Patch for Bug#12374486 - SEVERE MEMORY LEAK IN PREPARED STATEMENTS

THAT CALL STORED PROCEDURES.

The bug was introduced by WL#4435. The problem was that if a stored
procedure generated a few result sets with different set of columns,
a new memory would be allocated after every EXECUTE for every
result set.

The fix is to introduce a new memory root in scope of MYSQL_STMT,
and to store result-set metadata in that memory root.

include/mysql.h

@@ -573,6 +573,8 @@ typedef struct st_mysql_bind
 } MYSQL_BIND;
 
 
+struct st_mysql_stmt_extension;
+
 /* statement handler */
 typedef struct st_mysql_stmt
 {
@@ -618,7 +620,7 @@ typedef struct st_mysql_stmt
     metadata fields when doing mysql_stmt_store_result.
   */
   my_bool       update_max_length;     
-  void *extension;
+  struct st_mysql_stmt_extension *extension;
 } MYSQL_STMT;
 
 enum enum_stmt_attr_type

include/mysql.h.pp

@@ -512,6 +512,7 @@ typedef struct st_mysql_bind
   my_bool is_null_value;
   void *extension;
 } MYSQL_BIND;
+struct st_mysql_stmt_extension;
 typedef struct st_mysql_stmt
 {
   MEM_ROOT mem_root;
@@ -541,7 +542,7 @@ typedef struct st_mysql_stmt
   unsigned char bind_result_done;
   my_bool unbuffered_fetch_cancelled;
   my_bool update_max_length;
-  void *extension;
+  struct st_mysql_stmt_extension *extension;
 } MYSQL_STMT;
 enum enum_stmt_attr_type
 {

libmysql/libmysql.c

@@ -94,6 +94,11 @@ sig_handler my_pipe_sig_handler(int sig);
 static my_bool mysql_client_init= 0;
 static my_bool org_my_init_done= 0;
 
+typedef struct st_mysql_stmt_extension
+{
+  MEM_ROOT fields_mem_root;
+} MYSQL_STMT_EXT;
+
 
 /*
   Initialize the MySQL client library
@@ -1480,11 +1485,16 @@ mysql_stmt_init(MYSQL *mysql)
   MYSQL_STMT *stmt;
   DBUG_ENTER("mysql_stmt_init");
 
-  if (!(stmt= (MYSQL_STMT *) my_malloc(sizeof(MYSQL_STMT),
+  if (!(stmt=
+          (MYSQL_STMT *) my_malloc(sizeof (MYSQL_STMT),
+                                   MYF(MY_WME | MY_ZEROFILL))) ||
+      !(stmt->extension=
+          (MYSQL_STMT_EXT *) my_malloc(sizeof (MYSQL_STMT_EXT),
                                        MYF(MY_WME | MY_ZEROFILL))))
   {
     set_mysql_error(mysql, CR_OUT_OF_MEMORY, unknown_sqlstate);
-    DBUG_RETURN(0);
+    my_free(stmt);
+    DBUG_RETURN(NULL);
   }
 
   init_alloc_root(&stmt->mem_root, 2048, 2048);
@@ -1499,6 +1509,8 @@ mysql_stmt_init(MYSQL *mysql)
   strmov(stmt->sqlstate, not_error_sqlstate);
   /* The rest of statement members was bzeroed inside malloc */
 
+  init_alloc_root(&stmt->extension->fields_mem_root, 2048, 0);
+
   DBUG_RETURN(stmt);
 }
 
@@ -1571,6 +1583,7 @@ mysql_stmt_prepare(MYSQL_STMT *stmt, const char *query, ulong length)
     stmt->bind_param_done= stmt->bind_result_done= FALSE;
     stmt->param_count= stmt->field_count= 0;
     free_root(&stmt->mem_root, MYF(MY_KEEP_PREALLOC));
+    free_root(&stmt->extension->fields_mem_root, MYF(0));
 
     int4store(buff, stmt->stmt_id);
 
@@ -1631,21 +1644,21 @@ mysql_stmt_prepare(MYSQL_STMT *stmt, const char *query, ulong length)
 static void alloc_stmt_fields(MYSQL_STMT *stmt)
 {
   MYSQL_FIELD *fields, *field, *end;
-  MEM_ROOT *alloc= &stmt->mem_root;
+  MEM_ROOT *fields_mem_root= &stmt->extension->fields_mem_root;
   MYSQL *mysql= stmt->mysql;
 
-  DBUG_ASSERT(mysql->field_count);
+  DBUG_ASSERT(stmt->field_count);
 
