net: sched: flower: insert filter to ht before offloading it to hw

John reports:

Recent refactoring of fl_change aims to use the classifier spinlock to
avoid the need for rtnl lock. In doing so, the fl_hw_replace_filer()
function was moved to before the lock is taken. This can create problems
for drivers if duplicate filters are created (commmon in ovs tc offload
due to filters being triggered by user-space matches).

Drivers registered for such filters will now receive multiple copies of
the same rule, each with a different cookie value. This means that the
drivers would need to do a full match field lookup to determine
duplicates, repeating work that will happen in flower __fl_lookup().
Currently, drivers do not expect to receive duplicate filters.

To fix this, verify that filter with same key is not present in flower
classifier hash table and insert the new filter to the flower hash table
before offloading it to hardware. Implement helper function
fl_ht_insert_unique() to atomically verify/insert a filter.

This change makes filter visible to fast path at the beginning of
fl_change() function, which means it can no longer be freed directly in
case of error. Refactor fl_change() error handling code to deallocate the
filter with rcu timeout.

Fixes: 620da48 ("net: sched: flower: refactor fl_change")
Reported-by: John Hurley <john.hurley@netronome.com>
Signed-off-by: Vlad Buslov <vladbu@mellanox.com>
Acked-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/sched/cls_flower.c

@@ -1459,6 +1459,28 @@ static int fl_set_parms(struct net *net, struct tcf_proto *tp,
 	return 0;
 }
 
+static int fl_ht_insert_unique(struct cls_fl_filter *fnew,
+			       struct cls_fl_filter *fold,
+			       bool *in_ht)
+{
+	struct fl_flow_mask *mask = fnew->mask;
+	int err;
+
+	err = rhashtable_insert_fast(&mask->ht,
+				     &fnew->ht_node,
+				     mask->filter_ht_params);
+	if (err) {
+		*in_ht = false;
+		/* It is okay if filter with same key exists when
+		 * overwriting.
+		 */
+		return fold && err == -EEXIST ? 0 : err;
+	}
+
+	*in_ht = true;
+	return 0;
+}
+
 static int fl_change(struct net *net, struct sk_buff *in_skb,
 		     struct tcf_proto *tp, unsigned long base,
 		     u32 handle, struct nlattr **tca,
@@ -1470,6 +1492,7 @@ static int fl_change(struct net *net, struct sk_buff *in_skb,
 	struct cls_fl_filter *fnew;
 	struct fl_flow_mask *mask;
 	struct nlattr **tb;
+	bool in_ht;
 	int err;
 
 	if (!tca[TCA_OPTIONS]) {
@@ -1528,10 +1551,14 @@ static int fl_change(struct net *net, struct sk_buff *in_skb,
 	if (err)
 		goto errout;
 
+	err = fl_ht_insert_unique(fnew, fold, &in_ht);
+	if (err)
+		goto errout_mask;
+
 	if (!tc_skip_hw(fnew->flags)) {
 		err = fl_hw_replace_filter(tp, fnew, rtnl_held, extack);
 		if (err)
-			goto errout_mask;
+			goto errout_ht;
 	}
 
 	if (!tc_in_hw(fnew->flags))
@@ -1557,10 +1584,17 @@ static int fl_change(struct net *net, struct sk_buff *in_skb,
 
 		fnew->handle = handle;
 
-		err = rhashtable_insert_fast(&fnew->mask->ht, &fnew->ht_node,
-					     fnew->mask->filter_ht_params);
-		if (err)
-			goto errout_hw;
+		if (!in_ht) {
+			struct rhashtable_params params =
+				fnew->mask->filter_ht_params;
+
+			err = rhashtable_insert_fast(&fnew->mask->ht,
+						     &fnew->ht_node,
+						     params);
+			if (err)
+				goto errout_hw;
+			in_ht = true;
+		}
 
 		rhashtable_remove_fast(&fold->mask->ht,
 				       &fold->ht_node,
@@ -1582,11 +1616,6 @@ static int fl_change(struct net *net, struct sk_buff *in_skb,
 		refcount_dec(&fold->refcnt);
 		__fl_put(fold);
 	} else {
-		if (__fl_lookup(fnew->mask, &fnew->mkey)) {
-			err = -EEXIST;
-			goto errout_hw;
-		}
-
 		if (handle) {
 			/* user specifies a handle and it doesn't exist */
 			err = idr_alloc_u32(&head->handle_idr, fnew, &handle,
@@ -1609,12 +1638,6 @@ static int fl_change(struct net *net, struct sk_buff *in_skb,
 			goto errout_hw;
 
 		fnew->handle = handle;
-
-		err = rhashtable_insert_fast(&fnew->mask->ht, &fnew->ht_node,
-					     fnew->mask->filter_ht_params);
-		if (err)
-			goto errout_idr;
-
 		list_add_tail_rcu(&fnew->list, &fnew->mask->filters);
 		spin_unlock(&tp->lock);
 	}
@@ -1625,17 +1648,18 @@ static int fl_change(struct net *net, struct sk_buff *in_skb,
 	kfree(mask);
 	return 0;
 
-errout_idr:
-	idr_remove(&head->handle_idr, fnew->handle);
 errout_hw:
 	spin_unlock(&tp->lock);
 	if (!tc_skip_hw(fnew->flags))
 		fl_hw_destroy_filter(tp, fnew, rtnl_held, NULL);
+errout_ht:
+	if (in_ht)
+		rhashtable_remove_fast(&fnew->mask->ht, &fnew->ht_node,
+				       fnew->mask->filter_ht_params);
 errout_mask:
 	fl_mask_put(head, fnew->mask, true);
 errout:
-	tcf_exts_destroy(&fnew->exts);
-	kfree(fnew);
+	tcf_queue_work(&fnew->rwork, fl_destroy_filter_work);
 errout_tb:
 	kfree(tb);
 errout_mask_alloc: