[PATCH nf-next,RFC 0/5] Netfilter egress hook

[PATCH nf-next,RFC 0/5] Netfilter egress hook

[Lukas Wunner]

Introduce a netfilter egress hook to complement the existing ingress hook.

User space support for nft is submitted in a separate patch.

The need for this arose because I had to filter egress packets which do
not match a specific ethertype.  The most common solution appears to be
to enslave the interface to a bridge and use ebtables, but that's
cumbersome to configure and comes with a (small) performance penalty.
An alternative approach is tc, but that doesn't afford equivalent
matching options as netfilter.  A bit of googling reveals that more
people have expressed a desire for egress filtering in the past:

https://www.spinics.net/lists/netfilter/msg50038.html
https://unix.stackexchange.com/questions/512371

I am first performing traffic control with sch_handle_egress() before
performing filtering with nf_egress().  That order is identical to
ingress processing.  I'm wondering whether an inverse order would be
more logical or more beneficial.  Among other things it would allow
marking packets with netfilter on egress before performing traffic
control based on that mark.  Thoughts?

Lukas Wunner (5):
  netfilter: Clean up unnecessary #ifdef
  netfilter: Document ingress hook
  netfilter: Rename ingress hook include file
  netfilter: Generalize ingress hook
  netfilter: Introduce egress hook

 include/linux/netdevice.h         |   5 ++
 include/linux/netfilter_ingress.h |  58 -----------------
 include/linux/netfilter_netdev.h  | 102 ++++++++++++++++++++++++++++++
 include/uapi/linux/netfilter.h    |   1 +
 net/core/dev.c                    |  31 ++++++---
 net/netfilter/Kconfig             |   8 +++
 net/netfilter/core.c              |  24 +++++--
 net/netfilter/nft_chain_filter.c  |   4 +-
 8 files changed, 161 insertions(+), 72 deletions(-)
 delete mode 100644 include/linux/netfilter_ingress.h
 create mode 100644 include/linux/netfilter_netdev.h

-- 
2.23.0

[PATCH nf-next,RFC 1/5] netfilter: Clean up unnecessary #ifdef

[Lukas Wunner]

If CONFIG_NETFILTER_INGRESS is not enabled, nf_ingress() becomes a no-op
because it solely contains an if-clause calling nf_hook_ingress_active(),
for which an empty inline stub exists in <linux/netfilter_ingress.h>.

All the symbols used in the if-clause's body are still available even if
CONFIG_NETFILTER_INGRESS is not enabled.

The additional "#ifdef CONFIG_NETFILTER_INGRESS" in nf_ingress() is thus
unnecessary, so drop it.

Signed-off-by: Lukas Wunner <lukas@wunner.de>
Cc: Daniel Borkmann <daniel@iogearbox.net>
---
 net/core/dev.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/net/core/dev.c b/net/core/dev.c
index 74f593986524..e555a8656c47 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -5013,7 +5013,6 @@ static bool skb_pfmemalloc_protocol(struct sk_buff *skb)
 static inline int nf_ingress(struct sk_buff *skb, struct packet_type **pt_prev,
 			     int *ret, struct net_device *orig_dev)
 {
-#ifdef CONFIG_NETFILTER_INGRESS
 	if (nf_hook_ingress_active(skb)) {
 		int ingress_retval;
 
@@ -5027,7 +5026,6 @@ static inline int nf_ingress(struct sk_buff *skb, struct packet_type **pt_prev,
 		rcu_read_unlock();
 		return ingress_retval;
 	}
-#endif /* CONFIG_NETFILTER_INGRESS */
 	return 0;
 }
 
-- 
2.23.0

[PATCH nf-next,RFC 2/5] netfilter: Document ingress hook

[Lukas Wunner]

Amend kerneldoc of struct net_device to fix a "make htmldocs" warning:

include/linux/netdevice.h:2045: warning: Function parameter or member 'nf_hooks_ingress' not described in 'net_device'

Reported-by: kbuild test robot <lkp@intel.com>
Signed-off-by: Lukas Wunner <lukas@wunner.de>
Cc: Daniel Borkmann <daniel@iogearbox.net>
---
 include/linux/netdevice.h | 1 +
 1 file changed, 1 insertion(+)

