xfrm: Flushing empty SPD generates false events

To see the effect make sure you have an empty SPD.
On window1 "ip xfrm mon" and on window2 issue "ip xfrm policy flush"
You get prompt back in window2 and you see the flush event on window1.
With this fix, you still get prompt on window1 but no event on window2.

Thanks to Alexey Dobriyan for finding a bug in earlier version
when using pfkey to do the flushing.
Signed-off-by: Jamal Hadi Salim <hadi@cyberus.ca>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/key/af_key.c

@@ -2735,8 +2735,11 @@ static int pfkey_spdflush(struct sock *sk, struct sk_buff *skb, struct sadb_msg
 	audit_info.secid = 0;
 	err = xfrm_policy_flush(net, XFRM_POLICY_TYPE_MAIN, &audit_info);
 	err2 = unicast_flush_resp(sk, hdr);
-	if (err || err2)
-		return err ? err : err2;
+	if (err || err2) {
+		if (err == -ESRCH) /* empty table - old silent behavior */
+			return 0;
+		return err;
+	}
 
 	c.data.type = XFRM_POLICY_TYPE_MAIN;
 	c.event = XFRM_MSG_FLUSHPOLICY;

net/xfrm/xfrm_policy.c

@@ -771,7 +771,8 @@ xfrm_policy_flush_secctx_check(struct net *net, u8 type, struct xfrm_audit *audi
 
 int xfrm_policy_flush(struct net *net, u8 type, struct xfrm_audit *audit_info)
 {
-	int dir, err = 0;
+	int dir, err = 0, cnt = 0;
+	struct xfrm_policy *dp;
 
 	write_lock_bh(&xfrm_policy_lock);
 
@@ -789,8 +790,10 @@ int xfrm_policy_flush(struct net *net, u8 type, struct xfrm_audit *audit_info)
 				     &net->xfrm.policy_inexact[dir], bydst) {
 			if (pol->type != type)
 				continue;
-			__xfrm_policy_unlink(pol, dir);
+			dp = __xfrm_policy_unlink(pol, dir);
 			write_unlock_bh(&xfrm_policy_lock);
+			if (dp)
+				cnt++;
 
 			xfrm_audit_policy_delete(pol, 1, audit_info->loginuid,
 						 audit_info->sessionid,
@@ -809,8 +812,10 @@ int xfrm_policy_flush(struct net *net, u8 type, struct xfrm_audit *audit_info)
 					     bydst) {
 				if (pol->type != type)
 					continue;
-				__xfrm_policy_unlink(pol, dir);
+				dp = __xfrm_policy_unlink(pol, dir);
 				write_unlock_bh(&xfrm_policy_lock);
+				if (dp)
+					cnt++;
 
 				xfrm_audit_policy_delete(pol, 1,
 							 audit_info->loginuid,
@@ -824,6 +829,8 @@ int xfrm_policy_flush(struct net *net, u8 type, struct xfrm_audit *audit_info)
 		}
 
 	}
+	if (!cnt)
+		err = -ESRCH;
 	atomic_inc(&flow_cache_genid);
 out:
 	write_unlock_bh(&xfrm_policy_lock);

net/xfrm/xfrm_user.c

@@ -1679,8 +1679,12 @@ static int xfrm_flush_policy(struct sk_buff *skb, struct nlmsghdr *nlh,
 	audit_info.sessionid = NETLINK_CB(skb).sessionid;
 	audit_info.secid = NETLINK_CB(skb).sid;
 	err = xfrm_policy_flush(net, type, &audit_info);
-	if (err)
+	if (err) {
+		if (err == -ESRCH) /* empty table */
+			return 0;
 		return err;
+	}
+
 	c.data.type = type;
 	c.event = nlh->nlmsg_type;
 	c.seq = nlh->nlmsg_seq;