Bug#47627 SET @@{global.session}.local_variable in stored routine causes crash

This patch borrows ideas, text and code from Kristofer
Pettersson's patch.

An assignment of a system variable sharing the same base
name as a declared stored procedure variable in the same
context could lead to a crash.

The reason was that during the parsing of the syntactic
rule 'option_value' an uninitialized set_var object was
pushed to the parameter stack of the SET statement. The
parent rule 'option_type_value' interpreted the existence
of variables on the parameter stack as an assignment and
wrapped it in a sp_instr_set object.

As the procedure later was executed an attempt was made
to run the method 'check()' on an uninitialized member
object (NULL value) belonging to the previously created
but uninitialized object.

This patch refactors the 'internal_variable_name' rule and
copies the semantic analysis part to the depending parent
rule: 'option_value'. This makes it possible to account
for any prefixes affecting the interpretation of the
internal_variable_name.

mysql-test/r/sp.result:
  Add test case result.
mysql-test/t/sp.test:
  Add test case for bug.
sql/sql_yacc.yy:
  - Reduce churn in rule sys_option_value by moving to
    specialized functions.
  - Comment the the lookup in the rule internel_variable_name
    is a best effort operation.
  - Lookup for a system variable in the option_value if one was
    not found (the variable could have been shadowed)

1 files changed, 164 insertions, 88 deletions

diff --git a/sql/sql_yacc.yy b/sql/sql_yacc.yy
index 86bef83cf1a..b0f45fe845a 100644
--- a/sql/sql_yacc.yy
+++ b/sql/sql_yacc.yy
@@ -389,6 +389,138 @@ void case_stmt_action_end_case(LEX *lex, bool simple)
   lex->sphead->do_cont_backpatch();
 }
 
