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 <[email protected]>
> ---
>
[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.
> + 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.
> +
> + 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.
Nicolas