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 3207e0b9ec4e..bc6914ea3faf 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -1701,6 +1701,7 @@ enum netdev_priv_flags {
  *	@miniq_ingress:		ingress/clsact qdisc specific data for
  *				ingress processing
  *	@ingress_queue:		XXX: need comments on this one
+ *	@nf_hooks_ingress:	netfilter hooks executed for ingress packets
  *	@broadcast:		hw bcast address
  *
  *	@rx_cpu_rmap:	CPU reverse-mapping for RX completion interrupts,
-- 
2.23.0

[PATCH nf-next,RFC 3/5] netfilter: Rename ingress hook include file

[Lukas Wunner]

Prepare for addition of a netfilter egress hook by renaming
<linux/netfilter_ingress.h> to <linux/netfilter_netdev.h>.

The egress hook also necessitates a refactoring of the include file,
but that is done in a separate commit to ease reviewing.

No functional change intended.

Signed-off-by: Lukas Wunner <lukas@wunner.de>
Cc: Daniel Borkmann <daniel@iogearbox.net>
---
 include/linux/{netfilter_ingress.h => netfilter_netdev.h} | 0
 net/core/dev.c                                            | 2 +-
 2 files changed, 1 insertion(+), 1 deletion(-)
 rename include/linux/{netfilter_ingress.h => netfilter_netdev.h} (100%)

diff --git a/include/linux/netfilter_ingress.h b/include/linux/netfilter_netdev.h
similarity index 100%
rename from include/linux/netfilter_ingress.h
rename to include/linux/netfilter_netdev.h
diff --git a/net/core/dev.c b/net/core/dev.c
index e555a8656c47..c698a0fcfa02 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -135,7 +135,7 @@
 #include <linux/if_macvlan.h>
 #include <linux/errqueue.h>
 #include <linux/hrtimer.h>
-#include <linux/netfilter_ingress.h>
+#include <linux/netfilter_netdev.h>
 #include <linux/crash_dump.h>
 #include <linux/sctp.h>
 #include <net/udp_tunnel.h>
-- 
2.23.0

[PATCH nf-next,RFC 4/5] netfilter: Generalize ingress hook

[Lukas Wunner]

Prepare for addition of a netfilter egress hook by generalizing the
ingress hook introduced by commit e687ad60af09 ("netfilter: add
netfilter ingress hook after handle_ing() under unique static key").

In particular, rename and refactor the ingress hook's static inlines
such that they can be reused for an egress hook.

No functional change intended.

Signed-off-by: Lukas Wunner <lukas@wunner.de>
Cc: Daniel Borkmann <daniel@iogearbox.net>
---
 include/linux/netfilter_netdev.h | 45 ++++++++++++++++++++++----------
 net/core/dev.c                   |  2 +-
 2 files changed, 32 insertions(+), 15 deletions(-)

diff --git a/include/linux/netfilter_netdev.h b/include/linux/netfilter_netdev.h
index a13774be2eb5..49e26479642e 100644
--- a/include/linux/netfilter_netdev.h
+++ b/include/linux/netfilter_netdev.h
@@ -1,34 +1,37 @@
 /* SPDX-License-Identifier: GPL-2.0 */
-#ifndef _NETFILTER_INGRESS_H_
-#define _NETFILTER_INGRESS_H_
+#ifndef _NETFILTER_NETDEV_H_
+#define _NETFILTER_NETDEV_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_NETFILTER
+static __always_inline bool nf_hook_netdev_active(enum nf_dev_hooks hooknum,
+					  struct nf_hook_entries __rcu *hooks)
 {
 #ifdef CONFIG_JUMP_LABEL
-	if (!static_key_false(&nf_hooks_needed[NFPROTO_NETDEV][NF_NETDEV_INGRESS]))
+	if (!static_key_false(&nf_hooks_needed[NFPROTO_NETDEV][hooknum]))
 		return false;
 #endif
-	return rcu_access_pointer(skb->dev->nf_hooks_ingress);
+	return rcu_access_pointer(hooks);
 }
 
