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

From: Aaron Conole <[email-masked]>
Date: Wed, 28 Sep 2016 10:56:31 -0400

Eric Dumazet <[email-masked]> 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 <[email-masked]>
>> ---
>>  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.

> So that 100 different people in stable teams do not have to do the
> archeology themselves ...
>
> Thanks.

Thanks for the review, Eric.