linux-kernel - Re: [PATCH] x86/callthunks: Fix some potential string truncation in callthunks_debugfs

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Date: Tue, 19 Dec 2023 16:32:13 +0530
From: Sohil Mehta <sohil.mehta@...el.com>
To: Christophe JAILLET <christophe.jaillet@...adoo.fr>, Thomas Gleixner
	<tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov
	<bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>, <x86@...nel.org>,
	"H. Peter Anvin" <hpa@...or.com>
CC: <linux-kernel@...r.kernel.org>, <kernel-janitors@...r.kernel.org>
Subject: Re: [PATCH] x86/callthunks: Fix some potential string truncation in
 callthunks_debugfs_init()

On 12/17/2023 2:31 PM, Christophe JAILLET wrote:
> When compiled with W=1, we get:
>   arch/x86/kernel/callthunks.c: In function ‘callthunks_debugfs_init’:
>   arch/x86/kernel/callthunks.c:394:35: error: ‘%lu’ directive writing between 1 and 10 bytes into a region of size 7 [-Werror=format-overflow=]
>     394 |                 sprintf(name, "cpu%lu", cpu);
>         |                                   ^~~
>   arch/x86/kernel/callthunks.c:394:31: note: directive argument in the range [0, 4294967294]
>     394 |                 sprintf(name, "cpu%lu", cpu);
>         |                               ^~~~~~~~
>   arch/x86/kernel/callthunks.c:394:17: note: ‘sprintf’ output between 5 and 14 bytes into a destination of size 10
>     394 |                 sprintf(name, "cpu%lu", cpu);
>         |
> 
> So, give some more space to 'name' to silence the warning.

It might be useful to specify that "some more space" hasn't been
arbitrarily decided. It took me a few minutes to figure that out.

With the max cpu number being 4294967294 with 10 characters, a total of
14 chars would be enough to print "cpu%lu".


> (and fix the issue should a lucky one have a config with so many
> CPU!)
> Signed-off-by: Christophe JAILLET <christophe.jaillet@...adoo.fr>
> ---
>  arch/x86/kernel/callthunks.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 

Apart from that, please feel free to add:

Reviewed-by: Sohil Mehta <sohil.mehta@...el.com>

> diff --git a/arch/x86/kernel/callthunks.c b/arch/x86/kernel/callthunks.c
> index cf7e5be1b844..26182a7d12b3 100644
> --- a/arch/x86/kernel/callthunks.c
> +++ b/arch/x86/kernel/callthunks.c
> @@ -388,7 +388,7 @@ static int __init callthunks_debugfs_init(void)
>  	dir = debugfs_create_dir("callthunks", NULL);
>  	for_each_possible_cpu(cpu) {
>  		void *arg = (void *)cpu;
> -		char name [10];
> +		char name[14];
>  
>  		sprintf(name, "cpu%lu", cpu);
>  		debugfs_create_file(name, 0644, dir, arg, &dfs_ops);