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Subject: Re: [PATCH] printk: ringbuffer: Fix truncating buffer size min_t cast
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To:     Kees Cook <keescook@chromium.org>, Petr Mladek <pmladek@suse.com>
Cc:     Sergey Senozhatsky <senozhatsky@chromium.org>,
        Steven Rostedt <rostedt@goodmis.org>,
        John Ogness <john.ogness@linutronix.de>,
        stable@vger.kernel.org, Tony Luck <tony.luck@intel.com>,
        "Guilherme G. Piccoli" <gpiccoli@igalia.com>,
        "Paul E. McKenney" <paulmck@kernel.org>,
        linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org
References: <20230811054528.never.165-kees@kernel.org>
From:   Vijay Balakrishna <vijayb@linux.microsoft.com>
In-Reply-To: <20230811054528.never.165-kees@kernel.org>
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On 8/10/23 22:45, 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@suse.com>
> Cc: Sergey Senozhatsky <senozhatsky@chromium.org>
> Cc: Steven Rostedt <rostedt@goodmis.org>
> Cc: John Ogness <john.ogness@linutronix.de>
> Reported-by: Vijay Balakrishna <vijayb@linux.microsoft.com>
> Closes: https://lore.kernel.org/lkml/d8bb1ec7-a4c5-43a2-9de0-9643a70b899f@linux.microsoft.com/
> Fixes: b6cf8b3f3312 ("printk: add lockless ringbuffer")
> Cc: stable@vger.kernel.org
> Signed-off-by: Kees Cook <keescook@chromium.org>

Excellent.

I have verified on v5.10.

Tested-by: Vijay Balakrishna <vijayb@linux.microsoft.com>

Thanks,
Vijay