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

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Message-ID: <09445a96-4f86-4d34-9984-4769bd6f4bc1@embeddedor.com>
Date: Thu, 30 May 2024 10:12:13 +0200
From: "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 Jiri Slaby <jirislaby@...nel.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 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.

The flexible array is nested four struct layers deep, see:

ports[].port.buf.sentinel.data[]

The error report could be more specific, though.

--
Gustavo

> 
>> What does gcc say BTW?
>>
>>> Cc: stable@...r.kernel.org
>>> Closes: https://github.com/ClangBuiltLinux/linux/issues/2026
>>> Fixes: f34907ecca71 ("mxser: Annotate struct mxser_board with __counted_by")
>>
>> I would not say "Fixes" here. It only works around a broken compiler.
> 
> Agreed, don't add Fixes: for this, it's a compiler bug, not a kernel
> issue.
> 
> thanks,
> 
> greg k-h
>