Merge #14728: fix uninitialized read when stringifying an addrLocal

b7b36de fix uninitialized read when stringifying an addrLocal (Kaz Wesley)
8ebbef0 add test demonstrating addrLocal UB (Kaz Wesley)

Pull request description:

  Reachable from either place where SetIP is used when all of:
  - our best-guess addrLocal for a peer is IPv4
  - the peer tells us it's reaching us at an IPv6 address
  - NET logging is enabled

  In that case, SetIP turns an IPv4 address into an IPv6 address without
  setting the scopeId, which is subsequently read in GetSockAddr during
  CNetAddr::ToStringIP and passed to getnameinfo. Fix by ensuring every
  constructor initializes the scopeId field with something.

Tree-SHA512: 8f0159750995e08b985335ccf60a273ebd09003990bcf2c3838b550ed8dc2659552ac7611650e6dd8e29d786fe52ed57674f5880f2e18dc594a7a863134739e3

Author: laanwj

src/netaddress.cpp

@@ -17,7 +17,6 @@ static const unsigned char g_internal_prefix[] = { 0xFD, 0x6B, 0x88, 0xC0, 0x87,
 CNetAddr::CNetAddr()
 {
     memset(ip, 0, sizeof(ip));
-    scopeId = 0;
 }
 
 void CNetAddr::SetIP(const CNetAddr& ipIn)

src/netaddress.h

@@ -33,7 +33,7 @@ class CNetAddr
 {
     protected:
         unsigned char ip[16]; // in network byte order
-        uint32_t scopeId; // for scoped/link-local ipv6 addresses
+        uint32_t scopeId{0}; // for scoped/link-local ipv6 addresses
 
     public:
         CNetAddr();

src/test/net_tests.cpp

@@ -189,4 +189,42 @@ BOOST_AUTO_TEST_CASE(cnode_simple_test)
     BOOST_CHECK(pnode2->fFeeler == false);
 }
 
+// prior to PR #14728, this test triggers an undefined behavior
+BOOST_AUTO_TEST_CASE(ipv4_peer_with_ipv6_addrMe_test)
+{
+    // set up local addresses; all that's necessary to reproduce the bug is
+    // that a normal IPv4 address is among the entries, but if this address is
+    // !IsRoutable the undefined behavior is easier to trigger deterministically
+    {
+        LOCK(cs_mapLocalHost);
+        in_addr ipv4AddrLocal;
+        ipv4AddrLocal.s_addr = 0x0100007f;
+        CNetAddr addr = CNetAddr(ipv4AddrLocal);
+        LocalServiceInfo lsi;
+        lsi.nScore = 23;
+        lsi.nPort = 42;
+        mapLocalHost[addr] = lsi;
+    }
+
+    // create a peer with an IPv4 address
+    in_addr ipv4AddrPeer;
+    ipv4AddrPeer.s_addr = 0xa0b0c001;
+    CAddress addr = CAddress(CService(ipv4AddrPeer, 7777), NODE_NETWORK);
+    std::unique_ptr<CNode> pnode = MakeUnique<CNode>(0, NODE_NETWORK, 0, INVALID_SOCKET, addr, 0, 0, CAddress{}, std::string{}, false);
+    pnode->fSuccessfullyConnected.store(true);
+
+    // the peer claims to be reaching us via IPv6
+    in6_addr ipv6AddrLocal;
+    memset(ipv6AddrLocal.s6_addr, 0, 16);
+    ipv6AddrLocal.s6_addr[0] = 0xcc;
+    CAddress addrLocal = CAddress(CService(ipv6AddrLocal, 7777), NODE_NETWORK);
+    pnode->SetAddrLocal(addrLocal);
+
+    // before patch, this causes undefined behavior detectable with clang's -fsanitize=memory
+    AdvertiseLocal(&*pnode);
+
+    // suppress no-checks-run warning; if this test fails, it's by triggering a sanitizer
+    BOOST_CHECK(1);
+}
+
 BOOST_AUTO_TEST_SUITE_END()