 /* caller must hold rcu_read_lock */
-static inline int nf_hook_ingress(struct sk_buff *skb)
+static __always_inline int nf_hook_netdev(struct sk_buff *skb,
+					  enum nf_dev_hooks hooknum,
+					  struct nf_hook_entries __rcu *hooks)
 {
-	struct nf_hook_entries *e = rcu_dereference(skb->dev->nf_hooks_ingress);
+	struct nf_hook_entries *e = rcu_dereference(hooks);
 	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.
+	/* Must recheck the hook head, in the event it became NULL
+	 * after the check in nf_hook_netdev_active evaluated to true.
 	 */
 	if (unlikely(!e))
 		return 0;
 
-	nf_hook_state_init(&state, NF_NETDEV_INGRESS,
+	nf_hook_state_init(&state, hooknum,
 			   NFPROTO_NETDEV, skb->dev, NULL, NULL,
 			   dev_net(skb->dev), NULL);
 	ret = nf_hook_slow(skb, &state, e, 0);
@@ -37,10 +40,26 @@ static inline int nf_hook_ingress(struct sk_buff *skb)
 
 	return ret;
 }
+#endif /* CONFIG_NETFILTER */
 
-static inline void nf_hook_ingress_init(struct net_device *dev)
+static inline void nf_hook_netdev_init(struct net_device *dev)
 {
+#ifdef CONFIG_NETFILTER_INGRESS
 	RCU_INIT_POINTER(dev->nf_hooks_ingress, NULL);
+#endif
+}
+
+#ifdef CONFIG_NETFILTER_INGRESS
+static inline bool nf_hook_ingress_active(const struct sk_buff *skb)
+{
+	return nf_hook_netdev_active(NF_NETDEV_INGRESS,
+				     skb->dev->nf_hooks_ingress);
+}
+
+static inline int nf_hook_ingress(struct sk_buff *skb)
+{
+	return nf_hook_netdev(skb, NF_NETDEV_INGRESS,
+			      skb->dev->nf_hooks_ingress);
 }
 #else /* CONFIG_NETFILTER_INGRESS */
 static inline int nf_hook_ingress_active(struct sk_buff *skb)
@@ -52,7 +71,5 @@ 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_ */
diff --git a/net/core/dev.c b/net/core/dev.c
index c698a0fcfa02..e4976f68f2dd 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -9478,7 +9478,7 @@ struct net_device *alloc_netdev_mqs(int sizeof_priv, const char *name,
 	if (!dev->ethtool_ops)
 		dev->ethtool_ops = &default_ethtool_ops;
 
-	nf_hook_ingress_init(dev);
+	nf_hook_netdev_init(dev);
 
 	return dev;
 
-- 
2.23.0

[PATCH nf-next,RFC 5/5] netfilter: Introduce egress hook

[Lukas Wunner]

Commit e687ad60af09 ("netfilter: add netfilter ingress hook after
handle_ing() under unique static key") introduced the ability to
classify packets on ingress.

Allow the same on egress.

The need for this arose because I had to filter egress packets which do
not match a specific ethertype.  The most common solution appears to be
to enslave the interface to a bridge and use ebtables, but that's
cumbersome to configure and comes with a (small) performance penalty.
An alternative approach is tc, but that doesn't afford equivalent
matching options as netfilter.  A bit of googling reveals that more
people have expressed a desire for egress filtering in the past:

https://www.spinics.net/lists/netfilter/msg50038.html
https://unix.stackexchange.com/questions/512371

An egress hook therefore seems like an obvious addition.

