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

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Message-ID: <CAGG=3QXQkJ6n0J1gZcgxfEb68NWN2y200ZCuxxDtqPRgWPci=A@mail.gmail.com>
Date: Fri, 23 May 2025 15:56:36 -0700
From: Bill Wendling <morbo@...gle.com>
To: Randy Dunlap <rdunlap@...radead.org>
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 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.

-bw