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

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Date: Tue, 19 Dec 2023 18:55:35 +0100
From: Christophe JAILLET <christophe.jaillet@...adoo.fr>
To: Sohil Mehta <sohil.mehta@...el.com>, 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()

Le 19/12/2023 à 12:02, Sohil Mehta a écrit :
> 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".

 From my POV, it is what the gcc warning already says, but I (or anyone 
else) can tweak the wording to make it more explicit.

Let me know if you want a v2.

CJ

> 
> 
>> (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);
> 
> 
>