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136 lines
4.8 KiB
Diff
136 lines
4.8 KiB
Diff
From f171924dcf1d0b31fb7bd1cff113d7a1f7f05ec2 Mon Sep 17 00:00:00 2001
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From: Kevin Darbyshire-Bryant <ldir@darbyshire-bryant.me.uk>
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Date: Sat, 23 Mar 2019 09:29:49 +0000
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Subject: [PATCH] netfilter: connmark: introduce savedscp
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savedscp is a method of storing the DSCP of an ip packet into conntrack
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mark. In combination with a suitable tc filter action (act_ctinfo) DSCP
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values are able to be stored in the mark on egress and restored on
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ingress across links that otherwise alter or bleach DSCP.
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This is useful for qdiscs such as CAKE which are able to shape according
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to policies based on DSCP.
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Ingress classification is traditionally a challenging task since
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iptables rules haven't yet run and tc filter/eBPF programs are pre-NAT
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lookups, hence are unable to see internal IPv4 addresses as used on the
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typical home masquerading gateway.
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x_tables CONNMARK savedscp action solves the problem of storing the DSCP
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to the conntrack mark in a way suitable for the new act_ctinfo tc action
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to restore.
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The savedsp option accepts 2 parameters, a 32bit 'dscpmask' and a 32bit
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'statemask'. The dscp mask must be a minimum of 6 contiguous bits and
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represents the area where the DSCP will be stored in the connmark. The
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state mask is a minimum 1 bit length mask that must not overlap with the
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dscpmask. It represents a flag which is set when the DSCP has been
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stored in the conntrack mark. This is useful to implement a 'one shot'
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iptables based classification where the 'complicated' iptables rules are
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only run once to classify the connection on initial (egress) packet and
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subsequent packets are all marked/restored with the same DSCP. A state
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mask of zero disables the setting of a status bit/s.
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example syntax with a suitably modified iptables user space application:
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iptables -A QOS_MARK_eth0 -t mangle -j CONNMARK --savedscp-mark 0xfc000000/0x01000000
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Would store the DSCP in the top 6 bits of the 32bit mark field, and use
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the LSB of the top byte as the 'DSCP has been stored' marker.
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|----0xFC----conntrack mark----000000---|
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| Bits 31-26 | bit 25 | bit24 |~~~ Bit 0|
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| DSCP | unused | flag |unused |
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|-----------------------0x01---000000---|
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^ ^
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| |
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---| Conditional flag
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| set this when dscp
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|-ip diffserv-| stored in mark
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| 6 bits |
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|-------------|
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an identically configured tc action to restore looks like:
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tc filter show dev eth0 ingress
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filter parent ffff: protocol all pref 10 u32 chain 0
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filter parent ffff: protocol all pref 10 u32 chain 0 fh 800: ht divisor 1
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filter parent ffff: protocol all pref 10 u32 chain 0 fh 800::800 order 2048 key ht 800 bkt 0 flowid 1:1 not_in_hw
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match 00000000/00000000 at 0
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action order 1: ctinfo zone 0 pipe
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index 2 ref 1 bind 1 dscp 0xfc000000/0x1000000
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action order 2: mirred (Egress Redirect to device ifb4eth0) stolen
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index 1 ref 1 bind 1
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|----0xFC----conntrack mark----000000---|
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| Bits 31-26 | bit 25 | bit24 |~~~ Bit 0|
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| DSCP | unused | flag |unused |
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|-----------------------0x01---000000---|
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| |
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---| Conditional flag
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v only restore if set
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|-ip diffserv-|
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| 6 bits |
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|-------------|
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Signed-off-by: Kevin Darbyshire-Bryant <ldir@darbyshire-bryant.me.uk>
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---
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include/uapi/linux/netfilter/xt_connmark.h | 3 ++-
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net/netfilter/xt_connmark.c | 17 +++++++++++++++++
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2 files changed, 19 insertions(+), 1 deletion(-)
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--- a/include/uapi/linux/netfilter/xt_connmark.h
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+++ b/include/uapi/linux/netfilter/xt_connmark.h
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@@ -16,7 +16,8 @@
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enum {
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XT_CONNMARK_SET = 0,
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XT_CONNMARK_SAVE,
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- XT_CONNMARK_RESTORE
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+ XT_CONNMARK_RESTORE,
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+ XT_CONNMARK_SAVEDSCP
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};
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enum {
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--- a/net/netfilter/xt_connmark.c
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+++ b/net/netfilter/xt_connmark.c
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@@ -42,6 +42,7 @@ connmark_tg_shift(struct sk_buff *skb, c
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u_int32_t new_targetmark;
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struct nf_conn *ct;
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u_int32_t newmark;
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+ u_int8_t dscp;
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ct = nf_ct_get(skb, &ctinfo);
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if (ct == NULL)
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@@ -74,6 +75,21 @@ connmark_tg_shift(struct sk_buff *skb, c
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nf_conntrack_event_cache(IPCT_MARK, ct);
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}
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break;
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+ case XT_CONNMARK_SAVEDSCP:
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+ if (skb->protocol == htons(ETH_P_IP))
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+ dscp = ipv4_get_dsfield(ip_hdr(skb)) >> 2;
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+ else if (skb->protocol == htons(ETH_P_IPV6))
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+ dscp = ipv6_get_dsfield(ipv6_hdr(skb)) >> 2;
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+ else /* protocol doesn't have diffserv */
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+ break;
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+
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+ newmark = (ct->mark & ~info->ctmark) |
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+ (info->ctmask | (dscp << info->shift_bits));
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+ if (ct->mark != newmark) {
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+ ct->mark = newmark;
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+ nf_conntrack_event_cache(IPCT_MARK, ct);
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+ }
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+ break;
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case XT_CONNMARK_RESTORE:
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new_targetmark = (ct->mark & info->ctmask);
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if (info->shift_dir == D_SHIFT_RIGHT)
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@@ -86,6 +102,7 @@ connmark_tg_shift(struct sk_buff *skb, c
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skb->mark = newmark;
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break;
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}
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+out:
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return XT_CONTINUE;
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}
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