TOB-FUEL-23: Consensus parameters are potentially incompatible on 32bit platforms

[Dentosal]

Description

The consensus parameters define the maximum length of vectors such as max_inputs, max_outputs, max_witnesses to be 64-bit values.These values are cast to usize when validating that a transaction’s field does not contain a vector which exceeds these maximums (see figure 23.2). On 32-bit architectures, usize will truncate consensus parameter values larger than 32 bits and reject different transactions than 64-bit platforms.

Figure 23.1: The ConsensusParameters struct definition (fuel-core/crates/client/src/client/schema/chain.rs#11–27)

pub struct ConsensusParameters {
    pub contract_max_size: U64,
    pub max_inputs: U64,
    pub max_outputs: U64,
    pub max_witnesses: U64,
    pub max_gas_per_tx: U64,
    pub max_script_length: U64,
    pub max_script_data_length: U64,
    pub max_storage_slots: U64,
    pub max_predicate_length: U64,
    pub max_predicate_data_length: U64,
    pub max_gas_per_predicate: U64,
    pub gas_price_factor: U64,
    pub gas_per_byte: U64,
    pub max_message_data_length: U64,
    pub chain_id: U64,
}

Figure 23.2: Validation of transactions against consensus parameters (fuel-vm/fuel-tx/src/transaction/validity.rs#325–335)

if tx.inputs().len() > parameters.max_inputs as usize {
    Err(CheckError::TransactionInputsMax)?
}
if tx.outputs().len() > parameters.max_outputs as usize {
    Err(CheckError::TransactionOutputsMax)?
}
if tx.witnesses().len() > parameters.max_witnesses as usize {
    Err(CheckError::TransactionWitnessesMax)?
}

Recommendations

Short term, define the consensus parameters as 32-bit unsigned integers.
Long term, review platform-dependent behavior such as casts to usize and ensure that code is compatible across architectures.

Our thoughts

The actual use occurs here:
https://github.com/FuelLabs/fuel-vm/blob/20f1e9b888e359b9d1ac45214673e97277370543/fuel-tx/src/transaction/validity.rs#L325-L335

Either change the data types to be u32, or remove usize casts from the fuel-vm side. Or maybe specify that fuel-vm/core only work on 64bit platforms and add test to that effect.