Re: [PATCH nf V2] netfilter: invoke synchronize_rcu after set the _hook_ to NULL

[Pablo Neira Ayuso <pablo@netfilter.org>]

On Sat, Mar 25, 2017 at 08:53:12AM +0800, Liping Zhang wrote:
> From: Liping Zhang <zlpnobody@gmail.com>
> 
> Otherwise, another CPU may access the invalid pointer. For example:
>     CPU0                CPU1
>      -              rcu_read_lock();
>      -              pfunc = _hook_;
>   _hook_ = NULL;          -
>   mod unload              -
>      -                 pfunc(); // invalid, panic
>      -             rcu_read_unlock();
> 
> So we must call synchronize_rcu() to wait the rcu reader to finish.
> 
> Also note, in nf_nat_snmp_basic_fini, synchronize_rcu() will be invoked
> by later nf_conntrack_helper_unregister, but I'm inclined to add a
> explicit synchronize_rcu after set the nf_nat_snmp_hook to NULL. Depend
> on such obscure assumptions is not a good idea.
> 
> Last, in nfnetlink_cttimeout, we use kfree_rcu to free the time object,
> so in cttimeout_exit, invoking rcu_barrier() is not necessary at all,
> remove it too.

Applied, thanks.