linux-hardening - Re: [PATCH] tty: mxser: Remove __counted_by from mxser

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Message-ID: <6170ad64-ee1c-4049-97d3-33ce26b4b715@kernel.org>
Date: Thu, 30 May 2024 10:41:06 +0200
From: Jiri Slaby <jirislaby@...nel.org>
To: "Gustavo A. R. Silva" <gustavo@...eddedor.com>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 Nathan Chancellor <nathan@...nel.org>
Cc: Kees Cook <keescook@...omium.org>,
 "Gustavo A. R. Silva" <gustavoars@...nel.org>,
 Bill Wendling <morbo@...gle.com>, Justin Stitt <justinstitt@...gle.com>,
 linux-serial@...r.kernel.org, imx@...ts.linux.dev,
 linux-arm-kernel@...ts.infradead.org, linux-hardening@...r.kernel.org,
 llvm@...ts.linux.dev, patches@...ts.linux.dev, stable@...r.kernel.org
Subject: Re: [PATCH] tty: mxser: Remove __counted_by from mxser_board.ports[]

On 30. 05. 24, 10:33, Jiri Slaby wrote:
> On 30. 05. 24, 10:12, Gustavo A. R. Silva wrote:
>>
>>
>> On 30/05/24 09:40, Greg Kroah-Hartman wrote:
>>> On Thu, May 30, 2024 at 08:22:03AM +0200, Jiri Slaby wrote:
>>>>>   This will be an error in a future compiler version 
>>>>> [-Werror,-Wbounds-safety-counted-by-elt-type-unknown-size]
>>>>>       291 |         struct mxser_port ports[] __counted_by(nports);
>>>>>           |         ^~~~~~~~~~~~~~~~~~~~~~~~~
>>>>>     1 error generated.
>>>>>
>>>>> Remove this use of __counted_by to fix the warning/error. However,
>>>>> rather than remove it altogether, leave it commented, as it may be
>>>>> possible to support this in future compiler releases.
>>>>
>>>> This looks like a compiler bug/deficiency.
>>>
>>> I agree, why not just turn that option off in the compiler so that these
>>> "warnings" will not show up?
>>
>> It's not a compiler bug.
> 
> It is, provided the code compiles and runs.
> 
>> The flexible array is nested four struct layers deep, see:
>>
>> ports[].port.buf.sentinel.data[]
>>
>> The error report could be more specific, though.
> 
> Ah, ok. The assumption is sentinel.data[] shall be unused. That's why it 
> all works. The size is well known, [] is zero size, right?
> 
> Still, fix the compiler, not the code.

Or fix the code (properly).

Flex arrays (even empty) in the middle of structs (like 
ports[].port.buf.sentinel.data[] above is) are deprecated since gcc 14:
https://gcc.gnu.org/pipermail/gcc-patches/2023-August/626516.html

So we should get rid of all those. Sooner than later.

> thanks,
-- 
-- 
js
suse labs