[RFC] netfilter: cttimeout: remove VLA in ctnl_timeout_parse_policy

Message ID 20180306184755.GA7628@embeddedgus
State RFC
Delegated to: Pablo Neira
Headers show
Series
  • [RFC] netfilter: cttimeout: remove VLA in ctnl_timeout_parse_policy
Related show

Commit Message

Gustavo A. R. Silva March 6, 2018, 6:47 p.m.
In preparation to enabling -Wvla, remove VLA and replace it
with dynamic memory allocation.

Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
---
 net/netfilter/nfnetlink_cttimeout.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

Comments

Pablo Neira Ayuso March 11, 2018, 10:04 p.m. | #1
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@embeddedor.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?

>  
>  	if (likely(l4proto->ctnl_timeout.nlattr_to_obj)) {
> -		struct nlattr *tb[l4proto->ctnl_timeout.nlattr_max+1];
> +		tb = kcalloc(l4proto->ctnl_timeout.nlattr_max + 1, sizeof(*tb),
> +			     GFP_KERNEL);
> +
> +		if (!tb)
> +			return -ENOMEM;
>  
>  		ret = nla_parse_nested(tb, l4proto->ctnl_timeout.nlattr_max,
>  				       attr, l4proto->ctnl_timeout.nla_policy,
>  				       NULL);
>  		if (ret < 0)
> -			return ret;
> +			goto err;
>  
>  		ret = l4proto->ctnl_timeout.nlattr_to_obj(tb, net, timeouts);
>  	}
> +
> +err:
> +	kfree(tb);
>  	return ret;
>  }
>  
> -- 
> 2.7.4
> 
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Gustavo A. R. Silva March 11, 2018, 10:12 p.m. | #2
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@embeddedor.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.

Thanks
--
Gustavo

>>   
>>   	if (likely(l4proto->ctnl_timeout.nlattr_to_obj)) {
>> -		struct nlattr *tb[l4proto->ctnl_timeout.nlattr_max+1];
>> +		tb = kcalloc(l4proto->ctnl_timeout.nlattr_max + 1, sizeof(*tb),
>> +			     GFP_KERNEL);
>> +
>> +		if (!tb)
>> +			return -ENOMEM;
>>   
>>   		ret = nla_parse_nested(tb, l4proto->ctnl_timeout.nlattr_max,
>>   				       attr, l4proto->ctnl_timeout.nla_policy,
>>   				       NULL);
>>   		if (ret < 0)
>> -			return ret;
>> +			goto err;
>>   
>>   		ret = l4proto->ctnl_timeout.nlattr_to_obj(tb, net, timeouts);
>>   	}
>> +
>> +err:
>> +	kfree(tb);
>>   	return ret;
>>   }
>>   
>> -- 
>> 2.7.4
>>


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Pablo Neira Ayuso March 11, 2018, 10:21 p.m. | #3
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@embeddedor.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;

        netlink attribute parsing here.

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

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.

Thanks.
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Gustavo A. R. Silva March 11, 2018, 10:45 p.m. | #4
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@embeddedor.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
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Patch

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;
 
 	if (likely(l4proto->ctnl_timeout.nlattr_to_obj)) {
-		struct nlattr *tb[l4proto->ctnl_timeout.nlattr_max+1];
+		tb = kcalloc(l4proto->ctnl_timeout.nlattr_max + 1, sizeof(*tb),
+			     GFP_KERNEL);
+
+		if (!tb)
+			return -ENOMEM;
 
 		ret = nla_parse_nested(tb, l4proto->ctnl_timeout.nlattr_max,
 				       attr, l4proto->ctnl_timeout.nla_policy,
 				       NULL);
 		if (ret < 0)
-			return ret;
+			goto err;
 
 		ret = l4proto->ctnl_timeout.nlattr_to_obj(tb, net, timeouts);
 	}
+
+err:
+	kfree(tb);
 	return ret;
 }