On 04.07.2025 08:00, Kuniyuki Iwashima wrote:
From: Gabriel Goller <g.goller@xxxxxxxxxxx>
Date: Thu, 3 Jul 2025 18:01:53 +0200
diff --git a/Documentation/networking/ip-sysctl.rst b/Documentation/networking/ip-sysctl.rst
index 0f1251cce314..ec7fa1e890f1 100644
--- a/Documentation/networking/ip-sysctl.rst
+++ b/Documentation/networking/ip-sysctl.rst
@@ -2292,6 +2292,11 @@ conf/all/forwarding - BOOLEAN
proxy_ndp - BOOLEAN
Do proxy ndp.
+force_forwarding - BOOLEAN
+ Enable forwarding on this interface only -- regardless of the setting on
+ ``conf/all/forwarding``. When setting ``conf.all.forwarding`` to 0,
+ the ``force_forwarding`` flag will be reset on all interfaces.
Please update conf/all/forwarding too as it will be stale after
this patch.
I'll change the conf/all/forwarding section from:
IPv4 and IPv6 work differently here; e.g. netfilter must be used
to control which interfaces may forward packets and which not.
to:
IPv4 and IPv6 work differently here; the ``force_forwarding`` flag must
be used to control which interfaces may forward packets.
I hope that's all right.
+
fwmark_reflect - BOOLEAN
Controls the fwmark of kernel-generated IPv6 reply packets that are not
associated with a socket for example, TCP RSTs or ICMPv6 echo replies).
diff --git a/include/linux/ipv6.h b/include/linux/ipv6.h
index 5aeeed22f35b..5380107e466c 100644
--- a/include/linux/ipv6.h
+++ b/include/linux/ipv6.h
@@ -19,6 +19,7 @@ struct ipv6_devconf {
__s32 forwarding;
__s32 disable_policy;
__s32 proxy_ndp;
+ __s32 force_forwarding;
nit: place force_forwarding just after forwarding.
Agree.
__cacheline_group_end(ipv6_devconf_read_txrx);
__s32 accept_ra;
@@ -857,6 +859,15 @@ static void addrconf_forward_change(struct net *net, __s32 newf)
idev = __in6_dev_get_rtnl_net(dev);
if (idev) {
int changed = (!idev->cnf.forwarding) ^ (!newf);
+ /*
+ * With the introduction of force_forwarding, we need to be backwards
+ * compatible, so that means we need to set the force_forwarding flag
Strictly backward compatibility is not related I think because
the per iface conf is disabled by default, and this is a new
behaviour. Maybe simply say
/* Disabling all.forwarding sets 0 to force_forwarding for all interfaces */
Agree.
+ * on every interface to 0 if net.ipv6.conf.all.forwarding is set to 0.
+ * This allows the global forwarding flag to disable forwarding for
+ * all interfaces.
+ */
+ if (newf == 0)
+ WRITE_ONCE(idev->cnf.force_forwarding, newf);
WRITE_ONCE(idev->cnf.forwarding, newf);
if (changed)
@@ -5719,6 +5730,7 @@ static void ipv6_store_devconf(const struct ipv6_devconf *cnf,
array[DEVCONF_ACCEPT_UNTRACKED_NA] =
READ_ONCE(cnf->accept_untracked_na);
array[DEVCONF_ACCEPT_RA_MIN_LFT] = READ_ONCE(cnf->accept_ra_min_lft);
+ array[DEVCONF_FORCE_FORWARDING] = READ_ONCE(cnf->force_forwarding);
}
[...]
static inline size_t inet6_ifla6_size(void)
@@ -6747,6 +6759,78 @@ static int addrconf_sysctl_disable_policy(const struct ctl_table *ctl, int write
return ret;
}
+static void addrconf_force_forward_change(struct net *net, __s32 newf)
+{
+ ASSERT_RTNL();
__in6_dev_get_rtnl_net() has the same check so this is not needed.
Agree.
