Backport of WL#798 (MySQL IPv6 support) from 6.0.

The following 6.0 revisions were analyzed:
  - sp1r-brian@zim.(none)-20071228102738-21894
  - sp1r-brian@zim.(none)-20071228121841-56447
  - sp1r-brian@zim.(none)-20071228205403-56423
  - sp1r-brian@zim.(none)-20071228221139-55341
  - sp1r-brian@zim.(none)-20071228233443-55352
  - sp1r-brian@zim.(none)-20071229094527-61763
  - sp1r-brian@zim.(none)-20071230203739-61746
  - sp1r-brian@zim.(none)-20080102213805-61741
  - sp1r-brian@zim.(none)-20080103201041-61746
  - sp1r-brian@zim.(none)-20080104234927-59875
  - sp1r-brian@zim.(none)-20080105005827-59874
  - sp1r-brian@zim.(none)-20080105012020-59865
  - sp1r-brian@zim.(none)-20080106003858-59857
  - sp1r-brian@zim.(none)-20080123195552-31680
  - sp1r-brian@zim.(none)-20080124201848-29999
  - sp1r-brian@zim.(none)-20080129075144-36991
  - sp1r-cbell/Chuck@mysql_cab_desk.-20080215041806-21954
  - sp1r-vvaintroub@wva.-20080212124547-06272
  - sp1r-dfischer/mysqldev@mysql.com/production.mysql.com-20071223184258-15140
  - sp1r-brian@zim.(none)-20080206122216-35774
  - sp1r-baker@bk-internal.mysql.com-20080209005622-35947
  - sp1r-baker@bk-internal.mysql.com-20080224215608-24613
  - sp1r-baker@bk-internal.mysql.com-20080307170710-63543
  - sp1r-baker@bk-internal.mysql.com-20080312233205-13069
  - sp1r-Reggie@core.-20080402175211-28643
  - kpettersson@mysql.com-20080901101150-4ne74r8v0492vv42
  - alik@sun.com-20090805173811-9fzt0ymcp9tsvn7k
  - alik@sun.com-20090805173937-fcv1fdveodq5x9gb
  - alik@sun.com-20090805175009-g1od16i3t1xkw2qr
  - kostja@sun.com-20090805200643-j9i4fy7ii8ijho5c
  - alik@sun.com-20090807195303-j4fb5m4l1dgdahwo
  - alik@sun.com-20090808114848-3rkzr9kifrijzaqy
  - alik@sun.com-20090810041739-ugmx34h34uid8mox
  - alik@sun.com-20090810105306-rf43rfyzzblsy5e7
  - alik@sun.com-20090810123113-ccdjwai68b5woqdm
  - alik@sun.com-20090811080423-gb7pibec1znaydzy
  - alik@sun.com-20090811082130-5uckar1vx3kdsw7g
  - alik@sun.com-20090812202051-uqkfwwxxcjvo5ean

The following bugfixes are also backported within this patch:
  - Bug#34292: netdb.h missing in hostname.cc
  - Bug#39153: Failing to lookup a host name can lead to crash
    in current IPv6 implementation
  - Bug#38247: Server does not resolve connecting ip's
  - Bug#43006: main.skip_name_resolve fails on Windows in PB2
  - Bug#45606: ACL requires IPv4-mapped addresses to be used
  - Bug#45584: Host name cache does not work as a cache

1 files changed, 436 insertions, 157 deletions

diff --git a/sql/hostname.cc b/sql/hostname.cc
index b498c548e61..cf35e60061f 100644
--- a/sql/hostname.cc
+++ b/sql/hostname.cc
@@ -18,10 +18,10 @@
   @file
 
   @brief
-  Get hostname for an IP.
+  Get hostname for an IP address.
 
