https://github.com/with-backed/papr/blob/9528f2711ff0c1522076b9f93fba13f88d5bd5e6/src/ReservoirOracleUnderwriter.sol#L88
ecrecover returns a value of 0 for invalid signature. We also note that in the constructor, there is no check to ensure that oracleSigner is not address 0.
The only check for validity of signature is this,
If oracleSigner is set to address(0) then a malicious user can pass any price it wants into oracleInfo to bypass the check of signature used in underwritePriceForCollateral() and hence liquidate any collateral of any user, as well as being able to purchase this liquidated NFT at a price of 0.
It is recommendated to add the check if(signerAddress == address(0)) revert Error().
