The `pallet_bridge_grandpa` at Polkadot Bridge Hub is now in an inconsistent state, the Polkadot-GRANDPA-light-client running BH doesn’t correctly handle a corner case involving validator set changes following validator slashing. As a result of the bug, the GRANDPA light-client can fail to recognise the other side's validator set change and thus start refusing to accept subsequent validator set changes as well. More details can be found [on this forum post](https://forum.polkadot.network/t/polkadot-kusama-bridge/2971/45) .

We have encountered this bug on the BH, resulting in Kusama->Polkadot traffic being stuck. This upgrade fixes the bug so that it is protected from encountering the same issue.

Please note that there is a Polkadot runtime [upgrade](https://polkadot.polkassembly.io/referenda/648) (to 1.2.0) already up for a vote, so the goal is to wait for that to happen before enacting a subsequent patch fix on top.

Also, be aware that this proposal is submitted on the Whitelisted Caller track - a parallel submission should be up for a vote on Fellowship to whitelist this proposal shortly.

- The `pallet_bridge_grandpa` at Polkadot Bridge Hub is in an inconsistent state due to a bug.
- The bug involves how the GRANDPA light-client handles validator set changes after slashing.
- This bug caused Kusama to Polkadot traffic to get stuck.
- An upgrade is being prepared to fix this issue.
- A Polkadot runtime upgrade (to 1.2.0) is already up for a vote.
- The fix will be applied after the runtime upgrade.
- The proposal to fix the bug is on the Whitelisted Caller track.
- A parallel submission is being voted on by the Fellowship to whitelist the proposal.

call

Executed

Submitted

DecisionStarted

DecisionDepositPlaced

ConfirmStarted

Confirmed

whitelisted_caller

WHO: Polkadot Bridge Hub

WHAT: Fixing a bug in the Polkadot-GRANDPA-light-client running BH that causes traffic to be stuck between Kusama and Polkadot.

PRICE/TIMEFRAME/RESOURCES: Not specified.

Polkadot Bridge Hub 1.2.2 upgrade: Unstuck bridge with Kusama

root

wish_for_change

staking_admin

treasurer

lease_admin

fellowship_admin

general_admin

auction_admin

referendum_canceller

referendum_killer

small_tipper

big_tipper

small_spender

medium_spender

big_spender

Origin able to dispatch a whitelisted call.

Origin for signaling that the network wishes for some change

Origin able to cancel slashes and manage minimum commission.

Origin for spending up to 10,000,000 DOT from the treasury as well as generally administering it.

Origin for managing the composition of the fellowship.

Origin able to spend around 250 DOT from the treasury at once.

Origin able to spend around 1,000 DOT from the treasury at once.

Origin able to spend around 10,000 DOT from the treasury at once.

Origin able to spend around 100,000 DOT from the treasury at once.

Origin able to spend up to 1,000,000 DOT from the treasury at once.