Signed-off-by: Lukas Wunner <lukas@wunner.de>
Cc: Daniel Borkmann <daniel@iogearbox.net>
---
 include/linux/netdevice.h        |  4 ++++
 include/linux/netfilter_netdev.h | 27 +++++++++++++++++++++++++++
 include/uapi/linux/netfilter.h   |  1 +
 net/core/dev.c                   | 25 ++++++++++++++++++++-----
 net/netfilter/Kconfig            |  8 ++++++++
 net/netfilter/core.c             | 24 ++++++++++++++++++++----
 net/netfilter/nft_chain_filter.c |  4 +++-
 7 files changed, 83 insertions(+), 10 deletions(-)

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index bc6914ea3faf..111107aed50b 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -1720,6 +1720,7 @@ enum netdev_priv_flags {
  *	@xps_maps:	XXX: need comments on this one
  *	@miniq_egress:		clsact qdisc specific data for
  *				egress processing
+ *	@nf_hooks_egress:	netfilter hooks executed for egress packets
  *	@watchdog_timeo:	Represents the timeout that is used by
  *				the watchdog (see dev_watchdog())
  *	@watchdog_timer:	List of timers
@@ -1981,6 +1982,9 @@ struct net_device {
 #ifdef CONFIG_NET_CLS_ACT
 	struct mini_Qdisc __rcu	*miniq_egress;
 #endif
+#ifdef CONFIG_NETFILTER_EGRESS
+	struct nf_hook_entries __rcu *nf_hooks_egress;
+#endif
 
 	/* These may be needed for future network-power-down code. */
 	struct timer_list	watchdog_timer;
diff --git a/include/linux/netfilter_netdev.h b/include/linux/netfilter_netdev.h
index 49e26479642e..92d3611a782e 100644
--- a/include/linux/netfilter_netdev.h
+++ b/include/linux/netfilter_netdev.h
@@ -47,6 +47,9 @@ static inline void nf_hook_netdev_init(struct net_device *dev)
 #ifdef CONFIG_NETFILTER_INGRESS
 	RCU_INIT_POINTER(dev->nf_hooks_ingress, NULL);
 #endif
+#ifdef CONFIG_NETFILTER_EGRESS
+	RCU_INIT_POINTER(dev->nf_hooks_egress, NULL);
+#endif
 }
 
 #ifdef CONFIG_NETFILTER_INGRESS
@@ -72,4 +75,28 @@ static inline int nf_hook_ingress(struct sk_buff *skb)
 	return 0;
 }
 #endif /* CONFIG_NETFILTER_INGRESS */
+
+#ifdef CONFIG_NETFILTER_EGRESS
+static inline bool nf_hook_egress_active(const struct sk_buff *skb)
+{
+	return nf_hook_netdev_active(NF_NETDEV_EGRESS,
+				     skb->dev->nf_hooks_egress);
+}
+
+static inline int nf_hook_egress(struct sk_buff *skb)
+{
+	return nf_hook_netdev(skb, NF_NETDEV_EGRESS,
+			      skb->dev->nf_hooks_egress);
+}
+#else /* CONFIG_NETFILTER_EGRESS */
+static inline int nf_hook_egress_active(struct sk_buff *skb)
+{
+	return 0;
+}
+
+static inline int nf_hook_egress(struct sk_buff *skb)
+{
+	return 0;
+}
+#endif /* CONFIG_NETFILTER_EGRESS */
 #endif /* _NETFILTER_INGRESS_H_ */
diff --git a/include/uapi/linux/netfilter.h b/include/uapi/linux/netfilter.h
index ca9e63d6e0e4..d1616574c54f 100644
--- a/include/uapi/linux/netfilter.h
+++ b/include/uapi/linux/netfilter.h
@@ -50,6 +50,7 @@ enum nf_inet_hooks {
 
 enum nf_dev_hooks {
 	NF_NETDEV_INGRESS,
+	NF_NETDEV_EGRESS,
 	NF_NETDEV_NUMHOOKS
 };
 
diff --git a/net/core/dev.c b/net/core/dev.c
index e4976f68f2dd..d1e48fc4ae5c 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -3811,10 +3811,10 @@ int dev_loopback_xmit(struct net *net, struct sock *sk, struct sk_buff *skb)
 }
 EXPORT_SYMBOL(dev_loopback_xmit);
 
-#ifdef CONFIG_NET_EGRESS
 static struct sk_buff *
 sch_handle_egress(struct sk_buff *skb, int *ret, struct net_device *dev)
 {
+#ifdef CONFIG_NET_CLS_ACT
 	struct mini_Qdisc *miniq = rcu_dereference_bh(dev->miniq_egress);
 	struct tcf_result cl_res;
 
