On Thu, 1 Aug 2019 17:44:06 -0700
Jakub Kicinski <jakub.kicin...@netronome.com> wrote:
> On Thu, 01 Aug 2019 20:00:31 +0200, Jesper Dangaard Brouer wrote:
> > When generic-XDP was moved to a later processing step by commit
> > 458bf2f224f0 ("net: core: support XDP generic on stacked devices.")
> > a regression was introduced when using bpf_xdp_adjust_head.
> >
> > The issue is that after this commit the skb->network_header is now
> > changed prior to calling generic XDP and not after. Thus, if the header
> > is changed by XDP (via bpf_xdp_adjust_head), then skb->network_header
> > also need to be updated again. Fix by calling skb_reset_network_header().
> >
> > Fixes: 458bf2f224f0 ("net: core: support XDP generic on stacked devices.")
> > Reported-by: Brandon Cazander <brandon.cazan...@multapplied.net>
> > Signed-off-by: Jesper Dangaard Brouer <bro...@redhat.com>
>
> Out of curiosity what was your conclusion regarding resetting the
> transport header as well?
Well, I don't know... I need some review, from e.g. Stephen that
changed this... I've added code snippets below signature to helper
reviewers (also helps understand below paragraph).
I think, we perhaps should call skb_reset_transport_header(), as we
change skb->data (via either __skb_pull() or __skb_push()), *BUT* I'm
not sure it is needed/required, as someone/something afterwards still
need to call skb_set_transport_header(), which also calls
skb_reset_transport_header() anyway.
I also want to ask reviewers, if we should move the call to
skb_reset_mac_len() (which Stephen added) in __netif_receive_skb_core()
into netif_receive_generic_xdp() (after the call to
skb_reset_network_header()), (it would be more natural to keep them
together)?
- -
Best regards,
Jesper Dangaard Brouer
MSc.CS, Principal Kernel Engineer at Red Hat
LinkedIn: http://www.linkedin.com/in/brouer
Code snippet
/* check if bpf_xdp_adjust_head was used */
off = xdp->data - orig_data;
if (off) {
if (off > 0)
__skb_pull(skb, off);
else if (off < 0)
__skb_push(skb, -off);
skb->mac_header += off;
skb_reset_network_header(skb);
}
static inline bool skb_transport_header_was_set(const struct sk_buff *skb)
{
return skb->transport_header != (typeof(skb->transport_header))~0U;
}
static inline unsigned char *skb_transport_header(const struct sk_buff *skb)
{
return skb->head + skb->transport_header;
}
static inline void skb_reset_transport_header(struct sk_buff *skb)
{
skb->transport_header = skb->data - skb->head;
}
static inline void skb_set_transport_header(struct sk_buff *skb,
const int offset)
{
skb_reset_transport_header(skb);
skb->transport_header += offset;
}
