netfilter: revert introduction of egress hook

This reverts the following commits:

  8537f78647c0 ("netfilter: Introduce egress hook")
  5418d3881e1f ("netfilter: Generalize ingress hook")
  b030f194aed2 ("netfilter: Rename ingress hook include file")

>From the discussion in [0], the author's main motivation to add a hook
in fast path is for an out of tree kernel module, which is a red flag
to begin with. Other mentioned potential use cases like NAT{64,46}
is on future extensions w/o concrete code in the tree yet. Revert as
suggested [1] given the weak justification to add more hooks to critical
fast-path.

  [0] https://lore.kernel.org/netdev/cover.1583927267.git.lukas@wunner.de/
  [1] https://lore.kernel.org/netdev/20200318.011152.72770718915606186.davem@davemloft.net/

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Cc: David Miller <davem@davemloft.net>
Cc: Pablo Neira Ayuso <pablo@netfilter.org>
Cc: Alexei Starovoitov <ast@kernel.org>
Nacked-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 58 insertions, 0 deletions

diff --git a/include/linux/netfilter_ingress.h b/include/linux/netfilter_ingress.h
new file mode 100644
index 000000000000..a13774be2eb5
--- /dev/null
+++ b/include/linux/netfilter_ingress.h
@@ -0,0 +1,58 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _NETFILTER_INGRESS_H_
+#define _NETFILTER_INGRESS_H_
+
+#include <linux/netfilter.h>
+#include <linux/netdevice.h>
+
+#ifdef CONFIG_NETFILTER_INGRESS
+static inline bool nf_hook_ingress_active(const struct sk_buff *skb)
+{
+#ifdef CONFIG_JUMP_LABEL
+	if (!static_key_false(&nf_hooks_needed[NFPROTO_NETDEV][NF_NETDEV_INGRESS]))
+		return false;
+#endif
+	return rcu_access_pointer(skb->dev->nf_hooks_ingress);
+}
+
+/* caller must hold rcu_read_lock */
+static inline int nf_hook_ingress(struct sk_buff *skb)
+{
+	struct nf_hook_entries *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.
+	 */
+	if (unlikely(!e))
+		return 0;
+
+	nf_hook_state_init(&state, NF_NETDEV_INGRESS,
+			   NFPROTO_NETDEV, skb->dev, NULL, NULL,
+			   dev_net(skb->dev), NULL);
+	ret = nf_hook_slow(skb, &state, e, 0);
+	if (ret == 0)
+		return -1;
+
+	return ret;
+}
+
+static inline void nf_hook_ingress_init(struct net_device *dev)
+{
+	RCU_INIT_POINTER(dev->nf_hooks_ingress, NULL);
+}
+#else /* CONFIG_NETFILTER_INGRESS */
+static inline int nf_hook_ingress_active(struct sk_buff *skb)
+{
+	return 0;
+}
+
+static inline int nf_hook_ingress(struct sk_buff *skb)
+{
+	return 0;
+}
+
+static inline void nf_hook_ingress_init(struct net_device *dev) {}
+#endif /* CONFIG_NETFILTER_INGRESS */
+#endif /* _NETFILTER_INGRESS_H_ */