Merge #19628: net: change CNetAddr::ip to have flexible size

102867c587 net: change CNetAddr::ip to have flexible size (Vasil Dimov)
1ea57ad674 net: don't accept non-left-contiguous netmasks (Vasil Dimov)

Pull request description:

  (chopped off from #19031 to ease review)

  Before this change `CNetAddr::ip` was a fixed-size array of 16 bytes,
  not being able to store larger addresses (e.g. TORv3) and encoded
  smaller ones as 16-byte IPv6 addresses.

  Change its type to `prevector`, so that it can hold larger addresses and
  do not disguise non-IPv6 addresses as IPv6. So the IPv4 address
  `1.2.3.4` is now encoded as `01020304` instead of
  `00000000000000000000FFFF01020304`.

  Rename `CNetAddr::ip` to `CNetAddr::m_addr` because it is not an "IP" or
  "IP address" (TOR addresses are not IP addresses).

  In order to preserve backward compatibility with serialization (where
  e.g. `1.2.3.4` is serialized as `00000000000000000000FFFF01020304`)
  introduce `CNetAddr` dedicated legacy serialize/unserialize methods.

  Adjust `CSubNet` accordingly. Still use `CSubNet::netmask[]` of fixed 16
  bytes, but use the first 4 for IPv4 (not the last 4). Do not accept
  invalid netmasks that have 0-bits followed by 1-bits and only allow
  subnetting for IPv4 and IPv6.

  Co-authored-by: Carl Dong <contact@carldong.me>

ACKs for top commit:
  sipa:
    utACK 102867c587
  MarcoFalke:
    Concept ACK 102867c587
  ryanofsky:
    Code review ACK 102867c587. Just many suggested updates since last review. Thanks for following up on everything!
  jonatack:
    re-ACK 102867c587 diff review, code review, build/tests/running bitcoind with ipv4/ipv6/onion peers
  kallewoof:
    ACK 102867c587

Tree-SHA512: d60bf716cecf8d3e8146d2f90f897ebe956befb16f711a24cfe680024c5afc758fb9e4a0a22066b42f7630d52cf916318bedbcbc069ae07092d5250a11e8f762

src/test/fuzz/asmap.cpp

@@ -33,7 +33,7 @@ void test_one_input(const std::vector<uint8_t>& buffer)
     if (buffer.size() < 1 + 3 + 4) return;
     int asmap_size = 3 + (buffer[0] & 127);
     bool ipv6 = buffer[0] & 128;
-    int addr_size = ipv6 ? 16 : 4;
+    const size_t addr_size = ipv6 ? ADDR_IPV6_SIZE : ADDR_IPV4_SIZE;
     if (buffer.size() < size_t(1 + asmap_size + addr_size)) return;
     std::vector<bool> asmap = ipv6 ? IPV6_PREFIX_ASMAP : IPV4_PREFIX_ASMAP;
     asmap.reserve(asmap.size() + 8 * asmap_size);
@@ -43,7 +43,17 @@ void test_one_input(const std::vector<uint8_t>& buffer)
         }
     }
     if (!SanityCheckASMap(asmap)) return;
+
+    const uint8_t* addr_data = buffer.data() + 1 + asmap_size;
     CNetAddr net_addr;
-    net_addr.SetRaw(ipv6 ? NET_IPV6 : NET_IPV4, buffer.data() + 1 + asmap_size);
+    if (ipv6) {
+        assert(addr_size == ADDR_IPV6_SIZE);
+        net_addr.SetLegacyIPv6(Span<const uint8_t>(addr_data, addr_size));
+    } else {
+        assert(addr_size == ADDR_IPV4_SIZE);
+        in_addr ipv4;
+        memcpy(&ipv4, addr_data, addr_size);
+        net_addr.SetIP(CNetAddr{ipv4});
+    }
     (void)net_addr.GetMappedAS(asmap);
 }

src/test/fuzz/netaddress.cpp

@@ -17,9 +17,6 @@ void test_one_input(const std::vector<uint8_t>& buffer)
     FuzzedDataProvider fuzzed_data_provider(buffer.data(), buffer.size());
 
     const CNetAddr net_addr = ConsumeNetAddr(fuzzed_data_provider);
-    for (int i = 0; i < 15; ++i) {
-        (void)net_addr.GetByte(i);
-    }
     (void)net_addr.GetHash();
     (void)net_addr.GetNetClass();
     if (net_addr.GetNetwork() == Network::NET_IPV4) {
@@ -78,7 +75,7 @@ void test_one_input(const std::vector<uint8_t>& buffer)
     (void)net_addr.ToString();
     (void)net_addr.ToStringIP();
 
-    const CSubNet sub_net{net_addr, fuzzed_data_provider.ConsumeIntegral<int32_t>()};
+    const CSubNet sub_net{net_addr, fuzzed_data_provider.ConsumeIntegral<uint8_t>()};
     (void)sub_net.IsValid();
     (void)sub_net.ToString();
 

src/test/fuzz/util.h

@@ -257,7 +257,7 @@ CNetAddr ConsumeNetAddr(FuzzedDataProvider& fuzzed_data_provider) noexcept
 
 CSubNet ConsumeSubNet(FuzzedDataProvider& fuzzed_data_provider) noexcept
 {
-    return {ConsumeNetAddr(fuzzed_data_provider), fuzzed_data_provider.ConsumeIntegral<int32_t>()};
+    return {ConsumeNetAddr(fuzzed_data_provider), fuzzed_data_provider.ConsumeIntegral<uint8_t>()};
 }
 
 void InitializeFuzzingContext(const std::string& chain_name = CBaseChainParams::REGTEST)