netdev - Re: [PATCH net] ip6_tunnel: be careful when accessing the inner header

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Date:   Mon, 24 Sep 2018 13:03:17 +0200
From:   Paolo Abeni <pabeni@...hat.com>
To:     Cong Wang <xiyou.wangcong@...il.com>
Cc:     Linux Kernel Network Developers <netdev@...r.kernel.org>,
        David Miller <davem@...emloft.net>,
        Alexander Potapenko <glider@...gle.com>
Subject: Re: [PATCH net] ip6_tunnel: be careful when accessing the inner
 header

On Fri, 2018-09-21 at 11:51 -0700, Cong Wang wrote:
> On Wed, Sep 19, 2018 at 6:04 AM Paolo Abeni <pabeni@...hat.com> wrote:
> > diff --git a/net/ipv6/ip6_tunnel.c b/net/ipv6/ip6_tunnel.c
> > index 419960b0ba16..a0b6932c3afd 100644
> > --- a/net/ipv6/ip6_tunnel.c
> > +++ b/net/ipv6/ip6_tunnel.c
> > @@ -1234,7 +1234,7 @@ static inline int
> >  ip4ip6_tnl_xmit(struct sk_buff *skb, struct net_device *dev)
> >  {
> >         struct ip6_tnl *t = netdev_priv(dev);
> > -       const struct iphdr  *iph = ip_hdr(skb);
> > +       const struct iphdr  *iph;
> >         int encap_limit = -1;
> >         struct flowi6 fl6;
> >         __u8 dsfield;
> > @@ -1242,6 +1242,11 @@ ip4ip6_tnl_xmit(struct sk_buff *skb, struct net_device *dev)
> >         u8 tproto;
> >         int err;
> > 
> > +       /* ensure we can access the full inner ip header */
> > +       if (!pskb_may_pull(skb, sizeof(struct iphdr)))
> > +               return -1;
> > +
> > +       iph = ip_hdr(skb);
> 
> Hmm...
> 
> How do IPv4 tunnels ensure they have the right inner header to access?
> ip_tunnel_xmit() uses skb_inner_network_header() to access inner header
> which doesn't have any check either AFAIK.

You are right, I think we need similar checks for ip_tunnel_xmit(),
too.

I'll try to cook a patch.

Cheers,

Paolo