Sanity Check KeysInterface on ChannelManager Deserialization

[TheBlueMatt]

If the KeysInterface provided to the ChannelManager is generating different keys from what we had before being written, we need to fail, not try to run.

[TheBlueMatt]

Also on ChannelMonitors in and spend_spendable_outputs

[vss96]

@TheBlueMatt Hey I would like to pick this up. Can you guide me a little as to which modules I'll have to explore to fix the same issue? Will the sanity check happen when a new object for the ChannelManager is created?

[TheBlueMatt]

I think there's two parts to this:

1. a) In the impl Writeable for ChannelManager<Signer, M, T, K, F, L> block, in the write_tlv_fields macro call, store a new (odd, option) field containing the self.our_network_pubkey object.
   b) In the impl ReadableArgs<ChannelManagerReadArgs<'a, Signer, M, T, K, F, L>> for (BlockHash, ChannelManager<Signer, M, T, K, F, L>) block, in the read_tlv_fields!() macro call, load the same field, and, if set, compare it to the calculated our_network_pubkey value, returning an InvalidValue err if it does not match (after calling log_error!() with some error message).
2. a) In KeysManager::spend_spendable_outputs, when we derive a static key in SpendableOutputDescriptor::StaticOutput handling, we should compare that key with the expected value (currently we only compare once and assume the key we should use is the "other" of the two options, instead of always checking).
   b) In InMemoryChannelKeys's sign_counterparty_payment_input and sign_dynamic_p2wsh_input methods, the expected input script_pub_key should be compared with the script in DelayedPaymentOutputDescriptor and StaticPaymentOutputDescriptor's output fields.

[TheBlueMatt]

Regarding 2a: initially, there is a check for the output's script_pubkey and either 1 or 2 is assigned to the derivation_idx.

The check isn't really "1 or 2", though, its "does it match 1? no, okay, assume 2" - we never actually check that it matches 2. We should check that it matches at least either 1 or 2, and if neither, return an error.