xfrm: Flushing empty SAD generates false events

To see the effect make sure you have an empty SAD.
On window1 "ip xfrm mon" and on window2 issue "ip xfrm state 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

@@ -1768,8 +1768,11 @@ static int pfkey_flush(struct sock *sk, struct sk_buff *skb, struct sadb_msg *hd
 	audit_info.secid = 0;
 	err = xfrm_state_flush(net, proto, &audit_info);
 	err2 = unicast_flush_resp(sk, hdr);
-	if (err || err2)
+	if (err || err2) {
+		if (err == -ESRCH) /* empty table - go quietly */
+			err = 0;
 		return err ? err : err2;
+	}
 
 	c.data.proto = proto;
 	c.seq = hdr->sadb_msg_seq;

net/xfrm/xfrm_state.c

@@ -603,13 +603,14 @@ xfrm_state_flush_secctx_check(struct net *net, u8 proto, struct xfrm_audit *audi
 
 int xfrm_state_flush(struct net *net, u8 proto, struct xfrm_audit *audit_info)
 {
-	int i, err = 0;
+	int i, err = 0, cnt = 0;
 
 	spin_lock_bh(&xfrm_state_lock);
 	err = xfrm_state_flush_secctx_check(net, proto, audit_info);
 	if (err)
 		goto out;
 
+	err = -ESRCH;
 	for (i = 0; i <= net->xfrm.state_hmask; i++) {
 		struct hlist_node *entry;
 		struct xfrm_state *x;
@@ -626,13 +627,16 @@ restart:
 							audit_info->sessionid,
 							audit_info->secid);
 				xfrm_state_put(x);
+				if (!err)
+					cnt++;
 
 				spin_lock_bh(&xfrm_state_lock);
 				goto restart;
 			}
 		}
 	}
-	err = 0;
+	if (cnt)
+		err = 0;
 
 out:
 	spin_unlock_bh(&xfrm_state_lock);

net/xfrm/xfrm_user.c

@@ -1524,8 +1524,11 @@ static int xfrm_flush_sa(struct sk_buff *skb, struct nlmsghdr *nlh,
 	audit_info.sessionid = NETLINK_CB(skb).sessionid;
 	audit_info.secid = NETLINK_CB(skb).sid;
 	err = xfrm_state_flush(net, p->proto, &audit_info);
-	if (err)
+	if (err) {
+		if (err == -ESRCH) /* empty table */
+			return 0;
 		return err;
+	}
 	c.data.proto = p->proto;
 	c.event = nlh->nlmsg_type;
 	c.seq = nlh->nlmsg_seq;