-    Hostnames are checked with reverse name lookup and
-    checked that they doesn't resemble an ip.
+  Hostnames are checked with reverse name lookup and checked that they
+  doesn't resemble an IP address.
 */
 
 #include "mysql_priv.h"
@@ -34,24 +34,54 @@ extern "C" {					// Because of SCO 3.2V4.2
 #ifdef HAVE_SYS_UN_H
 #include <sys/un.h>
 #endif
-#include <netdb.h>
 #include <sys/utsname.h>
 #endif // __WIN__
 #ifdef	__cplusplus
 }
 #endif
 
+/*
+  HOST_ENTRY_KEY_SIZE -- size of IP address string in the hash cache.
+*/
+
+#define HOST_ENTRY_KEY_SIZE INET6_ADDRSTRLEN
+
+/**
+  An entry in the hostname hash table cache.
+
+  Host name cache does two things:
+    - caches host names to save DNS look ups;
+    - counts connect errors from IP.
 
-class host_entry :public hash_filo_element
+  Host name can be NULL (that means DNS look up failed), but connect errors
+  still are counted.
+*/
+
+class Host_entry :public hash_filo_element
 {
 public:
-  char	 ip[sizeof(((struct in_addr *) 0)->s_addr)];
-  uint	 errors;
-  char	 *hostname;
+  /**
+    Client IP address. This is the key used with the hash table.
+
+    The client IP address is always expressed in IPv6, even when the
+    network IPv6 stack is not present.
+
+    This IP address is never used to connect to a socket.
+  */
+  char ip_key[HOST_ENTRY_KEY_SIZE];
+
+  /**
+    Number of errors during handshake phase from the IP address.
+  */
+  uint connect_errors;
+
+  /**
+    One of the host names for the IP address. May be NULL.
+  */
+  const char *hostname;
 };
 
 static hash_filo *hostname_cache;
-static pthread_mutex_t LOCK_hostname;
 
 void hostname_cache_refresh()
 {
@@ -60,219 +90,468 @@ void hostname_cache_refresh()
 
 bool hostname_cache_init()
 {
-  host_entry tmp;
-  uint offset= (uint) ((char*) (&tmp.ip) - (char*) &tmp);
-  if (!(hostname_cache=new hash_filo(HOST_CACHE_SIZE, offset,
-				     sizeof(struct in_addr),NULL,
-				     (my_hash_free_key) free,
-				     &my_charset_bin)))
+  Host_entry tmp;
+  uint key_offset= (uint) ((char*) (&tmp.ip_key) - (char*) &tmp);
+
+  if (!(hostname_cache= new hash_filo(HOST_CACHE_SIZE,
+                                      key_offset, HOST_ENTRY_KEY_SIZE,
+                                      NULL, (my_hash_free_key) free,
+                                      &my_charset_bin)))
     return 1;
+
   hostname_cache->clear();
-  (void) pthread_mutex_init(&LOCK_hostname,MY_MUTEX_INIT_SLOW);
+
   return 0;
 }
 
 void hostname_cache_free()
 {
-  if (hostname_cache)
-  {
-    (void) pthread_mutex_destroy(&LOCK_hostname);
-    delete hostname_cache;
-    hostname_cache= 0;
-  }
+  delete hostname_cache;
+  hostname_cache= NULL;
 }
 
+static void prepare_hostname_cache_key(const char *ip_string,
+                                       char *ip_key)
+{
+  int ip_string_length= strlen(ip_string);
+  DBUG_ASSERT(ip_string_length < HOST_ENTRY_KEY_SIZE);
 
-static void add_hostname(struct in_addr *in,const char *name)
+  memset(ip_key, 0, HOST_ENTRY_KEY_SIZE);
+  memcpy_fixed(ip_key, ip_string, ip_string_length);
+}
+
+static inline Host_entry *hostname_cache_search(const char *ip_key)
 {
-  if (!(specialflag & SPECIAL_NO_HOST_CACHE))
+  return (Host_entry *) hostname_cache->search((uchar *) ip_key, 0);
+}
+
+static bool add_hostname_impl(const char *ip_key, const char *hostname)
+{
+  if (hostname_cache_search(ip_key))
+    return FALSE;
+
+  size_t hostname_size= hostname ? strlen(hostname) + 1 : 0;
+
+  Host_entry *entry= (Host_entry *) malloc(sizeof (Host_entry) + hostname_size);
+
+  if (!entry)
+    return TRUE;
+
+  char *hostname_copy;
+
+  memcpy_fixed(&entry->ip_key, ip_key, HOST_ENTRY_KEY_SIZE);
+
+  if (hostname_size)
   {
-    pthread_mutex_lock(&hostname_cache->lock);
-    host_entry *entry;
-    if (!(entry=(host_entry*) hostname_cache->search((uchar*) &in->s_addr,0)))
-    {
-      uint length=name ? (uint) strlen(name) : 0;
+    hostname_copy= (char *) (entry + 1);
+    memcpy(hostname_copy, hostname, hostname_size);
 