@@ -3848,10 +3848,22 @@ sch_handle_egress(struct sk_buff *skb, int *ret, struct net_device *dev)
 	default:
 		break;
 	}
-
+#endif /* CONFIG_NET_CLS_ACT */
 	return skb;
 }
-#endif /* CONFIG_NET_EGRESS */
+
+static int nf_egress(struct sk_buff *skb)
+{
+	if (nf_hook_egress_active(skb)) {
+		int ret;
+
+		rcu_read_lock();
+		ret = nf_hook_egress(skb);
+		rcu_read_unlock();
+		return ret;
+	}
+	return 0;
+}
 
 #ifdef CONFIG_XPS
 static int __get_xps_queue_idx(struct net_device *dev, struct sk_buff *skb,
@@ -4039,13 +4051,16 @@ static int __dev_queue_xmit(struct sk_buff *skb, struct net_device *sb_dev)
 	qdisc_pkt_len_init(skb);
 #ifdef CONFIG_NET_CLS_ACT
 	skb->tc_at_ingress = 0;
-# ifdef CONFIG_NET_EGRESS
+#endif
+#ifdef CONFIG_NET_EGRESS
 	if (static_branch_unlikely(&egress_needed_key)) {
 		skb = sch_handle_egress(skb, &rc, dev);
 		if (!skb)
 			goto out;
+
+		if (nf_egress(skb) < 0)
+			goto out;
 	}
-# endif
 #endif
 	/* If device/qdisc don't need skb->dst, release it right now while
 	 * its hot in this cpu cache.
diff --git a/net/netfilter/Kconfig b/net/netfilter/Kconfig
index 91efae88e8c2..a6ae141ec77e 100644
--- a/net/netfilter/Kconfig
+++ b/net/netfilter/Kconfig
@@ -10,6 +10,14 @@ config NETFILTER_INGRESS
 	  This allows you to classify packets from ingress using the Netfilter
 	  infrastructure.
 
+config NETFILTER_EGRESS
+	bool "Netfilter egress support"
+	default y
+	select NET_EGRESS
+	help
+	  This allows you to classify packets before transmission using the
+	  Netfilter infrastructure.
+
 config NETFILTER_NETLINK
 	tristate
 
diff --git a/net/netfilter/core.c b/net/netfilter/core.c
index 78f046ec506f..85e9c959aba7 100644
--- a/net/netfilter/core.c
+++ b/net/netfilter/core.c
@@ -306,6 +306,12 @@ nf_hook_entry_head(struct net *net, int pf, unsigned int hooknum,
 		if (dev && dev_net(dev) == net)
 			return &dev->nf_hooks_ingress;
 	}
+#endif
+#ifdef CONFIG_NETFILTER_EGRESS
+	if (hooknum == NF_NETDEV_EGRESS) {
+		if (dev && dev_net(dev) == net)
+			return &dev->nf_hooks_egress;
+	}
 #endif
 	WARN_ON_ONCE(1);
 	return NULL;
@@ -318,11 +324,13 @@ static int __nf_register_net_hook(struct net *net, int pf,
 	struct nf_hook_entries __rcu **pp;
 
