Bug #59884: setting charset to 2048 crashes

The retrieval of a charset by number was not
doing bounds checking before accessing the internal 
character sets array.
Added checks for valid charset number.
Added asserts for valid charset number to some of 
the internal functions.
Removed one superfluous check for charset_number 0
(since the all_charsets_array[0] is set to 0 anyway) for 
uniformity.
Test suite added.

mysql-test/r/variables.result

@@ -1732,3 +1732,25 @@ set @@session.autocommit=t1_min(), @@session.autocommit=t1_max(),
 drop table t1;
 drop function t1_min;
 drop function t1_max;
+#
+# Bug #59884: setting charset to 2048 crashes
+#
+set session character_set_results = 2048;
+ERROR 42000: Unknown character set: '2048'
+set session character_set_client=2048;
+ERROR 42000: Unknown character set: '2048'
+set session character_set_connection=2048;
+ERROR 42000: Unknown character set: '2048'
+set session character_set_server=2048;
+ERROR 42000: Unknown character set: '2048'
+set session collation_server=2048;
+ERROR HY000: Unknown collation: '2048'
+set session character_set_filesystem=2048;
+ERROR 42000: Unknown character set: '2048'
+set session character_set_database=2048;
+ERROR 42000: Unknown character set: '2048'
+set session collation_connection=2048;
+ERROR HY000: Unknown collation: '2048'
+set session collation_database=2048;
+ERROR HY000: Unknown collation: '2048'
+End of 5.5 tests

mysql-test/t/variables.test

@@ -1476,3 +1476,29 @@ drop function t1_max;
 
 
 ###########################################################################
+
+
+--echo #
+--echo # Bug #59884: setting charset to 2048 crashes
+--echo #
+
+--error ER_UNKNOWN_CHARACTER_SET
+set session character_set_results = 2048;
+--error ER_UNKNOWN_CHARACTER_SET
+set session character_set_client=2048;
+--error ER_UNKNOWN_CHARACTER_SET
+set session character_set_connection=2048;
+--error ER_UNKNOWN_CHARACTER_SET
+set session character_set_server=2048;
+--error ER_UNKNOWN_COLLATION
+set session collation_server=2048;
+--error ER_UNKNOWN_CHARACTER_SET
+set session character_set_filesystem=2048;
+--error ER_UNKNOWN_CHARACTER_SET
+set session character_set_database=2048;
+--error ER_UNKNOWN_COLLATION
+set session collation_connection=2048;
+--error ER_UNKNOWN_COLLATION
+set session collation_database=2048;
+
+--echo End of 5.5 tests

mysys/charset.c

@@ -419,6 +419,7 @@ CHARSET_INFO *default_charset_info = &my_charset_latin1;
 
 void add_compiled_collation(CHARSET_INFO *cs)
 {
+  DBUG_ASSERT(cs->number < array_elements(all_charsets));
   all_charsets[cs->number]= cs;
   cs->state|= MY_CS_AVAILABLE;
 }
@@ -529,14 +530,17 @@ uint get_charset_number(const char *charset_name, uint cs_flags)
 
 const char *get_charset_name(uint charset_number)
 {
-  CHARSET_INFO *cs;
   my_pthread_once(&charsets_initialized, init_available_charsets);
 
-  cs=all_charsets[charset_number];
-  if (cs && (cs->number == charset_number) && cs->name )
-    return (char*) cs->name;
+  if (charset_number < array_elements(all_charsets))
+  {
+    CHARSET_INFO *cs= all_charsets[charset_number];
+
+    if (cs && (cs->number == charset_number) && cs->name)
+      return (char*) cs->name;
+  }
   
-  return (char*) "?";   /* this mimics find_type() */
+  return "?";   /* this mimics find_type() */
 }
 
 
@@ -545,6 +549,8 @@ static CHARSET_INFO *get_internal_charset(uint cs_number, myf flags)
   char  buf[FN_REFLEN];
   CHARSET_INFO *cs;
 
+  DBUG_ASSERT(cs_number < array_elements(all_charsets));
+
   if ((cs= all_charsets[cs_number]))
   {
     if (cs->state & MY_CS_READY)  /* if CS is already initialized */
@@ -589,8 +595,8 @@ CHARSET_INFO *get_charset(uint cs_number, myf flags)
     return default_charset_info;
 
   my_pthread_once(&charsets_initialized, init_available_charsets);
-  
-  if (!cs_number || cs_number > array_elements(all_charsets))
+ 
+  if (cs_number >= array_elements(all_charsets)) 
     return NULL;
   
   cs=get_internal_charset(cs_number, flags);