 2);
return field(1);
}

Expand Down Expand Up @@ -6839,6 +6839,14 @@ void DescriptorBuilder::BuildMessage(const DescriptorProto& proto,
AllocateOptions(proto, result, DescriptorProto::kOptionsFieldNumber,
"google.protobuf.MessageOptions", alloc);

// Validate that map_entry messages have exactly 2 fields (key and value).
// Without this check, map_key()/map_value() can return wild pointers
// when called on a malformed map_entry descriptor with 0 fields.
if (result->options().map_entry() && result->field_count() != 2) {
AddError(result->full_name(), proto, DescriptorPool::ErrorCollector::OTHER,
"Map entry message must have exactly 2 fields (key and value).");
}

// Before building submessages, check recursion limit.
--recursion_depth_;
IncrementWhenDestroyed revert{recursion_depth_};
Expand Down
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