Bug #20181776 :- ACCESS CONTROL DOESN'T MATCH MOST SPECIFIC

                 HOST WHEN IT CONTAINS WILDCARD

Description :- Incorrect access privileges are provided to a
user due to wrong sorting of users when wildcard characters
is present in the hostname.

Analysis :- Function "get_sorts()" is used to sort the
strings of user name, hostname, database name. It is used
to arrange the users in the access privilege matching order.
When a user connects, it checks in the sorted user access
privilege list and finds a corresponding matching entry for
the user. Algorithm used in "get_sort()" sorts the strings
inappropriately. As a result, when a user connects to the
server, it is mapped to incorrect user access privileges.
Algorithm used in "get_sort()" counts the number of
characters before the first occurence of any one of the
wildcard characters (single-wildcard character '_' or
multi-wildcard character '%') and sorts in that order.
As a result of inconnect sorting it treats hostname "%" and
"%.mysql.com" as equally-specific values and therefore
the order is indeterminate.

Fix:- The "get_sort()" algorithm has been modified to treat
"%" seperately. Now "get_sort()" returns a number which, if
sorted in descending order, puts strings in the following
order:-
* strings with no wildcards
* strings containg wildcards and non-wildcard characters
* single muilt-wildcard character('%')
* empty string.

Author: Arun Kuruvila

sql/sql_acl.cc

@@ -801,7 +801,8 @@ static ulong get_access(TABLE *form, uint fieldnr, uint *next_field)
 /*
   Return a number which, if sorted 'desc', puts strings in this order:
     no wildcards
-    wildcards
+    strings containg wildcards and non-wildcard characters
+    single muilt-wildcard character('%')
     empty string
 */
 
@@ -818,7 +819,16 @@ static ulong get_sort(uint count,...)
   {
     char *start, *str= va_arg(args,char*);
     uint chars= 0;
-    uint wild_pos= 0;           /* first wildcard position */
+    uint wild_pos= 0;
+
+    /*
+      wild_pos
+        0                            if string is empty
+        1                            if string is a single muilt-wildcard
+                                     character('%')
+        first wildcard position + 1  if string containg wildcards and
+                                     non-wildcard characters
+    */
 
     if ((start= str))
     {
@@ -829,6 +839,8 @@ static ulong get_sort(uint count,...)
         else if (*str == wild_many || *str == wild_one)
         {
           wild_pos= (uint) (str - start) + 1;
+          if (!(wild_pos == 1 && *str == wild_many && *(++str) == '\0'))
+            wild_pos++;
           break;
         }
         chars= 128;                             // Marker that chars existed