On 7/7/25 11:43 AM, Gabriel Goller wrote: > 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> Does not apply cleanly anymore, please rebase and repost. Also a few nits below... > @@ -857,6 +859,9 @@ 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); > + /* Disabling all.forwarding sets 0 to force_forwarding for all interfaces */ > + if (newf == 0) > + WRITE_ONCE(idev->cnf.force_forwarding, newf); You could use: WRITE_ONCE(idev->cnf.force_forwarding, 0); > > WRITE_ONCE(idev->cnf.forwarding, newf); > if (changed) > @@ -5719,6 +5724,7 @@ 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 +6753,76 @@ 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) > +{ > + 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); > + } Brakets not needed for the above statement. Either drop them or move the WRITE_ONCE() inside the if () > diff --git a/tools/testing/selftests/net/ipv6_force_forwarding.sh b/tools/testing/selftests/net/ipv6_force_forwarding.sh > new file mode 100644 > index 000000000000..62adc9d4afc9 > --- /dev/null > +++ b/tools/testing/selftests/net/ipv6_force_forwarding.sh > @@ -0,0 +1,105 @@ > +#!/bin/bash > +# SPDX-License-Identifier: GPL-2.0 > +# > +# Test IPv6 force_forwarding interface property > +# > +# This test verifies that the force_forwarding property works correctly: > +# - When global forwarding is disabled, packets are not forwarded normally > +# - When force_forwarding is enabled on an interface, packets are forwarded > +# regardless of the global forwarding setting > + > +source lib.sh > + > +cleanup() { > + cleanup_ns $ns1 $ns2 $ns3 > +} > + > +trap cleanup EXIT > + > +setup_test() { > + # Create three namespaces: sender, router, receiver > + setup_ns ns1 ns2 ns3 > + > + # Create veth pairs: ns1 <-> ns2 <-> ns3 > + ip link add name veth12 type veth peer name veth21 > + ip link add name veth23 type veth peer name veth32 > + > + # Move interfaces to namespaces > + ip link set veth12 netns $ns1 > + ip link set veth21 netns $ns2 > + ip link set veth23 netns $ns2 > + ip link set veth32 netns $ns3 > + > + # Configure interfaces > + ip -n $ns1 addr add 2001:db8:1::1/64 dev veth12 > + ip -n $ns2 addr add 2001:db8:1::2/64 dev veth21 > + ip -n $ns2 addr add 2001:db8:2::1/64 dev veth23 > + ip -n $ns3 addr add 2001:db8:2::2/64 dev veth32 The above will trigger DaD... > + > + # Bring up interfaces > + ip -n $ns1 link set veth12 up > + ip -n $ns2 link set veth21 up > + ip -n $ns2 link set veth23 up > + ip -n $ns3 link set veth32 up > + > + # Add routes > + ip -n $ns1 route add 2001:db8:2::/64 via 2001:db8:1::2 > + ip -n $ns3 route add 2001:db8:1::/64 via 2001:db8:2::1 > + > + # Disable global forwarding > + ip netns exec $ns2 sysctl -qw net.ipv6.conf.all.forwarding=0 > +} > + > +test_force_forwarding() { > + local ret=0 > + > + echo "TEST: force_forwarding functionality" > + > + # Check if force_forwarding sysctl exists > + if ! ip netns exec $ns2 test -f /proc/sys/net/ipv6/conf/veth21/force_forwarding; then > + echo "SKIP: force_forwarding not available" > + return $ksft_skip > + fi > + > + # Test 1: Without force_forwarding, ping should fail > + ip netns exec $ns2 sysctl -qw net.ipv6.conf.veth21.force_forwarding=0 > + ip netns exec $ns2 sysctl -qw net.ipv6.conf.veth23.force_forwarding=0 > + > + if ip netns exec $ns1 ping -6 -c 1 -W 2 2001:db8:2::2 &>/dev/null; then > + echo "FAIL: ping succeeded when forwarding disabled" > + ret=1 > + else > + echo "PASS: forwarding disabled correctly" > + fi > + > + # Test 2: With force_forwarding enabled, ping should succeed > + ip netns exec $ns2 sysctl -qw net.ipv6.conf.veth21.force_forwarding=1 > + ip netns exec $ns2 sysctl -qw net.ipv6.conf.veth23.force_forwarding=1 > + > + if ip netns exec $ns1 ping -6 -c 1 -W 2 2001:db8:2::2 &>/dev/null; then > + echo "PASS: force_forwarding enabled forwarding" ... I'm wondering if it could sometimes race with the ping and cause sporadic failures? Possible using 'nodad' option for address creation could help. /P
