kconfig/menu.c: fix multiple references to expressions in menu_add_prop()

menu_add_prop() applies upper menus' visibilities to actual prompts
by AND-ing the prompts visibilities with the upper menus ones.

This creates a further reference to the menu's visibilities and when
the expression reduction functions do their work, they may remove or
modify expressions that have multiple references, thus causing
unpredictable side-effects.

The following example Kconfig constructs a case where this causes
problems: a menu and a prompt which's visibilities depend on the same
symbol.  When invoking mconf with this Kconfig and pressing "Z" we
see a problem caused by a free'd expression still referenced by the
menu's visibility:

------------------------------------------------------------------------
mainmenu "Kconfig Testing Configuration"

config VISIBLE
	def_bool n

config Placeholder
	bool "Place holder"

menu "Invisible"
	visible if VISIBLE

config TEST_VAR
	bool "Test option" if VISIBLE

endmenu
------------------------------------------------------------------------

This patch fixes this problem by creating copies of the menu's
visibility expressions before AND-ing them with the prompt's one.

Signed-off-by: Dirk Gouders <dirk@gouders.net>
[yann.morin.1998@free.fr: move variable into its block-scope,
                          keep lines <80 chars, typo]
Tested-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Reviewed-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>

1 files changed, 14 insertions, 1 deletions

diff --git a/scripts/kconfig/menu.c b/scripts/kconfig/menu.c
index b5c7d90df9df..fd3f0180e08f 100644
--- a/scripts/kconfig/menu.c
+++ b/scripts/kconfig/menu.c
@@ -146,11 +146,24 @@ struct property *menu_add_prop(enum prop_type type, char *prompt, struct expr *e
                         struct menu *menu = current_entry;
 
                         while ((menu = menu->parent) != NULL) {
+                                struct expr *dup_expr;
+
                                 if (!menu->visibility)
                                         continue;
+                                /*
+                                 * Do not add a reference to the
+                                 * menu's visibility expression but
+                                 * use a copy of it.  Otherwise the
+                                 * expression reduction functions
+                                 * will modify expressions that have
+                                 * multiple references which can
+                                 * cause unwanted side effects.
+                                 */
+                                dup_expr = expr_copy(menu->visibility);
+
                                 prop->visible.expr
                                         = expr_alloc_and(prop->visible.expr,
-                                                         menu->visibility);
+                                                         dup_expr);
                         }
                 }