netdev - Re: [PATCH] netfilter: fix percpu counter block leak on error path when creating new netns

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Message-ID: <Y/XaD3Dt0tiO2yuT@salvia>
Date:   Wed, 22 Feb 2023 10:02:07 +0100
From:   Pablo Neira Ayuso <pablo@...filter.org>
To:     Pavel Tikhomirov <ptikhomirov@...tuozzo.com>
Cc:     Jozsef Kadlecsik <kadlec@...filter.org>,
        Florian Westphal <fw@...len.de>,
        netfilter-devel@...r.kernel.org, coreteam@...filter.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        kernel@...nvz.org
Subject: Re: [PATCH] netfilter: fix percpu counter block leak on error path
 when creating new netns

On Wed, Feb 22, 2023 at 10:11:03AM +0800, Pavel Tikhomirov wrote:
> On 22.02.2023 07:25, Pablo Neira Ayuso wrote:
> > Hi,
> > 
> > On Mon, Feb 13, 2023 at 12:25:05PM +0800, Pavel Tikhomirov wrote:
> > > Here is the stack where we allocate percpu counter block:
> > > 
> > >    +-< __alloc_percpu
> > >      +-< xt_percpu_counter_alloc
> > >        +-< find_check_entry # {arp,ip,ip6}_tables.c
> > >          +-< translate_table
> > > 
> > > And it can be leaked on this code path:
> > > 
> > >    +-> ip6t_register_table
> > >      +-> translate_table # allocates percpu counter block
> > >      +-> xt_register_table # fails
> > > 
> > > there is no freeing of the counter block on xt_register_table fail.
> > > Note: xt_percpu_counter_free should be called to free it like we do in
> > > do_replace through cleanup_entry helper (or in __ip6t_unregister_table).
> > > 
> > > Probability of hitting this error path is low AFAICS (xt_register_table
> > > can only return ENOMEM here, as it is not replacing anything, as we are
> > > creating new netns, and it is hard to imagine that all previous
> > > allocations succeeded and after that one in xt_register_table failed).
> > > But it's worth fixing even the rare leak.
> > 
> > Any suggestion as Fixes: tag here? This issue seems to be rather old?
> 
> 
> If I'm correct:
> 
> 1) we have this exact percpu leak since commit 71ae0dff02d7
> ("netfilter: xtables: use percpu rule counters") which introduced
> the percpu allocation.
> 
> 2) but we don't call cleanup_entry on this path at least since
> commit 1da177e4c3f4 ("Linux-2.6.12-rc2") which is really old.
> 
> 3) I also see the same thing here https://github.com/mpe/linux-fullhistory/blame/1ab7e5ccf454483fb78998854dddd0bab398c3de/net/ipv4/netfilter/arp_tables.c#L1169
> which is probably the initiall commit which introduced
> net/ipv4/netfilter/arp_tables.c file.
> 
> So I'm not sure about Fixes: tag, probably one of those three commits.

Thanks, I will pick #1 as Fixes: tag.