linux-hardening - Re: [PATCH 3/3] printk: kunit: Fix __counted_by() in struct prbtest

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Message-ID: <841pqwkwto.fsf@jogness.linutronix.de>
Date: Fri, 04 Jul 2025 13:47:07 +0206
From: John Ogness <john.ogness@...utronix.de>
To: Petr Mladek <pmladek@...e.com>, Thomas Weißschuh
 <thomas.weissschuh@...utronix.de>, Dan Carpenter
 <dan.carpenter@...aro.org>
Cc: Steven Rostedt <rostedt@...dmis.org>, Sergey Senozhatsky
 <senozhatsky@...omium.org>, Kees Cook <kees@...nel.org>, "Gustavo A . R .
 Silva" <gustavoars@...nel.org>, David Gow <davidgow@...gle.com>, Arnd
 Bergmann <arnd@...nel.org>, Arnd Bergmann <arnd@...db.de>,
 linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org, Petr Mladek
 <pmladek@...e.com>
Subject: Re: [PATCH 3/3] printk: kunit: Fix __counted_by() in struct
 prbtest_rbdata

On 2025-07-02, Petr Mladek <pmladek@...e.com> wrote:
> diff --git a/kernel/printk/printk_ringbuffer_kunit_test.c b/kernel/printk/printk_ringbuffer_kunit_test.c
> index 0c3030fde8c2..088fe4d8c9b6 100644
> --- a/kernel/printk/printk_ringbuffer_kunit_test.c
> +++ b/kernel/printk/printk_ringbuffer_kunit_test.c
> @@ -114,10 +117,14 @@ static int prbtest_writer(void *data)
>  	kunit_info(tr->test_data->test, "start thread %03lu (writer)\n", tr->num);
>  
>  	for (;;) {
> -		/* ensure at least 1 character */
> -		text_size = get_random_u32_inclusive(1, MAX_RBDATA_TEXT_SIZE);
> -		/* +1 for terminator. */
> -		record_size = sizeof(struct prbtest_rbdata) + text_size + 1;
> +		/* ensure at least 1 character + trailing '\0' */
> +		text_size = get_random_u32_inclusive(2, MAX_RBDATA_TEXT_SIZE);
> +		if (WARN_ON_ONCE(text_size < 2))
> +			text_size = 2;
> +		if (WARN_ON_ONCE(text_size > MAX_RBDATA_TEXT_SIZE))
> +			text_size = MAX_RBDATA_TEXT_SIZE;

IMHO the WARN_ON_ONCE's are excessive. It is allowed to expect that
get_random_u32_inclusive() works correctly. But I am fine with it.

Reviewed-by: John Ogness <john.ogness@...utronix.de>