Unbounded channels and DoS attacks

[pavel-kokolemin]

We use unbounded channels in p2p. This makes the node more vulnerable to DoS attacks when the used memory grows without bounds (if peers overload the node with requests). It would be good to do something about this.

Maybe we can can apply back-pressure on the connected peers, when we read from the network socket?
Check how many pending requests there are, and stop reading from the socket until the number is below some threshold.
Something like this:

response = self.cmd_rx.recv() {
    // Request was processed, send response to the peer...
    request_count -= 1;
},
// Read from the socket if only there is some free capacity
request = self.socket.recv(), if request_count < 10 => {
    // New request received, send it to backend...
    request_count += 1;
}

[TheQuantumPhysicist]

Another idea is to monitor the size of the channel queues and how big they grow, and test that against DoS attacks.

[pavel-kokolemin]

We now use bounded channels to read network messages and send them to the BlockSyncManager tasks (PR #973). I think this should solve most of the problems with the unbounded channels.