src/lib/ares__sortaddrinfo.c

/*
 * Original file name getaddrinfo.c
 * Lifted from the 'Android Bionic' project with the BSD license.
 */

/*
 * Copyright (C) 1995, 1996, 1997, and 1998 WIDE Project.
 * Copyright (C) 2018 The Android Open Source Project
 * Copyright (C) 2019 by Andrew Selivanov
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the project nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE PROJECT AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE PROJECT OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#include "ares_setup.h"

#ifdef HAVE_NETINET_IN_H
#  include <netinet/in.h>
#endif
#ifdef HAVE_NETDB_H
#  include <netdb.h>
#endif
#ifdef HAVE_STRINGS_H
#  include <strings.h>
#endif

#include <assert.h>
#include <limits.h>

#include "ares.h"
#include "ares_private.h"

struct addrinfo_sort_elem
{
  struct ares_addrinfo_node *ai;
  int has_src_addr;
  ares_sockaddr src_addr;
  int original_order;
};

#define ARES_IPV6_ADDR_MC_SCOPE(a) ((a)->s6_addr[1] & 0x0f)

#define ARES_IPV6_ADDR_SCOPE_NODELOCAL       0x01
#define ARES_IPV6_ADDR_SCOPE_INTFACELOCAL    0x01
#define ARES_IPV6_ADDR_SCOPE_LINKLOCAL       0x02
#define ARES_IPV6_ADDR_SCOPE_SITELOCAL       0x05
#define ARES_IPV6_ADDR_SCOPE_ORGLOCAL        0x08
#define ARES_IPV6_ADDR_SCOPE_GLOBAL          0x0e

#define ARES_IN_LOOPBACK(a) ((((long int)(a)) & 0xff000000) == 0x7f000000)

/* RFC 4193. */
#define ARES_IN6_IS_ADDR_ULA(a) (((a)->s6_addr[0] & 0xfe) == 0xfc)

/* These macros are modelled after the ones in <netinet/in6.h>. */
/* RFC 4380, section 2.6 */
#define ARES_IN6_IS_ADDR_TEREDO(a)    \
        ((*(const unsigned int *)(const void *)(&(a)->s6_addr[0]) == ntohl(0x20010000)))
/* RFC 3056, section 2. */
#define ARES_IN6_IS_ADDR_6TO4(a)      \
        (((a)->s6_addr[0] == 0x20) && ((a)->s6_addr[1] == 0x02))
/* 6bone testing address area (3ffe::/16), deprecated in RFC 3701. */
#define ARES_IN6_IS_ADDR_6BONE(a)      \
        (((a)->s6_addr[0] == 0x3f) && ((a)->s6_addr[1] == 0xfe))


static int get_scope(const struct sockaddr *addr)
{
  if (addr->sa_family == AF_INET6)
    {
      const struct sockaddr_in6 *addr6 = CARES_INADDR_CAST(const struct sockaddr_in6 *, addr);
      if (IN6_IS_ADDR_MULTICAST(&addr6->sin6_addr))
        {
          return ARES_IPV6_ADDR_MC_SCOPE(&addr6->sin6_addr);
        }
      else if (IN6_IS_ADDR_LOOPBACK(&addr6->sin6_addr) ||
               IN6_IS_ADDR_LINKLOCAL(&addr6->sin6_addr))
        {
          /*
           * RFC 4291 section 2.5.3 says loopback is to be treated as having
           * link-local scope.
           */
          return ARES_IPV6_ADDR_SCOPE_LINKLOCAL;
        }
      else if (IN6_IS_ADDR_SITELOCAL(&addr6->sin6_addr))
        {
          return ARES_IPV6_ADDR_SCOPE_SITELOCAL;
        }
      else
        {
          return ARES_IPV6_ADDR_SCOPE_GLOBAL;
        }
    }
  else if (addr->sa_family == AF_INET)
    {
      const struct sockaddr_in *addr4 = CARES_INADDR_CAST(const struct sockaddr_in *, addr);
      unsigned long int na = ntohl(addr4->sin_addr.s_addr);
      if (ARES_IN_LOOPBACK(na) || /* 127.0.0.0/8 */
          (na & 0xffff0000) == 0xa9fe0000) /* 169.254.0.0/16 */
        {
          return ARES_IPV6_ADDR_SCOPE_LINKLOCAL;
        }
      else
        {
          /*
           * RFC 6724 section 3.2. Other IPv4 addresses, including private
           * addresses and shared addresses (100.64.0.0/10), are assigned global
           * scope.
           */
          return ARES_IPV6_ADDR_SCOPE_GLOBAL;
        }
    }
  else
    {
      /*
       * This should never happen.
       * Return a scope with low priority as a last resort.
       */
      return ARES_IPV6_ADDR_SCOPE_NODELOCAL;
    }
}

