linux-kernel - Re: [PATCH] UAPI: net/sched: Open-code __struct_group() in flex struct tc_u32

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Message-ID: <ff680866-b81f-48c1-8a59-1107b4ce14ff@embeddedor.com>
Date: Tue, 17 Dec 2024 10:25:29 -0600
From: "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To: Alexander Lobakin <aleksander.lobakin@...el.com>
Cc: Kees Cook <kees@...nel.org>, Jakub Kicinski <kuba@...nel.org>,
 cferris@...gle.com, Jamal Hadi Salim <jhs@...atatu.com>,
 Cong Wang <xiyou.wangcong@...il.com>, Jiri Pirko <jiri@...nulli.us>,
 netdev@...r.kernel.org, "Gustavo A. R. Silva" <gustavoars@...nel.org>,
 linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH] UAPI: net/sched: Open-code __struct_group() in flex
 struct tc_u32_sel

On 17/12/24 10:04, Alexander Lobakin wrote:
> From: Gustavo A. R. Silva <gustavo@...eddedor.com>
> Date: Tue, 17 Dec 2024 09:58:28 -0600
> 
>>
>>
>> On 17/12/24 08:55, Alexander Lobakin wrote:
>>> From: Kees Cook <kees@...nel.org>
>>> Date: Mon, 16 Dec 2024 18:59:55 -0800
>>>
>>>> This switches to using a manually constructed form of struct tagging
>>>> to avoid issues with C++ being unable to parse tagged structs within
>>>> anonymous unions, even under 'extern "C"':
>>>>
>>>>     ../linux/include/uapi/linux/pkt_cls.h:25124: error: ‘struct
>>>> tc_u32_sel::<unnamed union>::tc_u32_sel_hdr,’ invalid; an anonymous
>>>> union may only have public non-static data members [-fpermissive]
>>>
>>> I worked around that like this in the past: [0]
>>> As I'm not sure it would be fine to fix every such occurrence manually
>>> by open-coding.
>>> What do you think?
>>
>> The thing is that, in this particular case, we need a struct tag to change
>> the type of an object in another struct. See:
> 
> But the fix I mentioned still allows you to specify a tag in C code...
> cxgb4 is for sure not C++.

Oh yes, I see what you mean. If it works, then you should probably submit that
patch upstream. :)

Thanks
--
Gustavo