Bitcoin peer banning versus discouragement

1// Copyright (c) 2009-2010 Satoshi Nakamoto
2// Copyright (c) 2009-present The Bitcoin Core developers
3// Distributed under the MIT software license, see the accompanying
4// file COPYING or http://www.opensource.org/licenses/mit-license.php.
5#ifndef BITCOIN_BANMAN_H
6#define BITCOIN_BANMAN_H
7
8#include <addrdb.h>
9#include <common/bloom.h>
10#include <net_types.h>
11#include <sync.h>
12#include <util/fs.h>
13
14#include <chrono>
15#include <cstdint>
16#include <memory>
17
18// NOTE: When adjusting this, update rpcnet:setban's help ("24h")
19inline constexpr unsigned int DEFAULT_MISBEHAVING_BANTIME = 60 * 60 * 24; // Default 24-hour ban
20
21/// How often to dump banned addresses/subnets to disk.
22inline constexpr std::chrono::minutes DUMP_BANS_INTERVAL{15};
23
24class CClientUIInterface;
25class CNetAddr;
26class CSubNet;
27
28// Banman manages two related but distinct concepts:
29//
30// 1. Banning. This is configured manually by the user, through the setban RPC.
31// If an address or subnet is banned, we never accept incoming connections from
32// it and never create outgoing connections to it. We won't gossip its address
33// to other peers in addr messages. Banned addresses and subnets are stored to
34// disk on shutdown and reloaded on startup. Banning can be used to
35// prevent connections with spy nodes or other griefers.
36//
37// 2. Discouragement. If a peer misbehaves (see Misbehaving() in
38// net_processing.cpp), we'll mark that address as discouraged. We still allow
39// incoming connections from them, but they're preferred for eviction when
40// we receive new incoming connections. We never make outgoing connections to
41// them, and do not gossip their address to other peers. This is implemented as
42// a bloom filter. We can (probabilistically) test for membership, but can't
43// list all discouraged addresses or unmark them as discouraged. Discouragement
44// can prevent our limited connection slots being used up by incompatible
45// or broken peers.
46//
47// Neither banning nor discouragement are protections against denial-of-service
48// attacks, since if an attacker has a way to waste our resources and we
49// disconnect from them and ban that address, it's trivial for them to
50// reconnect from another IP address.
51//
52// Attempting to automatically disconnect or ban any class of peer carries the
53// risk of splitting the network. For example, if we banned/disconnected for a
54// transaction that fails a policy check and a future version changes the
55// policy check so the transaction is accepted, then that transaction could
56// cause the network to split between old nodes and new nodes.
57//
58// NOTE: previously a misbehaving peer would get banned instead of discouraged.
59// This meant a peer could unboundedly grow our in-memory map of banned ips. When
60// receiving an ADDR message we would also compare every address received to every
61// item in the map. See https://bitcoincore.org/en/2024/07/03/disclose-unbounded-banlist.
62
63class BanMan
64{
65public:
66    ~BanMan();
67    BanMan(fs::path ban_file, CClientUIInterface* client_interface, int64_t default_ban_time);
68    void Ban(const CNetAddr& net_addr, int64_t ban_time_offset = 0, bool since_unix_epoch = false) EXCLUSIVE_LOCKS_REQUIRED(!m_banned_mutex);
69    void Ban(const CSubNet& sub_net, int64_t ban_time_offset = 0, bool since_unix_epoch = false) EXCLUSIVE_LOCKS_REQUIRED(!m_banned_mutex);
70    void Discourage(const CNetAddr& net_addr) EXCLUSIVE_LOCKS_REQUIRED(!m_banned_mutex);
71    void ClearBanned() EXCLUSIVE_LOCKS_REQUIRED(!m_banned_mutex);
72
73    //! Return whether net_addr is banned
74    bool IsBanned(const CNetAddr& net_addr) EXCLUSIVE_LOCKS_REQUIRED(!m_banned_mutex);
75
76    //! Return whether sub_net is exactly banned
77    bool IsBanned(const CSubNet& sub_net) EXCLUSIVE_LOCKS_REQUIRED(!m_banned_mutex);
78
79    //! Return whether net_addr is discouraged.
80    bool IsDiscouraged(const CNetAddr& net_addr) EXCLUSIVE_LOCKS_REQUIRED(!m_banned_mutex);
81
82    bool Unban(const CNetAddr& net_addr) EXCLUSIVE_LOCKS_REQUIRED(!m_banned_mutex);
83    bool Unban(const CSubNet& sub_net) EXCLUSIVE_LOCKS_REQUIRED(!m_banned_mutex);
84    void GetBanned(banmap_t& banmap) EXCLUSIVE_LOCKS_REQUIRED(!m_banned_mutex);
85    void DumpBanlist() EXCLUSIVE_LOCKS_REQUIRED(!m_banned_mutex);
86
87private:
88    void LoadBanlist() EXCLUSIVE_LOCKS_REQUIRED(!m_banned_mutex);
89    //!clean unused entries (if bantime has expired)
90    void SweepBanned() EXCLUSIVE_LOCKS_REQUIRED(m_banned_mutex);
91
92    Mutex m_banned_mutex;
93    banmap_t m_banned GUARDED_BY(m_banned_mutex);
94    bool m_is_dirty GUARDED_BY(m_banned_mutex){false};
95    CClientUIInterface* m_client_interface = nullptr;
96    CBanDB m_ban_db;
97    const int64_t m_default_ban_time;
98    CRollingBloomFilter m_discouraged GUARDED_BY(m_banned_mutex) {50000, 0.000001};
99};
100
101#endif // BITCOIN_BANMAN_H
102