Re: [PATCH ipsec v2] xfrm: check MAC header is shown with both skb->mac_len and skb_mac_header_was_set()

[En-Wei WU]

> Seems like the __netif_receive_skb_core() and dev_gro_receive() are
> the places where it calls skb_reset_mac_len() with skb->mac_header =
> ~0U.
I believe it's the root cause.

My concern is that if we put something like:
+       if (!skb_mac_header_was_set(skb)) {
+               DEBUG_NET_WARN_ON_ONCE(1);
+               skb->mac_len = 0;
in skb_reset_mac_len(), it may degrade the RX path a bit.

Catching the bug in xfrm4_remove_tunnel_encap() and
xfrm6_remove_tunnel_encap() (the original patch) is nice because it
won't affect the systems which are not using the xfrm.

Kind Regards,
En-Wei.

On Mon, 14 Oct 2024 at 22:06, En-Wei WU <en-wei.wu@xxxxxxxxxxxxx> wrote:
>
> Hi, sorry for the late reply.
>
> I've tested this debug patch (with CONFIG_DEBUG_NET=y) on my machine,
> and the DEBUG_NET_WARN_ON_ONCE never got triggered.
>
> Thanks.
>
> On Wed, 2 Oct 2024 at 14:59, Eric Dumazet <edumazet@xxxxxxxxxx> wrote:
> >
> > On Wed, Oct 2, 2024 at 12:40 PM En-Wei WU <en-wei.wu@xxxxxxxxxxxxx> wrote:
> > >
> > > Hi,
> > >
> > > I would kindly ask if there is any progress :)
> >
> > Can you now try this debug patch (with CONFIG_DEBUG_NET=y ) :
> >
> > diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
> > index 39f1d16f362887821caa022464695c4045461493..e0e4154cbeb90474d92634d505869526c566f132
> > 100644
> > --- a/include/linux/skbuff.h
> > +++ b/include/linux/skbuff.h
> > @@ -2909,9 +2909,19 @@ static inline void
> > skb_reset_inner_headers(struct sk_buff *skb)
> >         skb->inner_transport_header = skb->transport_header;
> >  }
> >
> > +static inline int skb_mac_header_was_set(const struct sk_buff *skb)
> > +{
> > +       return skb->mac_header != (typeof(skb->mac_header))~0U;
> > +}
> > +
> >  static inline void skb_reset_mac_len(struct sk_buff *skb)
> >  {
> > -       skb->mac_len = skb->network_header - skb->mac_header;
> > +       if (!skb_mac_header_was_set(skb)) {
> > +               DEBUG_NET_WARN_ON_ONCE(1);
> > +               skb->mac_len = 0;
> > +       } else {
> > +               skb->mac_len = skb->network_header - skb->mac_header;
> > +       }
> >  }
> >
> >  static inline unsigned char *skb_inner_transport_header(const struct sk_buff
> > @@ -3014,11 +3024,6 @@ static inline void
> > skb_set_network_header(struct sk_buff *skb, const int offset)
> >         skb->network_header += offset;
> >  }
> >
> > -static inline int skb_mac_header_was_set(const struct sk_buff *skb)
> > -{
> > -       return skb->mac_header != (typeof(skb->mac_header))~0U;
> > -}
> > -
> >  static inline unsigned char *skb_mac_header(const struct sk_buff *skb)
> >  {
> >         DEBUG_NET_WARN_ON_ONCE(!skb_mac_header_was_set(skb));
> > @@ -3043,6 +3048,7 @@ static inline void skb_unset_mac_header(struct
> > sk_buff *skb)
> >
> >  static inline void skb_reset_mac_header(struct sk_buff *skb)
> >  {
> > +       DEBUG_NET_WARN_ON_ONCE(skb->data < skb->head);
> >         skb->mac_header = skb->data - skb->head;
> >  }
> >
> > @@ -3050,6 +3056,7 @@ static inline void skb_set_mac_header(struct
> > sk_buff *skb, const int offset)
> >  {
> >         skb_reset_mac_header(skb);
> >         skb->mac_header += offset;
> > +       DEBUG_NET_WARN_ON_ONCE(skb_mac_header(skb) < skb->head);
> >  }
> >
> >  static inline void skb_pop_mac_header(struct sk_buff *skb)