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

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Message-ID: <ZehsoPb/WZzUcFHa@gmail.com>
Date: Wed, 6 Mar 2024 05:16:16 -0800
From: Breno Leitao <leitao@...ian.org>
To: Jakub Kicinski <kuba@...nel.org>, keescook@...omium.org
Cc: "David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>, 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 Thu, Feb 29, 2024 at 10:59:10PM -0800, Jakub Kicinski wrote:
> On Thu, 29 Feb 2024 13:30:22 -0800 Kees Cook wrote:
> > Introduce a new struct net_device_priv that contains struct net_device
> > but also accounts for the commonly trailing bytes through the "size" and
> > "data" members.
> 
> I'm a bit unclear on the benefit. Perhaps I'm unaccustomed to "safe C".
> 
> > As many dummy struct net_device instances exist still,
> > it is non-trivial to but this flexible array inside struct net_device
> 
> put
> 
> Non-trivial, meaning what's the challenge?
> We also do somewhat silly things with netdev lifetime, because we can't
> assume netdev gets freed by netdev_free(). Cleaning up the "embedders"
> would be beneficial for multiple reasons.

I've been looking at some of these embedders as reported by Kees[1], and
most of them are for dummy interfaces. I.e, they are basically used for
schedule NAPI poll.

>From that list[1], most of the driver matches with:

	# git grep init_dummy_netdev

That said, do you think it is still worth cleaning up embedders for
dummy net_devices?

[1] https://lore.kernel.org/all/202402281554.C1CEEF744@keescook/