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avoid overflow in slashing penalty calculation (#1286) 

Change presentation to avoid uint64 overflow in slashing penalty calculation. (Factor out `EFFECTIVE_BALANCE_INCREMENT` from `validator.effective_balance`.)
This commit is contained in:
Danny Ryan 2019-07-11 02:53:51 -06:00 committed by Justin
parent 57c0eee197
commit 6dc306700b
2 changed files with 17 additions and 5 deletions
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4
specs/core/0_beacon-chain.md
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@ -1482,7 +1482,9 @@ def process_slashings(state: BeaconState) -> None:
total_balance = get_total_active_balance(state)
for index, validator in enumerate(state.validators):
if validator.slashed and epoch + EPOCHS_PER_SLASHINGS_VECTOR // 2 == validator.withdrawable_epoch:
penalty = validator.effective_balance * min(sum(state.slashings) * 3, total_balance) // total_balance
increment = EFFECTIVE_BALANCE_INCREMENT # Factored out from penalty numerator to avoid uint64 overflow
penalty_numerator = validator.effective_balance // increment * min(sum(state.slashings) * 3, total_balance)
penalty = penalty_numerator // total_balance * increment
decrease_balance(state, ValidatorIndex(index), penalty)
```

18
test_libs/pyspec/eth2spec/test/phase_0/epoch_processing/test_process_slashings.py
View File

@ -66,8 +66,13 @@ def test_small_penalty(spec, state):
spec.process_slashings(state)
yield 'post', state
assert state.balances[0] == pre_slash_balances[0] - (state.validators[0].effective_balance
* 3 * total_penalties // total_balance)
expected_penalty = (
state.validators[0].effective_balance // spec.EFFECTIVE_BALANCE_INCREMENT
* (3 * total_penalties)
// total_balance
* spec.EFFECTIVE_BALANCE_INCREMENT
)
assert state.balances[0] == pre_slash_balances[0] - expected_penalty
@with_all_phases
@ -121,5 +126,10 @@ def test_scaled_penalties(spec, state):
for i in slashed_indices:
v = state.validators[i]
penalty = v.effective_balance * total_penalties * 3 // total_balance
assert state.balances[i] == pre_slash_balances[i] - penalty
expected_penalty = (
v.effective_balance // spec.EFFECTIVE_BALANCE_INCREMENT
* (3 * total_penalties)
// (total_balance)
* spec.EFFECTIVE_BALANCE_INCREMENT
)
assert state.balances[i] == pre_slash_balances[i] - expected_penalty