linux-kernel - Re: [PATCH v2] hv_netvsc: Replace one-element array with flexible array member

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Message-ID: <4f1e37f0-d72d-4748-a5e4-0ee28d33ca38@intel.com>
Date: Fri, 17 Jan 2025 12:10:52 +0100
From: Przemek Kitszel <przemyslaw.kitszel@...el.com>
To: Jakub Kicinski <kuba@...nel.org>, Roman Kisel <romank@...ux.microsoft.com>
CC: Thorsten Blum <thorsten.blum@...ux.dev>, "K. Y. Srinivasan"
	<kys@...rosoft.com>, Haiyang Zhang <haiyangz@...rosoft.com>, Wei Liu
	<wei.liu@...nel.org>, Dexuan Cui <decui@...rosoft.com>, Andrew Lunn
	<andrew+netdev@...n.ch>, "David S. Miller" <davem@...emloft.net>, "Eric
 Dumazet" <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>,
	<linux-hardening@...r.kernel.org>, <linux-hyperv@...r.kernel.org>,
	<netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] hv_netvsc: Replace one-element array with flexible
 array member

On 1/17/25 01:17, Jakub Kicinski wrote:
> On Thu, 16 Jan 2025 13:39:52 -0800 Roman Kisel wrote:
>> On 1/16/2025 1:19 PM, Thorsten Blum wrote:
>>> Replace the deprecated one-element array with a modern flexible array
>>> member in the struct nvsp_1_message_send_receive_buffer_complete.
>>>
>>> Use struct_size_t(,,1) instead of sizeof() to maintain the same size.

I would add a struct-specific macro or at least put the info into this
struct' doc, that "there is legacy API requirement to allocate at least
one element for the flex array member".

>>
>> Thanks!
>>
>>>
>>> Compile-tested only.
>>
>> The code change looks good to me now. I'll build a VM with this change
>> to clear my conscience (maybe the change triggers a compiler bug,
>> however unlikely that sounds) before replying with any tags. Likely next
>> Monday, but feel free to beat me to it, or perhaps, someone else will
>> tag this as reviewed by them and/or tested by them.
> 
> Doesn't look like a real bug fix, so would be good to get some signal

If the actual usage would be with more than 1 element UBSAN will
complain.

> soon. The merge window is soon so we'll likely close the trees very
> very soon ..
>