netdev - Re: [PATCH nf] netfilter: conntrack: Avoid nf_ct_helper

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Date: Mon, 3 Jul 2023 16:42:30 +0200
From: Florent Revest <revest@...omium.org>
To: Florian Westphal <fw@...len.de>
Cc: Pablo Neira Ayuso <pablo@...filter.org>, netfilter-devel@...r.kernel.org, 
	coreteam@...filter.org, netdev@...r.kernel.org, linux-kernel@...r.kernel.org, 
	bpf@...r.kernel.org, kadlec@...filter.org, davem@...emloft.net, 
	edumazet@...gle.com, kuba@...nel.org, pabeni@...hat.com, lirongqing@...du.com, 
	daniel@...earbox.net, ast@...nel.org, kpsingh@...nel.org, 
	stable@...r.kernel.org
Subject: Re: [PATCH nf] netfilter: conntrack: Avoid nf_ct_helper_hash uses
 after free

On Wed, Jun 21, 2023 at 8:47 PM Florian Westphal <fw@...len.de> wrote:
>
> Florent Revest <revest@...omium.org> wrote:
> > > in this case an initcall is failing and I think panic is preferrable
> > > to a kernel that behaves like NF_CONNTRACK_FTP=n.
> >
> > In that case, it seems like what you'd want is
> > nf_conntrack_standalone_init() to BUG() instead of returning an error
> > then ? (so you'd never get to NF_CONNTRACK_FTP or any other if
> > nf_conntrack failed to initialize) If this is the prefered behavior,
> > then sure, why not.
> >
> > > AFAICS this problem is specific to NF_CONNTRACK_FTP=y
> > > (or any other helper module, for that matter).
> >
> > Even with NF_CONNTRACK_FTP=m, the initialization failure in
> > nf_conntrack_standalone_init() still happens. Therefore, the helper
> > hashtable gets freed and when the nf_conntrack_ftp.ko module gets
> > insmod-ed, it calls nf_conntrack_helpers_register() and this still
> > causes a use-after-free.
>
> Can you send a v2 with a slightly reworded changelog?
>
> It should mention that one needs NF_CONNTRACK=y, so that when
> the failure happens during the initcall (as oposed to module insertion),
> nf_conntrack_helpers_register() can fail cleanly without followup splat?

Sure! :) On it.