linux-hardening - Re: Coverity: console_prepend_dropped(): Memory

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Date:   Tue, 17 Jan 2023 08:16:48 +0106
From:   John Ogness <john.ogness@...utronix.de>
To:     Sergey Senozhatsky <senozhatsky@...omium.org>,
        Petr Mladek <pmladek@...e.com>
Cc:     Sergey Senozhatsky <senozhatsky@...omium.org>,
        coverity-bot <keescook@...omium.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        linux-kernel@...r.kernel.org,
        "Gustavo A. R. Silva" <gustavo@...eddedor.com>,
        linux-next@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: Coverity: console_prepend_dropped(): Memory - corruptions

On 2023-01-17, Sergey Senozhatsky <senozhatsky@...omium.org> wrote:
> On (23/01/16 17:35), Petr Mladek wrote:
>> 	len = snprintf(scratchbuf, scratchbuf_sz,
>> 		       "** %lu printk messages dropped **\n", dropped);
>
> Wouldn't
>
> 	if (WARN_ON_ONCE(len + PRINTK_PREFIX_MAX >= outbuf_sz))
> 		return;
>
> prevent us from doing something harmful?

Sure. But @0len is supposed to contain the number of bytes in
@scratchbuf, which theoretically it does not. snprintf() is the wrong
function to use here, even if there is not real danger in this
situation.

John Ogness