static int get_label(const struct sockaddr *addr)
{
  if (addr->sa_family == AF_INET)
    {
      return 4;
    }
  else if (addr->sa_family == AF_INET6)
    {
      const struct sockaddr_in6 *addr6 = CARES_INADDR_CAST(const struct sockaddr_in6 *, addr);
      if (IN6_IS_ADDR_LOOPBACK(&addr6->sin6_addr))
        {
          return 0;
        }
      else if (IN6_IS_ADDR_V4MAPPED(&addr6->sin6_addr))
        {
          return 4;
        }
      else if (ARES_IN6_IS_ADDR_6TO4(&addr6->sin6_addr))
        {
          return 2;
        }
      else if (ARES_IN6_IS_ADDR_TEREDO(&addr6->sin6_addr))
        {
          return 5;
        }
      else if (ARES_IN6_IS_ADDR_ULA(&addr6->sin6_addr))
        {
          return 13;
        }
      else if (IN6_IS_ADDR_V4COMPAT(&addr6->sin6_addr))
        {
          return 3;
        }
      else if (IN6_IS_ADDR_SITELOCAL(&addr6->sin6_addr))
        {
          return 11;
        }
      else if (ARES_IN6_IS_ADDR_6BONE(&addr6->sin6_addr))
        {
          return 12;
        }
      else
        {
          /* All other IPv6 addresses, including global unicast addresses. */
          return 1;
        }
    }
  else
    {
      /*
       * This should never happen.
       * Return a semi-random label as a last resort.
       */
      return 1;
    }
}

/*
 * Get the precedence for a given IPv4/IPv6 address.
 * RFC 6724, section 2.1.
 */
static int get_precedence(const struct sockaddr *addr)
{
  if (addr->sa_family == AF_INET)
    {
      return 35;
    }
  else if (addr->sa_family == AF_INET6)
    {
      const struct sockaddr_in6 *addr6 = CARES_INADDR_CAST(const struct sockaddr_in6 *, addr);
      if (IN6_IS_ADDR_LOOPBACK(&addr6->sin6_addr))
        {
          return 50;
        }
      else if (IN6_IS_ADDR_V4MAPPED(&addr6->sin6_addr))
        {
          return 35;
        }
      else if (ARES_IN6_IS_ADDR_6TO4(&addr6->sin6_addr))
        {
          return 30;
        }
      else if (ARES_IN6_IS_ADDR_TEREDO(&addr6->sin6_addr))
        {
          return 5;
        }
      else if (ARES_IN6_IS_ADDR_ULA(&addr6->sin6_addr))
        {
          return 3;
        }
      else if (IN6_IS_ADDR_V4COMPAT(&addr6->sin6_addr) ||
               IN6_IS_ADDR_SITELOCAL(&addr6->sin6_addr) ||
               ARES_IN6_IS_ADDR_6BONE(&addr6->sin6_addr))
        {
          return 1;
        }
      else
        {
          /* All other IPv6 addresses, including global unicast addresses. */
          return 40;
        }
    }
  else
    {
      return 1;
    }
}

