linux-hardening - Re: [PATCH] printk: ringbuffer: Fix truncating buffer size min

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Message-ID: <875y5i16xf.fsf@jogness.linutronix.de>
Date:   Mon, 14 Aug 2023 08:26:28 +0206
From:   John Ogness <john.ogness@...utronix.de>
To:     Kees Cook <keescook@...omium.org>, Petr Mladek <pmladek@...e.com>
Cc:     Kees Cook <keescook@...omium.org>,
        Sergey Senozhatsky <senozhatsky@...omium.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Vijay Balakrishna <vijayb@...ux.microsoft.com>,
        stable@...r.kernel.org, Tony Luck <tony.luck@...el.com>,
        "Guilherme G. Piccoli" <gpiccoli@...lia.com>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH] printk: ringbuffer: Fix truncating buffer size min_t cast

On 2023-08-10, Kees Cook <keescook@...omium.org> wrote:
> If an output buffer size exceeded U16_MAX, the min_t(u16, ...) cast in
> copy_data() was causing writes to truncate. This manifested as output
> bytes being skipped, seen as %NUL bytes in pstore dumps when the available
> record size was larger than 65536. Fix the cast to no longer truncate
> the calculation.

Thanks for tracking this down.

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