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

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Message-ID: <ZNoSyX0YtorbLy7V@alley>
Date:   Mon, 14 Aug 2023 13:40:57 +0200
From:   Petr Mladek <pmladek@...e.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     Sergey Senozhatsky <senozhatsky@...omium.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        John Ogness <john.ogness@...utronix.de>,
        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 Thu 2023-08-10 22:45:32, Kees Cook 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.
> 
> Cc: Petr Mladek <pmladek@...e.com>
> Cc: Sergey Senozhatsky <senozhatsky@...omium.org>
> Cc: Steven Rostedt <rostedt@...dmis.org>
> Cc: John Ogness <john.ogness@...utronix.de>
> Reported-by: Vijay Balakrishna <vijayb@...ux.microsoft.com>
> Closes: https://lore.kernel.org/lkml/d8bb1ec7-a4c5-43a2-9de0-9643a70b899f@linux.microsoft.com/

checkpatch.pl suggested that "Link:" should be used instead of "Closes:".

> Fixes: b6cf8b3f3312 ("printk: add lockless ringbuffer")
> Cc: stable@...r.kernel.org
> Signed-off-by: Kees Cook <keescook@...omium.org>

Reviewed-by: Petr Mladek <pmladek@...e.com>

Thanks a lot for tracking this down.

The patch has been comitted into printk/linux.git, branch for-6.6.

I though about pushing it for 5.5-rc7. But it is pretty old issue.
It does not break the system. I wanted to give it some spin in
linux-next. And I leave for vacation on Thursday. I will not
have internet connection until Aug 28.

Best Regards,
Petr