QID 982036

A flaw was repoted at 2020-08-11 by John Youngseok Yang (Software Platform Lab), where a particular sequence of transactions could cause a consensus failure.

- Tx 1:
- `sender` invokes `caller`.
- `caller` invokes `0xaa`. `0xaa` has 3 wei, does a self-destruct-to-self
- `caller` does a `1 wei` -call to `0xaa`, who thereby has 1 wei (the code in `0xaa` still executed, since the tx is still ongoing, but doesn't redo the selfdestruct, it takes a different path if callvalue is non-zero)

- Tx 2:
- `sender` does a 5-wei call to 0xaa. No exec (since no code).

In geth, the result would be that `0xaa` had `6 wei`, whereas OE reported (correctly) `5` wei. Furthermore, in geth, if the second tx was not executed, the `0xaa` would be destructed, resulting in `0 wei`. Thus obviously wrong.

It was determined that the root cause was this [commit](https://github.com/ethereum/go-ethereum/commit/223b950944f494a5b4e0957fd9f92c48b09037ad) from [this PR](https://github.com/ethereum/go-ethereum/pull/19953). The semantics of `createObject` was subtly changd, into returning a non-nil object (with `deleted=true`) where it previously did not if the account had been destructed. This return value caused the new object to inherit the old `balance`:

```golang
func (s *StateDB) CreateAccount(addr common.Address) {
newObj, prev := s.createObject(addr)
if prev != nil {
newObj.setBalance(prev.data.Balance)
}
}
```

It was determined that the minimal possible correct fix was

```diff
+++ b/core/state/statedb.go
@@ -589,7 +589,10 @@ func (s *StateDB) createObject(addr common.Address) (newobj, prev *stateObject)
s.journal.append(resetObjectChange{prev: prev, prevdestruct: prevdestruct})
}
s.setStateObject(newobj)
- return newobj, prev
+ if prev != nil && !prev.deleted {
+ return newobj, prev
+ }
+ return newobj, nil
```

A consensus-vulnerability in Geth could cause a chain split, where vulnerable versions refuse to accept the canonical chain.