linux-kernel - Re: [PATCH v2 08/10] drivers/auxdisplay: add a KFuzzTest for parse

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Message-ID: <CAHp75VdyZudJkskL0E9DEzYXgFeUwCBEwXEVUMuKSx0R9NUxmQ@mail.gmail.com>
Date: Sat, 20 Sep 2025 13:53:38 +0300
From: Andy Shevchenko <andy.shevchenko@...il.com>
To: Ethan Graham <ethan.w.s.graham@...il.com>
Cc: ethangraham@...gle.com, glider@...gle.com, andreyknvl@...il.com, 
	andy@...nel.org, brauner@...nel.org, brendan.higgins@...ux.dev, 
	davem@...emloft.net, davidgow@...gle.com, dhowells@...hat.com, 
	dvyukov@...gle.com, elver@...gle.com, herbert@...dor.apana.org.au, 
	ignat@...udflare.com, jack@...e.cz, jannh@...gle.com, 
	johannes@...solutions.net, kasan-dev@...glegroups.com, kees@...nel.org, 
	kunit-dev@...glegroups.com, linux-crypto@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-mm@...ck.org, lukas@...ner.de, 
	rmoar@...gle.com, shuah@...nel.org, sj@...nel.org, tarasmadan@...gle.com
Subject: Re: [PATCH v2 08/10] drivers/auxdisplay: add a KFuzzTest for parse_xy()

On Fri, Sep 19, 2025 at 5:58 PM Ethan Graham <ethan.w.s.graham@...il.com> wrote:
>
> From: Ethan Graham <ethangraham@...gle.com>
>
> Add a KFuzzTest fuzzer for the parse_xy() function, located in a new
> file under /drivers/auxdisplay/tests.
>
> To validate the correctness and effectiveness of this KFuzzTest target,
> a bug was injected into parse_xy() like so:
>
> drivers/auxdisplay/charlcd.c:179
> - s = p;
> + s = p + 1;
>
> Although a simple off-by-one bug, it requires a specific input sequence
> in order to trigger it, thus demonstrating the power of pairing
> KFuzzTest with a coverage-guided fuzzer like syzkaller.

...

> --- a/drivers/auxdisplay/charlcd.c
> +++ b/drivers/auxdisplay/charlcd.c
> @@ -682,3 +682,11 @@ EXPORT_SYMBOL_GPL(charlcd_unregister);
>
>  MODULE_DESCRIPTION("Character LCD core support");
>  MODULE_LICENSE("GPL");
> +
> +/*
> + * When CONFIG_KFUZZTEST is enabled, we include this _kfuzz.c file to ensure
> + * that KFuzzTest targets are built.
> + */
> +#ifdef CONFIG_KFUZZTEST
> +#include "tests/charlcd_kfuzz.c"
> +#endif /* CONFIG_KFUZZTEST */

No, NAK. We don't want to see these in each and every module. Please,
make sure that nothing, except maybe Kconfig, is modified in this
folder (yet, you may add a _separate_ test module, as you already have
done in this patch).

-- 
With Best Regards,
Andy Shevchenko