add test demonstrating addrLocal UB

Author: kazcw

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()