Extrinsic to restore corrupt staking ledgers (#3706)

This PR adds a new extrinsic `Call::restore_ledger ` gated by
`StakingAdmin` origin that restores a corrupted staking ledger. This
extrinsic will be used to recover ledgers that were affected by the
issue discussed in
https://github.com/paritytech/polkadot-sdk/issues/3245.

The extrinsic will re-write the storage items associated with a stash
account provided as input parameter. The data used to reset the ledger
can be either i) fetched on-chain or ii) partially/totally set by the
input parameters of the call.

In order to use on-chain data to restore the staking locks, we need a
way to read the current lock in the balances pallet. This PR adds a
`InspectLockableCurrency` trait and implements it in the pallet
balances. An alternative would be to tightly couple staking with the
pallet balances but that's inelegant (an example of how it would look
like in [this
branch](https://github.com/paritytech/polkadot-sdk/tree/gpestana/ledger-badstate-clean_tightly)).

More details on the type of corruptions and corresponding fixes
https://hackmd.io/DLb5jEYWSmmvqXC9ae4yRg?view#/

We verified that the `Call::restore_ledger` does fix all current
corrupted ledgers in Polkadot and Kusama. You can verify it here
https://hackmd.io/v-XNrEoGRpe7APR-EZGhOA.

**Changes introduced**
- Adds `Call::restore_ledger ` extrinsic to recover a corrupted ledger;
- Adds trait `frame_support::traits::currency::InspectLockableCurrency`
to allow external pallets to read current locks given an account and
lock ID;
- Implements the `InspectLockableCurrency` in the pallet-balances.
- Adds staking locks try-runtime checks
(https://github.com/paritytech/polkadot-sdk/issues/3751)

**Todo**
- [x] benchmark `Call::restore_ledger`
- [x] throughout testing of all ledger recovering cases
- [x] consider adding the staking locks try-runtime checks to this PR
(https://github.com/paritytech/polkadot-sdk/issues/3751)
- [x] simulate restoring all ledgers
(https://hackmd.io/Dsa2tvhISNSs7zcqriTaxQ?view) in Polkadot and Kusama
using chopsticks -- https://hackmd.io/v-XNrEoGRpe7APR-EZGhOA

Related to https://github.com/paritytech/polkadot-sdk/issues/3245
Closes https://github.com/paritytech/polkadot-sdk/issues/3751

---------

Co-authored-by: command-bot <>

substrate/frame/staking/src/lib.rs

@@ -491,6 +491,20 @@ pub struct StakingLedger<T: Config> {
 	controller: Option<T::AccountId>,
 }
 
+/// State of a ledger with regards with its data and metadata integrity.
+#[derive(PartialEq, Debug)]
+enum LedgerIntegrityState {
+	/// Ledger, bond and corresponding staking lock is OK.
+	Ok,
+	/// Ledger and/or bond is corrupted. This means that the bond has a ledger with a different
+	/// stash than the bonded stash.
+	Corrupted,
+	/// Ledger was corrupted and it has been killed.
+	CorruptedKilled,
+	/// Ledger and bond are OK, however the ledger's stash lock is out of sync.
+	LockCorrupted,
+}
+
 impl<T: Config> StakingLedger<T> {
 	/// Remove entries from `unlocking` that are sufficiently old and reduce the
 	/// total by the sum of their balances.