 	if (pf == NFPROTO_NETDEV) {
-#ifndef CONFIG_NETFILTER_INGRESS
-		if (reg->hooknum == NF_NETDEV_INGRESS)
+		if ((!IS_ENABLED(CONFIG_NETFILTER_INGRESS) &&
+		     reg->hooknum == NF_NETDEV_INGRESS) ||
+		    (!IS_ENABLED(CONFIG_NETFILTER_EGRESS) &&
+		     reg->hooknum == NF_NETDEV_EGRESS))
 			return -EOPNOTSUPP;
-#endif
-		if (reg->hooknum != NF_NETDEV_INGRESS ||
+		if ((reg->hooknum != NF_NETDEV_INGRESS &&
+		     reg->hooknum != NF_NETDEV_EGRESS) ||
 		    !reg->dev || dev_net(reg->dev) != net)
 			return -EINVAL;
 	}
@@ -348,6 +356,10 @@ static int __nf_register_net_hook(struct net *net, int pf,
 	if (pf == NFPROTO_NETDEV && reg->hooknum == NF_NETDEV_INGRESS)
 		net_inc_ingress_queue();
 #endif
+#ifdef CONFIG_NETFILTER_EGRESS
+	if (pf == NFPROTO_NETDEV && reg->hooknum == NF_NETDEV_EGRESS)
+		net_inc_egress_queue();
+#endif
 #ifdef CONFIG_JUMP_LABEL
 	static_key_slow_inc(&nf_hooks_needed[pf][reg->hooknum]);
 #endif
@@ -406,6 +418,10 @@ static void __nf_unregister_net_hook(struct net *net, int pf,
 		if (pf == NFPROTO_NETDEV && reg->hooknum == NF_NETDEV_INGRESS)
 			net_dec_ingress_queue();
 #endif
+#ifdef CONFIG_NETFILTER_EGRESS
+		if (pf == NFPROTO_NETDEV && reg->hooknum == NF_NETDEV_EGRESS)
+			net_dec_egress_queue();
+#endif
 #ifdef CONFIG_JUMP_LABEL
 		static_key_slow_dec(&nf_hooks_needed[pf][reg->hooknum]);
 #endif
diff --git a/net/netfilter/nft_chain_filter.c b/net/netfilter/nft_chain_filter.c
index c78d01bc02e9..67ce6dbb5496 100644
--- a/net/netfilter/nft_chain_filter.c
+++ b/net/netfilter/nft_chain_filter.c
@@ -277,9 +277,11 @@ static const struct nft_chain_type nft_chain_filter_netdev = {
 	.name		= "filter",
 	.type		= NFT_CHAIN_T_DEFAULT,
 	.family		= NFPROTO_NETDEV,
-	.hook_mask	= (1 << NF_NETDEV_INGRESS),
+	.hook_mask	= (1 << NF_NETDEV_INGRESS) |
+			  (1 << NF_NETDEV_EGRESS),
 	.hooks		= {
 		[NF_NETDEV_INGRESS]	= nft_do_chain_netdev,
+		[NF_NETDEV_EGRESS]	= nft_do_chain_netdev,
 	},
 };
 
-- 
2.23.0

Re: [PATCH nf-next,RFC 5/5] netfilter: Introduce egress hook

[Daniel Borkmann]

On 10/31/19 2:41 PM, Lukas Wunner wrote:
> Commit e687ad60af09 ("netfilter: add netfilter ingress hook after
> handle_ing() under unique static key") introduced the ability to
> classify packets on ingress.
> 
> Allow the same on egress.
> 
> The need for this arose because I had to filter egress packets which do
> not match a specific ethertype.  The most common solution appears to be

This seems like a /very/ weak justification for something that sits in
critical fastpath. NAK.

> to enslave the interface to a bridge and use ebtables, but that's
> cumbersome to configure and comes with a (small) performance penalty.
> An alternative approach is tc, but that doesn't afford equivalent
> matching options as netfilter.
Hmm, have you tried tc BPF on the egress hook (via sch_cls_act -> cls_bpf)?

> people have expressed a desire for egress filtering in the past:
> 
> https://www.spinics.net/lists/netfilter/msg50038.html

Adding another hook to catch misconfigurations of NAT in postrouting ...?

> https://unix.stackexchange.com/questions/512371

This talks about filtering / limiting ARP packets which can be done today
easily with existing means, including writing ARP responders sitting on tc
ingress/egress hook.

> An egress hook therefore seems like an obvious addition.
> 
> Signed-off-by: Lukas Wunner <lukas@wunner.de>
> Cc: Daniel Borkmann <daniel@iogearbox.net>

Re: [PATCH nf-next,RFC 5/5] netfilter: Introduce egress hook

[Lukas Wunner]

On Thu, Oct 31, 2019 at 11:39:58PM +0100, Daniel Borkmann wrote:
> On 10/31/19 2:41 PM, Lukas Wunner wrote:
> > Commit e687ad60af09 ("netfilter: add netfilter ingress hook after
> > handle_ing() under unique static key") introduced the ability to
> > classify packets on ingress.
> > 
> > Allow the same on egress.
> > 
> > The need for this arose because I had to filter egress packets which do
> > not match a specific ethertype.  The most common solution appears to be
> > to enslave the interface to a bridge and use ebtables, but that's
> > cumbersome to configure and comes with a (small) performance penalty.
> > An alternative approach is tc, but that doesn't afford equivalent
> > matching options as netfilter.
> 
> Hmm, have you tried tc BPF on the egress hook (via sch_cls_act -> cls_bpf)?

