kernel: bridge: ebtables: Avoid resetting limit rule state

This is needed for the Gluon ARP limiter to work without hiccups in
traffic.

Link: https://patchwork.ozlabs.org/patch/841210/
Signed-off-by: Linus Lüssing <linus.luessing@c0d3.blue>

patches/lede/0061-kernel-bridge-ebtables-Avoid-resetting-limit-rule-state.patch

@@ -0,0 +1,63 @@
+From: Linus Lüssing <linus.luessing@c0d3.blue>
+Date: Sun, 26 Nov 2017 05:19:21 +0100
+Subject: kernel: bridge: ebtables: Avoid resetting limit rule state
+
+Link: https://patchwork.ozlabs.org/patch/841210/
+Signed-off-by: Linus Lüssing <linus.luessing@c0d3.blue>
+
+diff --git a/target/linux/generic/patches-4.4/121-bridge-ebtables-Avoid-resetting-limit-rule-state.patch b/target/linux/generic/patches-4.4/121-bridge-ebtables-Avoid-resetting-limit-rule-state.patch
+new file mode 100644
+index 0000000000000000000000000000000000000000..417fdd75e543ebb6a3fdd56cb97fc83324eeb104
+--- /dev/null
++++ b/target/linux/generic/patches-4.4/121-bridge-ebtables-Avoid-resetting-limit-rule-state.patch
+@@ -0,0 +1,50 @@
++From 535097827e437bfa1906ed3210e6504750f4342b Mon Sep 17 00:00:00 2001
++From: =?UTF-8?q?Linus=20L=C3=BCssing?= <linus.luessing@c0d3.blue>
++Date: Sat, 25 Nov 2017 00:36:13 +0100
++Subject: [PATCH] bridge: ebtables: Avoid resetting limit rule state
++MIME-Version: 1.0
++Content-Type: text/plain; charset=UTF-8
++Content-Transfer-Encoding: 8bit
++
++So far any changes with ebtables will reset the state of limit rules,
++leading to spikes in traffic. This is especially noticeable if changes
++are done frequently, for instance via a daemon.
++
++This patch fixes this by bailing out from (re)setting if the limit
++rule was initialized before.
++
++When sending packets every 250ms for 600s, with a
++"--limit 1/sec --limit-burst 50" rule and a command like this
++in the background:
++
++$ ebtables -N VOIDCHAIN
++$ while true; do ebtables -F VOIDCHAIN; sleep 30; done
++
++The results are:
++
++Before: ~1600 packets
++After: 650 packets
++
++Signed-off-by: Linus Lüssing <linus.luessing@c0d3.blue>
++---
++ net/bridge/netfilter/ebt_limit.c | 4 ++++
++ 1 file changed, 4 insertions(+)
++
++diff --git a/net/bridge/netfilter/ebt_limit.c b/net/bridge/netfilter/ebt_limit.c
++index 61a9f1be1263..f74b48633feb 100644
++--- a/net/bridge/netfilter/ebt_limit.c
+++++ b/net/bridge/netfilter/ebt_limit.c
++@@ -69,6 +69,10 @@ static int ebt_limit_mt_check(const struct xt_mtchk_param *par)
++ {
++ 	struct ebt_limit_info *info = par->matchinfo;
++ 
+++	/* Do not reset state on unrelated table changes */
+++	if (info->prev)
+++		return 0;
+++
++ 	/* Check for overflow. */
++ 	if (info->burst == 0 ||
++ 	    user2credits(info->avg * info->burst) < user2credits(info->avg)) {
++-- 
++2.11.0
++