linux-hardening - Re: [PATCH] greybus: Avoid fake flexible array for response data

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Date: Sun, 18 Feb 2024 10:48:33 -0600
From: Alex Elder <elder@...e.org>
To: Kees Cook <keescook@...omium.org>
Cc: Viresh Kumar <vireshk@...nel.org>, Johan Hovold <johan@...nel.org>,
 Alex Elder <elder@...nel.org>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 "Gustavo A . R . Silva" <gustavo@...eddedor.com>,
 greybus-dev@...ts.linaro.org, linux-staging@...ts.linux.dev,
 linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH] greybus: Avoid fake flexible array for response data

On 2/17/24 3:58 PM, Kees Cook wrote:
> On Sat, Feb 17, 2024 at 02:17:33PM -0600, Alex Elder wrote:
>> On 2/16/24 5:28 PM, Kees Cook wrote:
>>> FORTIFY_SOURCE has been ignoring 0-sized destinations while the kernel
>>> code base has been converted to flexible arrays. In order to enforce
>>> the 0-sized destinations (e.g. with __counted_by), the remaining 0-sized
>>> destinations need to be handled. Instead of converting an empty struct
>>> into using a flexible array, just directly use a pointer without any
>>> additional indirection. Remove struct gb_bootrom_get_firmware_response
>>> and struct gb_fw_download_fetch_firmware_response.
>>
>> The only down side I see is that it sort of disrupts a pattern
>> used on Greybus request handlers (and the response structure definitions).
>>
>> I think a one-line comment in place of each of these two
>> definitions would be helpful, something like:
>> /* gb_fw_download_fetch_firmware_response contains no data */
> 
> Er, maybe this should be "no other data" ? Do you want a v2 of this
> patch?

Sending v2 is probably best, because I'd like to see these
comments.  Greg could fix it up himself but he probably wants
to pull it from the list

And yes, "no other data" is fine, or maybe "no payload"
or "has an empty payload".  Any of those is better than
nothing; you choose.

Thank you.

					-Alex

> 
>> And then add a similar comment above the calls to
>> gb_operation_response_alloc().
>>
>> Otherwise this looks good.
>>
>> Reviewed-by: Alex Elder <elder@...aro.org>
> 
> Thanks!
>