kernel: netfilter add connmark savedscp support

savedscp is a method of storing the DSCP of an ip packet into conntrack
mark.  In combination with a suitable tc filter action (conndscp but may
end up being integrated into connmark) DSCP values are able to be stored
on egress and restored on ingress across links that otherwise alter or
bleach DSCP.

This is useful for qdiscs such as CAKE which are able to shape according
to policies based on DSCP.

Ingress classification is traditionally a challenging task since
iptables rules haven't yet run and tc filter/eBPF programs are pre-NAT
lookups, hence are unable to see internal IPv4 addresses as used on the
typical home masquerading gateway.

The ingress problem is solved by the tc filter, but the tc people didn't
like the idea of tc setting conntrack mark values, though they are ok
with reading conntrack values and hence restoring DSCP from conntrack
marks.

x_tables CONNMARK with the new savedscp action solves the problem of
storing the DSCP to the conntrack mark.

It accepts 2 parameters.  The mark is a 32bit value with usually one 1
bit set.  This bit is set when savedscp saves the DSCP to the mark.
This is useful to implement a 'one shot'
iptables based classification where the 'complicated' iptables rules are
only run once to classify the connection on initial (egress) packet and
subsequent packets are all marked/restored with the same DSCP.  A mark
of zero disables the setting of a status bit/s.

The mask is a 32bit value of at least 6 contiguous bits and represents
the area where the DSCP will be stored.

e.g.

iptables -A QOS_MARK_eth0 -t mangle -j CONNMARK --savedscp-mark 0xfc000000/0x01000000

Would store the DSCP in the top 6 bits of the 32bit mark field, and use
the LSB of the top byte as the 'DSCP has been stored' marker.

Signed-off-by: Kevin Darbyshire-Bryant <ldir@darbyshire-bryant.me.uk>

1 files changed, 107 insertions, 0 deletions

diff --git a/target/linux/generic/hack-4.14/645-netfilter-connmark-introduce-savedscp.patch b/target/linux/generic/hack-4.14/645-netfilter-connmark-introduce-savedscp.patch
new file mode 100644
index 0000000000..1681ed5db8
--- /dev/null
+++ b/target/linux/generic/hack-4.14/645-netfilter-connmark-introduce-savedscp.patch
@@ -0,0 +1,107 @@
+From 5a4d7714faa28c03e85d696fba82716fbda5c432 Mon Sep 17 00:00:00 2001
+From: Kevin Darbyshire-Bryant <ldir@darbyshire-bryant.me.uk>
+Date: Sat, 23 Mar 2019 09:29:49 +0000
+Subject: [PATCH] netfilter: connmark: introduce savedscp
+
+savedscp is a method of storing the DSCP of an ip packet into conntrack
+mark.  In combination with a suitable tc filter action (conndscp but may
+end up being integrated into connmark) DSCP values are able to be stored
+on egress and restored on ingress across links that otherwise alter or
+bleach DSCP.
+
+This is useful for qdiscs such as CAKE which are able to shape according
+to policies based on DSCP.
+
+Ingress classification is traditionally a challenging task since
+iptables rules haven't yet run and tc filter/eBPF programs are pre-NAT
+lookups, hence are unable to see internal IPv4 addresses as used on the
+typical home masquerading gateway.
+
+The ingress problem is solved by the tc filter, but the tc people didn't
+like the idea of tc setting conntrack mark values, though they are ok
+with reading conntrack values and hence restoring DSCP from conntrack
+marks.
+
+x_tables CONNMARK with the new savedscp action solves the problem of
+storing the DSCP to the conntrack mark.
+
+It accepts 2 parameters.  The mark is a 32bit value with usually one 1
+bit set.  This bit is set when savedscp saves the DSCP to the mark.
+This is useful to implement a 'one shot'
+iptables based classification where the 'complicated' iptables rules are
+only run once to classify the connection on initial (egress) packet and
+subsequent packets are all marked/restored with the same DSCP.  A mark
+of zero disables the setting of a status bit/s.
+
+The mask is a 32bit value of at least 6 contiguous bits and represents
+the area where the DSCP will be stored.
+
+e.g.
+
+iptables -A QOS_MARK_eth0 -t mangle -j CONNMARK --savedscp-mark 0xfc000000/0x01000000
+
+Would store the DSCP in the top 6 bits of the 32bit mark field, and use
+the LSB of the top byte as the 'DSCP has been stored' marker.
+
+Signed-off-by: Kevin Darbyshire-Bryant <ldir@darbyshire-bryant.me.uk>
+---
+ include/uapi/linux/netfilter/xt_connmark.h |  3 ++-
+ net/netfilter/xt_connmark.c                | 21 ++++++++++++++++++++-
+ 2 files changed, 22 insertions(+), 2 deletions(-)
+
+diff --git a/include/uapi/linux/netfilter/xt_connmark.h b/include/uapi/linux/netfilter/xt_connmark.h
+index 408a9654f05c..e63ad3c89b92 100644
+--- a/include/uapi/linux/netfilter/xt_connmark.h
++++ b/include/uapi/linux/netfilter/xt_connmark.h
+@@ -16,7 +16,8 @@
+ enum {
+ 	XT_CONNMARK_SET = 0,
+ 	XT_CONNMARK_SAVE,
+-	XT_CONNMARK_RESTORE
++	XT_CONNMARK_RESTORE,
++	XT_CONNMARK_SAVEDSCP
+ };
+ 
+ struct xt_connmark_tginfo1 {
+diff --git a/net/netfilter/xt_connmark.c b/net/netfilter/xt_connmark.c
+index ec377cc6a369..aa5bcea8f9ba 100644
+--- a/net/netfilter/xt_connmark.c
++++ b/net/netfilter/xt_connmark.c
+@@ -42,6 +42,7 @@ connmark_tg(struct sk_buff *skb, const struct xt_action_param *par)
+ 	enum ip_conntrack_info ctinfo;
+ 	struct nf_conn *ct;
+ 	u_int32_t newmark;
++	u_int8_t dscp, maskshift;
+ 
+ 	ct = nf_ct_get(skb, &ctinfo);
+ 	if (ct == NULL)
+@@ -57,7 +58,25 @@ connmark_tg(struct sk_buff *skb, const struct xt_action_param *par)
+ 		break;
+ 	case XT_CONNMARK_SAVE:
+ 		newmark = (ct->mark & ~info->ctmask) ^
+-		          (skb->mark & info->nfmask);
++			  (skb->mark & info->nfmask);
++		if (ct->mark != newmark) {
++			ct->mark = newmark;
++			nf_conntrack_event_cache(IPCT_MARK, ct);
++		}
++		break;
++	case XT_CONNMARK_SAVEDSCP:
++		if (skb->protocol == htons(ETH_P_IP))
++			dscp = ipv4_get_dsfield(ip_hdr(skb)) >> 2;
++		else if (skb->protocol == htons(ETH_P_IPV6))
++			dscp = ipv6_get_dsfield(ipv6_hdr(skb)) >> 2;
++		else	/* protocol doesn't have diffserv */
++			break;
++
++		/* nfmask contains the mask shift value */
++		maskshift = info->nfmask & 0x1f;
++		newmark = (ct->mark & ~info->ctmark) |
++			  (info->ctmask | (dscp << maskshift));
++
+ 		if (ct->mark != newmark) {
+ 			ct->mark = newmark;
+ 			nf_conntrack_event_cache(IPCT_MARK, ct);
+-- 
+2.20.1 (Apple Git-117)
+