-      if ((entry=(host_entry*) malloc(sizeof(host_entry)+length+1)))
-      {
-	char *new_name;
-	memcpy_fixed(&entry->ip, &in->s_addr, sizeof(in->s_addr));
-	if (length)
-	  memcpy(new_name= (char *) (entry+1), name, length+1);
-	else
-	  new_name=0;
-	entry->hostname=new_name;
-	entry->errors=0;
-	(void) hostname_cache->add(entry);
-      }
-    }
-    pthread_mutex_unlock(&hostname_cache->lock);
+    DBUG_PRINT("info", ("Adding '%s' -> '%s' to the hostname cache...'",
+                        (const char *) ip_key,
+                        (const char *) hostname_copy));
   }
-}
+  else
+  {
+    hostname_copy= NULL;
+
+    DBUG_PRINT("info", ("Adding '%s' -> NULL to the hostname cache...'",
+                        (const char *) ip_key));
+  }
+
+  entry->hostname= hostname_copy;
+  entry->connect_errors= 0;
 
+  return hostname_cache->add(entry);
+}
 
-inline void add_wrong_ip(struct in_addr *in)
+static bool add_hostname(const char *ip_key, const char *hostname)
 {
-  add_hostname(in,NullS);
+  if (specialflag & SPECIAL_NO_HOST_CACHE)
+    return FALSE;
+
+  pthread_mutex_lock(&hostname_cache->lock);
+
+  bool err_status= add_hostname_impl(ip_key, hostname);
+
+  pthread_mutex_unlock(&hostname_cache->lock);
+
+  return err_status;
 }
 
-void inc_host_errors(struct in_addr *in)
+void inc_host_errors(const char *ip_string)
 {
+  if (!ip_string)
+    return;
+
+  char ip_key[HOST_ENTRY_KEY_SIZE];
+  prepare_hostname_cache_key(ip_string, ip_key);
+
   pthread_mutex_lock(&hostname_cache->lock);
-  host_entry *entry;
-  if ((entry=(host_entry*) hostname_cache->search((uchar*) &in->s_addr,0)))
-    entry->errors++;
+
+  Host_entry *entry= hostname_cache_search(ip_key);
+
+  if (entry)
+    entry->connect_errors++;
+
   pthread_mutex_unlock(&hostname_cache->lock);
 }
 
-void reset_host_errors(struct in_addr *in)
+
+void reset_host_errors(const char *ip_string)
 {
+  if (!ip_string)
+    return;
+
+  char ip_key[HOST_ENTRY_KEY_SIZE];
+  prepare_hostname_cache_key(ip_string, ip_key);
+
   pthread_mutex_lock(&hostname_cache->lock);
-  host_entry *entry;
-  if ((entry=(host_entry*) hostname_cache->search((uchar*) &in->s_addr,0)))
-    entry->errors=0;
+
+  Host_entry *entry= hostname_cache_search(ip_key);
+
+  if (entry)
+    entry->connect_errors= 0;
+
   pthread_mutex_unlock(&hostname_cache->lock);
 }
 
-/* Deal with systems that don't defined INADDR_LOOPBACK */
-#ifndef INADDR_LOOPBACK
-#define INADDR_LOOPBACK 0x7f000001UL
-#endif
 
