Subject: Re: Coverity: console_prepend_dropped(): Memory - corruptions

From: Sergey Senozhatsky <[email-masked]>
Date: Sat, 14 Jan 2023 19:14:29 +0900

On (23/01/13 15:46), coverity-bot wrote:
> *** 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 */
[..]
> 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).

Cannot imagine how "** %lu printk messages dropped **\n" can expand into
1998 bytes. Does coverity have a "verbose" mode?