+ struct net_device *dev;
+ struct inet6_dev *idev;
+
+ for_each_netdev(net, dev) {
+ idev = __in6_dev_get_rtnl_net(dev);
+ if (idev) {
+ int changed = (!idev->cnf.force_forwarding) ^ (!newf);
+
+ WRITE_ONCE(idev->cnf.force_forwarding, newf);
+ if (changed) {
+ inet6_netconf_notify_devconf(dev_net(dev), RTM_NEWNETCONF,
+ NETCONFA_FORCE_FORWARDING,
+ dev->ifindex, &idev->cnf);
+ }
+ }
+ }
+}
+
+static int addrconf_sysctl_force_forwarding(const struct ctl_table *ctl, int write,
+ void *buffer, size_t *lenp, loff_t *ppos)
+{
+ struct inet6_dev *idev = ctl->extra1;
+ struct net *net = ctl->extra2;
+ int *valp = ctl->data;
+ loff_t pos = *ppos;
nit: Please keep the reverse xmas tree order.
https://www.kernel.org/doc/html/latest/process/maintainer-netdev.html#local-variable-ordering-reverse-xmas-tree-rcs
+ int new_val = *valp;
+ int old_val = *valp;
+ int ret;
+
+ struct ctl_table tmp_ctl = *ctl;
same here.
Will do; moved this up.
+
+ tmp_ctl.extra1 = SYSCTL_ZERO;
+ tmp_ctl.extra2 = SYSCTL_ONE;
As you are copying *ctl, please specify this in addrconf_sysctl[].
Umm how would I do that? Do you want me to add a comment explaining it?
I need extra1 and extra2 to be the network device so that I can set
NETCONFA_FORCE_FORWARDING but I also want to use proc_douintvec_minmax.
+ tmp_ctl.data = &new_val;
+
+ ret = proc_douintvec_minmax(&tmp_ctl, write, buffer, lenp, ppos);
+
+ if (write && old_val != new_val) {
+ if (!rtnl_net_trylock(net))
+ return restart_syscall();
+
+ if (valp == &net->ipv6.devconf_dflt->force_forwarding) {
+ inet6_netconf_notify_devconf(net, RTM_NEWNETCONF,
+ NETCONFA_FORCE_FORWARDING,
+ NETCONFA_IFINDEX_DEFAULT,
+ net->ipv6.devconf_dflt);
+ } else if (valp == &net->ipv6.devconf_all->force_forwarding) {
+ inet6_netconf_notify_devconf(net, RTM_NEWNETCONF,
+ NETCONFA_FORCE_FORWARDING,
+ NETCONFA_IFINDEX_ALL,
+ net->ipv6.devconf_all);
+
+ addrconf_force_forward_change(net, new_val);
+ } else {
+ inet6_netconf_notify_devconf(net, RTM_NEWNETCONF,
+ NETCONFA_FORCE_FORWARDING,
+ idev->dev->ifindex,
+ &idev->cnf);
+ }
+ rtnl_net_unlock(net);
+ }
+
+ if (write)
+ WRITE_ONCE(*valp, new_val);
+ if (ret)
+ *ppos = pos;
+ return ret;
+}
+
static int minus_one = -1;
static const int two_five_five = 255;
static u32 ioam6_if_id_max = U16_MAX;
@@ -7217,6 +7301,13 @@ static const struct ctl_table addrconf_sysctl[] = {
.extra1 = SYSCTL_ZERO,
.extra2 = SYSCTL_TWO,
},
+ {
+ .procname = "force_forwarding",
+ .data = &ipv6_devconf.force_forwarding,
+ .maxlen = sizeof(int),
+ .mode = 0644,
+ .proc_handler = addrconf_sysctl_force_forwarding,
Here for extra{1,2}.
See above.
+ },
};
static int __addrconf_sysctl_register(struct net *net, char *dev_name,
diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
index 7bd29a9ff0db..440b9efced72 100644
--- a/net/ipv6/ip6_output.c
+++ b/net/ipv6/ip6_output.c
@@ -509,7 +509,8 @@ int ip6_forward(struct sk_buff *skb)
u32 mtu;
idev = __in6_dev_get_safely(dev_get_by_index_rcu(net, IP6CB(skb)->iif));
- if (READ_ONCE(net->ipv6.devconf_all->forwarding) == 0)
+ if (idev && !READ_ONCE(idev->cnf.force_forwarding) &&
+ !READ_ONCE(net->ipv6.devconf_all->forwarding))
Now this ignores devconf_all when !idev whose dev was not
found or has not had a valid mtu.
if (!READ_ONCE(net->ipv6.devconf_all->forwarding) &&
(!idev || !READ_ONCE(idev->cnf.force_forwarding)))
Oof yeah, you're right this is my mistake. I'll use your solution.
Thanks for the review!