-char * ip_to_hostname(struct in_addr *in, uint *errors)
+static inline bool is_ip_loopback(const struct sockaddr *ip)
+{
+  switch (ip->sa_family) {
+  case AF_INET:
+    {
+      /* Check for IPv4 127.0.0.1. */
+      struct in_addr *ip4= &((struct sockaddr_in *) ip)->sin_addr;
+      return ntohl(ip4->s_addr) == INADDR_LOOPBACK;
+    }
+
+#ifdef HAVE_IPV6
+  case AF_INET6:
+    {
+      /* Check for IPv6 ::1. */
+      struct in6_addr *ip6= &((struct sockaddr_in6 *) ip)->sin6_addr;
+      return IN6_IS_ADDR_LOOPBACK(ip6);
+    }
+#endif /* HAVE_IPV6 */
+
+  default:
+    return FALSE;
+  }
+}
+
+static inline bool is_hostname_valid(const char *hostname)
 {
-  uint i;
-  host_entry *entry;
+  /*
+    A hostname is invalid if it starts with a number followed by a dot
+    (IPv4 address).
+  */
+
+  if (!my_isdigit(&my_charset_latin1, hostname[0]))
+    return TRUE;
+
+  const char *p= hostname + 1;
+
+  while (my_isdigit(&my_charset_latin1, *p))
+    ++p;
+
+  return *p != '.';
+}
+
+/**
+  Resolve IP-address to host name.
+
+  This function does the following things:
+    - resolves IP-address;
+    - employs Forward Confirmed Reverse DNS technique to validate IP-address;
+    - returns host name if IP-address is validated;
+    - set value to out-variable connect_errors -- this variable represents the
+      number of connection errors from the specified IP-address.
+
+  NOTE: connect_errors are counted (are supported) only for the clients
+  where IP-address can be resolved and FCrDNS check is passed.
+
+  @param [in]  ip_storage IP address (sockaddr). Must be set.
+  @param [in]  ip_string  IP address (string). Must be set.
+  @param [out] hostname
+  @param [out] connect_errors
+
+  @return Error status
+  @retval FALSE Success
+  @retval TRUE Error
+
+  The function does not set/report MySQL server error in case of failure.
+  It's caller's responsibility to handle failures of this function
+  properly.
+*/
+
+bool ip_to_hostname(struct sockaddr_storage *ip_storage,
+                    const char *ip_string,
+                    char **hostname, uint *connect_errors)
+{
+  const struct sockaddr *ip= (const sockaddr *) ip_storage;
+  int err_code;
+  bool err_status;
+
   DBUG_ENTER("ip_to_hostname");
-  *errors=0;
+  DBUG_PRINT("info", ("IP address: '%s'; family: %d.",
+                      (const char *) ip_string,
+                      (int) ip->sa_family));
 
-  /* We always treat the loopback address as "localhost". */
-  if (in->s_addr == htonl(INADDR_LOOPBACK))   // is expanded inline by gcc
-    DBUG_RETURN((char *)my_localhost);
+  /* Check if we have loopback address (127.0.0.1 or ::1). */
+
+  if (is_ip_loopback(ip))
+  {
+    DBUG_PRINT("info", ("Loopback address detected."));
+
+    *connect_errors= 0; /* Do not count connect errors from localhost. */
+    *hostname= (char *) my_localhost;
+
+    DBUG_RETURN(FALSE);
+  }
+
+  /* Prepare host name cache key. */
+
+  char ip_key[HOST_ENTRY_KEY_SIZE];
+  prepare_hostname_cache_key(ip_string, ip_key);
+
+  /* Check first if we have host name in the cache. */
 
