Re: [PATCH] netfilter: ipv4: Fix use-after-free in send_reset

[Pablo Neira Ayuso <pablo@netfilter.org>]

On Wed, Nov 01, 2017 at 01:36:36AM +0100, Pablo Neira Ayuso wrote:
> On Mon, Oct 23, 2017 at 11:46:03AM +0530, Tejaswi Tanikella wrote:
> > niph is not updated after pskb_expand_head changes the skb head.
> > It still points to the freed data, which is then used to update
> > tot_len and checksum. This could cause use-after-free poison crash.
> > 
> > Update niph, if ip_route_me_harder does not fail.
> > 
> > Signed-off-by: Tejaswi Tanikella <tejaswit@codeaurora.org>
> > ---
> >  net/ipv4/netfilter/nf_reject_ipv4.c | 2 ++
> >  1 file changed, 2 insertions(+)
> > 
> > diff --git a/net/ipv4/netfilter/nf_reject_ipv4.c b/net/ipv4/netfilter/nf_reject_ipv4.c
> > index eeacbda..b2e0f90 100644
> > --- a/net/ipv4/netfilter/nf_reject_ipv4.c
> > +++ b/net/ipv4/netfilter/nf_reject_ipv4.c
> > @@ -131,6 +131,8 @@ void nf_send_reset(struct net *net, struct sk_buff *oldskb, int hook)
> >  
> >  	if (ip_route_me_harder(net, nskb, RTN_UNSPEC))
> >  		goto free_nskb;
> > +	else
> > +		niph = ip_hdr(nskb);
> 
> No need for else here, right? So we can just turn this into a one
> liner to inconditionally reload this pointer.

I'm just going to remove the 'else' and push out this.