linux-hardening - Re: [PATCH] netdev: Use flexible array for trailing private bytes

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Date: Mon, 4 Mar 2024 07:24:49 -0800
From: Jakub Kicinski <kuba@...nel.org>
To: Alexander Lobakin <aleksander.lobakin@...el.com>
Cc: Eric Dumazet <edumazet@...gle.com>, Kees Cook <keescook@...omium.org>,
 "David S. Miller" <davem@...emloft.net>, Paolo Abeni <pabeni@...hat.com>,
 Andy Shevchenko <andriy.shevchenko@...ux.intel.com>, "Gustavo A. R. Silva"
 <gustavoars@...nel.org>, <netdev@...r.kernel.org>,
 <linux-hardening@...r.kernel.org>, Simon Horman <horms@...nel.org>, "Jiri
 Pirko" <jiri@...nulli.us>, Daniel Borkmann <daniel@...earbox.net>, Coco Li
 <lixiaoyan@...gle.com>, Amritha Nambiar <amritha.nambiar@...el.com>,
 <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] netdev: Use flexible array for trailing private bytes

On Mon, 4 Mar 2024 15:32:51 +0100 Alexander Lobakin wrote:
> > 100% I should have linked to the thread that led to Kees's work.
> > Adding directly to net_device would be way better but there's
> > a handful of drivers which embed the struct.  
> 
> I think it's okay to embed a struct with flex array at the end as long
> as it's not used? Or the compiler will say that the flex array is not at
> the end of the structure?

Technically, yes. Practically it ties the lifetime of a refcounted
object to something semi-related with different lifetime rules :(