+
+static bool
+find_sys_var_null_base(THD *thd, struct sys_var_with_base *tmp)
+{
+  tmp->var= find_sys_var(thd, tmp->base_name.str, tmp->base_name.length);
+
+  if (tmp->var == NULL)
+    my_error(ER_UNKNOWN_SYSTEM_VARIABLE, MYF(0), tmp->base_name.str);
+  else
+    tmp->base_name= null_lex_str;
+
+  return thd->is_error();
+}
+
+
+/**
+  Helper action for a SET statement.
+  Used to push a system variable into the assignment list.
+
+  @param thd      the current thread
+  @param tmp      the system variable with base name
+  @param var_type the scope of the variable
+  @param val      the value being assigned to the variable
+
+  @return TRUE if error, FALSE otherwise.
+*/
+
+static bool
+set_system_variable(THD *thd, struct sys_var_with_base *tmp,
+                    enum enum_var_type var_type, Item *val)
+{
+  set_var *var;
+  LEX *lex= thd->lex;
+
+  /* No AUTOCOMMIT from a stored function or trigger. */
+  if (lex->spcont && tmp->var == &sys_autocommit)
+    lex->sphead->m_flags|= sp_head::HAS_SET_AUTOCOMMIT_STMT;
+
+  if (! (var= new set_var(var_type, tmp->var, &tmp->base_name, val)))
+    return TRUE;
+
+  return lex->var_list.push_back(var);
+}
+
+
+/**
+  Helper action for a SET statement.
+  Used to push a SP local variable into the assignment list.
+
+  @param thd      the current thread
+  @param var_type the SP local variable
+  @param val      the value being assigned to the variable
+
+  @return TRUE if error, FALSE otherwise.
+*/
+
+static bool
+set_local_variable(THD *thd, sp_variable_t *spv, Item *val)
+{
+  Item *it;
+  LEX *lex= thd->lex;
+  sp_instr_set *sp_set;
+
+  if (val)
+    it= val;
+  else if (spv->dflt)
+    it= spv->dflt;
+  else
+  {
+    it= new (thd->mem_root) Item_null();
+    if (it == NULL)
+      return TRUE;
+  }
+
+  sp_set= new sp_instr_set(lex->sphead->instructions(), lex->spcont,
+                           spv->offset, it, spv->type, lex, TRUE);
+
+  return (sp_set == NULL || lex->sphead->add_instr(sp_set));
+}
+
+
+/**
+  Helper action for a SET statement.
+  Used to SET a field of NEW row.
+
+  @param thd      the current thread
+  @param name     the field name
+  @param val      the value being assigned to the row
+
+  @return TRUE if error, FALSE otherwise.
+*/
+
+static bool
+set_trigger_new_row(THD *thd, LEX_STRING *name, Item *val)
+{
+  LEX *lex= thd->lex;
+  Item_trigger_field *trg_fld;
+  sp_instr_set_trigger_field *sp_fld;
+
+  /* QQ: Shouldn't this be field's default value ? */
+  if (! val)
+    val= new Item_null();
+
+  DBUG_ASSERT(lex->trg_chistics.action_time == TRG_ACTION_BEFORE &&
+              (lex->trg_chistics.event == TRG_EVENT_INSERT ||
+               lex->trg_chistics.event == TRG_EVENT_UPDATE));
+
+  trg_fld= new (thd->mem_root)
+            Item_trigger_field(lex->current_context(),
+                               Item_trigger_field::NEW_ROW,
+                               name->str, UPDATE_ACL, FALSE);
+
+  if (trg_fld == NULL)
+    return TRUE;
+
+  sp_fld= new sp_instr_set_trigger_field(lex->sphead->instructions(),
+                                         lex->spcont, trg_fld, val, lex);
+
+  if (sp_fld == NULL)
+    return TRUE;
+
+  /*
+    Let us add this item to list of all Item_trigger_field
+    objects in trigger.
+  */
+  lex->trg_table_fields.link_in_list((uchar *) trg_fld,
+                                     (uchar **) &trg_fld->next_trg_field);
+
+  return lex->sphead->add_instr(sp_fld);
+}
+
+
 /**
   Helper to resolve the SQL:2003 Syntax exception 1) in <in predicate>.
   See SQL:2003, Part 2, section 8.4 <in predicate>, Note 184, page 383.
@@ -11809,98 +11941,42 @@ sys_option_value:
           option_type internal_variable_name equal set_expr_or_default
           {
             THD *thd= YYTHD;
-            LEX *lex=Lex;
+            LEX *lex= Lex;
+            LEX_STRING *name= &$2.base_name;
 
             if ($2.var == trg_new_row_fake_var)
             {
               /* We are in trigger and assigning value to field of new row */
-              Item *it;
-              Item_trigger_field *trg_fld;
-              sp_instr_set_trigger_field *sp_fld;
-              LINT_INIT(sp_fld);
               if ($1)
               {
                 my_parse_error(ER(ER_SYNTAX_ERROR));
                 MYSQL_YYABORT;
               }
-              if ($4)
-                it= $4;
-              else
-              {
-                /* QQ: Shouldn't this be field's default value ? */
-                it= new Item_null();
-              }
-
-              DBUG_ASSERT(lex->trg_chistics.action_time == TRG_ACTION_BEFORE &&
-                          (lex->trg_chistics.event == TRG_EVENT_INSERT ||
-                           lex->trg_chistics.event == TRG_EVENT_UPDATE));
-
-              trg_fld= new (thd->mem_root)
-                         Item_trigger_field(Lex->current_context(),
-                                            Item_trigger_field::NEW_ROW,
-                                            $2.base_name.str,
-                                            UPDATE_ACL, FALSE);
-              if (trg_fld == NULL)
-                MYSQL_YYABORT;
-
-              sp_fld= new sp_instr_set_trigger_field(lex->sphead->
-                                                     instructions(),
-                                                     lex->spcont,
-                                                     trg_fld,
-                                                     it, lex);
-              if (sp_fld == NULL)
-                MYSQL_YYABORT;
-
-              /*
-                Let us add this item to list of all Item_trigger_field
-                objects in trigger.
-              */
-              lex->trg_table_fields.link_in_list((uchar *)trg_fld,
-                                                 (uchar **) &trg_fld->
-                                                   next_trg_field);
-
-              if (lex->sphead->add_instr(sp_fld))
+              if (set_trigger_new_row(YYTHD, name, $4))
                 MYSQL_YYABORT;
             }
             else if ($2.var)
-            { /* System variable */
+            {
               if ($1)
                 lex->option_type= $1;
-              set_var *var= new set_var(lex->option_type, $2.var,
-                                        &$2.base_name, $4);
-              if (var == NULL)
+
+              /* It is a system variable. */
+              if (set_system_variable(thd, &$2, lex->option_type, $4))
                 MYSQL_YYABORT;
-              lex->var_list.push_back(var);
             }
             else
             {
-              /* An SP local variable */
-              sp_pcontext *ctx= lex->spcont;
-              sp_variable_t *spv;
-              sp_instr_set *sp_set;
-              Item *it;
+              sp_pcontext *spc= lex->spcont;
+              sp_variable_t *spv= spc->find_variable(name);
+
               if ($1)
               {
                 my_parse_error(ER(ER_SYNTAX_ERROR));
                 MYSQL_YYABORT;
               }
 
