linux-kernel - Coverity: console_prepend_dropped(): Memory

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Date:   Fri, 13 Jan 2023 15:46:27 -0800
From:   coverity-bot <keescook@...omium.org>
To:     John Ogness <john.ogness@...utronix.de>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Sergey Senozhatsky <senozhatsky@...omium.org>,
        Petr Mladek <pmladek@...e.com>, linux-kernel@...r.kernel.org,
        "Gustavo A. R. Silva" <gustavo@...eddedor.com>,
        linux-next@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Coverity: console_prepend_dropped(): Memory - corruptions

Hello!

This is an experimental semi-automated report about issues detected by
Coverity from a scan of next-20230113 as part of the linux-next scan project:
https://scan.coverity.com/projects/linux-next-weekly-scan

You're getting this email because you were associated with the identified
lines of code (noted below) that were touched by commits:

  Wed Jan 11 15:35:11 2023 +0100
    c4fcc617e148 ("printk: introduce console_prepend_dropped() for dropped messages")

Coverity reported the following:

*** CID 1530570:  Memory - corruptions  (OVERRUN)
kernel/printk/printk.c:2738 in console_prepend_dropped()
2732     		/* Truncate the message, but keep it terminated. */
2733     		pmsg->outbuf_len = outbuf_sz - (len + 1);
2734     		outbuf[pmsg->outbuf_len] = 0;
2735     	}
2736
2737     	memmove(outbuf + len, outbuf, pmsg->outbuf_len + 1);
vvv     CID 1530570:  Memory - corruptions  (OVERRUN)
vvv     Overrunning buffer pointed to by "scratchbuf" of 1024 bytes by passing it to a function which accesses it at byte offset 1998 using argument "len" (which evaluates to 1999). [Note: The source code implementation of the function has been overridden by a builtin model.]
2738     	memcpy(outbuf, scratchbuf, len);
2739     	pmsg->outbuf_len += len;
2740     }
2741     #else
2742     #define console_prepend_dropped(pmsg, dropped)
2743     #endif /* CONFIG_PRINTK */

If this is a false positive, please let us know so we can mark it as
such, or teach the Coverity rules to be smarter. If not, please make
sure fixes get into linux-next. :) For patches fixing this, please
include these lines (but double-check the "Fixes" first):

Reported-by: coverity-bot <keescook+coverity-bot@...omium.org>
Addresses-Coverity-ID: 1530570 ("Memory - corruptions")
Fixes: c4fcc617e148 ("printk: introduce console_prepend_dropped() for dropped messages")

Thanks for your attention!

Human notes from Kees:

I'm not sure how it got 1998, but I do see that snprintf() should
probably be scnprintf(), otherwise "len" might be a lie (i.e. it'll hold
what it WANTED to write, rather than what it actually wrote).

-- 
Coverity-bot