Pablo Neira Ayuso <pablo@xxxxxxxxxxxxx> wrote: [ CC Willem ] > On Wed, Jun 05, 2024 at 08:14:50PM +0200, Florian Westphal wrote: > > Christoph Paasch <cpaasch@xxxxxxxxx> wrote: > > > > Reported-by: Christoph Paasch <cpaasch@xxxxxxxxx> > > > > Suggested-by: Paolo Abeni <pabeni@xxxxxxxxxx> > > > > Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/494 > > > > Signed-off-by: Florian Westphal <fw@xxxxxxxxx> > > > > > > I just gave this one a shot in my syzkaller instances and am still hitting the issue. > > > > No, different bug, this patch is correct. > > > > I refuse to touch the flow dissector. > > I see callers of ip_local_out() in the tree which do not set skb->dev. > > I don't understand this: > > bool __skb_flow_dissect(const struct net *net, > const struct sk_buff *skb, > struct flow_dissector *flow_dissector, > void *target_container, const void *data, > __be16 proto, int nhoff, int hlen, unsigned int flags) > { > [...] > WARN_ON_ONCE(!net); > if (net) { > > it was added by 9b52e3f267a6 ("flow_dissector: handle no-skb use case") > > Is this WARN_ON_ONCE() bogus? When this was added (handle dissection from bpf prog, per netns), the correct solution would have been to pass 'struct net' explicitly via skb_get_hash() and all variants. As that was likely deemed to be too much code churn it tries to infer struct net via skb->{dev,sk}. So there are several options here: 1. remove the WARN_ON_ONCE and be done with it 2. remove the WARN_ON_ONCE and pretend net was init_net 3. also look at skb_dst(skb)->dev if skb->dev is unset, then back to 1) or 2) 4. stop using skb_get_hash() from netfilter (but there are likely other callers that might hit this). 5. fix up callers, one by one 6. assign skb->dev inside netfilter if its unset 3 and 2 combined are probably going to be the least invasive. 5 might take some time, we now know two, namely tcp resets generated from netfilter and igmp_send_report(). No idea if there are more. I dislike 3) mainly because of the 'guess the netns' design, not because it adds more code to a way too large function however, so maybe its acceptable?
