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fix overflow in slashing logic (#1263)

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This commit is contained in:
Robert Habermeier
2018-12-13 12:33:03 +01:00
committed by Benjamin Kampmann
parent bd2a206e40
commit c61d03a86f
3 changed files with 63 additions and 3 deletions
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substrate/srml/staking/src/lib.rs
+19 -2
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@@ -499,6 +499,8 @@ impl<T: Trait> Module<T> {
/// Call when a validator is determined to be offline. `count` is the
/// number of offences the validator has committed.
pub fn on_offline_validator(v: T::AccountId, count: usize) {
use primitives::traits::CheckedShl;
for _ in 0..count {
let slash_count = Self::slash_count(&v);
<SlashCount<T>>::insert(v.clone(), slash_count + 1);
@@ -506,8 +508,23 @@ impl<T: Trait> Module<T> {
let event = if slash_count >= grace {
let instances = slash_count - grace;
let slash = Self::current_offline_slash() << instances;
let next_slash = slash << 1u32;
let base_slash = Self::current_offline_slash();
let slash = match base_slash.checked_shl(instances) {
Some(slash) => slash,
None => {
// freeze at last maximum valid slash if this starts
// to overflow.
<SlashCount<T>>::insert(v.clone(), slash_count);
base_slash.checked_shl(instances - 1)
.expect("slash count no longer incremented after overflow; \
prior check only fails with instances >= 1; \
thus instances - 1 always works and is a valid amount of bits; qed")
}
};
let next_slash = slash << 1;
let _ = Self::slash_validator(&v, slash);
if instances >= Self::validator_preferences(&v).unstake_threshold
|| Self::slashable_balance(&v) < next_slash