netdev - Re: [PATCH nf-next v2 1/2] netfilter: Fix potential null pointer dereference

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Message-ID: <CA+6hz4q_Fjc7mVZq7RG+RnioXFnD0w8Ows0AqwEy-5CJ7zg0yQ@mail.gmail.com>
Date:   Wed, 28 Sep 2016 09:23:34 +0800
From:   Feng Gao <gfree.wind@...il.com>
To:     Aaron Conole <aconole@...heb.org>
Cc:     Netfilter Developer Mailing List 
        <netfilter-devel@...r.kernel.org>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        Florian Westphal <fw@...len.de>,
        Pablo Neira Ayuso <pablo@...filter.org>
Subject: Re: [PATCH nf-next v2 1/2] netfilter: Fix potential null pointer dereference

Hi Aaraon,

On Tue, Sep 27, 2016 at 9:38 PM, Aaron Conole <aconole@...heb.org> wrote:
> It's possible for nf_hook_entry_head to return NULL if two
> nf_unregister_net_hook calls happen simultaneously with a single hook

The critical region of nf_unregister_net_hook is protected by &nf_hook_mutex.
When it would be called simultaneously?

Regards
Feng

> entry in the list.  This fix ensures that no null pointer dereference
> could occur when such a race happens.
>
> Signed-off-by: Aaron Conole <aconole@...heb.org>
> ---
>  net/netfilter/core.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/net/netfilter/core.c b/net/netfilter/core.c
> index 360c63d..e58e420 100644
> --- a/net/netfilter/core.c
> +++ b/net/netfilter/core.c
> @@ -160,7 +160,7 @@ void nf_unregister_net_hook(struct net *net, const struct nf_hook_ops *reg)
>
>         mutex_lock(&nf_hook_mutex);
>         hooks_entry = nf_hook_entry_head(net, reg);
> -       if (hooks_entry->orig_ops == reg) {
> +       if (hooks_entry && hooks_entry->orig_ops == reg) {
>                 nf_set_hooks_head(net, reg,
>                                   nf_entry_dereference(hooks_entry->next));
>                 goto unlock;
> --
> 2.7.4
>
> --
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