RFC6761: special case "localhost" (#430)

As per RFC6761 Section 6.3, "localhost" lookups need to be special cased to return loopback addresses, and not forward queries to recursive dns servers.

We first look up via files (/etc/hosts or equivalent), and if that fails, we then attempt a system-specific address enumeration for loopback addresses (currently Windows-only), and finally fallback to ::1 and 127.0.0.1.

Fix By: Brad House (@bradh352)
Fixes Bug: #399

CMakeLists.txt

@@ -236,7 +236,7 @@ IF (HAVE_LIBRT)
 	LIST (APPEND CARES_DEPENDENT_LIBS rt)
 ENDIF ()
 IF (WIN32)
-	LIST (APPEND CARES_DEPENDENT_LIBS ws2_32 advapi32)
+	LIST (APPEND CARES_DEPENDENT_LIBS ws2_32 advapi32 iphlpapi)
 ENDIF ()
 
 

Makefile.m32

@@ -20,7 +20,7 @@ CP	= cp -afv
 CFLAGS	= $(CARES_CFLAG_EXTRAS) -O2 -Wall -I./include -I./src/lib -D_WIN32_WINNT=0x0600
 CFLAGS	+= -DCARES_STATICLIB
 LDFLAGS	= $(CARES_LDFLAG_EXTRAS) -s
-LIBS	= -lwsock32
+LIBS	= -lws2_32 -liphlpapi
 
 # Makefile.inc provides the CSOURCES and HHEADERS defines
 include src/lib/Makefile.inc

Makefile.msvc

@@ -184,8 +184,8 @@ EX_LIBS_REL = $(WATT_ROOT)\lib\wattcpvc_imp.lib
 EX_LIBS_DBG = $(WATT_ROOT)\lib\wattcpvc_imp_d.lib
 !ELSE
 CFLAGS  = /DWIN32 /D_WIN32_WINNT=0x0600
-EX_LIBS_REL = ws2_32.lib advapi32.lib kernel32.lib
+EX_LIBS_REL = ws2_32.lib advapi32.lib kernel32.lib iphlpapi.lib
-EX_LIBS_DBG = ws2_32.lib advapi32.lib kernel32.lib
+EX_LIBS_DBG = ws2_32.lib advapi32.lib kernel32.lib iphlpapi.lib
 !ENDIF
 
 # -------------------------------------------------

src/lib/Makefile.inc

@@ -1,5 +1,6 @@
 
 CSOURCES = ares__addrinfo2hostent.c	\
+  ares__addrinfo_localhost.c	\
   ares__close_sockets.c	\
   ares__get_hostent.c			\
   ares__parse_into_addrinfo.c		\

