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Date: Tue, 12 Mar 2024 15:05:35 +0100
From: Florian Westphal <fw@strlen.de>
To: Quan Tian <tianquan23@gmail.com>
Cc: netfilter-devel@vger.kernel.org, pablo@netfilter.org,
	kadlec@netfilter.org, fw@strlen.de
Subject: Re: [PATCH v3 nf-next 1/2] netfilter: nf_tables: use struct nlattr *
 to store userdata for nft_table
Message-ID: <20240312140535.GC1529@breakpoint.cc>
References: <20240311141454.31537-1-tianquan23@gmail.com>
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User-Agent: Mutt/1.10.1 (2018-07-13)

Quan Tian <tianquan23@gmail.com> wrote:
>  	u32				nlpid;
>  	char				*name;
> -	u16				udlen;
> -	u8				*udata;
> +	struct nlattr			*udata;

I missed this detail.  As Pablo pointed out this pointer
now needs a __rcu annotation.

And this needs something like:

struct nlattr *udata = rcu_dereference(table->udata);

if (udata) {
 	if (nla_put(skb, NFTA_TABLE_USERDATA, nla_len(udata), nla_data(udata)))

> +		if (nla_put(skb, NFTA_TABLE_USERDATA, nla_len(table->udata),
> +			    nla_data(table->udata)))

... because this version can observe different table->udata for
nla_len() and nla_data() calls if the swap() has the "right" / "wrong"
timing.