netdev - Re: [PATCH net 1/1] netfilter: flowtable: Fix use after free after freeing flow table

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Message-ID: <11b87f33-98fb-e49a-5f63-491d4f27e908@nvidia.com>
Date:   Sun, 21 Aug 2022 12:23:39 +0300
From:   Paul Blakey <paulb@...dia.com>
To:     Pablo Neira Ayuso <pablo@...filter.org>
Cc:     Oz Shlomo <ozsh@...dia.com>, Roi Dayan <roid@...dia.com>,
        netdev@...r.kernel.org, Saeed Mahameed <saeedm@...dia.com>,
        netfilter-devel@...r.kernel.org
Subject: Re: [PATCH net 1/1] netfilter: flowtable: Fix use after free after
 freeing flow table



On 19/08/2022 02:04, Pablo Neira Ayuso wrote:
> Hi Paul,
> 
> On Thu, Aug 18, 2022 at 10:27:54AM +0300, Paul Blakey wrote:
> [...]
>> diff --git a/net/netfilter/nf_flow_table_core.c b/net/netfilter/nf_flow_table_core.c
>> index f2def06d1070..19fd3b5f8a1b 100644
>> --- a/net/netfilter/nf_flow_table_core.c
>> +++ b/net/netfilter/nf_flow_table_core.c
>> @@ -605,6 +605,7 @@ void nf_flow_table_free(struct nf_flowtable *flow_table)
>>   	mutex_unlock(&flowtable_lock);
>>   
>>   	cancel_delayed_work_sync(&flow_table->gc_work);
>> +	nf_flow_table_offload_flush(flow_table);
>>   	nf_flow_table_iterate(flow_table, nf_flow_table_do_cleanup, NULL);
>>   	nf_flow_table_iterate(flow_table, nf_flow_offload_gc_step, NULL);
>>   	nf_flow_table_offload_flush(flow_table);
> 
> patch looks very similar to:
> 
> https://patchwork.ozlabs.org/project/netfilter-devel/patch/1633854320-12326-1-git-send-email-volodymyr.mytnyk@plvision.eu/
> 
> I proposed these two instead to avoid reiterative calls to flush from
> the cleanup path (see attached).
> 
> It should be possible to either take your patch to nf.git (easier for
> -stable backport), then look into my patches for nf-next.git, would
> you pick up on these follow up?


Hi!

The only functional difference here (for HW table) is your patches call 
flush just for the del workqueue instead of del/stats/add, right?

Because in the end you do:
cancel_delayed_work_sync(&flow_table->gc_work);
nf_flow_table_offload_flush(flow_table);
nf_flow_table_iterate(flow_table, nf_flow_table_do_cleanup, NULL);
nf_flow_table_gc_run(flow_table);
nf_flow_table_offload_flush_cleanup(flow_table);


resulting in the following sequence (after expending flush_cleanup()):

cancel_delayed_work_sync(&flow_table->gc_work);
nf_flow_table_offload_flush(flow_table);
nf_flow_table_iterate(flow_table, nf_flow_table_do_cleanup, NULL);
nf_flow_table_gc_run(flow_table);
flush_workqueue(nf_flow_offload_del_wq);
nf_flow_table_gc_run(flowtable);


Where as my (and Volodymyr's) patch does:

cancel_delayed_work_sync(&flow_table->gc_work);
nf_flow_table_offload_flush(flow_table);
nf_flow_table_iterate(flow_table, nf_flow_table_do_cleanup, NULL);
nf_flow_table_iterate(flow_table, nf_flow_offload_gc_step, NULL);
nf_flow_table_offload_flush(flow_table);
nf_flow_table_iterate(flow_table, nf_flow_offload_gc_step, NULL);


so almost identical, I don't see "extra reiterative calls to flush" 
here,  but I'm fine with just your patch as it's more efficient, can we 
take yours to both gits?

Thanks,
Paul.