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

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Date:   Wed, 22 Feb 2023 10:11:03 +0800
From:   Pavel Tikhomirov <ptikhomirov@...tuozzo.com>
To:     Pablo Neira Ayuso <pablo@...filter.org>
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 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.
-- 
Best regards, Tikhomirov Pavel
Software Developer, Virtuozzo.