linux-kernel - Re: [PATCH] printk: fix buffer overflow potential for print

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Message-ID: <87k0s2n45n.fsf@jogness.linutronix.de>
Date:   Sun, 24 Jan 2021 09:19:40 +0106
From:   John Ogness <john.ogness@...utronix.de>
To:     Sven Schnelle <svens@...ux.ibm.com>
Cc:     Petr Mladek <pmladek@...e.com>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] printk: fix buffer overflow potential for print_text()

Hi Sven,

Thanks for the outstanding analysis!

On 2021-01-23, Sven Schnelle <svens@...ux.ibm.com> wrote:
>> 1401		if (buf_size > 0)
>> 1402			text[len] = 0;
>
> I don't think i have really understood how all the printk magic works,
> but using r->text_buf[len] seems to be the correct place to put the
> zero byte in that case?

Yes, you are correct! @text is pointing to the beginning of the
currently processed line, not the beginning of the buffer.

I will submit a patch to fix our recent fix (unless you would like to do
that).

Thank you for all your help with this!

John Ogness