Re: [PATCH] netfilter: cttimeout: remove VLA usage

[Joe Perches <joe@perches.com>]

On Tue, 2018-03-13 at 15:59 +0100, Pablo Neira Ayuso wrote:
> On Mon, Mar 12, 2018 at 04:58:38PM -0700, Joe Perches wrote:
> > On Mon, 2018-03-12 at 18:14 -0500, Gustavo A. R. Silva wrote:
> > > In preparation to enabling -Wvla, remove VLA and replace it
> > > with dynamic memory allocation.
> > > 
> > > From a security viewpoint, the use of Variable Length Arrays can be
> > > a vector for stack overflow attacks. Also, in general, as the code
> > > evolves it is easy to lose track of how big a VLA can get. Thus, we
> > > can end up having segfaults that are hard to debug.
> > > 
> > > Also, fixed as part of the directive to remove all VLAs from
> > 
> > []
> > > diff --git a/net/netfilter/nfnetlink_cttimeout.c b/net/netfilter/nfnetlink_cttimeout.c
> > 
> > []
> > > @@ -51,19 +51,27 @@ ctnl_timeout_parse_policy(void *timeouts,
> > >  			  const struct nf_conntrack_l4proto *l4proto,
> > >  			  struct net *net, const struct nlattr *attr)
> > >  {
> > > +	struct nlattr **tb;
> > >  	int ret = 0;
> > >  
> > > -	if (likely(l4proto->ctnl_timeout.nlattr_to_obj)) {
> > > -		struct nlattr *tb[l4proto->ctnl_timeout.nlattr_max+1];
> > > +	if (!l4proto->ctnl_timeout.nlattr_to_obj)
> > > +		return 0;
> > 
> > Why not
> > 	if unlikely(!...)
> 
> This is control plane code - not packet path - I think we should just
> let the compiler decide on this one, not really need to provide an
> explicit hint here.

I don't have an issue with that, but it should probably be
mentioned in the changelog as it's unrelated to VLA removal.