xfrm: notify default policy on update

This configuration knob is very sensible, it should be notified when
changing.

Fixes: 2d151d3907 ("xfrm: Add possibility to set the default to block if we have no policy")
Signed-off-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>

net/xfrm/xfrm_user.c

@@ -1961,6 +1961,36 @@ static struct sk_buff *xfrm_policy_netlink(struct sk_buff *in_skb,
 	return skb;
 }
 
+static int xfrm_notify_userpolicy(struct net *net)
+{
+	struct xfrm_userpolicy_default *up;
+	int len = NLMSG_ALIGN(sizeof(*up));
+	struct nlmsghdr *nlh;
+	struct sk_buff *skb;
+
+	skb = nlmsg_new(len, GFP_ATOMIC);
+	if (skb == NULL)
+		return -ENOMEM;
+
+	nlh = nlmsg_put(skb, 0, 0, XFRM_MSG_GETDEFAULT, sizeof(*up), 0);
+	if (nlh == NULL) {
+		kfree_skb(skb);
+		return -EMSGSIZE;
+	}
+
+	up = nlmsg_data(nlh);
+	up->in = net->xfrm.policy_default & XFRM_POL_DEFAULT_IN ?
+			XFRM_USERPOLICY_BLOCK : XFRM_USERPOLICY_ACCEPT;
+	up->fwd = net->xfrm.policy_default & XFRM_POL_DEFAULT_FWD ?
+			XFRM_USERPOLICY_BLOCK : XFRM_USERPOLICY_ACCEPT;
+	up->out = net->xfrm.policy_default & XFRM_POL_DEFAULT_OUT ?
+			XFRM_USERPOLICY_BLOCK : XFRM_USERPOLICY_ACCEPT;
+
+	nlmsg_end(skb, nlh);
+
+	return xfrm_nlmsg_multicast(net, skb, 0, XFRMNLGRP_POLICY);
+}
+
 static int xfrm_set_default(struct sk_buff *skb, struct nlmsghdr *nlh,
 			    struct nlattr **attrs)
 {
@@ -1984,6 +2014,7 @@ static int xfrm_set_default(struct sk_buff *skb, struct nlmsghdr *nlh,
 
 	rt_genid_bump_all(net);
 
+	xfrm_notify_userpolicy(net);
 	return 0;
 }