src/lib/ares__addrinfo_localhost.c

@@ -0,0 +1,236 @@
+/* Copyright (C) 2019 by Andrew Selivanov
+ *
+ * Permission to use, copy, modify, and distribute this
+ * software and its documentation for any purpose and without
+ * fee is hereby granted, provided that the above copyright
+ * notice appear in all copies and that both that copyright
+ * notice and this permission notice appear in supporting
+ * documentation, and that the name of M.I.T. not be used in
+ * advertising or publicity pertaining to distribution of the
+ * software without specific, written prior permission.
+ * M.I.T. makes no representations about the suitability of
+ * this software for any purpose.  It is provided "as is"
+ * without express or implied warranty.
+ */
+
+#include "ares_setup.h"
+
+#ifdef HAVE_NETINET_IN_H
+#  include <netinet/in.h>
+#endif
+#ifdef HAVE_NETDB_H
+#  include <netdb.h>
+#endif
+#ifdef HAVE_ARPA_INET_H
+#  include <arpa/inet.h>
+#endif
+
+#if defined(_WIN32) && defined(_WIN32_WINNT) && _WIN32_WINNT >= 0x0600
+#include <ws2ipdef.h>
+#include <iphlpapi.h>
+#endif
+
+#include "ares.h"
+#include "ares_inet_net_pton.h"
+#include "ares_nowarn.h"
+#include "ares_private.h"
+
+
+
+static int ares_append_ai_node(int aftype,
+                               unsigned short port,
+                               const void *adata,
+                               struct ares_addrinfo_node **nodes)
+{
+  struct ares_addrinfo_node *node;
+
+  node = ares__append_addrinfo_node(nodes);
+  if (!node)
+    {
+      return ARES_ENOMEM;
+    }
+
+  memset(node, 0, sizeof(*node));
+
+  if (aftype == AF_INET)
+    {
+      struct sockaddr_in *sin = ares_malloc(sizeof(*sin));
+      if (!sin)
+        {
+          return ARES_ENOMEM;
+        }
+
+      memset(sin, 0, sizeof(*sin));
+      memcpy(&sin->sin_addr.s_addr, adata, sizeof(struct in_addr));
+      sin->sin_family = AF_INET;
+      sin->sin_port = htons(port);
+
+      node->ai_addr = (struct sockaddr *)sin;
+      node->ai_family = AF_INET;
+      node->ai_addrlen = sizeof(struct sockaddr_in);
+      node->ai_addr = (struct sockaddr *)sin;
+    }
+
+  if (aftype == AF_INET6)
+    {
+      struct sockaddr_in6 *sin6 = ares_malloc(sizeof(*sin6));
+      if (!sin6)
+        {
+          return ARES_ENOMEM;
+        }
+
+      memset(sin6, 0, sizeof(*sin6));
+      memcpy(&sin6->sin6_addr.s6_addr, adata, sizeof(struct ares_in6_addr));
+      sin6->sin6_family = AF_INET6;
+      sin6->sin6_port = htons(port);
+
+      node->ai_addr = (struct sockaddr *)sin6;
+      node->ai_family = AF_INET6;
+      node->ai_addrlen = sizeof(struct ares_in6_addr);
+      node->ai_addr = (struct sockaddr *)sin6;
+    }
+
+  return ARES_SUCCESS;
+}
+
+
+static int ares__default_loopback_addrs(int aftype,
+                                        unsigned short port,
+                                        struct ares_addrinfo_node **nodes)
+{
+  int status = ARES_SUCCESS;
+
+  if (aftype == AF_UNSPEC || aftype == AF_INET6)
+    {
+      struct ares_in6_addr addr6;
+      ares_inet_pton(AF_INET6, "::1", &addr6);
+      status = ares_append_ai_node(AF_INET6, port, &addr6, nodes);
+      if (status != ARES_SUCCESS)
+        {
+          return status;
+       }
+    }
+
+  if (aftype == AF_UNSPEC || aftype == AF_INET)
+    {
+      struct in_addr addr4;
+      ares_inet_pton(AF_INET, "127.0.0.1", &addr4);
+      status = ares_append_ai_node(AF_INET, port, &addr4, nodes);
+      if (status != ARES_SUCCESS)
+        {
+          return status;
+       }
+    }
+
+  return status;
+}
+
+
+static int ares__system_loopback_addrs(int aftype,
+                                       unsigned short port,
+                                       struct ares_addrinfo_node **nodes)
+{
+#if defined(_WIN32) && defined(_WIN32_WINNT) && _WIN32_WINNT >= 0x0600
+  PMIB_UNICASTIPADDRESS_TABLE table;
+  unsigned int i;
+  int status;
+
+  *nodes = NULL;
+
+  if (GetUnicastIpAddressTable(aftype, &table) != NO_ERROR)
+    return ARES_ENOTFOUND;
+
+  for (i=0; i<table->NumEntries; i++)
+    {
+      if (table->Table[i].InterfaceLuid.Info.IfType !=
+          IF_TYPE_SOFTWARE_LOOPBACK)
+        {
+          continue;
+        }
+
+      if (table->Table[i].Address.si_family == AF_INET)
+        {
+          status = ares_append_ai_node(table->Table[i].Address.si_family, port,
+                                       &table->Table[i].Address.Ipv4.sin_addr,
+                                       nodes);
+        }
+      else if (table->Table[i].Address.si_family == AF_INET6)
+        {
+          status = ares_append_ai_node(table->Table[i].Address.si_family, port,
+                                       &table->Table[i].Address.Ipv6.sin6_addr,
+                                       nodes);
+        }
+      else
+        {
+          /* Ignore any others */
+          continue;
+        }
+
+      if (status != ARES_SUCCESS)
+        {
+          goto fail;
+        }
+    }
+
+    if (*nodes == NULL)
+      status = ARES_ENOTFOUND;
+
+fail:
+  FreeMibTable(table);
+
+  if (status != ARES_SUCCESS)
+    {
+      ares__freeaddrinfo_nodes(*nodes);
+      *nodes = NULL;
+    }
+
+  return status;
+
+#else
+  /* Not supported on any other OS at this time */
+  return ARES_ENOTFOUND;
+#endif
+}
+
+
+int ares__addrinfo_localhost(const char *name,
+                             unsigned short port,
+                             const struct ares_addrinfo_hints *hints,
+                             struct ares_addrinfo *ai)
+{
+  struct ares_addrinfo_node *nodes = NULL;
+  int result;
+
+  /* Validate family */
+  switch (hints->ai_family) {
+    case AF_INET:
+    case AF_INET6:
+    case AF_UNSPEC:
+      break;
+    default:
+      return ARES_EBADFAMILY;
+  }
+
+  ai->name = ares_strdup(name);
+  if(!ai->name)
+    {
+      goto enomem;
+    }
+
+  result = ares__system_loopback_addrs(hints->ai_family, port, &nodes);
+
+  if (result == ARES_ENOTFOUND)
+    {
+      result = ares__default_loopback_addrs(hints->ai_family, port, &nodes);
+    }
+
+  ares__addrinfo_cat_nodes(&ai->nodes, nodes);
+
+  return result;
+
+enomem:
+  ares__freeaddrinfo_nodes(nodes);
+  ares_free(ai->name);
+  ai->name = NULL;
+  return ARES_ENOMEM;
+}

