linux-kernel - Re: [PATCH 2/2] kconfig/nconf: prevent segfault on empty menu

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Date:	Mon, 11 Jul 2011 09:19:32 +0300
From:	Nir Tzachar <nir.tzachar@...il.com>
To:	Arnaud Lacombe <lacombar@...il.com>
Cc:	linux-kbuild@...r.kernel.org, Michal Marek <mmarek@...e.cz>,
	linux-kernel@...r.kernel.org,
	Andrej Gelenberg <andrej.gelenberg@....edu>
Subject: Re: [PATCH 2/2] kconfig/nconf: prevent segfault on empty menu

On Sun, Jul 10, 2011 at 7:18 PM, Arnaud Lacombe <lacombar@...il.com> wrote:
> Hi,
>
> On Sun, Jul 10, 2011 at 6:32 AM, Nir Tzachar <nir.tzachar@...il.com> wrote:
>> Hello.
>>
>> On Sun, Jul 10, 2011 at 10:27 AM, Arnaud Lacombe <lacombar@...il.com> wrote:
>>> 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.
>>
>> I do not believe the correct solution is silently ignoring the user's
>> key presses. I think the correct behavior would be to display a
>> nohelp_text window.
>>
>> something like this (untested):
>> show_scroll_win(main_window, nohelp_text);
>>
> This would be:
>
> show_scroll_win(main_window, _(menu_get_prompt(menu)), nohelp_text);

show_scroll_win(main_window, _("No help available"), nohelp_text);

would also work, and have none of the complications.

> but we would fall back on the original issue as requesting the prompt
> of an invalid menu does not make sense, so the menu_get_prompt(menu)
> would still have to be replaced with something valid. It would be nice
> to come up with a solution valid at least for nconf and mconf.
> Currently mconf just silently discard the key pressed.
>
> To some extend I do not think any frontend should display a menu which
> has no visible child, but that may require more changes and affect
> performance...
>
>  - Arnaud
>
>> The other patches in the series seem gr8.
>>
>> Cheers.
>>
>>> Cc: Nir Tzachar <nir.tzachar@...il.com>
>>> Cc: Andrej Gelenberg <andrej.gelenberg@....edu>
>>> Reported-by: Andrej Gelenberg <andrej.gelenberg@....edu>
>>> Signed-off-by: Arnaud Lacombe <lacombar@...il.com>
>>> ---
>>>  scripts/kconfig/nconf.c |    7 ++++++-
>>>  1 files changed, 6 insertions(+), 1 deletions(-)
>>>
>>> diff --git a/scripts/kconfig/nconf.c b/scripts/kconfig/nconf.c
>>> index 24fc79a..eb9e49d 100644
>>> --- a/scripts/kconfig/nconf.c
>>> +++ b/scripts/kconfig/nconf.c
>>> @@ -1222,7 +1222,12 @@ 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);
>>> --
>>> 1.7.3.4.574.g608b.dirty
>>>
>>>
>>
>
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