netdev - Re: [PATCH net-next] net: ethtool: Fix out-of-bounds copy to user

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Date: Mon, 5 Jun 2023 11:39:15 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: Ding Hui <dinghui@...gfor.com.cn>
Cc: Alexander Duyck <alexander.duyck@...il.com>, Andrew Lunn
 <andrew@...n.ch>, davem@...emloft.net, edumazet@...gle.com,
 pabeni@...hat.com, netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
 pengdonglin@...gfor.com.cn, huangcun@...gfor.com.cn
Subject: Re: [PATCH net-next] net: ethtool: Fix out-of-bounds copy to user

On Mon, 5 Jun 2023 11:39:59 +0800 Ding Hui wrote:
> Case 1:
> If the user len/n_stats is not zero, we will treat it as correct usage
> (although we cannot distinguish between the real correct usage and
> uninitialized usage). Return -EINVAL if current length exceed the one
> user specified.

This assumes user will zero-initialize the value rather than do
something like:

	buf = malloc(1 << 16); // 64k should always be enough
	ioctl(s, ETHTOOL_GSTATS, buf)

	for (i = 0; i < buf.n_stats; i++)
		/* use stats */

:(

> Case 2:
> If it is zero, we will treat it as incorrect usage, we can add a
> pr_err_once() for it and keep to be compatible with it for a period of time.
> At a suitable time in the future, this part can be removed by maintainers.