src/lib/ares__readaddrinfo.c

@@ -265,5 +265,7 @@ enomem:
   ares_free(line);
   ares__freeaddrinfo_cnames(cnames);
   ares__freeaddrinfo_nodes(nodes);
+  ares_free(ai->name);
+  ai->name = NULL;
   return ARES_ENOMEM;
 }

src/lib/ares_getaddrinfo.c

@@ -503,6 +503,16 @@ static int file_lookup(struct host_query *hquery)
     }
   status = ares__readaddrinfo(fp, hquery->name, hquery->port, &hquery->hints, hquery->ai);
   fclose(fp);
+
+  /* RFC6761 section 6.3 #3 states that "Name resolution APIs and libraries
+   * SHOULD recognize localhost names as special and SHOULD always return the
+   * IP loopback address for address queries" */
+  if (status == ARES_ENOTFOUND && strcmp(hquery->name, "localhost") == 0)
+    {
+      return ares__addrinfo_localhost(hquery->name, hquery->port,
+                                      &hquery->hints, hquery->ai);
+    }
+
   return status;
 }
 
@@ -511,9 +521,15 @@ static void next_lookup(struct host_query *hquery, int status)
   switch (*hquery->remaining_lookups)
     {
       case 'b':
+          /* RFC6761 section 6.3 #3 says "Name resolution APIs SHOULD NOT send
+           * queries for localhost names to their configured caching DNS
+           * server(s)." */
+          if (strcmp(hquery->name, "localhost") != 0)
+            {
               /* DNS lookup */
               if (next_dns_lookup(hquery))
                 break;
+            }
 
           hquery->remaining_lookups++;
           next_lookup(hquery, status);

src/lib/ares_private.h

@@ -399,6 +399,9 @@ int ares__addrinfo2hostent(const struct ares_addrinfo *ai, int family,
 int ares__addrinfo2addrttl(const struct ares_addrinfo *ai, int family,
                            int req_naddrttls, struct ares_addrttl *addrttls,
                            struct ares_addr6ttl *addr6ttls, int *naddrttls);
+int ares__addrinfo_localhost(const char *name, unsigned short port,
+                             const struct ares_addrinfo_hints *hints,
+                             struct ares_addrinfo *ai);
 
 #if 0 /* Not used */
 long ares__tvdiff(struct timeval t1, struct timeval t2);

test/Makefile.m32

@@ -17,7 +17,7 @@ GMOCK_DIR = gmock-1.8.0
 CPPFLAGS = -I$(ARES_SRC_DIR)/include -I$(ARES_SRC_DIR)/src/lib -I$(GMOCK_DIR) -DCARES_STATICLIB
 CXXFLAGS = -Wall $(PTHREAD_CFLAGS) -std=gnu++11
 LDFLAGS =
-LDLIBS = -lwsock32
+LDLIBS = -lws2_32 -liphlpapi
 
 # Makefile.inc provides the TESTSOURCES and TESTHEADERS defines
 include Makefile.inc

test/Makefile.msvc

@@ -140,8 +140,8 @@ LIB_OUTDIR = $(LIB_DIR)\$(CFG)
 # TCP/IP stack settings
 # -------------------------------------
 CFLAGS  = /DWIN32
-EX_LIBS_REL = ws2_32.lib advapi32.lib kernel32.lib
+EX_LIBS_REL = ws2_32.lib advapi32.lib kernel32.lib iphlpapi.lib
-EX_LIBS_DBG = ws2_32.lib advapi32.lib kernel32.lib
+EX_LIBS_DBG = ws2_32.lib advapi32.lib kernel32.lib iphlpapi.lib
 
 # -------------------------------------------------
 # Switches that depend on ancient compiler versions

test/ares-test-live.cc

@@ -145,7 +145,7 @@ TEST_P(DefaultChannelModeTest, LiveGetLocalhostByNameV4) {
   ares_gethostbyname(channel_, "localhost", AF_INET, HostCallback, &result);
   Process();
   EXPECT_TRUE(result.done_);
-  if ((result.status_ != ARES_ENOTFOUND) && (result.status_ != ARES_ECONNREFUSED)) {
+  if (result.status_ != ARES_ECONNREFUSED) {
     EXPECT_EQ(ARES_SUCCESS, result.status_);
     EXPECT_EQ(1, (int)result.host_.addrs_.size());
     EXPECT_EQ(AF_INET, result.host_.addrtype_);
@@ -158,7 +158,7 @@ TEST_P(DefaultChannelModeTest, LiveGetLocalhostByNameV6) {
   ares_gethostbyname(channel_, "localhost", AF_INET6, HostCallback, &result);
   Process();
   EXPECT_TRUE(result.done_);
-  if (result.status_ == ARES_SUCCESS) {
+  if (result.status_ != ARES_ECONNREFUSED) {
     EXPECT_EQ(1, (int)result.host_.addrs_.size());
     EXPECT_EQ(AF_INET6, result.host_.addrtype_);
     std::stringstream ss;