Omisego Plasma MVP

The contract RootChain.sol uses the constant CHILD_BLOCK_INTERVAL to distinguish between child chain and deposit blocks. It protects against reorgs, i.e., block and transaction order changing on the root chain. Reorgs can lead to spurious invalidity of the child chain. The check in line 161, however, can be bypassed and, consequently, the invariant that deposit blocks should never appear in child block indices and vice-versa can be violated. We note that the issue may be exploited by a malicious token contract which can be added by any user. Exploit Scenario: 1. Add malicious token contract to RootChain.sol via the function addToken(). 2. depositFrom() calls transferFrom() (line 164). 3. transferFrom() of a malicious token calls deposit() multiple times till currentDepositBlock == CHILD_BLOCK_INTERVAL - 1. 4. transferFrom() returns true allowing writeDepositBlock() to increment currentDepositBlock beyond CHILD_BLOCK_INTERVAL. 5. This allows a malicious token to enable transfers without a real deposit as the deposit block will be overwritten by the next submitted plasma block.

The function depositFrom() takes owner as parameter instead of relying on msg.sender. Consequently, once an allowance is approved, anybody may initiate a deposit on behalf of the owner at any time, even against the actual owner's will.

Trufe is a prominent tool used for organizing Solidity code projects. It helps to manage dependencies, run tests, and process the code with other tools.