-  stmt->field_count= mysql->field_count;
+  free_root(fields_mem_root, MYF(0));
 
   /*
     Get the field information for non-select statements
     like SHOW and DESCRIBE commands
   */
-  if (!(stmt->fields= (MYSQL_FIELD *) alloc_root(alloc,
+  if (!(stmt->fields= (MYSQL_FIELD *) alloc_root(fields_mem_root,
 						 sizeof(MYSQL_FIELD) *
 						 stmt->field_count)) ||
-      !(stmt->bind= (MYSQL_BIND *) alloc_root(alloc,
+      !(stmt->bind= (MYSQL_BIND *) alloc_root(fields_mem_root,
 					      sizeof(MYSQL_BIND) *
 					      stmt->field_count)))
   {
@@ -1658,18 +1671,36 @@ static void alloc_stmt_fields(MYSQL_STMT *stmt)
        field && fields < end; fields++, field++)
   {
     *field= *fields; /* To copy all numeric parts. */
-    field->catalog=   strmake_root(alloc, fields->catalog,
+    field->catalog=   strmake_root(fields_mem_root,
+                                   fields->catalog,
                                    fields->catalog_length);
-    field->db=        strmake_root(alloc, fields->db, fields->db_length);
-    field->table=     strmake_root(alloc, fields->table, fields->table_length);
-    field->org_table= strmake_root(alloc, fields->org_table,
+    field->db=        strmake_root(fields_mem_root,
+                                   fields->db,
+                                   fields->db_length);
+    field->table=     strmake_root(fields_mem_root,
+                                   fields->table,
+                                   fields->table_length);
+    field->org_table= strmake_root(fields_mem_root,
+                                   fields->org_table,
                                    fields->org_table_length);
-    field->name=      strmake_root(alloc, fields->name, fields->name_length);
-    field->org_name=  strmake_root(alloc, fields->org_name,
+    field->name=      strmake_root(fields_mem_root,
+                                   fields->name,
+                                   fields->name_length);
+    field->org_name=  strmake_root(fields_mem_root,
+                                   fields->org_name,
                                    fields->org_name_length);
-    field->def=       fields->def ? strmake_root(alloc, fields->def,
-                                                 fields->def_length) : 0;
-    field->def_length= field->def ? fields->def_length : 0;
+    if (fields->def)
+    {
+      field->def= strmake_root(fields_mem_root,
+                               fields->def,
+                               fields->def_length);
+      field->def_length= fields->def_length;
+    }
+    else
+    {
+      field->def= NULL;
+      field->def_length= 0;
+    }
     field->extension= 0; /* Avoid dangling links. */
     field->max_length= 0; /* max_length is set in mysql_stmt_store_result() */
   }
@@ -2387,6 +2418,9 @@ static void reinit_result_set_metadata(MYSQL_STMT *stmt)
       prepared statements can't send result set metadata for these queries
       on prepare stage. Read it now.
     */
+
+    stmt->field_count= stmt->mysql->field_count;
+
     alloc_stmt_fields(stmt);
   }
   else
@@ -2404,7 +2438,7 @@ static void reinit_result_set_metadata(MYSQL_STMT *stmt)
       previous branch always works.
       TODO: send metadata only when it's really necessary and add a warning
       'Metadata changed' when it's sent twice.
-      */
+    */
     update_stmt_fields(stmt);
   }
 }
@@ -4605,6 +4639,7 @@ my_bool STDCALL mysql_stmt_close(MYSQL_STMT *stmt)
 
   free_root(&stmt->result.alloc, MYF(0));
   free_root(&stmt->mem_root, MYF(0));
+  free_root(&stmt->extension->fields_mem_root, MYF(0));
 
   if (mysql)
   {
@@ -4639,6 +4674,7 @@ my_bool STDCALL mysql_stmt_close(MYSQL_STMT *stmt)
     }
   }
 
+  my_free(stmt->extension);
   my_free(stmt);
 
   DBUG_RETURN(test(rc));
@@ -4805,16 +4841,13 @@ int STDCALL mysql_stmt_next_result(MYSQL_STMT *stmt)
 
   stmt->state= MYSQL_STMT_EXECUTE_DONE;
   stmt->bind_result_done= FALSE;
+  stmt->field_count= mysql->field_count;
 
   if (mysql->field_count)
   {
     alloc_stmt_fields(stmt);
     prepare_to_fetch_result(stmt);
   }
-  else
-  {
-    stmt->field_count= mysql->field_count;
-  }
 
   DBUG_RETURN(0);
 }