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balancer / balancer-core

Balancer on the EVM
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The normalized sum of the weight is not always equal to 1 #208

Closed ggrieco-tob closed 4 years ago

ggrieco-tob commented 4 years ago

Severity: Informational Difficulty: Low

Description

It is possible to have a normalized sum of the token weight that is not equal to 1.

The whitepaper states the sum of normalized token weights should be equal to 1. However, inherent rounding issues in the division performed getNormalizedWeight function can accumulate in the sum and result in a values less than 1.

Exploit Scenario

Alice creates a new pool. She reviews the documentation and incorrectly assumes that the sum of normalized weight token will be 1. As a result of that, she incorrectly implement onchain/offchain code to interact with the pool, potentially causing unexpected results (e.g. rounding issues, zero division) in her code.

Recommendation

Short term, properly document this rounding issue and make sure users understand that this property is not strictly enforced.

Long term, consider using Echidna and Manticore to normalized weights are correctly computed.

mikemcdonald commented 4 years ago

Documented at: https://docs.balancer.finance/-LtRAKuhb1ZIm1X-H-IS/smart-contracts/api#getnormalizedweight

mikemcdonald commented 4 years ago

https://docs.balancer.finance/smart-contracts/api#getnormalizedweight