Bug #28477 innodb assertion and crash during alter table to add/drop partition.

The bug was repeated on MyISAM tables, so isn't InnoDB specific.
Reason of the bug is that partition-related members of TABLE_SHARE
wasn't properly updated after ALTER command. So if other thread doesn't
reread frm file, and just uses cached SHARE, it uses wrong data

sql/sql_table.cc

@@ -1329,6 +1329,7 @@ bool mysql_write_frm(ALTER_PARTITION_PARAM_TYPE *lpt, uint flags)
 
       if (part_info)
       {
+        TABLE_SHARE *share= lpt->table->s;
         if (!(part_syntax_buf= generate_partition_syntax(part_info,
                                                          &syntax_len,
                                                          TRUE, TRUE)))
@@ -1336,7 +1337,16 @@ bool mysql_write_frm(ALTER_PARTITION_PARAM_TYPE *lpt, uint flags)
           DBUG_RETURN(TRUE);
         }
         part_info->part_info_string= part_syntax_buf;
-        part_info->part_info_len= syntax_len;
+        share->partition_info_len= part_info->part_info_len= syntax_len;
+        if (share->partition_info_buffer_size < syntax_len + 1)
+        {
+          share->partition_info_buffer_size= syntax_len+1;
+          if (!(share->partition_info=
+                  alloc_root(&share->mem_root, syntax_len+1)))
+            DBUG_RETURN(TRUE);
+
+        }
+        memcpy((char*) share->partition_info, part_syntax_buf, syntax_len + 1);
       }
     }
 #endif

sql/table.cc

@@ -720,7 +720,8 @@ static int open_binary_frm(THD *thd, TABLE_SHARE *share, uchar *head,
     {
       uint32 partition_info_len = uint4korr(next_chunk);
 #ifdef WITH_PARTITION_STORAGE_ENGINE
-      if ((share->partition_info_len= partition_info_len))
+      if ((share->partition_info_buffer_size=
+             share->partition_info_len= partition_info_len))
       {
         if (!(share->partition_info=
               memdup_root(&share->mem_root, next_chunk + 4,

sql/table.h

@@ -243,6 +243,7 @@ typedef struct st_table_share
   bool auto_partitioned;
   const char *partition_info;
   uint  partition_info_len;
+  uint  partition_info_buffer_size;
   const char *part_state;
   uint part_state_len;
   handlerton *default_part_db_type;