Out-of-bounds string access in create_schema_table()

CURRENT_TEST: innodb.innodb_bug12400341

mysqltest: At line 64: query 'select count(*) from information_schema.processlist' failed: 2013: Lost connection to MySQL server during query

this one is something definitely outside InnoDB:

==32392==ERROR: AddressSanitizer: global-buffer-overflow on address 0x0000018b90ac at pc 0x00000176c633 bp 0x7f8ceda19960 sp 0x7f8ceda19958

READ of size 1 at 0x0000018b90ac thread T55

   #0 0x176c632 in my_string_repertoire_8bit /home/marko/mariadb/server/strings/ctype.c:829:18

   #1 0x176c6bf in my_string_metadata_get /home/marko/mariadb/server/strings/ctype.c:895:27

   #2 0x6f6312 in Item_string::Item_string(THD*, char const*, unsigned int, charset_info_st const*, Derivation) /home/marko/mariadb/server/sql/item.h:2978:37

   #3 0x6f61ee in Item_partition_func_safe_string::Item_partition_func_safe_string(THD*, char const*, unsigned int, charset_info_st const*) /home/marko/mariadb/server/sql/item.h:3183:5

   #4 0x94d293 in Item_blob::Item_blob(THD*, char const*, unsigned int) /home/marko/mariadb/server/sql/item.h:3209:5

   #5 0x93761f in create_schema_table(THD*, TABLE_LIST*) /home/marko/mariadb/server/sql/sql_show.cc:7557:13

   #6 0x93955c in mysql_schema_table(THD*, LEX*, TABLE_LIST*) /home/marko/mariadb/server/sql/sql_show.cc:7806:16

…

0x0000018b90ac is located 52 bytes to the left of global variable '<string literal>' defined in '/home/marko/mariadb/server/sql/sql_show.cc:8837:4' (0x18b90e0) of size 12

 '<string literal>' is ascii string 'Info_binary'

0x0000018b90ac is located 0 bytes to the right of global variable '<string literal>' defined in '/home/marko/mariadb/server/sql/sql_show.cc:8836:4' (0x18b90a0) of size 12

 '<string literal>' is ascii string 'INFO_BINARY'

diff --git a/sql/sql_show.cc b/sql/sql_show.cc

index ae3874506dd..c3610da05af 100644

--- a/sql/sql_show.cc

+++ b/sql/sql_show.cc

@@ -7555,7 +7555,8 @@ TABLE *create_schema_table(THD *thd, TABLE_LIST *table_list)

     case MYSQL_TYPE_BLOB:

       if (!(item= new (mem_root)

             Item_blob(thd, fields_info->field_name,

-                      fields_info->field_length)))

+                      std::min(unsigned (strlen(fields_info->field_name)),

+                               fields_info->field_length))))

       {

         DBUG_RETURN(0);

       }