[PATCH 2/2 net-next v2] ipv4: handle devconf post-set actions on netlink updates

[Fernando Fernandez Mancera <fmancera@suse.de>]

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
---
 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