On 04.07.2025 10:07, Nicolas Dichtel wrote:
Le 03/07/2025 à 18:01, Gabriel Goller a écrit :
It is currently impossible to enable ipv6 forwarding on a per-interface
basis like in ipv4. To enable forwarding on an ipv6 interface we need to
enable it on all interfaces and disable it on the other interfaces using
a netfilter rule. This is especially cumbersome if you have lots of
interface and only want to enable forwarding on a few. According to the
sysctl docs [0] the `net.ipv6.conf.all.forwarding` enables forwarding
for all interfaces, while the interface-specific
`net.ipv6.conf.<interface>.forwarding` configures the interface
Host/Router configuration.
Introduce a new sysctl flag `force_forwarding`, which can be set on every
interface. The ip6_forwarding function will then check if the global
forwarding flag OR the force_forwarding flag is active and forward the
packet.
To preserver backwards-compatibility reset the flag (on all interfaces)
to 0 if the net.ipv6.conf.all.forwarding flag is set to 0.
Add a short selftest that checks if a packet gets forwarded with and
without `force_forwarding`.
[0]: https://www.kernel.org/doc/Documentation/networking/ip-sysctl.txt
Signed-off-by: Gabriel Goller <g.goller@xxxxxxxxxxx>
---
[snip]
@@ -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();
+ struct net_device *dev;
+ struct inet6_dev *idev;
+
ASSERT_RTNL() is always put after variables declaration.
I removed ASSERT_RTNL completely, this is already checked by __in6_dev_get_rtnl_net.
+ 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;
+ int new_val = *valp;
+ int old_val = *valp;
+ int ret;
+
+ struct ctl_table tmp_ctl = *ctl;
This declaration should be put with other declarations.
Agree.
+
+ tmp_ctl.extra1 = SYSCTL_ZERO;
+ tmp_ctl.extra2 = SYSCTL_ONE;
+ 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);
Why not putting this in the above block?
And maybe under the rtnl_lock to avoid race if two users change the value at the
same time.
Yep, you're right.
Nicolas
Thanks for the review!
