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Date: Thu, 25 Apr 2024 12:04:10 +0200
From: Florian Westphal <fw@strlen.de>
To: Eric Dumazet <edumazet@google.com>
Cc: Pablo Neira Ayuso <pablo@netfilter.org>, linke li <lilinke99@qq.com>,
	xujianhao01@gmail.com, Jozsef Kadlecsik <kadlec@netfilter.org>,
	Florian Westphal <fw@strlen.de>,
	"David S. Miller" <davem@davemloft.net>,
	Jakub Kicinski <kuba@kernel.org>, Paolo Abeni <pabeni@redhat.com>,
	netfilter-devel@vger.kernel.org, coreteam@netfilter.org,
	netdev@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] netfilter: mark racy access on ext->gen_id
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References: <tencent_284407955020261D1B2BD142194A87C9EB0A@qq.com>
 <ZiokCzm41m21CxLR@calendula>
 <CANn89iLxRgYSsFokDo327B4CwwwN9B1Q8e+OHvQenn0a5SfxDQ@mail.gmail.com>
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User-Agent: Mutt/1.10.1 (2018-07-13)

Eric Dumazet <edumazet@google.com> wrote:
> > There are a more uses ext->gen_id in the code, my understanding this
> > patch is just a stub.
> 
> Anyway, ext->gen_id was already read and stored in @this_id
> 
> I would probably avoid reading it a second time.
 
> diff --git a/net/netfilter/nf_conntrack_extend.c
> b/net/netfilter/nf_conntrack_extend.c
> index dd62cc12e7750734fec9be8a90fd0defcbc815e0..747797b20bc7417a2b7270d84f62d24991a4b982
> 100644
> --- a/net/netfilter/nf_conntrack_extend.c
> +++ b/net/netfilter/nf_conntrack_extend.c
> @@ -141,7 +141,7 @@ void *__nf_ct_ext_find(const struct nf_ct_ext *ext, u8 id)
>         if (!__nf_ct_ext_exist(ext, id))
>                 return NULL;
> 
> -       if (this_id == 0 || ext->gen_id == gen_id)
> +       if (this_id == 0 || this_id == gen_id)
>                 return (void *)ext + ext->offset[id];
> 
>         return NULL;
> 

Right, that should work, unconfirmed entries are not exposed to other
cpus and confirmed entries get their id set to 0.