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

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Message-ID: <Y8ZTlVX3HQUVkU13@google.com>
Date:   Tue, 17 Jan 2023 16:51:49 +0900
From:   Sergey Senozhatsky <senozhatsky@...omium.org>
To:     John Ogness <john.ogness@...utronix.de>
Cc:     Sergey Senozhatsky <senozhatsky@...omium.org>,
        Petr Mladek <pmladek@...e.com>,
        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 (23/01/17 08:16), John Ogness wrote:
> 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.

Oh, yes, I agree that snprintf() should be replaced. Maybe we can go
even a bit furhter and replace all snprintf()-s in kernel/printk/*
(well, in a similar fashion, just in case). I'm just trying to understand
what type of assumptions does coverity make here and so far everything
looks rather peculiar.