kconfig/nconf: prevent segfault on empty menu

nconf does not check the validity of the current menu when help is
requested (with either <F2>, '?' or 'h'). This leads to a NULL pointer
dereference when an empty menu is encountered.

The following reduced testcase exposes the problem:

config DEP
        bool

menu "FOO"

config BAR
        bool "BAR"
        depends on DEP

endmenu

Issue will happen when entering menu "FOO" and requesting help.

nconf is the only front-end which do not filter the validity of the
current menu. Such filter can not really happen beforehand as other key
which does not deals with the current menu might be entered by the user,
so just bails out earlier if we encounter an invalid menu.

Cc: Nir Tzachar <nir.tzachar@gmail.com>
Cc: Andrej Gelenberg <andrej.gelenberg@udo.edu>
Reported-by: Andrej Gelenberg <andrej.gelenberg@udo.edu>
Signed-off-by: Arnaud Lacombe <lacombar@gmail.com>
Signed-off-by: Michal Marek <mmarek@suse.cz>

diff --git a/scripts/kconfig/nconf.c b/scripts/kconfig/nconf.c
index d55666d2dd85dfe8e6b4460b39fe07c45e915505..d6345df1ce1289471f87da8b94227617ccdab0a5 100644 (file)
--- a/scripts/kconfig/nconf.c
+++ b/scripts/kconfig/nconf.c
@@ -1220,7 +1220,12 @@ static void conf_message_callback(const char *fmt, va_list ap)
 
 static void show_help(struct menu *menu)
 {
-       struct gstr help = str_new();
+       struct gstr help;
+
+       if (!menu)
+               return;
+
+       help = str_new();
        menu_get_ext_help(menu, &help);
        show_scroll_win(main_window, _(menu_get_prompt(menu)), str_get(&help));
        str_free(&help);