linux-kernel - Re: [PATCH nf] netfilter: conntrack: Avoid nf_ct_helper

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Message-ID: <20230621184738.GG24035@breakpoint.cc>
Date:   Wed, 21 Jun 2023 20:47:38 +0200
From:   Florian Westphal <fw@...len.de>
To:     Florent Revest <revest@...omium.org>
Cc:     Florian Westphal <fw@...len.de>,
        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

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?

Thanks.