Merge #18991: Cache responses to GETADDR to prevent topology leaks

3bd67ba5a4ef3c20ef1f873b63c9f53a6c8608b6 Test addr response caching (Gleb Naumenko)
cf1569e074505dbbb9d29422803dd31bb62072d4 Add addr permission flag enabling non-cached addr sharing (Gleb Naumenko)
acd6135b43941fa51d52f5fcdb2ce944280ad01e Cache responses to addr requests (Gleb Naumenko)
7cc0e8101f01891aa8be093a00d993bb7579c385 Remove useless 2500 limit on AddrMan queries (Gleb Naumenko)
ded742bc5b96e3215d69c11fb3628d224e7ae034 Move filtering banned addrs inside GetAddresses() (Gleb Naumenko)

Pull request description:

  This is a very simple code change with a big p2p privacy benefit.

  It’s currently trivial to scrape any reachable node’s AddrMan (a database of all nodes known to them along with the timestamps).
  We do have a limit of one GETADDR per connection, but a spy can disconnect and reconnect even from the same IP, and send GETADDR again and again.

  Since we respond with 1,000 random records at most, depending on the AddrMan size it takes probably up to 100 requests for an spy to make sure they scraped (almost) everything.
  I even have a script for that. It is totally doable within couple minutes.

  Then, with some extra protocol knowledge a spy can infer the direct peers of the victim, and other topological stuff.

  I suggest to cache responses to GETADDR on a daily basis, so that an attacker gets at most 1,000 records per day, and can’t track the changes in real time. I will be following up with more improvements to addr relay privacy, but this one alone is a very effective. And simple!

  I doubt any of the real software does *reconnect to get new addrs from a given peer*, so we shouldn’t be cutting anyone.
  I also believe it doesn’t have any negative implications on the overall topology quality. And the records being “outdated” for at most a day doesn’t break any honest assumptions either.

ACKs for top commit:
  jnewbery:
    reACK 3bd67ba5a4ef3c20ef1f873b63c9f53a6c8608b6
  promag:
    Code review ACK 3bd67ba5a4ef3c20ef1f873b63c9f53a6c8608b6.
  ariard:
    Code Review ACK 3bd67ba

Tree-SHA512: dfa5d03205c2424e40a3f8a41af9306227e1ca18beead3b3dda44aa2a082175bb1c6d929dbc7ea8e48e01aed0d50f0d54491caa1147471a2b72a46c3ca06b66f

1 files changed, 18 insertions, 1 deletions

diff --git a/src/net.cpp b/src/net.cpp
index 0c56cddbdc..bf29d928a1 100644
--- a/src/net.cpp
+++ b/src/net.cpp
@@ -2530,7 +2530,24 @@ void CConnman::AddNewAddresses(const std::vector<CAddress>& vAddr, const CAddres
 
 std::vector<CAddress> CConnman::GetAddresses()
 {
-    return addrman.GetAddr();
+    std::vector<CAddress> addresses = addrman.GetAddr();
+    if (m_banman) {
+        addresses.erase(std::remove_if(addresses.begin(), addresses.end(),
+                        [this](const CAddress& addr){return m_banman->IsDiscouraged(addr) || m_banman->IsBanned(addr);}),
+                        addresses.end());
+    }
+    return addresses;
+}
+
+std::vector<CAddress> CConnman::GetAddresses(Network requestor_network)
+{
+    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();
+        m_addr_response_caches[requestor_network].m_update_addr_response = current_time + std::chrono::hours(21) + GetRandMillis(std::chrono::hours(6));
+    }
+    return m_addr_response_caches[requestor_network].m_addrs_response_cache;
 }
 
 bool CConnman::AddNode(const std::string& strNode)