-  /* Check first if we have name in cache */
   if (!(specialflag & SPECIAL_NO_HOST_CACHE))
   {
     pthread_mutex_lock(&hostname_cache->lock);
-    if ((entry=(host_entry*) hostname_cache->search((uchar*) &in->s_addr,0)))
+
+    Host_entry *entry= hostname_cache_search(ip_key);
+
+    if (entry)
     {
-      char *name;
-      if (!entry->hostname)
-	name=0;					// Don't allow connection
-      else
-	name=my_strdup(entry->hostname,MYF(0));
-      *errors= entry->errors;
+      *connect_errors= entry->connect_errors;
+      *hostname= NULL;
+
+      if (entry->hostname)
+        *hostname= my_strdup(entry->hostname, MYF(0));
+
+      DBUG_PRINT("info",("IP (%s) has been found in the cache. "
+                         "Hostname: '%s'; connect_errors: %d",
+                         (const char *) ip_key,
+                         (const char *) (*hostname? *hostname : "null"),
+                         (int) *connect_errors));
+
       pthread_mutex_unlock(&hostname_cache->lock);
-      DBUG_RETURN(name);
+
+      DBUG_RETURN(FALSE);
     }
+
     pthread_mutex_unlock(&hostname_cache->lock);
   }
 
-  struct hostent *hp, *check;
-  char *name;
-  LINT_INIT(check);
-#if defined(HAVE_GETHOSTBYADDR_R) && defined(HAVE_SOLARIS_STYLE_GETHOST)
-  char buff[GETHOSTBYADDR_BUFF_SIZE],buff2[GETHOSTBYNAME_BUFF_SIZE];
-  int tmp_errno;
-  struct hostent tmp_hostent, tmp_hostent2;
-#ifdef HAVE_purify
-  bzero(buff,sizeof(buff));		// Bug in purify
-#endif
-  if (!(hp=gethostbyaddr_r((char*) in,sizeof(*in),
-			   AF_INET,
-			   &tmp_hostent,buff,sizeof(buff),&tmp_errno)))
-  {
-    DBUG_PRINT("error",("gethostbyaddr_r returned %d",tmp_errno));
-    return 0;
-  }
-  if (!(check=my_gethostbyname_r(hp->h_name,&tmp_hostent2,buff2,sizeof(buff2),
-				 &tmp_errno)))
+  /*
+    Resolve host name. Return an error if a host name can not be resolved
+    (instead of returning the numeric form of the host name).
+  */
+
+  char hostname_buffer[NI_MAXHOST];
+
+  DBUG_PRINT("info", ("Resolving '%s'...", (const char *) ip_key));
+
+  err_code= vio_getnameinfo(ip, hostname_buffer, NI_MAXHOST, NULL, 0,
+                            NI_NAMEREQD);
+
+  if (err_code == EAI_NONAME)
   {
-    DBUG_PRINT("error",("gethostbyname_r returned %d",tmp_errno));
     /*
-      Don't cache responses when the DSN server is down, as otherwise
-      transient DNS failure may leave any number of clients (those
-      that attempted to connect during the outage) unable to connect
-      indefinitely.
+      There is no reverse address mapping for the IP address. A host name
+      can not be resolved.
     */
-    if (tmp_errno == HOST_NOT_FOUND || tmp_errno == NO_DATA)
-      add_wrong_ip(in);
-    my_gethostbyname_r_free();
-    DBUG_RETURN(0);
-  }
-  if (!hp->h_name[0])
-  {
-    DBUG_PRINT("error",("Got an empty hostname"));
-    add_wrong_ip(in);
-    my_gethostbyname_r_free();
-    DBUG_RETURN(0);				// Don't allow empty hostnames
-  }
-  if (!(name=my_strdup(hp->h_name,MYF(0))))
-  {
-    my_gethostbyname_r_free();
-    DBUG_RETURN(0);				// out of memory
+
+    DBUG_PRINT("error", ("IP address '%s' could not be resolved: "
+                         "no reverse address mapping.",
+                         (const char *) ip_key));
+
+    sql_print_warning("IP address '%s' could not be resolved: "
+                      "no reverse address mapping.",
+                      (const char *) ip_key);
+
+    err_status= add_hostname(ip_key, NULL);
+
+    *hostname= NULL;
+    *connect_errors= 0; /* New IP added to the cache. */
+
+    DBUG_RETURN(err_status);
   }
-  my_gethostbyname_r_free();
-#else
-  pthread_mutex_lock(&LOCK_hostname);
-  if (!(hp=gethostbyaddr((char*) in,sizeof(*in), AF_INET)))
+  else if (err_code)
   {
-    pthread_mutex_unlock(&LOCK_hostname);
-    DBUG_PRINT("error",("gethostbyaddr returned %d",errno));
+    DBUG_PRINT("error", ("IP address '%s' could not be resolved: "
+                         "getnameinfo() returned %d.",
+                         (const char *) ip_key,
+                         (int) err_code));
+
+    sql_print_warning("IP address '%s' could not be resolved: "
+                      "getnameinfo() returned error (code: %d).",
+                      (const char *) ip_key,
+                      (int) err_code);
 
