Broadcast Slashing on equivocation

[shyam-patel-kira]

fixes #13088

The PR implements immediate broadcasting of slashing messages when detecting equivocating blocks, helping the network react more quickly to malicious behavior without relying on the full slasher service processing.

[0xalpharush]

this should probably log instead of returning and preventing FCU? could not check for block equivocation seems more accurate

[0xalpharush]

I think this should probably be done in the gossip validation of beacon blocks for two reasons:

1. I may not understand the spec properly but I believe signing equivocating blocks even if they're invalid should bet met with a slashing proposal
2. There is probably no need for the slashing service to be sent a block which was already deemed equivocating and resulted in a slashing proposal being broadcast
   

   prysm/beacon-chain/sync/validate_beacon_blocks.go

   Lines 84 to 95 in 30a136f

   	if features.Get().EnableSlasher {
   	// Feed the block header to slasher if enabled. This action
   	// is done in the background to avoid adding more load to this critical code path.
   	go func() {
   	blockHeader, err := interfaces.SignedBeaconBlockHeaderFromBlockInterface(blk)
   	if err != nil {
   	log.WithError(err).WithField("blockSlot", blk.Block().Slot()).Warn("Could not extract block header")
   	return
   	}
   	s.cfg.slasherBlockHeadersFeed.Send(blockHeader)
   	}()
   	}

Fwiw I am just an interested bystander using this as a learning opportunity. Feel free to ignore or let me know if this is unhelpful

[potuz]

When moving this check to the right spot instead after the call to ReceiveBlock we don't have the root yet (since we only hash after we know we haven't seen the block), we should check if the signatures are different instead, as a different root will result in a different signature.

[shyam-patel-kira]

Hey @potuz, Thanks for the review, addressed the changes that were requested

[potuz]

s.seenBlockCache in the Sync package never returns a block , we set it for example in setSeenBlockIndexSlot

[shyam-patel-kira]

okay, current approach wouldn't work then. As suggested by you, made changes to use headBlock instead of blockCache for equivocation Detection.