-              spv= ctx->find_variable(&$2.base_name);
-
-              if ($4)
-                it= $4;
-              else if (spv->dflt)
-                it= spv->dflt;
-              else
-              {
-                it= new (thd->mem_root) Item_null();
-                if (it == NULL)
-                  MYSQL_YYABORT;
-              }
-              sp_set= new sp_instr_set(lex->sphead->instructions(), ctx,
-                                       spv->offset, it, spv->type, lex, TRUE);
-              if (sp_set == NULL ||
-                  lex->sphead->add_instr(sp_set))
+              /* It is a local variable. */
+              if (set_local_variable(thd, spv, $4))
                 MYSQL_YYABORT;
             }
           }
@@ -11936,11 +12012,16 @@ option_value:
           }
         | '@' '@' opt_var_ident_type internal_variable_name equal set_expr_or_default
           {
-            LEX *lex=Lex;
-            set_var *var= new set_var($3, $4.var, &$4.base_name, $6);
-            if (var == NULL)
+            THD *thd= YYTHD;
+            struct sys_var_with_base tmp= $4;
+            /* Lookup if necessary: must be a system variable. */
+            if (tmp.var == NULL)
+            {
+              if (find_sys_var_null_base(thd, &tmp))
+                MYSQL_YYABORT;
+            }
+            if (set_system_variable(thd, &tmp, $3, $6))
               MYSQL_YYABORT;
-            lex->var_list.push_back(var);
           }
         | charset old_or_new_charset_name_or_default
           {
@@ -12033,31 +12114,26 @@ internal_variable_name:
           ident
           {
             THD *thd= YYTHD;
-            LEX *lex= thd->lex;
-            sp_pcontext *spc= lex->spcont;
+            sp_pcontext *spc= thd->lex->spcont;
             sp_variable_t *spv;
 
-            /* We have to lookup here since local vars can shadow sysvars */
+            /* Best effort lookup for system variable. */
             if (!spc || !(spv = spc->find_variable(&$1)))
             {
+              struct sys_var_with_base tmp= {NULL, $1};
+
               /* Not an SP local variable */
-              sys_var *tmp=find_sys_var(thd, $1.str, $1.length);
-              if (!tmp)
+              if (find_sys_var_null_base(thd, &tmp))
                 MYSQL_YYABORT;
-              $$.var= tmp;
-              $$.base_name= null_lex_str;
-              if (spc && tmp == &sys_autocommit)
-              {
-                /*
-                  We don't allow setting AUTOCOMMIT from a stored function
-                  or trigger.
-                */
-                lex->sphead->m_flags|= sp_head::HAS_SET_AUTOCOMMIT_STMT;
-              }
+
+              $$= tmp;
             }
             else
             {
-              /* An SP local variable */
+              /*
+                Possibly an SP local variable (or a shadowed sysvar).
+                Will depend on the context of the SET statement.
+              */
               $$.var= NULL;
               $$.base_name= $1;
             }