netdev - Re: [PATCH] hv_netvsc: Replace one-element array with flexible array member

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Message-Id: <6624650C-6D9E-49FA-8CC0-7E5B53C2AAB3@linux.dev>
Date: Thu, 16 Jan 2025 22:14:17 +0100
From: Thorsten Blum <thorsten.blum@...ux.dev>
To: Roman Kisel <romank@...ux.microsoft.com>
Cc: "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>,
 Jakub Kicinski <kuba@...nel.org>,
 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] hv_netvsc: Replace one-element array with flexible array
 member

On 16. Jan 2025, at 21:45, Roman Kisel wrote:
> On 1/16/2025 12:16 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.
>> Link: https://github.com/KSPP/linux/issues/79
>> Signed-off-by: Thorsten Blum <thorsten.blum@...ux.dev>
>> ---
>>  drivers/net/hyperv/hyperv_net.h | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>> diff --git a/drivers/net/hyperv/hyperv_net.h b/drivers/net/hyperv/hyperv_net.h
>> index e690b95b1bbb..234db693cefa 100644
>> --- a/drivers/net/hyperv/hyperv_net.h
>> +++ b/drivers/net/hyperv/hyperv_net.h
>> @@ -464,7 +464,7 @@ struct nvsp_1_message_send_receive_buffer_complete {
>>    *  LargeOffset                            SmallOffset
>>    */
>>  - struct nvsp_1_receive_buffer_section sections[1];
>> + struct nvsp_1_receive_buffer_section sections[];
>>  } __packed;
>>    /*
> 
> 1. How have you tested the change?

Compile-tested only.

> 2. There is an instance of
> 
> `sizeof(struct nvsp_1_message_send_receive_buffer_complete))`
> 
> and your change decreases the size of the struct. Why do you think
> that is fine?

Sorry, I actually changed this to struct_size_t(,,1), but forgot to add
it to the commit - will submit a v2 shortly.

Thanks,
Thorsten