/*
 * Find number of matching initial bits between the two addresses a1 and a2.
 */
static int common_prefix_len(const struct in6_addr *a1,
                             const struct in6_addr *a2)
{
  const char *p1 = (const char *)a1;
  const char *p2 = (const char *)a2;
  unsigned i;
  for (i = 0; i < sizeof(*a1); ++i)
    {
      int x, j;
      if (p1[i] == p2[i])
        {
          continue;
        }
      x = p1[i] ^ p2[i];
      for (j = 0; j < CHAR_BIT; ++j)
        {
          if (x & (1 << (CHAR_BIT - 1)))
            {
              return i * CHAR_BIT + j;
            }
          x <<= 1;
        }
    }
  return sizeof(*a1) * CHAR_BIT;
}

/*
 * Compare two source/destination address pairs.
 * RFC 6724, section 6.
 */
static int rfc6724_compare(const void *ptr1, const void *ptr2)
{
  const struct addrinfo_sort_elem *a1 = (const struct addrinfo_sort_elem *)ptr1;
  const struct addrinfo_sort_elem *a2 = (const struct addrinfo_sort_elem *)ptr2;
  int scope_src1, scope_dst1, scope_match1;
  int scope_src2, scope_dst2, scope_match2;
  int label_src1, label_dst1, label_match1;
  int label_src2, label_dst2, label_match2;
  int precedence1, precedence2;
  int prefixlen1, prefixlen2;

  /* Rule 1: Avoid unusable destinations. */
  if (a1->has_src_addr != a2->has_src_addr)
    {
      return a2->has_src_addr - a1->has_src_addr;
    }

  /* Rule 2: Prefer matching scope. */
  scope_src1 = ARES_IPV6_ADDR_SCOPE_NODELOCAL;
  if (a1->has_src_addr)
    scope_src1 = get_scope(&a1->src_addr.sa);
  scope_dst1 = get_scope(a1->ai->ai_addr);
  scope_match1 = (scope_src1 == scope_dst1);

  scope_src2 = ARES_IPV6_ADDR_SCOPE_NODELOCAL;
  if (a2->has_src_addr)
    scope_src2 = get_scope(&a2->src_addr.sa);
  scope_dst2 = get_scope(a2->ai->ai_addr);
  scope_match2 = (scope_src2 == scope_dst2);

  if (scope_match1 != scope_match2)
    {
      return scope_match2 - scope_match1;
    }

  /* Rule 3: Avoid deprecated addresses.  */

  /* Rule 4: Prefer home addresses.  */

  /* Rule 5: Prefer matching label. */
  label_src1 = 1;
  if (a1->has_src_addr)
    label_src1 = get_label(&a1->src_addr.sa);
  label_dst1 = get_label(a1->ai->ai_addr);
  label_match1 = (label_src1 == label_dst1);

  label_src2 = 1;
  if (a2->has_src_addr)
    label_src2 = get_label(&a2->src_addr.sa);
  label_dst2 = get_label(a2->ai->ai_addr);
  label_match2 = (label_src2 == label_dst2);

  if (label_match1 != label_match2)
    {
      return label_match2 - label_match1;
    }

  /* Rule 6: Prefer higher precedence. */
  precedence1 = get_precedence(a1->ai->ai_addr);
  precedence2 = get_precedence(a2->ai->ai_addr);
  if (precedence1 != precedence2)
    {
      return precedence2 - precedence1;
    }

  /* Rule 7: Prefer native transport.  */

  /* Rule 8: Prefer smaller scope. */
  if (scope_dst1 != scope_dst2)
    {
      return scope_dst1 - scope_dst2;
    }

  /* Rule 9: Use longest matching prefix. */
  if (a1->has_src_addr && a1->ai->ai_addr->sa_family == AF_INET6 &&
      a2->has_src_addr && a2->ai->ai_addr->sa_family == AF_INET6)
    {
      const struct sockaddr_in6 *a1_src = &a1->src_addr.sa6;
      const struct sockaddr_in6 *a1_dst =
          CARES_INADDR_CAST(const struct sockaddr_in6 *, a1->ai->ai_addr);
      const struct sockaddr_in6 *a2_src = &a2->src_addr.sa6;
      const struct sockaddr_in6 *a2_dst =
          CARES_INADDR_CAST(const struct sockaddr_in6 *, a2->ai->ai_addr);
      prefixlen1 = common_prefix_len(&a1_src->sin6_addr, &a1_dst->sin6_addr);
      prefixlen2 = common_prefix_len(&a2_src->sin6_addr, &a2_dst->sin6_addr);
      if (prefixlen1 != prefixlen2)
        {
          return prefixlen2 - prefixlen1;
        }
    }