There's another reason I chose netfilter over tc:  I need to activate the
filter from a kernel module, hence need an in-kernel (rather than user space)
API.

netfilter provides that via nf_register_net_hook(), I couldn't find
anything similar for tc.  And an egress netfilter hook seemed like
an obvious missing feature given the presence of an ingress hook.

The module I need this for is out-of-tree:
https://github.com/RevolutionPi/piControl/commit/da199ccd2099

In my experience the argument that a feature is needed for an out-of-tree
module holds zero value upstream.  If there's no in-tree user, the feature
isn't merged, I've seen this more than enough.  Which is why I didn't mention
it in the first place.

For our use case I wouldn't even need the nft user space support which I
posted separately, I just implemented it for completeness and to increase
acceptability of the present series.

Thanks,

Lukas

Re: [PATCH nf-next,RFC 0/5] Netfilter egress hook

[Pablo Neira Ayuso]

Hi,

On Thu, Oct 31, 2019 at 02:41:00PM +0100, Lukas Wunner wrote:
> Introduce a netfilter egress hook to complement the existing ingress hook.
> 
> User space support for nft is submitted in a separate patch.
> 
> The need for this arose because I had to filter egress packets which do
> not match a specific ethertype.  The most common solution appears to be
> to enslave the interface to a bridge and use ebtables, but that's
> cumbersome to configure and comes with a (small) performance penalty.
> An alternative approach is tc, but that doesn't afford equivalent
> matching options as netfilter.  A bit of googling reveals that more
> people have expressed a desire for egress filtering in the past:
> 
> https://www.spinics.net/lists/netfilter/msg50038.html
> https://unix.stackexchange.com/questions/512371
> 
> I am first performing traffic control with sch_handle_egress() before
> performing filtering with nf_egress().  That order is identical to
> ingress processing.  I'm wondering whether an inverse order would be
> more logical or more beneficial.  Among other things it would allow
> marking packets with netfilter on egress before performing traffic
> control based on that mark.  Thoughts?

Would you provide some numbers on the performance impact for this new
hook?

Thanks.

Re: [PATCH nf-next,RFC 0/5] Netfilter egress hook

[Lukas Wunner]

On Thu, Nov 07, 2019 at 11:51:49PM +0100, Pablo Neira Ayuso wrote:
> On Thu, Oct 31, 2019 at 02:41:00PM +0100, Lukas Wunner wrote:
> > Introduce a netfilter egress hook to complement the existing ingress hook.
> 
> Would you provide some numbers on the performance impact for this new
> hook?

For some reason the numbers are slightly better with this series.

Could be caused by the __always_inline in patch 4, I'd have to compare
the disassembly to confirm this hunch.


* Without this patch:
  Result: OK: 34205373(c34202809+d2564) usec, 100000000 (60byte,0frags)
  2923517pps 1403Mb/sec (1403288160bps) errors: 0

* With this patch:
  Result: OK: 34106013(c34103172+d2841) usec, 100000000 (60byte,0frags)
  2932034pps 1407Mb/sec (1407376320bps) errors: 0


* Without this patch + tc egress:
  Result: OK: 37848652(c37846140+d2511) usec, 100000000 (60byte,0frags)
  2642102pps 1268Mb/sec (1268208960bps) errors: 0

* With this patch + tc egress:
  Result: OK: 37784817(c37782026+d2791) usec, 100000000 (60byte,0frags)
  2646565pps 1270Mb/sec (1270351200bps) errors: 0


* With this patch + nft egress:
  Result: OK: 43911936(c43908932+d3003) usec, 100000000 (60byte,0frags)
  2277285pps 1093Mb/sec (1093096800bps) errors: 0


Tested on a bare-metal Core i7-3615QM, each measurement was performed
twice to verify that the numbers are stable.

