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Merge #19697: Improvements on ADDR caching

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0d04784af1 Refactor the functional test (Gleb Naumenko)
83ad65f31b Address nits in ADDR caching (Gleb Naumenko)
81b00f8780 Add indexing ADDR cache by local socket addr (Gleb Naumenko)
42ec558542 Justify the choice of ADDR cache lifetime (Gleb Naumenko)

Pull request description:

  This is a follow-up on #18991 which does 3 things:
  - improves privacy of a node listening to multiple addresses via adding cache index by local socket addr (suggested [here](https://github.com/bitcoin/bitcoin/pull/18991#issuecomment-668219345))
  - documents on the choice of 24h cache lifetime
  - addresses nits from #18991

ACKs for top commit:
  jnewbery:
    utACK 0d04784af1
  vasild:
    ACK 0d04784
  jonatack:
    Code review ACK 0d04784

Tree-SHA512: bb65a34dd1ce2811186d3e4469bc33e8399cebaaa494ce13041c7cff23275870e4176a719f7a72f8d779c49f8b2344bf4fa1aeb3ea4e2626d5ae76514f00a750
This commit is contained in:
Wladimir J. van der Laan
2020-09-21 18:46:52 +02:00
parent b99a1633b2 0d04784af1
commit c0c409dcd3
4 changed files with 64 additions and 46 deletions
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45
src/net.cpp
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@@ -94,6 +94,7 @@ const std::string NET_MESSAGE_COMMAND_OTHER = "*other*";
static const uint64_t RANDOMIZER_ID_NETGROUP = 0x6c0edd8036ef4036ULL; // SHA256("netgroup")[0:8]
static const uint64_t RANDOMIZER_ID_LOCALHOSTNONCE = 0xd93e69e2bbfa5735ULL; // SHA256("localhostnonce")[0:8]
static const uint64_t RANDOMIZER_ID_ADDRCACHE = 0x1cf2e4ddd306dda9ULL; // SHA256("addrcache")[0:8]
//
// Global state variables
//
@@ -2560,15 +2561,47 @@ std::vector<CAddress> CConnman::GetAddresses(size_t max_addresses, size_t max_pc
return addresses;
}
std::vector<CAddress> CConnman::GetAddresses(Network requestor_network, size_t max_addresses, size_t max_pct)
std::vector<CAddress> CConnman::GetAddresses(CNode& requestor, size_t max_addresses, size_t max_pct)
{
SOCKET socket;
WITH_LOCK(requestor.cs_hSocket, socket = requestor.hSocket);
auto local_socket_bytes = GetBindAddress(socket).GetAddrBytes();
uint64_t cache_id = GetDeterministicRandomizer(RANDOMIZER_ID_ADDRCACHE)
.Write(requestor.addr.GetNetwork())
.Write(local_socket_bytes.data(), local_socket_bytes.size())
.Finalize();
const auto current_time = GetTime<std::chrono::microseconds>();
if (m_addr_response_caches.find(requestor_network) == m_addr_response_caches.end() ||
m_addr_response_caches[requestor_network].m_update_addr_response < current_time) {
m_addr_response_caches[requestor_network].m_addrs_response_cache = GetAddresses(max_addresses, max_pct);
m_addr_response_caches[requestor_network].m_update_addr_response = current_time + std::chrono::hours(21) + GetRandMillis(std::chrono::hours(6));
auto r = m_addr_response_caches.emplace(cache_id, CachedAddrResponse{});
CachedAddrResponse& cache_entry = r.first->second;
if (cache_entry.m_cache_entry_expiration < current_time) { // If emplace() added new one it has expiration 0.
cache_entry.m_addrs_response_cache = GetAddresses(max_addresses, max_pct);
// Choosing a proper cache lifetime is a trade-off between the privacy leak minimization
// and the usefulness of ADDR responses to honest users.
//
// Longer cache lifetime makes it more difficult for an attacker to scrape
// enough AddrMan data to maliciously infer something useful.
// By the time an attacker scraped enough AddrMan records, most of
// the records should be old enough to not leak topology info by
// e.g. analyzing real-time changes in timestamps.
//
// It takes only several hundred requests to scrape everything from an AddrMan containing 100,000 nodes,
// so ~24 hours of cache lifetime indeed makes the data less inferable by the time
// most of it could be scraped (considering that timestamps are updated via
// ADDR self-announcements and when nodes communicate).
// We also should be robust to those attacks which may not require scraping *full* victim's AddrMan
// (because even several timestamps of the same handful of nodes may leak privacy).
//
// On the other hand, longer cache lifetime makes ADDR responses
// outdated and less useful for an honest requestor, e.g. if most nodes
// in the ADDR response are no longer active.
//
// However, the churn in the network is known to be rather low. Since we consider
// nodes to be "terrible" (see IsTerrible()) if the timestamps are older than 30 days,
// max. 24 hours of "penalty" due to cache shouldn't make any meaningful difference
// in terms of the freshness of the response.
cache_entry.m_cache_entry_expiration = current_time + std::chrono::hours(21) + GetRandMillis(std::chrono::hours(6));
}
return m_addr_response_caches[requestor_network].m_addrs_response_cache;
return cache_entry.m_addrs_response_cache;
}
bool CConnman::AddNode(const std::string& strNode)