  /*
   * Rule 10: Leave the order unchanged.
   * We need this since qsort() is not necessarily stable.
   */
  return a1->original_order - a2->original_order;
}

/*
 * Find the source address that will be used if trying to connect to the given
 * address.
 *
 * Returns 1 if a source address was found, 0 if the address is unreachable,
 * and -1 if a fatal error occurred. If 0 or 1, the contents of src_addr are
 * undefined.
 */
static int find_src_addr(ares_channel channel,
                         const struct sockaddr *addr,
                         struct sockaddr *src_addr)
{
  ares_socket_t sock;
  int ret;
  ares_socklen_t len;

  switch (addr->sa_family)
    {
    case AF_INET:
      len = sizeof(struct sockaddr_in);
      break;
    case AF_INET6:
      len = sizeof(struct sockaddr_in6);
      break;
    default:
      /* No known usable source address for non-INET families. */
      return 0;
    }

  sock = ares__open_socket(channel, addr->sa_family, SOCK_DGRAM, IPPROTO_UDP);
  if (sock == ARES_SOCKET_BAD)
    {
      if (errno == EAFNOSUPPORT)
        {
          return 0;
        }
      else
        {
          return -1;
        }
    }

  do
    {
      ret = ares__connect_socket(channel, sock, addr, len);
    }
  while (ret == -1 && errno == EINTR);

  if (ret == -1)
    {
      ares__close_socket(channel, sock);
      return 0;
    }

  if (getsockname(sock, src_addr, &len) != 0)
    {
      ares__close_socket(channel, sock);
      return -1;
    }
  ares__close_socket(channel, sock);
  return 1;
}

/*
 * Sort the linked list starting at sentinel->ai_next in RFC6724 order.
 * Will leave the list unchanged if an error occurs.
 */
int ares__sortaddrinfo(ares_channel channel, struct ares_addrinfo_node *list_sentinel)
{
  struct ares_addrinfo_node *cur;
  int nelem = 0, i;
  int has_src_addr;
  struct addrinfo_sort_elem *elems;

  cur = list_sentinel->ai_next;
  while (cur)
    {
      ++nelem;
      cur = cur->ai_next;
    }

  if (!nelem)
      return ARES_ENODATA;

  elems = (struct addrinfo_sort_elem *)ares_malloc(
      nelem * sizeof(struct addrinfo_sort_elem));
  if (!elems)
    {
      return ARES_ENOMEM;
    }

  /*
   * Convert the linked list to an array that also contains the candidate
   * source address for each destination address.
   */
  for (i = 0, cur = list_sentinel->ai_next; i < nelem; ++i, cur = cur->ai_next)
    {
      assert(cur != NULL);
      elems[i].ai = cur;
      elems[i].original_order = i;
      has_src_addr = find_src_addr(channel, cur->ai_addr, &elems[i].src_addr.sa);
      if (has_src_addr == -1)
        {
          ares_free(elems);
          return ARES_ENOTFOUND;
        }
      elems[i].has_src_addr = has_src_addr;
    }

  /* Sort the addresses, and rearrange the linked list so it matches the sorted
   * order. */
  qsort((void *)elems, nelem, sizeof(struct addrinfo_sort_elem),
        rfc6724_compare);

  list_sentinel->ai_next = elems[0].ai;
  for (i = 0; i < nelem - 1; ++i)
    {
      elems[i].ai->ai_next = elems[i + 1].ai;
    }
  elems[nelem - 1].ai->ai_next = NULL;

  ares_free(elems);
  return ARES_SUCCESS;
}