linux-kernel - Re: [PATCH] kconfig: check for a NULL pointer before access

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Message-ID: <998f5987-12ea-4bdc-b86a-35b904a34acf@infradead.org>
Date: Fri, 23 May 2025 16:47:52 -0700
From: Randy Dunlap <rdunlap@...radead.org>
To: Bill Wendling <morbo@...gle.com>
Cc: Masahiro Yamada <masahiroy@...nel.org>,
 Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
 LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] kconfig: check for a NULL pointer before access



On 5/23/25 3:56 PM, Bill Wendling wrote:
> On Thu, May 22, 2025 at 5:16 PM Randy Dunlap <rdunlap@...radead.org> wrote:
>>
>> Hi,
>>
>> On 5/22/25 5:07 PM, Bill Wendling wrote:
>>> The call to 'prop_get_symbol' may return NULL in some cases. The if-then
>>> statement accesses the returned value without checking if it's
>>> non-NULL. After inlining, the compiler may treat the conditional as
>>> 'undefined behavior', which the compiler may take the opportunity to do
>>> whatever it wants with the UB path. This patch simply adds a check to
>>> ensure that 'def_sym' is non-NULL to avoid this behavior.
>>>
>>> Signed-off-by: Bill Wendling <morbo@...gle.com>
>>> ---
>>> Cc: Masahiro Yamada <masahiroy@...nel.org>
>>> Cc: linux-kbuild@...r.kernel.org
>>> Cc: linux-kernel@...r.kernel.org
>>> ---
>>>  scripts/kconfig/symbol.c | 2 +-
>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/scripts/kconfig/symbol.c b/scripts/kconfig/symbol.c
>>> index d57f8cbba291..9c5068225328 100644
>>> --- a/scripts/kconfig/symbol.c
>>> +++ b/scripts/kconfig/symbol.c
>>> @@ -272,7 +272,7 @@ struct symbol *sym_choice_default(struct menu *choice)
>>>   if (prop->visible.tri == no)
>>>   continue;
>>>   def_sym = prop_get_symbol(prop);
>>> - if (def_sym->visible != no)
>>> + if (def_sym && def_sym->visible != no)
>>>   return def_sym;
>>>   }
>>>
>>
>> The patch is missing the source file's indentation.
>> (spaces/tabs are lost)
>>
> Crud! My mailer borked. I sent v2 and it looks to have kept the whitespaces.

I don't think v2 worked either.
See  https://lore.kernel.org/linux-kbuild/CAGG=3QXQkJ6n0J1gZcgxfEb68NWN2y200ZCuxxDtqPRgWPci=A@mail.gmail.com/T/#mf64c7afd19235d3dee4e572f96ff76936f921c6e

-- 
~Randy