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PATCH] net: allow user to set metric on default route learned via Rou…
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…ter Advertisement (#326)

Add patch from Linux 5.12 to allow user to set metric on default route learned via Router Advertisement message for IPv6

Signed-off-by: Abhishek Dosi <abdosi@microsoft.com>
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abdosi authored Aug 24, 2023
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262 changes: 262 additions & 0 deletions patch/0001-net-allow-user-to-set-metric-on-default-route-learne.patch
Original file line number Diff line number Diff line change
@@ -0,0 +1,262 @@
From 23d559efa7ddfccb29dfe2df772217e55402cd71 Mon Sep 17 00:00:00 2001
From: Praveen Chaudhary <praveen5582@gmail.com>
Date: Mon, 25 Jan 2021 13:44:30 -0800
Subject: [PATCH] net: allow user to set metric on default route learned via
Router Advertisement

For IPv4, default route is learned via DHCPv4 and user is allowed to change
metric using config etc/network/interfaces. But for IPv6, default route can
be learned via RA, for which, currently a fixed metric value 1024 is used.

Ideally, user should be able to configure metric on default route for IPv6
similar to IPv4. This patch adds sysctl for the same.

Logs:

For IPv4:

Config in etc/network/interfaces:
auto eth0
iface eth0 inet dhcp
metric 4261413864

IPv4 Kernel Route Table:
$ ip route list
default via 172.21.47.1 dev eth0 metric 4261413864

FRR Table, if a static route is configured:
[In real scenario, it is useful to prefer BGP learned default route over DHCPv4 default route.]
Codes: K - kernel route, C - connected, S - static, R - RIP,
O - OSPF, I - IS-IS, B - BGP, P - PIM, E - EIGRP, N - NHRP,
T - Table, v - VNC, V - VNC-Direct, A - Babel, D - SHARP,
> - selected route, * - FIB route

S>* 0.0.0.0/0 [20/0] is directly connected, eth0, 00:00:03
K 0.0.0.0/0 [254/1000] via 172.21.47.1, eth0, 6d08h51m

i.e. User can prefer Default Router learned via Routing Protocol in IPv4.
Similar behavior is not possible for IPv6, without this fix.

After fix [for IPv6]:
sudo sysctl -w net.ipv6.conf.eth0.net.ipv6.conf.eth0.ra_defrtr_metric=1996489705

IP monitor: [When IPv6 RA is received]
default via fe80::xx16:xxxx:feb3:ce8e dev eth0 proto ra metric 1996489705 pref high

Kernel IPv6 routing table
$ ip -6 route list
default via fe80::be16:65ff:feb3:ce8e dev eth0 proto ra metric 1996489705 expires 21sec hoplimit 64 pref high

FRR Table, if a static route is configured:
[In real scenario, it is useful to prefer BGP learned default route over IPv6 RA default route.]
Codes: K - kernel route, C - connected, S - static, R - RIPng,
O - OSPFv3, I - IS-IS, B - BGP, N - NHRP, T - Table,
v - VNC, V - VNC-Direct, A - Babel, D - SHARP,
> - selected route, * - FIB route

S>* ::/0 [20/0] is directly connected, eth0, 00:00:06
K ::/0 [119/1001] via fe80::xx16:xxxx:feb3:ce8e, eth0, 6d07h43m

If the metric is changed later, the effect will be seen only when next IPv6
RA is received, because the default route must be fully controlled by RA msg.
Below metric is changed from 1996489705 to 1996489704.

$ sudo sysctl -w net.ipv6.conf.eth0.ra_defrtr_metric=1996489704
net.ipv6.conf.eth0.ra_defrtr_metric = 1996489704

IP monitor:
[On next IPv6 RA msg, Kernel deletes prev route and installs new route with updated metric]

Deleted default via fe80::xx16:xxxx:feb3:ce8e dev eth0 proto ra metric 1996489705 expires 3sec hoplimit 64 pref high
default via fe80::xx16:xxxx:feb3:ce8e dev eth0 proto ra metric 1996489704 pref high

Signed-off-by: Praveen Chaudhary <pchaudhary@linkedin.com>
Signed-off-by: Zhenggen Xu <zxu@linkedin.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Link: https://lore.kernel.org/r/20210125214430.24079-1-pchaudhary@linkedin.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
---
Documentation/networking/ip-sysctl.rst | 10 ++++++++++
include/linux/ipv6.h | 1 +
include/net/ip6_route.h | 3 ++-
include/uapi/linux/ipv6.h | 1 +
include/uapi/linux/sysctl.h | 1 +
net/ipv6/addrconf.c | 11 +++++++++++
net/ipv6/ndisc.c | 12 ++++++++----
net/ipv6/route.c | 5 +++--
8 files changed, 37 insertions(+), 7 deletions(-)

diff --git a/Documentation/networking/ip-sysctl.rst b/Documentation/networking/ip-sysctl.rst
index bf1f0ec9740b..e4e1216e6a7d 100644
--- a/Documentation/networking/ip-sysctl.rst
+++ b/Documentation/networking/ip-sysctl.rst
@@ -1876,6 +1876,16 @@ accept_ra_defrtr - BOOLEAN
- enabled if accept_ra is enabled.
- disabled if accept_ra is disabled.

