MDEV-20366 Server crashes in get_current_user upon SET PASSWORD via SP

The opt_for_user subrule was incorrectly scanned before sp_create_assignment_lex(),
so the user name and the host were created on a wrong memory root.

- Reoganizing the grammar to make sure that sp_create_assignment_lex()
  is called immediately after PASSWORD_SYM is scanned, so all attributes
  are then allocated on its memory root.

- Moving the semantic code as methods to LEX, so the grammar looks as simple as possible.

- Changing text_or_password to be of the data type USER_AUTH*.
  As a side effect, the LEX::definer member is now not used when processing
  the SET PASSWORD statement. Everything is done using Bison's stack.

The bug sas introduced by this commit:
commit bf5a144e1692f6cc6a6d781b7e75ff4abf32bdf3

5 files changed, 118 insertions, 36 deletions

diff --git a/mysql-test/main/sp-security.result b/mysql-test/main/sp-security.result
index 7d2098f62be..2c48883a509 100644
--- a/mysql-test/main/sp-security.result
+++ b/mysql-test/main/sp-security.result
@@ -802,3 +802,21 @@ connection default;
 DROP DATABASE u1;
 DROP USER u1@localhost;
 set @@global.character_set_server=@save_character_set_server;
+#
+# Start of 10.5 tests
+#
+#
+# MDEV-20366 Server crashes in get_current_user upon SET PASSWORD via SP
+#
+CREATE PROCEDURE p1() SET PASSWORD FOR foo@localhost=PASSWORD('x');
+CALL p1();
+ERROR 28000: Can't find any matching row in the user table
+DROP PROCEDURE p1;
+CREATE USER foo@localhost;
+CREATE  PROCEDURE p1() SET PASSWORD FOR foo@localhost=PASSWORD('x');
+CALL p1();
+DROP PROCEDURE p1;
+DROP USER foo@localhost;
+#
+# End of 10.5 tests
+#
diff --git a/mysql-test/main/sp-security.test b/mysql-test/main/sp-security.test
index c375815b29a..e7790bf703a 100644
--- a/mysql-test/main/sp-security.test
+++ b/mysql-test/main/sp-security.test
@@ -1078,3 +1078,30 @@ DROP DATABASE u1;
 DROP USER u1@localhost;
 
 set @@global.character_set_server=@save_character_set_server;
+
+
+--echo #
+--echo # Start of 10.5 tests
+--echo #
+
+--echo #
+--echo # MDEV-20366 Server crashes in get_current_user upon SET PASSWORD via SP
+--echo #
+
+# Testing without the user
+CREATE PROCEDURE p1() SET PASSWORD FOR foo@localhost=PASSWORD('x');
+--error ER_PASSWORD_NO_MATCH
+CALL p1();
+DROP PROCEDURE p1;
+
+# Testing with the user
+CREATE USER foo@localhost;
+CREATE  PROCEDURE p1() SET PASSWORD FOR foo@localhost=PASSWORD('x');
+CALL p1();
+DROP PROCEDURE p1;
+DROP USER foo@localhost;
+
+
+--echo #
+--echo # End of 10.5 tests
+--echo #
diff --git a/sql/sql_lex.cc b/sql/sql_lex.cc
index 477401c793f..671948f8e8d 100644
--- a/sql/sql_lex.cc
+++ b/sql/sql_lex.cc
@@ -11393,3 +11393,36 @@ bool LEX::stmt_revoke_proxy(THD *thd, LEX_USER *user)
   return !(m_sql_cmd= new (thd->mem_root) Sql_cmd_grant_proxy(sql_command,
                                                               NO_ACL));
 }
+
+
+LEX_USER *LEX::current_user_for_set_password(THD *thd)
+{
+  LEX_CSTRING pw= { STRING_WITH_LEN("password") };
+  if (unlikely(spcont && spcont->find_variable(&pw, false)))
+  {
+    my_error(ER_SP_BAD_VAR_SHADOW, MYF(0), pw.str);
+    return NULL;
+  }
+  LEX_USER *res;
+  if (unlikely(!(res= (LEX_USER*) thd->calloc(sizeof(LEX_USER)))))
+    return NULL;
+  res->user= current_user;
+  return res;
+}
+
+
+bool LEX::sp_create_set_password_instr(THD *thd,
+                                       LEX_USER *user,
+                                       USER_AUTH *auth,
+                                       bool no_lookahead)
+{
+  user->auth= auth;
+  set_var_password *var= new (thd->mem_root) set_var_password(user);
+  if (unlikely(var == NULL) ||
+      unlikely(var_list.push_back(var, thd->mem_root)))
+    return true;
+  autocommit= true;
+  if (sphead)
+    sphead->m_flags|= sp_head::HAS_SET_AUTOCOMMIT_STMT;
+  return sp_create_assignment_instr(thd, no_lookahead);
+}
diff --git a/sql/sql_lex.h b/sql/sql_lex.h
index 0a802b9652c..49edce508ca 100644
--- a/sql/sql_lex.h
+++ b/sql/sql_lex.h
@@ -3864,6 +3864,21 @@ public:
                                                    const Column_definition &ref,
                                                    Row_definition_list *fields,
                                                    Item *def);
+
+  LEX_USER *current_user_for_set_password(THD *thd);
+  bool sp_create_set_password_instr(THD *thd,
+                                    LEX_USER *user,
+                                    USER_AUTH *auth,
+                                    bool no_lookahead);
+  bool sp_create_set_password_instr(THD *thd,
+                                    USER_AUTH *auth,
+                                    bool no_lookahead)
+  {
+    LEX_USER *user;
+    return !(user= current_user_for_set_password(thd)) ||
+           sp_create_set_password_instr(thd, user, auth, no_lookahead);
+  }
+
   bool sp_handler_declaration_init(THD *thd, int type);
   bool sp_handler_declaration_finalize(THD *thd, int type);
 
