linux-kernel - Re: [PATCH][next] overflow: Fix direct struct member initialization in _DEFINE

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Message-ID: <a9c0ab40-6907-46d8-9107-7afe2f1782ca@embeddedor.com>
Date: Thu, 1 May 2025 16:57:24 -0600
From: "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To: Kees Cook <kees@...nel.org>, "Gustavo A. R. Silva" <gustavoars@...nel.org>
Cc: linux-hardening@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH][next] overflow: Fix direct struct member initialization
 in _DEFINE_FLEX()


> Earlier up in the file:
> 
> ...
>   * @initializer: initializer expression (could be empty for no init).
>     ^^^^^^^^^
>   */
> #define _DEFINE_FLEX(type, name, member, count, initializer...)
> 
> This argument now becomes required, which is fine, but we should keep

Nice catch!

> the docs updated and double check any existing "_DEFINE_FLEX" users that
> may have an empty final argument (I don't see any, so that's nice).

Yep, I build-tested it and saw no errors.

> 
>>   	union {									\
>>   		u8 bytes[struct_size_t(type, member, count)];			\
>>   		type obj;							\
>> -	} name##_u initializer;							\
>> +	} name##_u = { .obj initializer };					\
>>   	type *name = (type *)&name##_u
>>   
>>   /**
>> @@ -444,7 +444,7 @@ static inline size_t __must_check size_sub(size_t minuend, size_t subtrahend)
>>    * elements in array @member.
>>    */
>>   #define DEFINE_FLEX(TYPE, NAME, MEMBER, COUNTER, COUNT)	\
>> -	_DEFINE_FLEX(TYPE, NAME, MEMBER, COUNT, = { .obj.COUNTER = COUNT, })
>> +	_DEFINE_FLEX(TYPE, NAME, MEMBER, COUNT, = { .COUNTER = COUNT, })
>>   
>>   /**
>>    * STACK_FLEX_ARRAY_SIZE() - helper macro for DEFINE_FLEX() family.
> 
> But otherwise, yes, let's do this!
> 

Here you go :)

https://lore.kernel.org/linux-hardening/aBP0b3gfurLFDlwY@kspp/

Thanks!
-Gustavo