Better bug fix for #5569: "Incorrect "Access Denied" error with SAME login DIFFERENT host"

This fixes also the reverse lookup bug introduced by the previous patch

mysql-test/t/group_by.test

@@ -455,4 +455,3 @@ select min(a) is null from t1;
 select min(a) is null or null from t1;
 select 1 and min(a) is null from t1;
 drop table t1;
-

sql/sql_parse.cc

@@ -504,8 +504,6 @@ check_connections(THD *thd)
   DBUG_PRINT("info",("New connection received on %s",
 			vio_description(net->vio)));
 
-  vio_in_addr(net->vio,&thd->remote.sin_addr);
-
   if (!thd->host)                           // If TCP/IP connection
   {
     char ip[30];
@@ -515,6 +513,7 @@ check_connections(THD *thd)
     if (!(thd->ip = my_strdup(ip,MYF(0))))
       return (ER_OUT_OF_RESOURCES);
     thd->host_or_ip=thd->ip;
+    vio_in_addr(net->vio, &thd->remote.sin_addr);
 #if !defined(HAVE_SYS_UN_H) || defined(HAVE_mit_thread)
     /* Fast local hostname resolve for Win32 */
     if (!strcmp(thd->ip,"127.0.0.1"))
@@ -524,6 +523,7 @@ check_connections(THD *thd)
     }
     else
 #endif
+    {
       if (!(specialflag & SPECIAL_NO_RESOLVE))
       {
         thd->host=ip_to_hostname(&thd->remote.sin_addr,&connect_errors);
@@ -536,6 +536,7 @@ check_connections(THD *thd)
         if (connect_errors > max_connect_errors)
           return(ER_HOST_IS_BLOCKED);
       }
+    }
     DBUG_PRINT("info",("Host: %s  ip: %s",
 		       thd->host ? thd->host : "unknown host",
 		       thd->ip ? thd->ip : "unknown ip"));
@@ -547,6 +548,8 @@ check_connections(THD *thd)
     DBUG_PRINT("info",("Host: %s",thd->host));
     thd->host_or_ip= thd->host;
     thd->ip= 0;
+    /* Reset sin_addr */
+    bzero((char*) &thd->remote, sizeof(thd->remote));
   }
   vio_keepalive(net->vio, TRUE);
 

vio/viosocket.c

@@ -291,6 +291,18 @@ my_bool vio_peer_addr(Vio * vio, char *buf, uint16 *port)
 }
 
 
+/*
+  Get in_addr for a TCP/IP connection
+
+  SYNOPSIS
+    vio_in_addr()
+    vio		vio handle
+    in		put in_addr here
+
+  NOTES
+    one must call vio_peer_addr() before calling this one
+*/
+
 void vio_in_addr(Vio *vio, struct in_addr *in)
 {
   DBUG_ENTER("vio_in_addr");