[PATCH net-next v2] ipv6: Add NETCONFA_FORCE_FORWARDING to netconf messages

[PATCH net-next v2] ipv6: Add NETCONFA_FORCE_FORWARDING to netconf messages

[Gabriel Goller]

Since force_forwarding was added, changing the sysctl sends an
RTM_NEWNETCONF notification of type NETCONFA_FORCE_FORWARDING, but
inet6_netconf_fill_devconf() never emits the attribute. Listeners only
receive NETCONFA_IFINDEX without the new value, and RTM_GETNETCONF
replies and dumps omit it as well.

Also send a notification when disabling all.forwarding resets
force_forwarding on an interface, which previously happened silently.

Fixes: f24987ef6959 ("ipv6: add `force_forwarding` sysctl to enable per-interface forwarding")
Signed-off-by: Gabriel Goller <g.goller@proxmox.com>
---
iproute2 patch here:
https://lore.kernel.org/netdev/20261028-ip_netconf_show-v1-1-a20fc6b20025@proxmox.com/

Changes in v2:
- Emit when net.ipv6.conf.all.forwarding is disabled (thanks @Ido Schimmel)
- Rebase onto net-next
- Link to v1: https://lore.kernel.org/20261023-ipv6_add_netconfa-v1-1-94d14b07d621@proxmox.com
---
 net/ipv6/addrconf.c | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
index c8c0dd04982d..1df6c1db472f 100644
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c
@@ -529,6 +529,9 @@ static int inet6_netconf_msgsize_devconf(int type)
 	if (all || type == NETCONFA_IGNORE_ROUTES_WITH_LINKDOWN)
 		size += nla_total_size(4);
 
+	if (all || type == NETCONFA_FORCE_FORWARDING)
+		size += nla_total_size(4);
+
 	return size;
 }
 
@@ -578,6 +581,11 @@ static int inet6_netconf_fill_devconf(struct sk_buff *skb, int ifindex,
 			READ_ONCE(devconf->ignore_routes_with_linkdown)) < 0)
 		goto nla_put_failure;
 
+	if ((all || type == NETCONFA_FORCE_FORWARDING) &&
+	    nla_put_s32(skb, NETCONFA_FORCE_FORWARDING,
+			READ_ONCE(devconf->force_forwarding)) < 0)
+		goto nla_put_failure;
+
 out:
 	nlmsg_end(skb, nlh);
 	return 0;
@@ -863,8 +871,12 @@ static void addrconf_forward_change(struct net *net, __s32 newf)
 		if (idev) {
 			int changed = (!idev->cnf.forwarding) ^ (!newf);
 			/* Disabling all.forwarding sets 0 to force_forwarding for all interfaces */
-			if (newf == 0)
+			if (newf == 0 && idev->cnf.force_forwarding) {
 				WRITE_ONCE(idev->cnf.force_forwarding, 0);
+				inet6_netconf_notify_devconf(net, RTM_NEWNETCONF,
+							     NETCONFA_FORCE_FORWARDING,
+							     dev->ifindex, &idev->cnf);
+			}
 
 			WRITE_ONCE(idev->cnf.forwarding, newf);
 			if (changed)

---
base-commit: 7b6ab4dbc156e2f96419715130b3d5738a306c93
base-tree: git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next.git main
change-id: 20261023-ipv6_add_netconfa-b87b66b35272

Best regards,
--  
Gabriel Goller <g.goller@proxmox.com>

Re: [PATCH net-next v2] ipv6: Add NETCONFA_FORCE_FORWARDING to netconf messages

[Ido Schimmel]

On Wed, Nov 04, 2026 at 10:46:10AM +0100, Gabriel Goller wrote:
> Since force_forwarding was added, changing the sysctl sends an
> RTM_NEWNETCONF notification of type NETCONFA_FORCE_FORWARDING, but
> inet6_netconf_fill_devconf() never emits the attribute. Listeners only
> receive NETCONFA_IFINDEX without the new value, and RTM_GETNETCONF
> replies and dumps omit it as well.
> 
> Also send a notification when disabling all.forwarding resets
> force_forwarding on an interface, which previously happened silently.
> 
> Fixes: f24987ef6959 ("ipv6: add `force_forwarding` sysctl to enable per-interface forwarding")

Fixes tag on net-next is only valid when the blamed commit is only in
net-next, but maybe Paolo / Jakub will agree to strip it, so wait with
v3.

> Signed-off-by: Gabriel Goller <g.goller@proxmox.com>

Reviewed-by: Ido Schimmel <idosch@nvidia.com>

There's a report from Sashiko [1] about a pre-existing issue:
all.force_forwarding not being cleared when all.forwarding is cleared.

# ip link add name dummy1 type dummy
# sysctl -wq net.ipv6.conf.all.forwarding=1
# sysctl -wq net.ipv6.conf.all.force_forwarding=1
# sysctl -wq net.ipv6.conf.all.forwarding=0
# sysctl net.ipv6.conf.dummy1.force_forwarding
net.ipv6.conf.dummy1.force_forwarding = 0
# sysctl net.ipv6.conf.all.force_forwarding
net.ipv6.conf.all.force_forwarding = 1

[1] https://netdev-ai.bots.linux.dev/sashiko/#/patchset/20261104-ipv6_add_netconfa-v2-1-6f660990062f@proxmox.com