-    if (errno == HOST_NOT_FOUND || errno == NO_DATA)
-      goto add_wrong_ip_and_return;
-    /* Failure, don't cache responce */
-    DBUG_RETURN(0);
+    DBUG_RETURN(TRUE);
   }
-  if (!hp->h_name[0])				// Don't allow empty hostnames
+
+  DBUG_PRINT("info", ("IP '%s' resolved to '%s'.",
+                      (const char *) ip_key,
+                      (const char *) hostname_buffer));
+
+  /*
+    Validate hostname: the server does not accept host names, which
+    resemble IP addresses.
+
+    The thing is that theoretically, a host name can be in a form of IPv4
+    address (123.example.org, or 1.2 or even 1.2.3.4). We have to deny such
+    host names because ACL-systems is not designed to work with them.
+
+    For example, it is possible to specify a host name mask (like
+    192.168.1.%) for an ACL rule. Then, if IPv4-like hostnames are allowed,
+    there is a security hole: instead of allowing access for
+    192.168.1.0/255 network (which was assumed by the user), the access
+    will be allowed for host names like 192.168.1.example.org.
+  */
+
+  if (!is_hostname_valid(hostname_buffer))
   {
-    pthread_mutex_unlock(&LOCK_hostname);
-    DBUG_PRINT("error",("Got an empty hostname"));
-    goto add_wrong_ip_and_return;
+    DBUG_PRINT("error", ("IP address '%s' has been resolved "
+                         "to the host name '%s', which resembles "
+                         "IPv4-address itself.",
+                         (const char *) ip_key,
+                         (const char *) hostname_buffer));
+
+    sql_print_warning("IP address '%s' has been resolved "
+                      "to the host name '%s', which resembles "
+                      "IPv4-address itself.",
+                      (const char *) ip_key,
+                      (const char *) hostname_buffer);
+
+    err_status= add_hostname(ip_key, NULL);
+
+    *hostname= NULL;
+    *connect_errors= 0; /* New IP added to the cache. */
+
+    DBUG_RETURN(err_status);
   }
-  if (!(name=my_strdup(hp->h_name,MYF(0))))
+
+  /* Get IP-addresses for the resolved host name (FCrDNS technique). */
+
+  struct addrinfo hints;
+  struct addrinfo *addr_info_list;
+
+  memset(&hints, 0, sizeof (struct addrinfo));
+  hints.ai_flags= AI_PASSIVE;
+  hints.ai_socktype= SOCK_STREAM;
+  hints.ai_family= AF_UNSPEC;
+
+  DBUG_PRINT("info", ("Getting IP addresses for hostname '%s'...",
+                      (const char *) hostname_buffer));
+
+  err_code= getaddrinfo(hostname_buffer, NULL, &hints, &addr_info_list);
+
+  if (err_code == EAI_NONAME)
   {
-    pthread_mutex_unlock(&LOCK_hostname);
-    DBUG_RETURN(0);				// out of memory
+    /*
+      Don't cache responses when the DNS server is down, as otherwise
+      transient DNS failure may leave any number of clients (those
+      that attempted to connect during the outage) unable to connect
+      indefinitely.
+    */
+
+    err_status= add_hostname(ip_key, NULL);
+
+    *hostname= NULL;
+    *connect_errors= 0; /* New IP added to the cache. */
+
+    DBUG_RETURN(err_status);
   }
-  check=gethostbyname(name);
-  pthread_mutex_unlock(&LOCK_hostname);
-  if (!check)
+  else if (err_code)
   {
-    DBUG_PRINT("error",("gethostbyname returned %d",errno));
-    my_free(name,MYF(0));
-    DBUG_RETURN(0);
+    DBUG_PRINT("error", ("getaddrinfo() failed with error code %d.", err_code));
+    DBUG_RETURN(TRUE);
   }
-#endif
 