Commands to perform a measurement:
modprobe pktgen
echo "add_device lo@3" > /proc/net/pktgen/kpktgend_3
samples/pktgen/pktgen_bench_xmit_mode_queue_xmit.sh -i 'lo@3' -n 100000000

Commands for testing tc egress:
tc qdisc add dev lo clsact
tc filter add dev lo egress protocol ip prio 1 u32 match ip dst 4.3.2.1/32

Commands for testing nft egress:
nft add table netdev t
nft add chain netdev t co \{ type filter hook egress device lo priority 0 \; \}
nft add rule netdev t co ip daddr 4.3.2.1/32 drop

All testing was performed on the loopback interface to avoid distorting
measurements by the packet handling in the low-level Ethernet driver.
This required the following small patch:


diff --git a/net/core/pktgen.c b/net/core/pktgen.c
index bb99152..020c825 100644
--- a/net/core/pktgen.c
+++ b/net/core/pktgen.c
@@ -2003,8 +2003,8 @@ static int pktgen_setup_dev(const struct pktgen_net *pn,
 		return -ENODEV;
 	}
 
-	if (odev->type != ARPHRD_ETHER) {
-		pr_err("not an ethernet device: \"%s\"\n", ifname);
+	if (odev->type != ARPHRD_ETHER && odev->type != ARPHRD_LOOPBACK) {
+		pr_err("not an ethernet or loopback device: \"%s\"\n", ifname);
 		err = -EINVAL;
 	} else if (!netif_running(odev)) {
 		pr_err("device is down: \"%s\"\n", ifname);

Re: [PATCH nf-next,RFC 0/5] Netfilter egress hook

[Lukas Wunner]

On Thu, Nov 07, 2019 at 11:51:49PM +0100, Pablo Neira Ayuso wrote:
> On Thu, Oct 31, 2019 at 02:41:00PM +0100, Lukas Wunner wrote:
> > Introduce a netfilter egress hook to complement the existing ingress hook.
> > 
> > User space support for nft is submitted in a separate patch.
> > 
> > The need for this arose because I had to filter egress packets which do
> > not match a specific ethertype.  The most common solution appears to be
> > to enslave the interface to a bridge and use ebtables, but that's
> > cumbersome to configure and comes with a (small) performance penalty.
> > An alternative approach is tc, but that doesn't afford equivalent
> > matching options as netfilter.  A bit of googling reveals that more
> > people have expressed a desire for egress filtering in the past:
> > 
> > https://www.spinics.net/lists/netfilter/msg50038.html
> > https://unix.stackexchange.com/questions/512371
> > 
> > I am first performing traffic control with sch_handle_egress() before
> > performing filtering with nf_egress().  That order is identical to
> > ingress processing.  I'm wondering whether an inverse order would be
> > more logical or more beneficial.  Among other things it would allow
> > marking packets with netfilter on egress before performing traffic
> > control based on that mark.  Thoughts?
> 
> Would you provide some numbers on the performance impact for this new
> hook?

Just a gentle ping for this series.  I'd still be very interested to
get it upstream.  When posting the above-quoted RFC, Daniel NAK'ed it
saying that "weak justification" was provided "for something that sits
in critical fastpath".

However I followed up with numbers showing that the series actually
results in a speedup rather than a slowdown if the feature isn't used:

https://lore.kernel.org/netfilter-devel/20191123131108.dlnrbutabh5i55ix@wunner.de/

So what's the consensus?  Shall I post a non-RFC version, rebased on
current nf-next/master?

Thanks!

Lukas

Re: [PATCH nf-next,RFC 0/5] Netfilter egress hook

[Pablo Neira Ayuso]

On Wed, Mar 04, 2020 at 10:50:32AM +0100, Lukas Wunner wrote:
[...]
> So what's the consensus?  Shall I post a non-RFC version, rebased on
> current nf-next/master?

Please, move on and rebase on top of nf-next/master.

Thank you.