xfrm: Flushing empty SAD generates false events

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

I was tempted to return -ESRCH on window1 (which would
show "RTNETLINK answers: No such process") but didnt want
to change current behavior.

cheers,
jamal
commit 5f3dd4a772326166e1bcf54acc2391df00dc7ab5
Author: Jamal Hadi Salim <hadi@cyberus.ca>
Date:   Thu Feb 11 04:41:36 2010 -0500

    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 window1 and you see the flush event on window2.
    With this fix, you still get prompt on window1 but no event on window2.

    Signed-off-by: Jamal Hadi Salim <hadi@cyberus.ca>

Signed-off-by: David S. Miller <davem@davemloft.net>

net/key/af_key.c

@@ -1751,7 +1751,7 @@ 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);
 	if (err)
-		return err;
+		return 0;
 	c.data.proto = proto;
 	c.seq = hdr->sadb_msg_seq;
 	c.pid = hdr->sadb_msg_pid;

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;
@@ -626,12 +627,15 @@ restart:
 							audit_info->sessionid,
 							audit_info->secid);
 				xfrm_state_put(x);
+				if (!err)
+					cnt++;
 
 				spin_lock_bh(&xfrm_state_lock);
 				goto restart;
 			}
 		}
 	}
+	if (cnt)
 		err = 0;
 
 out:

net/xfrm/xfrm_user.c

@@ -1525,7 +1525,7 @@ static int xfrm_flush_sa(struct sk_buff *skb, struct nlmsghdr *nlh,
 	audit_info.secid = NETLINK_CB(skb).sid;
 	err = xfrm_state_flush(net, p->proto, &audit_info);
 	if (err)
-		return err;
+		return 0;
 	c.data.proto = p->proto;
 	c.event = nlh->nlmsg_type;
 	c.seq = nlh->nlmsg_seq;