-  /* Don't accept hostnames that starts with digits because they may be
-     false ip:s */
-  if (my_isdigit(&my_charset_latin1,name[0]))
+  /* Check that getaddrinfo() returned the used IP (FCrDNS technique). */
+
+  DBUG_PRINT("info", ("The following IP addresses found for '%s':",
+                      (const char *) hostname_buffer));
+
+  for (struct addrinfo *addr_info= addr_info_list;
+       addr_info; addr_info= addr_info->ai_next)
   {
-    char *pos;
-    for (pos= name+1 ; my_isdigit(&my_charset_latin1,*pos); pos++) ;
-    if (*pos == '.')
+    char ip_buffer[HOST_ENTRY_KEY_SIZE];
+
+    {
+      err_status=
+        vio_get_normalized_ip_string(addr_info->ai_addr, addr_info->ai_addrlen,
+                                     ip_buffer, sizeof (ip_buffer));
+      DBUG_ASSERT(!err_status);
+    }
+
+    DBUG_PRINT("info", ("  - '%s'", (const char *) ip_buffer));
+
+    if (strcmp(ip_key, ip_buffer) == 0)
     {
-      DBUG_PRINT("error",("mysqld doesn't accept hostnames that starts with a number followed by a '.'"));
-      my_free(name,MYF(0));
-      goto add_wrong_ip_and_return;
+      /* Copy host name string to be stored in the cache. */
+
+      *hostname= my_strdup(hostname_buffer, MYF(0));
+
+      if (!*hostname)
+      {
+        DBUG_PRINT("error", ("Out of memory."));
+
+        freeaddrinfo(addr_info_list);
+        DBUG_RETURN(TRUE);
+      }
+
+      break;
     }
   }
 
-  /* Check that 'gethostbyname' returned the used ip */
-  for (i=0; check->h_addr_list[i]; i++)
+  /* Log resolved IP-addresses if no match was found. */
+
+  if (!*hostname)
   {
-    if (*(uint32*)(check->h_addr_list)[i] == in->s_addr)
+    sql_print_information("Hostname '%s' does not resolve to '%s'.",
+                          (const char *) hostname_buffer,
+                          (const char *) ip_key);
+    sql_print_information("Hostname '%s' has the following IP addresses:",
+                          (const char *) hostname_buffer);
+
+    for (struct addrinfo *addr_info= addr_info_list;
+         addr_info; addr_info= addr_info->ai_next)
     {
-      add_hostname(in,name);
-      DBUG_RETURN(name);
+      char ip_buffer[HOST_ENTRY_KEY_SIZE];
+
+      err_status=
+        vio_get_normalized_ip_string(addr_info->ai_addr, addr_info->ai_addrlen,
+                                     ip_buffer, sizeof (ip_buffer));
+      DBUG_ASSERT(!err_status);
+
+      sql_print_information(" - %s\n", (const char *) ip_buffer);
     }
   }
-  DBUG_PRINT("error",("Couldn't verify hostname with gethostbyname"));
-  my_free(name,MYF(0));
 
-add_wrong_ip_and_return:
-  add_wrong_ip(in);
-  DBUG_RETURN(0);
+  /* Free the result of getaddrinfo(). */
+
+  freeaddrinfo(addr_info_list);
+
+  /* Add an entry for the IP to the cache. */
+
+  if (*hostname)
+  {
+    err_status= add_hostname(ip_key, *hostname);
+    *connect_errors= 0;
+  }
+  else
+  {
+    DBUG_PRINT("error",("Couldn't verify hostname with getaddrinfo()."));
+
+    err_status= add_hostname(ip_key, NULL);
+    *hostname= NULL;
+    *connect_errors= 0;
+  }
+
+  DBUG_RETURN(err_status);
 }