[PATCH 2/2 net-next] ipv4: 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>
---
 net/ipv4/devinet.c | 22 ++++++++++++++++++++--
 1 file changed, 20 insertions(+), 2 deletions(-)

diff --git a/net/ipv4/devinet.c b/net/ipv4/devinet.c
index c81bb948d59f..555f85139fb5 100644
--- a/net/ipv4/devinet.c
+++ b/net/ipv4/devinet.c
@@ -2128,11 +2128,16 @@ static int inet_validate_link_af(const struct net_device *dev,
 	return 0;
 }
 
+static bool devinet_conf_post_set(struct net *net, struct ipv4_devconf *cnf,
+				  int attr, int new, int old, int index);
+
 static int inet_set_link_af(struct net_device *dev, const struct nlattr *nla,
 			    struct netlink_ext_ack *extack)
 {
 	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)
@@ -2142,8 +2147,17 @@ 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;
@@ -2507,6 +2521,10 @@ static bool devinet_conf_post_set(struct net *net, struct ipv4_devconf *cnf,
 		return false;
 
 	switch (attr) {
+	case IPV4_DEVCONF_FORWARDING:
+		if (new == 1)
+			return true;
+		break;
 	case IPV4_DEVCONF_ROUTE_LOCALNET:
 	case IPV4_DEVCONF_ACCEPT_LOCAL:
 		if (new == 0)
-- 
2.53.0