[PATCH 2/3 net-next v3] ipv4: handle devconf post-set actions on netlink updates

Fernando Fernandez Mancera
2026-05-04T12:32:03Z

When IPv4 device configuration parameters are updated via netlink, the
kernel currently only updates the value. This bypasses several
post-modification actions that occur when these same parameters are
updated via sysctl, such as flushing the routing cache or emitting
RTM_NEWNETCONF notifications.

This patch addresses the inconsistency by calling the
devinet_conf_post_set() helper inside inet_set_link_af(). If a flush is
required, we defer it until the netlink attribute parsing loop
completes.

This ensures consistent behavior and side-effects for devconf changes,
regardless of whether they are initiated via sysctl or netlink.

Signed-off-by: Fernando Fernandez Mancera <fmancera@suse.de>
---
v2: handled forwarding notification and disabling LRO
v3: no changes
---
net/ipv4/devinet.c | 29 +++++++++++++++++++++++++++--
1 file changed, 27 insertions(+), 2 deletions(-)

diff --git a/net/ipv4/devinet.c b/net/ipv4/devinet.c
index 8300516fb38f..a35b72662e43 100644
--- a/net/ipv4/devinet.c
+++ b/net/ipv4/devinet.c
@@ -2161,6 +2161,20 @@ static bool devinet_conf_post_set(struct net *net, struct ipv4_devconf *cnf,
NETCONFA_IGNORE_ROUTES_WITH_LINKDOWN,
ifindex, cnf);
break;
+ case IPV4_DEVCONF_FORWARDING:
+ if (new == 1) {
+ /* it is safe to use container_of() because forwarding case
+ * is only used by the netlink path
+ */
+ struct in_device *idev = container_of(cnf, struct in_device, cnf);
+
+ netif_disable_lro(idev->dev);
+ }
+
+ inet_netconf_notify_devconf(net, RTM_NEWNETCONF,
+ NETCONFA_FORWARDING,
+ ifindex, cnf);
+ return true;
default:
break;
}
@@ -2173,6 +2187,8 @@ static int inet_set_link_af(struct net_device *dev, const struct nlattr *nla,
{
struct in_device *in_dev = __in_dev_get_rtnl(dev);
struct nlattr *a, *tb[IFLA_INET_MAX+1];
+ struct net *net = dev_net(dev);
+ bool flush_cache = false;
int rem;

if (!in_dev)
@@ -2182,8 +2198,17 @@ static int inet_set_link_af(struct net_device *dev, const struct nlattr *nla,
return -EINVAL;

if (tb[IFLA_INET_CONF]) {
- nla_for_each_nested(a, tb[IFLA_INET_CONF], rem)
- ipv4_devconf_set(in_dev, nla_type(a), nla_get_u32(a));
+ nla_for_each_nested(a, tb[IFLA_INET_CONF], rem) {
+ int old_value = ipv4_devconf_get(in_dev, nla_type(a));
+ int new_value = nla_get_u32(a);
+
+ ipv4_devconf_set(in_dev, nla_type(a), new_value);
+ if (devinet_conf_post_set(net, &in_dev->cnf, nla_type(a), new_value,
+ old_value, dev->ifindex))
+ flush_cache = true;
+ }
+ if (flush_cache)
+ rt_cache_flush(net);
}

return 0;
--
2.53.0