linux-kernel - Re: kernel/printk/printk.c: Invalid access when buffer wraps around?

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Date:	Fri, 5 Aug 2016 07:14:38 +0200
From:	Vincent Brillault <vincent.brillault@...n.ch>
To:	Ivan Delalande <colona@...sta.com>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Petr Mladek <pmladek@...e.com>,
	Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
	Andrey Ryabinin <aryabinin@...tuozzo.com>,
	Kees Cook <keescook@...omium.org>,
	Thierry Reding <treding@...dia.com>,
	Geliang Tang <geliangtang@....com>, Tejun Heo <tj@...nel.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: kernel/printk/printk.c: Invalid access when buffer wraps around?

Dear Ivan, all

Sorry for the delay, I currently have limited internet access.

> Thanks for your very detailled write-up but I believe you are mistaken
> on the value of log_first_idx between these two last steps you describe.

After re-reading log_next and log_make_free_space, I believe that you
are right and that I was wrong. Your explanation is crystal-clear and I
now don't understand how I missed this (it's even explained in the
comments...). This means that we might be removing the first element in
the buffer while there was enough space to store it at the end of the
buffer, but I guess this is better than having a bug ;)

I'm sorry for the noise everyone. Thank you for your patience and great
explanation.

Sincerely yours,
Vincent Brillault

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