kconfig: Don't leak main menus during parsing

BugLink: https://bugs.launchpad.net/bugs/1775771

[ Upstream commit 0724a7c3 ]

If a 'mainmenu' entry appeared in the Kconfig files, two things would
leak:

	- The 'struct property' allocated for the default "Linux Kernel
	  Configuration" prompt.

	- The string for the T_WORD/T_WORD_QUOTE prompt after the
	  T_MAINMENU token, allocated on the heap in zconf.l.

To fix it, introduce a new 'no_mainmenu_stmt' nonterminal that matches
if there's no 'mainmenu' and adds the default prompt. That means the
prompt only gets allocated once regardless of whether there's a
'mainmenu' statement or not, and managing it becomes simple.

Summary from Valgrind on 'menuconfig' (ARCH=x86) before the fix:

	LEAK SUMMARY:
	   definitely lost: 344,568 bytes in 14,352 blocks
	   ...

Summary after the fix:

	LEAK SUMMARY:
	   definitely lost: 344,440 bytes in 14,350 blocks
	   ...
Signed-off-by: Ulf Magnusson <ulfalizer@gmail.com>
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Juerg Haefliger <juergh@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>

scripts/kconfig/zconf.y

@@ -107,7 +107,27 @@ static struct menu *current_menu, *current_entry;
 %%
 input: nl start | start;
 
-start: mainmenu_stmt stmt_list | stmt_list;
+start: mainmenu_stmt stmt_list | no_mainmenu_stmt stmt_list;
+
+/* mainmenu entry */
+
+mainmenu_stmt: T_MAINMENU prompt nl
+{
+	menu_add_prompt(P_MENU, $2, NULL);
+};
+
+/* Default main menu, if there's no mainmenu entry */
+
+no_mainmenu_stmt: /* empty */
+{
+	/*
+	 * Hack: Keep the main menu title on the heap so we can safely free it
+	 * later regardless of whether it comes from the 'prompt' in
+	 * mainmenu_stmt or here
+	 */
+	menu_add_prompt(P_MENU, strdup("Linux Kernel Configuration"), NULL);
+};
+
 
 stmt_list:
 	  /* empty */
@@ -344,13 +364,6 @@ if_block:
 	| if_block choice_stmt
 ;
 
-/* mainmenu entry */
-
-mainmenu_stmt: T_MAINMENU prompt nl
-{
-	menu_add_prompt(P_MENU, $2, NULL);
-};
-
 /* menu entry */
 
 menu: T_MENU prompt T_EOL
@@ -495,6 +508,7 @@ word_opt: /* empty */			{ $$ = NULL; }
 
 void conf_parse(const char *name)
 {
+	const char *tmp;
 	struct symbol *sym;
 	int i;
 
@@ -502,7 +516,6 @@ void conf_parse(const char *name)
 
 	sym_init();
 	_menu_init();
-	rootmenu.prompt = menu_add_prompt(P_MENU, "Linux Kernel Configuration", NULL);
 
 	if (getenv("ZCONF_DEBUG"))
 		zconfdebug = 1;
@@ -512,8 +525,10 @@ void conf_parse(const char *name)
 	if (!modules_sym)
 		modules_sym = sym_find( "n" );
 
+	tmp = rootmenu.prompt->text;
 	rootmenu.prompt->text = _(rootmenu.prompt->text);
 	rootmenu.prompt->text = sym_expand_string_value(rootmenu.prompt->text);
+	free((char*)tmp);
 
 	menu_finalize(&rootmenu);
 	for_all_symbols(i, sym) {