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

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Date:   Wed, 28 Sep 2016 08:30:03 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Aaron Conole <aconole@...hat.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

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.