--- /dev/null
+From f1627abea333781d3e2a61bac4c7fd4502395741 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 set-dscpmark
+
+set-dscpmark is a method of storing the DSCP of an ip packet into
+conntrack mark. In combination with a suitable tc filter action
+(act_ctinfo) DSCP values are able to be stored in the mark 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.
+
+x_tables CONNMARK set-dscpmark target solves the problem of storing the
+DSCP to the conntrack mark in a way suitable for the new act_ctinfo tc
+action to restore.
+
+The set-dscpmark option accepts 2 parameters, a 32bit 'dscpmask' and a
+32bit 'statemask'. The dscp mask must be 6 contiguous bits and
+represents the area where the DSCP will be stored in the connmark. The
+state mask is a minimum 1 bit length mask that must not overlap with the
+dscpmask. It represents a flag which is set when the DSCP has been
+stored in the conntrack 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 state
+mask of zero disables the setting of a status bit/s.
+
+example syntax with a suitably modified iptables user space application:
+
+iptables -A QOS_MARK_eth0 -t mangle -j CONNMARK --set-dscpmark 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.
+
+|----0xFC----conntrack mark----000000---|
+| Bits 31-26 | bit 25 | bit24 |~~~ Bit 0|
+| DSCP | unused | flag |unused |
+|-----------------------0x01---000000---|
+ ^ ^
+ | |
+ ---| Conditional flag
+ | set this when dscp
+|-ip diffserv-| stored in mark
+| 6 bits |
+|-------------|
+
+an identically configured tc action to restore looks like:
+
+tc filter show dev eth0 ingress
+filter parent ffff: protocol all pref 10 u32 chain 0
+filter parent ffff: protocol all pref 10 u32 chain 0 fh 800: ht divisor 1
+filter parent ffff: protocol all pref 10 u32 chain 0 fh 800::800 order 2048 key ht 800 bkt 0 flowid 1: not_in_hw
+ match 00000000/00000000 at 0
+ action order 1: ctinfo zone 0 pipe
+ index 2 ref 1 bind 1 dscp 0xfc000000/0x1000000
+
+ action order 2: mirred (Egress Redirect to device ifb4eth0) stolen
+ index 1 ref 1 bind 1
+
+|----0xFC----conntrack mark----000000---|
+| Bits 31-26 | bit 25 | bit24 |~~~ Bit 0|
+| DSCP | unused | flag |unused |
+|-----------------------0x01---000000---|
+ | |
+ | |
+ ---| Conditional flag
+ v only restore if set
+|-ip diffserv-|
+| 6 bits |
+|-------------|
+
+Signed-off-by: Kevin Darbyshire-Bryant <ldir@darbyshire-bryant.me.uk>
+---
+ net/netfilter/xt_connmark.c | 19 +++++++++++++++++--
+ 1 file changed, 17 insertions(+), 2 deletions(-)
+
+diff --git a/net/netfilter/xt_connmark.c b/net/netfilter/xt_connmark.c
+index ec377cc6a369..823d925b3aaf 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)
+@@ -49,7 +50,21 @@ connmark_tg(struct sk_buff *skb, const struct xt_action_param *par)
+
+ switch (info->mode) {
+ case XT_CONNMARK_SET:
+- newmark = (ct->mark & ~info->ctmask) ^ info->ctmark;
++ if (info->nfmask & 0x80000000) {
++ newmark = (ct->mark & ~info->ctmask) ^ info->ctmark;
++ } else {
++ 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);
+@@ -57,7 +72,7 @@ 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);
+--
+2.21.0 (Apple Git-122.2)
+
projects / openwrt / openwrt.git / blobdiff