linux-kernel - Re: [PATCH] Kbuild: Disable the -Wformat-security gcc flag

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Date:	Wed, 04 Feb 2009 17:48:42 -0600
From:	Robert Hancock <hancockrwd@...il.com>
To:	Roland Dreier <rdreier@...co.com>
CC:	Sam Ravnborg <sam@...nborg.org>, Floris Kraak <randakar@...il.com>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Trivial Patch Monkey <trivial@...nel.org>
Subject: Re: [PATCH] Kbuild: Disable the -Wformat-security gcc flag

Roland Dreier wrote:
>  > Before judging on this patch could you please post what warning it
>  > triggers and one or a few patches to fix some of them.
> 
> The warnings are things like:
> 
>     init/main.c: In function 'start_kernel':
>     init/main.c:557: warning: format not a string literal and no format arguments
> 
> where the patch to fix this would be:
> 
> diff --git a/init/main.c b/init/main.c
> index 8442094..78fc0d8 100644
> --- a/init/main.c
> +++ b/init/main.c
> @@ -554,7 +554,7 @@ asmlinkage void __init start_kernel(void)
>  	boot_cpu_init();
>  	page_address_init();
>  	printk(KERN_NOTICE);
> -	printk(linux_banner);
> +	printk("%s", linux_banner);
>  	setup_arch(&command_line);
>  	mm_init_owner(&init_mm, &init_task);
>  	setup_command_line(command_line);
> 
> with the impact:
> 
> add/remove: 0/0 grow/shrink: 1/0 up/down: 7/0 (7)
> function                                     old     new   delta
> start_kernel                                 689     696      +7

Just how many of these warnings are showing up? In the cases you posted 
it's presumably no problem, but if the string could either a) be 
potentially set by a malicious user or b) accidentally contain printk 
format characters then this code has a risk that things could blow up..
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