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Message-ID: <b4c2ea7ec34aaf05d53264b19a6c40245ed361c0.camel@perches.com>
Subject: Re: [PATCH next v2 1/2] printk: avoid and/or handle record
 truncation
From:   Joe Perches <joe@perches.com>
To:     John Ogness <john.ogness@linutronix.de>,
        Petr Mladek <pmladek@suse.com>
Cc:     Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>,
        Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Marek Szyprowski <m.szyprowski@samsung.com>,
        linux-kernel@vger.kernel.org
Date:   Wed, 30 Sep 2020 08:25:24 -0700
In-Reply-To: <20200930090134.8723-2-john.ogness@linutronix.de>
References: <20200930090134.8723-1-john.ogness@linutronix.de>
         <20200930090134.8723-2-john.ogness@linutronix.de>
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On Wed, 2020-09-30 at 11:07 +0206, John Ogness wrote:
> If a reader provides a buffer that is smaller than the message text,
> the @text_len field of @info will have a value larger than the buffer
> size. If readers blindly read @text_len bytes of data without
> checking the size, they will read beyond their buffer.
> 
> Add this check to record_print_text() to properly recognize when such
> truncation has occurred.
> 
> Add a maximum size argument to the ringbuffer function to extend
> records so that records can not be created that are larger than the
> buffer size of readers.
> 
> When extending records (LOG_CONT), do not extend records beyond
> LOG_LINE_MAX since that is the maximum size available in the buffers
> used by consoles and syslog.

I still think it better to support backspace by rewinding
the buffer rather than truncation of the output.