netdev - Re: [RFC] netfilter: cttimeout: remove VLA in ctnl_timeout_parse

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Date:   Sun, 11 Mar 2018 17:45:46 -0500
From:   "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To:     Pablo Neira Ayuso <pablo@...filter.org>
Cc:     Jozsef Kadlecsik <kadlec@...ckhole.kfki.hu>,
        Florian Westphal <fw@...len.de>,
        "David S. Miller" <davem@...emloft.net>,
        netfilter-devel@...r.kernel.org, coreteam@...filter.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        "Gustavo A. R. Silva" <garsilva@...eddedor.com>
Subject: Re: [RFC] netfilter: cttimeout: remove VLA in
 ctnl_timeout_parse_policy



On 03/11/2018 05:21 PM, Pablo Neira Ayuso wrote:
> On Sun, Mar 11, 2018 at 05:12:09PM -0500, Gustavo A. R. Silva wrote:
>> Hi Pablo,
>>
>> On 03/11/2018 05:04 PM, Pablo Neira Ayuso wrote:
>>> On Tue, Mar 06, 2018 at 12:47:55PM -0600, Gustavo A. R. Silva wrote:
>>>> In preparation to enabling -Wvla, remove VLA and replace it
>>>> with dynamic memory allocation.
>>>
>>> Looks good but...
>>>
>>>> Signed-off-by: Gustavo A. R. Silva <gustavo@...eddedor.com>
>>>> ---
>>>>    net/netfilter/nfnetlink_cttimeout.c | 12 ++++++++++--
>>>>    1 file changed, 10 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/net/netfilter/nfnetlink_cttimeout.c b/net/netfilter/nfnetlink_cttimeout.c
>>>> index 95b0470..a2f7d92 100644
>>>> --- a/net/netfilter/nfnetlink_cttimeout.c
>>>> +++ b/net/netfilter/nfnetlink_cttimeout.c
>>>> @@ -52,18 +52,26 @@ ctnl_timeout_parse_policy(void *timeouts,
>>>>    			  struct net *net, const struct nlattr *attr)
>>>>    {
>>>>    	int ret = 0;
>>>> +	struct nlattr **tb = NULL;
>>>
>>> I think we don't need to initialize this, right?
>>>
>>
>> We actually do have to initialized it because in the unlikely case that the
>> code block inside the 'if' below is not executed, then we will end up
>> freeing an uninitialized pointer.
> 
> I see, you're right indeed.
> 
> We can probably simplify this code, but just doing:
> 
>          if (!l4proto->ctnl_timeout.nlattr_to_obj))
>                  return 0;
> 

I wonder if it is better to code this instead:

if (unlikely(!l4proto->ctnl_timeout.nlattr_to_obj)))
	return 0;


>          netlink attribute parsing here.
> 
> You could even remove the likely() thing, which doesn't make much
> sense for control plane code.
> 

Why is that?

> I understand this is a larger change, but I think this function will
> look better while we're removing VLA.
> 
> Would you mind having a look? I'd appreciate if so.
> 

I can do that. No problem.

Thanks
--
Gustavo