On Mon, Nov 28, 2016 at 11:40:05AM +0100, Florian Westphal wrote:
> The caller assumes that < 0 means that skb was stolen (or free'd).
>
> All other return values continue skb processing.
>
> nf_hook_slow returns 3 different return value types:
>
> A) a (negative) errno value: the skb was dropped (NF_DROP, e.g.
> by iptables '-j DROP' rule).
>
> B) 0. The skb was stolen by the hook or queued to userspace.
>
> C) 1. all hooks returned NF_ACCEPT so the caller should invoke
> the okfn so packet processing can continue.
>
> nft ingress facility currently doesn't have the 'okfn' that
> the NF_HOOK() macros use; there is no nfqueue support either.
>
> So 1 means that nf_hook_ingress() caller should go on processing the skb.
>
> In order to allow use of NF_STOLEN from ingress we need to translate
> this to an errno number, else we'd crash because we continue with
> already-free'd (or about to be free-d) skb.
>
> Random dice roll has chosen EINPROGRESS. The errno value isn't checked,
> its just important that its less than 0.
Not really comments to block anything, so take them lightly.
Probably we can just set this to -1, I know this maps to some errno
value, but at least from code reading it will be make think that we
meant to return EINPROGRESS. If you agree, I can just mangle the
patch.
One more question below.
> Signed-off-by: Florian Westphal <fw@xxxxxxxxx>
> ---
> include/linux/netfilter_ingress.h | 7 ++++++-
> 1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/netfilter_ingress.h b/include/linux/netfilter_ingress.h
> index 2dc3b49b804a..d5027e470a24 100644
> --- a/include/linux/netfilter_ingress.h
> +++ b/include/linux/netfilter_ingress.h
> @@ -19,6 +19,7 @@ static inline int nf_hook_ingress(struct sk_buff *skb)
> {
> struct nf_hook_entry *e = rcu_dereference(skb->dev->nf_hooks_ingress);
> struct nf_hook_state state;
> + int ret;
>
> /* Must recheck the ingress hook head, in the event it became NULL
> * after the check in nf_hook_ingress_active evaluated to true.
> @@ -29,7 +30,11 @@ static inline int nf_hook_ingress(struct sk_buff *skb)
> nf_hook_state_init(&state, NF_NETDEV_INGRESS,
> NFPROTO_NETDEV, skb->dev, NULL, NULL,
> dev_net(skb->dev), NULL);
> - return nf_hook_slow(skb, &state, e);
> + ret = nf_hook_slow(skb, &state, e);
> + if (unlikely(ret == 0))
> + return -EINPROGRESS;
Do you prefer to keep this branch as unlikely? I understand most
people are not using fwd much so far, but we're targeting to enrich
ingress so I would expect users will be using this more and more.
Anyway, we can revisit this later on.
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