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

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Message-ID: <68293959-9141-4184-a436-ea67efa9aa7c@kernel.org>
Date: Thu, 30 May 2024 10:33:03 +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, 10:12, 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.

thanks,
-- 
js
suse labs