net: sched: traverse classifiers in chain with tcf_get_next_proto()

All users of chain->filters_chain rely on rtnl lock and assume that no new
classifier instances are added when traversing the list. Use
tcf_get_next_proto() to traverse filters list without relying on rtnl
mutex. This function iterates over classifiers by taking reference to
current iterator classifier only and doesn't assume external
synchronization of filters list.

Signed-off-by: Vlad Buslov <vladbu@mellanox.com>
Acked-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/pkt_cls.h

@@ -46,6 +46,8 @@ struct tcf_chain *tcf_chain_get_by_act(struct tcf_block *block,
 void tcf_chain_put_by_act(struct tcf_chain *chain);
 struct tcf_chain *tcf_get_next_chain(struct tcf_block *block,
 				     struct tcf_chain *chain);
+struct tcf_proto *tcf_get_next_proto(struct tcf_chain *chain,
+				     struct tcf_proto *tp);
 void tcf_block_netif_keep_dst(struct tcf_block *block);
 int tcf_block_get(struct tcf_block **p_block,
 		  struct tcf_proto __rcu **p_filter_chain, struct Qdisc *q,

net/sched/cls_api.c

@@ -980,6 +980,45 @@ tcf_get_next_chain(struct tcf_block *block, struct tcf_chain *chain)
 }
 EXPORT_SYMBOL(tcf_get_next_chain);
 
+static struct tcf_proto *
+__tcf_get_next_proto(struct tcf_chain *chain, struct tcf_proto *tp)
+{
+	ASSERT_RTNL();
+	mutex_lock(&chain->filter_chain_lock);
+
+	if (!tp)
+		tp = tcf_chain_dereference(chain->filter_chain, chain);
+	else
+		tp = tcf_chain_dereference(tp->next, chain);
+
+	if (tp)
+		tcf_proto_get(tp);
+
+	mutex_unlock(&chain->filter_chain_lock);
+
+	return tp;
+}
+
+/* Function to be used by all clients that want to iterate over all tp's on
+ * chain. Users of this function must be tolerant to concurrent tp
+ * insertion/deletion or ensure that no concurrent chain modification is
+ * possible. Note that all netlink dump callbacks cannot guarantee to provide
+ * consistent dump because rtnl lock is released each time skb is filled with
+ * data and sent to user-space.
+ */
+
+struct tcf_proto *
+tcf_get_next_proto(struct tcf_chain *chain, struct tcf_proto *tp)
+{
+	struct tcf_proto *tp_next = __tcf_get_next_proto(chain, tp);
+
+	if (tp)
+		tcf_proto_put(tp, NULL);
+
+	return tp_next;
+}
+EXPORT_SYMBOL(tcf_get_next_proto);
+
 static void tcf_block_flush_all_chains(struct tcf_block *block)
 {
 	struct tcf_chain *chain;
@@ -1352,16 +1391,18 @@ tcf_block_playback_offloads(struct tcf_block *block, tc_setup_cb_t *cb,
 			    struct netlink_ext_ack *extack)
 {
 	struct tcf_chain *chain, *chain_prev;
-	struct tcf_proto *tp;
+	struct tcf_proto *tp, *tp_prev;
 	int err;
 
 	for (chain = __tcf_get_next_chain(block, NULL);
 	     chain;
 	     chain_prev = chain,
 		     chain = __tcf_get_next_chain(block, chain),
 		     tcf_chain_put(chain_prev)) {
-		for (tp = rtnl_dereference(chain->filter_chain); tp;
-		     tp = rtnl_dereference(tp->next)) {
+		for (tp = __tcf_get_next_proto(chain, NULL); tp;
+		     tp_prev = tp,
+			     tp = __tcf_get_next_proto(chain, tp),
+			     tcf_proto_put(tp_prev, NULL)) {
 			if (tp->ops->reoffload) {
 				err = tp->ops->reoffload(tp, add, cb, cb_priv,
 							 extack);
@@ -1378,6 +1419,7 @@ tcf_block_playback_offloads(struct tcf_block *block, tc_setup_cb_t *cb,
 	return 0;
 
 err_playback_remove:
+	tcf_proto_put(tp, NULL);
 	tcf_chain_put(chain);
 	tcf_block_playback_offloads(block, cb, cb_priv, false, offload_in_use,
 				    extack);
@@ -1677,8 +1719,8 @@ static void tfilter_notify_chain(struct net *net, struct sk_buff *oskb,
 {
 	struct tcf_proto *tp;
 
-	for (tp = rtnl_dereference(chain->filter_chain);
-	     tp; tp = rtnl_dereference(tp->next))
+	for (tp = tcf_get_next_proto(chain, NULL);
+	     tp; tp = tcf_get_next_proto(chain, tp))
 		tfilter_notify(net, oskb, n, tp, block,
 			       q, parent, NULL, event, false);
 }
@@ -2104,11 +2146,15 @@ static bool tcf_chain_dump(struct tcf_chain *chain, struct Qdisc *q, u32 parent,
 	struct net *net = sock_net(skb->sk);
 	struct tcf_block *block = chain->block;
 	struct tcmsg *tcm = nlmsg_data(cb->nlh);
+	struct tcf_proto *tp, *tp_prev;
 	struct tcf_dump_args arg;
-	struct tcf_proto *tp;
 
-	for (tp = rtnl_dereference(chain->filter_chain);
-	     tp; tp = rtnl_dereference(tp->next), (*p_index)++) {
+	for (tp = __tcf_get_next_proto(chain, NULL);
+	     tp;
+	     tp_prev = tp,
+		     tp = __tcf_get_next_proto(chain, tp),
+		     tcf_proto_put(tp_prev, NULL),
+		     (*p_index)++) {
 		if (*p_index < index_start)
 			continue;
 		if (TC_H_MAJ(tcm->tcm_info) &&
@@ -2125,7 +2171,7 @@ static bool tcf_chain_dump(struct tcf_chain *chain, struct Qdisc *q, u32 parent,
 					  NETLINK_CB(cb->skb).portid,
 					  cb->nlh->nlmsg_seq, NLM_F_MULTI,
 					  RTM_NEWTFILTER) <= 0)
-				return false;
+				goto errout;
 
 			cb->args[1] = 1;
 		}
@@ -2145,9 +2191,13 @@ static bool tcf_chain_dump(struct tcf_chain *chain, struct Qdisc *q, u32 parent,
 		cb->args[2] = arg.w.cookie;
 		cb->args[1] = arg.w.count + 1;
 		if (arg.w.stop)
-			return false;
+			goto errout;
 	}
 	return true;
+
+errout:
+	tcf_proto_put(tp, NULL);
+	return false;
 }
 
 /* called with RTNL */

net/sched/sch_api.c

@@ -1914,8 +1914,8 @@ static void tc_bind_tclass(struct Qdisc *q, u32 portid, u32 clid,
 	     chain = tcf_get_next_chain(block, chain)) {
 		struct tcf_proto *tp;
 
-		for (tp = rtnl_dereference(chain->filter_chain);
-		     tp; tp = rtnl_dereference(tp->next)) {
+		for (tp = tcf_get_next_proto(chain, NULL);
+		     tp; tp = tcf_get_next_proto(chain, tp)) {
 			struct tcf_bind_args arg = {};
 
 			arg.w.fn = tcf_node_bind;