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Running under Manticore

Table of contents:

Introduction

We will see how to explore a smart contract with the Manticore API. The target is the following smart contract (examples/example.sol):

pragma solidity >=0.4.24 <0.6.0;
contract Simple {
    function f(uint a) payable public{
        if (a == 65) {
            revert();
        }
    }
}

Run a standalone exploration

You can run Manticore directly on the smart contract by the following command (project can be a Solidity File, or a project directory):

$ manticore project

You will get the output of testcases like this one (the order may change):

...
... m.c.manticore:INFO: Generated testcase No. 0 - STOP
... m.c.manticore:INFO: Generated testcase No. 1 - REVERT
... m.c.manticore:INFO: Generated testcase No. 2 - RETURN
... m.c.manticore:INFO: Generated testcase No. 3 - REVERT
... m.c.manticore:INFO: Generated testcase No. 4 - STOP
... m.c.manticore:INFO: Generated testcase No. 5 - REVERT
... m.c.manticore:INFO: Generated testcase No. 6 - REVERT
... m.c.manticore:INFO: Results in /home/ethsec/workshops/Automated Smart Contracts Audit - TruffleCon 2018/manticore/examples/mcore_t6vi6ij3
...

Without additional information, Manticore will explore the contract with new symbolic transactions until it does not explore new paths on the contract. Manticore does not run new transactions after a failing one (e.g: after a revert).

Manticore will output the information in a mcore_* directory. Among other, you will find in this directory:

  • global.summary: coverage and compiler warnings
  • test_XXXXX.summary: coverage, last instruction, account balances per test case
  • test_XXXXX.tx: detailed list of transactions per test case

Here Manticore founds 7 test cases, which correspond to (the filename order may change):

Transaction 0 Transaction 1 Transaction 2 Result
test_00000000.tx Contract creation f(!=65) f(!=65) STOP
test_00000001.tx Contract creation fallback function REVERT
test_00000002.tx Contract creation RETURN
test_00000003.tx Contract creation f(65) REVERT
test_00000004.tx Contract creation f(!=65) STOP
test_00000005.tx Contract creation f(!=65) f(65) REVERT
test_00000006.tx Contract creation f(!=65) fallback function REVERT

Exploration summary f(!=65) denotes f called with any value different than 65.

As you can notice, Manticore generates an unique test case for every successful or reverted transaction.

Use the --quick-mode flag if you want fast code exploration (it disable bug detectors, gas computation, ...)

Manipulate a smart contract through the API

This section describes details how to manipulate a smart contract through the Manticore Python API. You can create new file with python extension *.py and write the necessary code by adding the API commands (basics of which will be described below) into this file and then run it with the command $ python3 *.py. Also you can execute the commands below directly into the python console, to run the console use the command $ python3.

Creating Accounts

The first thing you should do is to initiate a new blockchain with the following commands:

from manticore.ethereum import ManticoreEVM

m = ManticoreEVM()

A non-contract account is created using m.create_account:

user_account = m.create_account(balance=1 * 10**18)

A Solidity contract can be deployed using m.solidity_create_contract:

source_code = '''
pragma solidity >=0.4.24 <0.6.0;
contract Simple {
    function f(uint a) payable public{
        if (a == 65) {
            revert();
        }
    }
}
'''
# Initiate the contract
contract_account = m.solidity_create_contract(source_code, owner=user_account)

Summary

Executing transactions

Manticore supports two types of transaction:

  • Raw transaction: all the functions are explored
  • Named transaction: only one function is explored

Raw transaction

A raw transaction is executed using m.transaction:

m.transaction(caller=user_account,
              address=contract_account,
              data=data,
              value=value)

The caller, the address, the data, or the value of the transaction can be either concrete or symbolic:

For example:

symbolic_value = m.make_symbolic_value()
symbolic_data = m.make_symbolic_buffer(320)
m.transaction(caller=user_account,
              address=contract_address,
              data=symbolic_data,
              value=symbolic_value)

If the data is symbolic, Manticore will explore all the functions of the contract during the transaction execution. It will be helpful to see the Fallback Function explanation in the Hands on the Ethernaut CTF article for understanding how the function selection works.

Named transaction

Functions can be executed through their name. To execute f(uint var) with a symbolic value, from user_account, and with 0 ether, use:

symbolic_var = m.make_symbolic_value()
contract_account.f(symbolic_var, caller=user_account, value=0)

If value of the transaction is not specified, it is 0 by default.

Summary

  • Arguments of a transaction can be concrete or symbolic
  • A raw transaction will explore all the functions
  • Function can be called by their name

Workspace

m.workspace is the directory used as output directory for all the files generated:

print("Results are in {}".format(m.workspace))

Terminate the Exploration

To stop the exploration use m.finalize(). No further transactions should be sent once this method is called and Manticore generates test cases for each of the path explored.

Summary: Running under Manticore

Putting all the previous steps together, we obtain:

from manticore.ethereum import ManticoreEVM

m = ManticoreEVM()

with open('example.sol') as f:
    source_code = f.read()

user_account = m.create_account(balance=1*10**18)
contract_account = m.solidity_create_contract(source_code, owner=user_account)

symbolic_var = m.make_symbolic_value()
contract_account.f(symbolic_var)

print("Results are in {}".format(m.workspace))
m.finalize() # stop the exploration

All the code above you can find into the examples/example_run.py

The next step is to accessing the paths.