1. don't crash on failing to load a plugin with newer MYSQL_PLUGIN_INTERFACE_VERSION

2. don't copy st_mysql_plugin structure unnecessary (sizeof hasn't changed)

sql/sql_plugin.cc

@@ -333,7 +333,7 @@ static inline void free_plugin_mem(struct st_plugin_dl *p)
     dlclose(p->handle);
 #endif
   my_free(p->dl.str, MYF(MY_ALLOW_ZERO_PTR));
-  if (p->version != MYSQL_PLUGIN_INTERFACE_VERSION)
+  if (p->allocated)
     my_free((uchar*)p->plugins, MYF(MY_ALLOW_ZERO_PTR));
 }
 
@@ -454,13 +454,15 @@ static st_plugin_dl *plugin_dl_add(const LEX_STRING *dl, int report)
 #endif
     }
 
+    if (sizeof_st_plugin != sizeof(st_mysql_plugin))
+    {
       for (i= 0;
            ((struct st_mysql_plugin *)(ptr+i*sizeof_st_plugin))->info;
            i++)
         /* no op */;
 
       cur= (struct st_mysql_plugin*)
-          my_malloc(i*sizeof(struct st_mysql_plugin), MYF(MY_ZEROFILL|MY_WME));
+            my_malloc((i+1)*sizeof(struct st_mysql_plugin), MYF(MY_ZEROFILL|MY_WME));
       if (!cur)
       {
         free_plugin_mem(&plugin_dl);
@@ -481,6 +483,8 @@ static st_plugin_dl *plugin_dl_add(const LEX_STRING *dl, int report)
         memcpy(cur+i, old, min(sizeof(cur[i]), sizeof_st_plugin));
 
       sym= cur;
+      plugin_dl.allocated= true;
+    }
   }
   plugin_dl.plugins= (struct st_mysql_plugin *)sym;
 

sql/sql_plugin.h

@@ -64,6 +64,7 @@ struct st_plugin_dl
   void *handle;
   struct st_mysql_plugin *plugins;
   int    version;
+  bool   allocated;
   uint ref_count;            /* number of plugins loaded from the library */
 };