Invalid pallet session/pallet staking flow: purge_keys can decrement consumer ref count on wrong controller.

[gui1117]

if I have 3 account: stash, controller_1 and controller_2.

I bound stash to controller_1,
then call set_keys from this controller_1, controller_1 has one consumer refcount increase.
then call unbond, and later call withdraw_unbonded.
then bond stash to controller_2,
than call purge_keys from this controller_2, the consumer refcount decrement silently fails and logs an error.

While it is not possible to do an attack with this. I think it is still an error to have a dec_consumer which fails silently. And an account with a consumer refcount which is not removable.

Fixing this issue can also fix ppl having issue with unbonded stash and controller still being used by pallet_session #975, but I think it is more a UI issue.
Maybe a solution could be to have a consumer refcount increase on the stash instead of the controller in pallet_session.

[stale]

Hey, is anyone still working on this? Due to the inactivity this issue has been automatically marked as stale. It will be closed if no further activity occurs. Thank you for your contributions.

[gui1117]

the invalid refcount is still sensible to me, it is not harmful, but it shouldn't be possible to trigger this