linux-kernel - Re: [PATCH 3/3] module: Add compile-time check for embedded NUL characters

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Message-ID: <CABCJKufWw4VQA_k6Deuf5Bn6401cbYv_St8VV_0-LAau6F0nTw@mail.gmail.com>
Date: Thu, 11 Dec 2025 09:03:02 -0800
From: Sami Tolvanen <samitolvanen@...gle.com>
To: Dan Carpenter <dan.carpenter@...aro.org>
Cc: "Luck, Tony" <tony.luck@...el.com>, Chris Li <sparse@...isli.org>, 
	Daniel Gomez <da.gomez@...nel.org>, Eric Biggers <ebiggers@...nel.org>, Kees Cook <kees@...nel.org>, 
	Luis Chamberlain <mcgrof@...nel.org>, Rusty Russell <rusty@...tcorp.com.au>, 
	Petr Pavlu <petr.pavlu@...e.com>, 
	"linux-modules@...r.kernel.org" <linux-modules@...r.kernel.org>, Malcolm Priestley <tvboxspy@...il.com>, 
	Mauro Carvalho Chehab <mchehab@...nel.org>, Hans Verkuil <hverkuil@...nel.org>, 
	Uwe Kleine-König <u.kleine-koenig@...gutronix.de>, 
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, 
	"linux-media@...r.kernel.org" <linux-media@...r.kernel.org>, 
	"linux-hardening@...r.kernel.org" <linux-hardening@...r.kernel.org>
Subject: Re: [PATCH 3/3] module: Add compile-time check for embedded NUL characters

On Thu, Dec 11, 2025 at 12:28 AM Dan Carpenter <dan.carpenter@...aro.org> wrote:
>
> On Wed, Dec 10, 2025 at 02:29:45PM -0800, Luck, Tony wrote:
> > > diff --git a/expand.c b/expand.c
> > > index f14e7181..71221d35 100644
> > > --- a/expand.c
> > > +++ b/expand.c
> > > @@ -535,6 +535,8 @@ static int expand_compare(struct expression *expr)
> > >                     expr->taint = 0;
> > >                     return 0;
> > >             }
> > > +           if (left->flags & CEF_ICE && right->flags & CEF_ICE)
> > > +                   expr->flags |= CEF_SET_ICE;
> > >             if (simplify_cmp_binop(expr, left->ctype))
> > >                     return 0;
> > >             if (simplify_float_cmp(expr, left->ctype))
>
> I'm not an expert in the C standard, but this feels correct to me.

It only fixes comparisons though, the problem still exists for other
expressions. For example, while `_Static_assert(__builtin_strlen("")
== 0);` works with this change,
`_Static_assert(!__builtin_strlen(""));` still fails. Perhaps there's
a better way to fix this than changing each expression expansion
function to handle this flag?

Sami