+ra_defrtr_metric - UNSIGNED INTEGER
+ Route metric for default route learned in Router Advertisement. This value
+ will be assigned as metric for the default route learned via IPv6 Router
+ Advertisement. Takes affect only if accept_ra_defrtr is enabled.
+
+ Possible values:
+ 1 to 0xFFFFFFFF
+
+ Default: IP6_RT_PRIO_USER i.e. 1024.
+
accept_ra_from_local - BOOLEAN
Accept RA with source-address that is found on local machine
if the RA is otherwise proper and able to be accepted.
diff --git a/include/linux/ipv6.h b/include/linux/ipv6.h
index 7a918daa3b19..88641e3b1cc4 100644
--- a/include/linux/ipv6.h
+++ b/include/linux/ipv6.h
@@ -31,6 +31,7 @@ struct ipv6_devconf {
__s32 max_desync_factor;
__s32 max_addresses;
__s32 accept_ra_defrtr;
+ __u32 ra_defrtr_metric;
__s32 accept_ra_min_hop_limit;
__s32 accept_ra_pinfo;
__s32 ignore_routes_with_linkdown;
diff --git a/include/net/ip6_route.h b/include/net/ip6_route.h
index 44969d03debf..0bf09a9bca4e 100644
--- a/include/net/ip6_route.h
+++ b/include/net/ip6_route.h
@@ -174,7 +174,8 @@ struct fib6_info *rt6_get_dflt_router(struct net *net,
struct net_device *dev);
struct fib6_info *rt6_add_dflt_router(struct net *net,
const struct in6_addr *gwaddr,
- struct net_device *dev, unsigned int pref);
+ struct net_device *dev, unsigned int pref,
+ u32 defrtr_usr_metric);

void rt6_purge_dflt_routers(struct net *net);

diff --git a/include/uapi/linux/ipv6.h b/include/uapi/linux/ipv6.h
index 9cdbc5b04855..a5e93062315b 100644
--- a/include/uapi/linux/ipv6.h
+++ b/include/uapi/linux/ipv6.h
@@ -190,6 +190,7 @@ enum {
DEVCONF_NDISC_TCLASS,
DEVCONF_RPL_SEG_ENABLED,
DEVCONF_ACCEPT_UNTRACKED_NA,
+ DEVCONF_RA_DEFRTR_METRIC,
DEVCONF_MAX
};

diff --git a/include/uapi/linux/sysctl.h b/include/uapi/linux/sysctl.h
index 09dabb76a113..6a3b194c50fe 100644
--- a/include/uapi/linux/sysctl.h
+++ b/include/uapi/linux/sysctl.h
@@ -572,6 +572,7 @@ enum {
NET_IPV6_ACCEPT_SOURCE_ROUTE=25,
NET_IPV6_ACCEPT_RA_FROM_LOCAL=26,
NET_IPV6_ACCEPT_RA_RT_INFO_MIN_PLEN=27,
+ NET_IPV6_RA_DEFRTR_METRIC=28,
__NET_IPV6_MAX
};

diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
index 038708de6ef9..cac1e63dac54 100644
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c
@@ -205,6 +205,7 @@ static struct ipv6_devconf ipv6_devconf __read_mostly = {
.max_desync_factor = MAX_DESYNC_FACTOR,
.max_addresses = IPV6_MAX_ADDRESSES,
.accept_ra_defrtr = 1,
+ .ra_defrtr_metric = IP6_RT_PRIO_USER,
.accept_ra_from_local = 0,
.accept_ra_min_hop_limit= 1,
.accept_ra_pinfo = 1,
@@ -260,6 +261,7 @@ static struct ipv6_devconf ipv6_devconf_dflt __read_mostly = {
.max_desync_factor = MAX_DESYNC_FACTOR,
.max_addresses = IPV6_MAX_ADDRESSES,
.accept_ra_defrtr = 1,
+ .ra_defrtr_metric = IP6_RT_PRIO_USER,
.accept_ra_from_local = 0,
.accept_ra_min_hop_limit= 1,
.accept_ra_pinfo = 1,
@@ -5512,6 +5514,7 @@ static inline void ipv6_store_devconf(struct ipv6_devconf *cnf,
array[DEVCONF_MAX_DESYNC_FACTOR] = cnf->max_desync_factor;
array[DEVCONF_MAX_ADDRESSES] = cnf->max_addresses;
array[DEVCONF_ACCEPT_RA_DEFRTR] = cnf->accept_ra_defrtr;
+ array[DEVCONF_RA_DEFRTR_METRIC] = cnf->ra_defrtr_metric;
array[DEVCONF_ACCEPT_RA_MIN_HOP_LIMIT] = cnf->accept_ra_min_hop_limit;
array[DEVCONF_ACCEPT_RA_PINFO] = cnf->accept_ra_pinfo;
#ifdef CONFIG_IPV6_ROUTER_PREF
@@ -6705,6 +6708,14 @@ static const struct ctl_table addrconf_sysctl[] = {
.mode = 0644,
.proc_handler = proc_dointvec,
},
+ {
+ .procname = "ra_defrtr_metric",
+ .data = &ipv6_devconf.ra_defrtr_metric,
+ .maxlen = sizeof(u32),
+ .mode = 0644,
+ .proc_handler = proc_douintvec_minmax,
+ .extra1 = (void *)SYSCTL_ONE,
+ },
{
.procname = "accept_ra_min_hop_limit",
.data = &ipv6_devconf.accept_ra_min_hop_limit,
diff --git a/net/ipv6/ndisc.c b/net/ipv6/ndisc.c
index f236ed938efd..85cd34710a04 100644
--- a/net/ipv6/ndisc.c
+++ b/net/ipv6/ndisc.c
@@ -1199,6 +1199,7 @@ static void ndisc_router_discovery(struct sk_buff *skb)
struct neighbour *neigh = NULL;
struct inet6_dev *in6_dev;
struct fib6_info *rt = NULL;
+ u32 defrtr_usr_metric;
struct net *net;
int lifetime;
struct ndisc_options ndopts;
@@ -1329,18 +1330,21 @@ static void ndisc_router_discovery(struct sk_buff *skb)
return;
}
}
- if (rt && lifetime == 0) {
+ /* Set default route metric as specified by user */
+ defrtr_usr_metric = in6_dev->cnf.ra_defrtr_metric;
+ /* delete the route if lifetime is 0 or if metric needs change */
+ if (rt && (lifetime == 0 || rt->fib6_metric != defrtr_usr_metric)) {
ip6_del_rt(net, rt, false);
rt = NULL;
}

- ND_PRINTK(3, info, "RA: rt: %p lifetime: %d, for dev: %s\n",
- rt, lifetime, skb->dev->name);
+ ND_PRINTK(3, info, "RA: rt: %p lifetime: %d, metric: %d, for dev: %s\n",
+ rt, lifetime, defrtr_usr_metric, skb->dev->name);
if (!rt && lifetime) {
ND_PRINTK(3, info, "RA: adding default router\n");

rt = rt6_add_dflt_router(net, &ipv6_hdr(skb)->saddr,
- skb->dev, pref);
+ skb->dev, pref, defrtr_usr_metric);
if (!rt) {
ND_PRINTK(0, err,
"RA: %s failed to add default route\n",
diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index cdf215442d37..2a32cc7db014 100644
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -4269,11 +4269,12 @@ struct fib6_info *rt6_get_dflt_router(struct net *net,
struct fib6_info *rt6_add_dflt_router(struct net *net,
const struct in6_addr *gwaddr,
struct net_device *dev,
- unsigned int pref)
+ unsigned int pref,
+ u32 defrtr_usr_metric)
{
struct fib6_config cfg = {
.fc_table = l3mdev_fib_table(dev) ? : RT6_TABLE_DFLT,
- .fc_metric = IP6_RT_PRIO_USER,
+ .fc_metric = defrtr_usr_metric,
.fc_ifindex = dev->ifindex,
.fc_flags = RTF_GATEWAY | RTF_ADDRCONF | RTF_DEFAULT |
RTF_UP | RTF_EXPIRES | RTF_PREF(pref),
--
2.25.1

3 changes: 3 additions & 0 deletions patch/series
Original file line number Diff line number Diff line change
Expand Up @@ -50,6 +50,9 @@ kernel-compat-always-include-linux-compat.h-from-net-compat.patch
0001-net-ipv6-Introduce-accept_unsolicited_na-knob-to-imp.patch
0002-net-ipv6-Expand-and-rename-accept_unsolicited_na-to-.patch

# Backport from 5.12
0001-net-allow-user-to-set-metric-on-default-route-learne.patch

#
# This series applies on GIT commit 1451b36b2b0d62178e42f648d8a18131af18f7d8
# Tkernel-sched-core-fix-cgroup-fork-race.patch
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