On Tue, 2013-03-19 at 17:25 +0800, Jason Wang wrote:
> I believe before doing header check for untrusted packets, the only
> thing we can trust is skb->len and that's we've used before
> 1def9238d4aa2. But after that, we're trying to use unchecked or
> meaningless value (e.g gso_segs were reset to zero in
> tun/macvtap/packet), and guest then can utilize this to result a very
> huge (-1U) pkt_len by filling evil value in the header. Can all kinds of
> packet scheduler survive this kinds of possible DOS?
I would use the flow dissector to fix the transport header from all
DODGY providers.
Daniel Borkmann is working on a patch serie adding nhoff into flow_keys,
and adding __skb_get_poff(const struct sk_buff *skb), for a BPF
extension we talked about in Copenhagen / Netfilter Workshop.
You could then set the transport header offset to the right value.
(and drop evil packets before they go further in the stack)
if (gso_packet(skb)) {
u32 poff = __skb_get_poff(skb);
if (!poff) {
drop_evil_packet(skb);
} else {
skb_set_transport_header(skb, poff);
...
}
}
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