netdev - Re: [PATCH nf-next v3 1/2] netfilter: Fix potential null pointer dereference

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Message-ID: <f7tbmz8hw5o.fsf@redhat.com>
Date:   Wed, 28 Sep 2016 11:38:27 -0400
From:   Aaron Conole <aconole@...heb.org>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     netfilter-devel@...r.kernel.org, netdev@...r.kernel.org,
        Florian Westphal <fw@...len.de>,
        Pablo Neira Ayuso <pablo@...filter.org>
Subject: Re: [PATCH nf-next v3 1/2] netfilter: Fix potential null pointer dereference

Eric Dumazet <eric.dumazet@...il.com> writes:

> On Wed, 2016-09-28 at 10:56 -0400, Aaron Conole wrote:
>> Eric Dumazet <eric.dumazet@...il.com> writes:
>> 
>> > On Wed, 2016-09-28 at 09:12 -0400, Aaron Conole 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
>> >> entry in the list, both will enter the nf_hook_mutex critical section.
>> >> The first will successfully delete the head, but the second will see
>> >> this NULL pointer and attempt to dereference.
>> >> 
>> >> This fix ensures that no null pointer dereference could occur when such
>> >> a condition 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;
>> >
>> > When was the bug added exactly ?
>> 
>> Sunday, on the nf-next tree.
>> 
>> > For all bug fixes, you need to add a Fixes: tag.
>> >
>> > Like :
>> >
>> > Fixes: e3b37f11e6e4 ("netfilter: replace list_head with single linked list")
>> 
>> I would but it's in nf-next tree, and I'm not sure how pulls go.  If
>> they are done via patch imports, then the sha sums will be wrong and the
>> commit message will be misleading.  If the sums are preserved, then I
>> can resubmit with this information.
>> 
>
> I gave the (12 digits) sha-1 as present in David Miller net-next tree.
>
> https://git.kernel.org/cgit/linux/kernel/git/davem/net-next.git/commit/?id=e3b37f11e6e4e6b6f02cc762f182ce233d2c1c9d
>
>
> This wont change, because David never rebases his tree under normal
> operations.
>
> Thanks.

Thank you very much, Eric.  I've reposted.

-Aaron