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

Dirk Gouders
2013-05-21T08:54:13Z

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>
---
scripts/kconfig/menu.c | 15 +++++++++++++--
1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/scripts/kconfig/menu.c b/scripts/kconfig/menu.c
index b5c7d90..567939c 100644
--- a/scripts/kconfig/menu.c
+++ b/scripts/kconfig/menu.c
@@ -143,14 +143,25 @@ struct property *menu_add_prop(enum prop_type type, char *prompt, struct expr *e

/* Apply all upper menus' visibilities to actual prompts. */
if(type == P_PROMPT) {
+ struct expr *dup_expr;
struct menu *menu = current_entry;

while ((menu = menu->parent) != NULL) {
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);
+ = expr_alloc_and(prop->visible.expr, dup_expr);
}
}

--
1.8.2.1