Messages in this thread | | | Subject | Re: [PATCH net-next 1/2] net_sched: don't do precise pkt_len computation for untrusted packets | From | Eric Dumazet <> | Date | Tue, 19 Mar 2013 05:10:40 -0700 |
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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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