linux-hardening - Re: [PATCH] md/bcache: Mark _

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Message-ID: <994E520B-64B1-4387-8DFF-88755346FE55@kernel.org>
Date: Thu, 17 Apr 2025 00:10:53 -0700
From: Kees Cook <kees@...nel.org>
To: Ard Biesheuvel <ardb@...nel.org>
CC: Coly Li <colyli@...nel.org>, Kent Overstreet <kent.overstreet@...ux.dev>,
 linux-bcache@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-hardening@...r.kernel.org
Subject: Re: [PATCH] md/bcache: Mark __nonstring look-up table



On April 16, 2025 11:16:45 PM PDT, Ard Biesheuvel <ardb@...nel.org> wrote:
>On Thu, 17 Apr 2025 at 00:01, Kees Cook <kees@...nel.org> wrote:
>>
>> GCC 15's new -Wunterminated-string-initialization notices that the 16
>> character lookup table "zero_uuid" (which is not used as a C-String)
>> needs to be marked as "nonstring":
>>
>> drivers/md/bcache/super.c: In function 'uuid_find_empty':
>> drivers/md/bcache/super.c:549:43: warning: initializer-string for array of 'char' truncates NUL terminator but destination lacks 'nonstring' attribute (17 chars into 16 available) [-Wunterminated-string-initialization]
>>   549 |         static const char zero_uuid[16] = "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0";
>>       |                                           ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>>
>> Add the annotation to silence the GCC warning.
>>
>> Signed-off-by: Kees Cook <kees@...nel.org>
>> ---
>> Cc: Coly Li <colyli@...nel.org>
>> Cc: Kent Overstreet <kent.overstreet@...ux.dev>
>> Cc: linux-bcache@...r.kernel.org
>> ---
>>  drivers/md/bcache/super.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c
>> index e42f1400cea9..577d048170fe 100644
>> --- a/drivers/md/bcache/super.c
>> +++ b/drivers/md/bcache/super.c
>> @@ -546,7 +546,7 @@ static struct uuid_entry *uuid_find(struct cache_set *c, const char *uuid)
>>
>>  static struct uuid_entry *uuid_find_empty(struct cache_set *c)
>>  {
>> -       static const char zero_uuid[16] = "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0";
>> +       static const char zero_uuid[] __nonstring = "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0";
>>
>
>Just
>
>static const char zero_uuid[16] = {};
>
>should work fine here too. No need for the initializer.

🤦 Yes. This is what I get for fixing dozens of these. I'll send a v2...

-Kees


-- 
Kees Cook