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`.
Signed-off-by: Gabriel Goller g.goller@proxmox.com
[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!