diff --git a/sql/sql_yacc.yy b/sql/sql_yacc.yy
index 6fe7d871f40..da752c0a3cb 100644
--- a/sql/sql_yacc.yy
+++ b/sql/sql_yacc.yy
@@ -1543,6 +1543,7 @@ End SQL_MODE_ORACLE_SPECIFIC */
                  admin_option_for_role user_maybe_role
 
 %type <user_auth> opt_auth_str auth_expression auth_token
+                  text_or_password
 
 %type <charset>
         opt_collate
@@ -16433,25 +16434,30 @@ option_value_no_option_type:
                 unlikely(sp_create_assignment_instr(thd, yychar == YYEMPTY)))
               MYSQL_YYABORT;
           }
-        | PASSWORD_SYM opt_for_user text_or_password
+        | PASSWORD_SYM equal
           {
             if (sp_create_assignment_lex(thd, $1.pos()))
               MYSQL_YYABORT;
-            LEX *lex = Lex;
-            set_var_password *var= (new (thd->mem_root)
-                                    set_var_password(lex->definer));
-            if (unlikely(var == NULL) ||
-                unlikely(lex->var_list.push_back(var, thd->mem_root)))
+          }
+          text_or_password
+          {
+            if (unlikely(Lex->sp_create_set_password_instr(thd, $4,
+                                                           yychar == YYEMPTY)))
               MYSQL_YYABORT;
-            lex->autocommit= TRUE;
-            if (lex->sphead)
-              lex->sphead->m_flags|= sp_head::HAS_SET_AUTOCOMMIT_STMT;
-            if (unlikely(sp_create_assignment_instr(thd, yychar == YYEMPTY)))
+          }
+        | PASSWORD_SYM FOR_SYM
+          {
+            if (sp_create_assignment_lex(thd, $1.pos()))
+              MYSQL_YYABORT;
+          }
+          user equal text_or_password
+          {
+            if (unlikely(Lex->sp_create_set_password_instr(thd, $4, $6,
+                                                           yychar == YYEMPTY)))
               MYSQL_YYABORT;
           }
         ;
 
-
 transaction_characteristics:
           transaction_access_mode
         | isolation_level
@@ -16508,42 +16514,25 @@ isolation_types:
         | SERIALIZABLE_SYM         { $$= ISO_SERIALIZABLE; }
         ;
 
-opt_for_user:
-        equal
-          {
-            LEX *lex= thd->lex;
-            sp_pcontext *spc= lex->spcont;
-            LEX_CSTRING pw= { STRING_WITH_LEN("password") };
-
-            if (unlikely(spc && spc->find_variable(&pw, false)))
-              my_yyabort_error((ER_SP_BAD_VAR_SHADOW, MYF(0), pw.str));
-            if (unlikely(!(lex->definer= (LEX_USER*)
-                           thd->calloc(sizeof(LEX_USER)))))
-              MYSQL_YYABORT;
-            lex->definer->user= current_user;
-            lex->definer->auth= new (thd->mem_root) USER_AUTH();
-          }
-        | FOR_SYM user equal { Lex->definer= $2; }
-        ;
 
 text_or_password:
           TEXT_STRING
           {
-            Lex->definer->auth= new (thd->mem_root) USER_AUTH();
-            Lex->definer->auth->auth_str= $1;
+            $$= new (thd->mem_root) USER_AUTH();
+            $$->auth_str= $1;
           }
         | PASSWORD_SYM '(' TEXT_STRING ')'
           {
-            Lex->definer->auth= new (thd->mem_root) USER_AUTH();
-            Lex->definer->auth->pwtext= $3;
+            $$= new (thd->mem_root) USER_AUTH();
+            $$->pwtext= $3;
           }
         | OLD_PASSWORD_SYM '(' TEXT_STRING ')'
           {
-            Lex->definer->auth= new (thd->mem_root) USER_AUTH();
-            Lex->definer->auth->pwtext= $3;
-            Lex->definer->auth->auth_str.str= Item_func_password::alloc(thd,
+            $$= new (thd->mem_root) USER_AUTH();
+            $$->pwtext= $3;
+            $$->auth_str.str= Item_func_password::alloc(thd,
                                    $3.str, $3.length, Item_func_password::OLD);
-            Lex->definer->auth->auth_str.length=  SCRAMBLED_PASSWORD_CHAR_LENGTH_323;
+            $$->auth_str.length=  SCRAMBLED_PASSWORD_CHAR_LENGTH_323;
           }
         ;