[framework] Redundant Existence Check in add_additional_metadata Function

[miker83z]

FROM THE AUDIT:

Summary

The add_additional_metadata function in the CoinManager module enforces a redundant check to verify the non-existence of a value before adding additional metadata. However, the underlying df::add function already performs this check and aborts if the value with the same name exists.

Vulnerability Detail

In the CoinManager module, the add_additional_metadata function is defined as follows:

public fun add_additional_metadata<T, Value: store>(
    _: &CoinManagerMetadataCap<T>,
    manager: &mut CoinManager<T>,
    value: Value
) {
@>> assert!(!df::exists_(&manager.id, b"additional_metadata"), EAdditionalMetadataAlreadyExists);
    df::add(&mut manager.id, b"additional_metadata", value);
}

This function verifies that the additional_metadata field does not already exist before invoking df::add. However, the df::add function internally performs this exact check and aborts with EFieldAlreadyExists if a field with the same name already exists. The relevant portion of the df::add implementation is as follows:

public fun add<Name: copy + drop + store, Value: store>(
    object: &mut UID,
    name: Name,
    value: Value,
) {
     let object_addr = object.to_address();
     let hash = hash_type_and_key(object_addr, name);
@>>  assert!(!has_child_object(object_addr, hash), EFieldAlreadyExists);
     let field = Field {
        id: object::new_uid_from_hash(hash),
        name,
        value,
     };
     add_child_object(object_addr, field)
}

Since the existence check is already handled by df::add, the additional assertion in add_additional_metadata is redundant and unnecessarily duplicates logic.

Tool used

Manual Review

Recommendation

public fun add_additional_metadata<T, Value: store>(
    _: &CoinManagerMetadataCap<T>,
    manager: &mut CoinManager<T>,
    value: Value
) {
-   assert!(!df::exists_(&manager.id, b"additional_metadata"), EAdditionalMetadataAlreadyExists);
    df::add(&mut manager.id, b"additional_metadata", value);
}