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>
Signed-off-by: Christian Lamparter <chunkeey@googlemail.com>

diff --git a/config/menu.c b/config/menu.c
index b5c7d90df9df801dac0ca12d64b609e686e74b62..fd3f0180e08fbafb537e128c9e46641288c68774 100644 (file)
--- a/config/menu.c
+++ b/config/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);
                        }
                }