Bug #44768: SIGFPE crash when selecting rand from a view containing null

The RAND(N) function where the N is a field of "constant" table
(table of single row) failed with a SIGFPE.

Evaluation of RAND(N) rely on constant status of its argument.
Current server "seeded" random value for each constant argument
only once, in the Item_func_rand::fix_fields method.
Then the server skipped a call to seed_random() in the
Item_func_rand::val_real method for such constant arguments.

However, non-constant state of an argument may be changed
after the call to fix_fields, if an argument is a field of
"constant" table. Thus, pre-initialization of random value
in the fix_fields method is too early.


Initialization of random value by seed_random() has been
removed from Item_func_rand::fix_fields method.
The Item_func_rand::val_real method has been modified to
call seed_random() on the first evaluation of this method
if an argument is a function.

mysql-test/r/func_math.result

@@ -456,4 +456,23 @@ NULL
 SELECT POW(10, 309);
 POW(10, 309)
 NULL
+#
+# Bug #44768: SIGFPE crash when selecting rand from a view
+#             containing null
+#
+CREATE OR REPLACE VIEW v1 AS SELECT NULL AS a;
+SELECT RAND(a) FROM v1;
+RAND(a)
+0.155220427694936
+DROP VIEW v1;
+SELECT RAND(a) FROM (SELECT NULL AS a) b;
+RAND(a)
+0.155220427694936
+CREATE TABLE t1 (i INT);
+INSERT INTO t1 VALUES (NULL);
+SELECT RAND(i) FROM t1;
+RAND(i)
+0.155220427694936
+DROP TABLE t1;
+#
 End of 5.1 tests

mysql-test/t/func_math.test

@@ -282,4 +282,22 @@ SELECT 1e300 / 1e-300;
 SELECT EXP(750);
 SELECT POW(10, 309);
 
+--echo #
+--echo # Bug #44768: SIGFPE crash when selecting rand from a view
+--echo #             containing null
+--echo #
+
+CREATE OR REPLACE VIEW v1 AS SELECT NULL AS a;
+SELECT RAND(a) FROM v1;
+DROP VIEW v1;
+
+SELECT RAND(a) FROM (SELECT NULL AS a) b;
+
+CREATE TABLE t1 (i INT);
+INSERT INTO t1 VALUES (NULL);
+SELECT RAND(i) FROM t1;
+DROP TABLE t1;
+
+--echo #
+
 --echo End of 5.1 tests

sql/item_func.cc

@@ -2143,9 +2143,6 @@ bool Item_func_rand::fix_fields(THD *thd,Item **ref)
     if (!rand && !(rand= (struct rand_struct*)
                    thd->stmt_arena->alloc(sizeof(*rand))))
       return TRUE;
-
-    if (args[0]->const_item())
-      seed_random (args[0]);
   }
   else
   {
@@ -2175,8 +2172,21 @@ void Item_func_rand::update_used_tables()
 double Item_func_rand::val_real()
 {
   DBUG_ASSERT(fixed == 1);
-  if (arg_count && !args[0]->const_item())
-    seed_random (args[0]);
+  if (arg_count)
+  {
+    if (!args[0]->const_item())
+      seed_random(args[0]);
+    else if (first_eval)
+    {
+      /*
+        Constantness of args[0] may be set during JOIN::optimize(), if arg[0]
+        is a field item of "constant" table. Thus, we have to evaluate
+        seed_random() for constant arg there but not at the fix_fields method.
+      */
+      first_eval= FALSE;
+      seed_random(args[0]);
+    }
+  }
   return my_rnd(rand);
 }
 

sql/item_func.h

@@ -696,14 +696,16 @@ public:
 class Item_func_rand :public Item_real_func
 {
   struct rand_struct *rand;
+  bool first_eval; // TRUE if val_real() is called 1st time
 public:
-  Item_func_rand(Item *a) :Item_real_func(a), rand(0) {}
+  Item_func_rand(Item *a) :Item_real_func(a), rand(0), first_eval(TRUE) {}
   Item_func_rand()	  :Item_real_func() {}
   double val_real();
   const char *func_name() const { return "rand"; }
   bool const_item() const { return 0; }
   void update_used_tables();
   bool fix_fields(THD *thd, Item **ref);
+  void cleanup() { first_eval= TRUE; Item_real_func::cleanup(); }
 private:
   void seed_random (Item * val);  
 };