[PATCH net-next 09/15] batman-adv: split fragment forwarding into lookup and forward

[Simon Wunderlich <sw@simonwunderlich.de>]

From: Sven Eckelmann <sven@narfation.org>

batadv_frag_skb_fwd() consumed the skb only when it returned true, and
passed the receive result back through an out-parameter that was only
valid in that case.

To ensure that the forwarding functions either borrow or consume the skb,
split it into:

* batadv_frag_fwd_neigh_get(): borrows the skb and returns the next-hop
  (with a reference) when the merged packet would exceed its MTU
* batadv_frag_skb_fwd(): always consumes the skb and returns
  NET_RX_SUCCESS or NET_RX_DROP (instead of using the out-parameter
  "rx_result")

Signed-off-by: Sven Eckelmann <sven@narfation.org>
Signed-off-by: Simon Wunderlich <sw@simonwunderlich.de>
---
 net/batman-adv/fragmentation.c | 99 ++++++++++++++++++----------------
 net/batman-adv/fragmentation.h |  9 ++--
 net/batman-adv/routing.c       | 15 ++++--
 3 files changed, 69 insertions(+), 54 deletions(-)

diff --git a/net/batman-adv/fragmentation.c b/net/batman-adv/fragmentation.c
index 493af3091aa8a..9025d5f651464 100644
--- a/net/batman-adv/fragmentation.c
+++ b/net/batman-adv/fragmentation.c
@@ -385,70 +385,79 @@ bool batadv_frag_skb_buffer(struct sk_buff **skb,
 }
 
 /**
- * batadv_frag_skb_fwd() - forward fragments that would exceed MTU when merged
- * @skb: skb to forward
+ * batadv_frag_fwd_neigh_get() - get next-hop for fragments that would exceed
+ *  MTU when merged
+ * @skb: received fragment
  * @recv_if: interface that the skb is received on
- * @orig_node_src: originator that the skb is received from
- * @rx_result: set to NET_RX_SUCCESS when the fragment was forwarded and
- *  NET_RX_DROP when it was dropped; only valid when true is returned
  *
  * Look up the next-hop of the fragments payload and check if the merged packet
- * will exceed the MTU towards the next-hop. If so, the fragment is forwarded
- * without merging it.
+ * will exceed the MTU towards the next-hop.
  *
- * Return: true if the fragment is consumed/forwarded, false otherwise.
+ * Return: the next-hop neighbor (with increased refcounter) when the fragment
+ * has to be forwarded without merging it, NULL otherwise
  */
-bool batadv_frag_skb_fwd(struct sk_buff *skb,
-			 struct batadv_hard_iface *recv_if,
-			 struct batadv_orig_node *orig_node_src,
-			 int *rx_result)
+struct batadv_neigh_node *
+batadv_frag_fwd_neigh_get(const struct sk_buff *skb,
+			  struct batadv_hard_iface *recv_if)
 {
 	struct batadv_priv *bat_priv = netdev_priv(recv_if->mesh_iface);
-	struct batadv_neigh_node *neigh_node = NULL;
-	struct batadv_frag_packet *packet;
-	bool ret = false;
+	const struct batadv_frag_packet *packet;
+	struct batadv_neigh_node *neigh_node;
 	u16 total_size;
 
-	packet = (struct batadv_frag_packet *)skb->data;
+	packet = (const struct batadv_frag_packet *)skb->data;
 
 	neigh_node = batadv_orig_to_router(bat_priv, packet->dest, recv_if);
 	if (!neigh_node)
-		goto out;
+		return NULL;
 
-	/* Forward the fragment, if the merged packet would be too big to
-	 * be assembled.
-	 */
 	total_size = ntohs(packet->total_size);
-	if (total_size > neigh_node->if_incoming->net_dev->mtu) {
-		if (packet->ttl < 2) {
-			kfree_skb(skb);
-			*rx_result = NET_RX_DROP;
-			ret = true;
-			goto out;
-		}
+	if (total_size <= neigh_node->if_incoming->net_dev->mtu) {
+		batadv_neigh_node_put(neigh_node);
+		return NULL;
+	}
 
-		if (skb_cow(skb, ETH_HLEN) < 0) {
-			kfree_skb(skb);
-			*rx_result = NET_RX_DROP;
-			ret = true;
-			goto out;
-		}
+	return neigh_node;
+}
+
+/**
+ * batadv_frag_skb_fwd() - forward fragment without merging it
+ * @bat_priv: the bat priv with all the mesh interface information
+ * @skb: skb to forward
+ * @neigh_node: next-hop to forward the fragment to
+ *
+ * The skb is always consumed by this function.
+ *
+ * Return: NET_RX_SUCCESS when the fragment was forwarded and NET_RX_DROP when
+ * it was dropped
+ */
+int batadv_frag_skb_fwd(struct batadv_priv *bat_priv, struct sk_buff *skb,
+			struct batadv_neigh_node *neigh_node)
+{
+	struct batadv_frag_packet *packet;
 
-		packet = (struct batadv_frag_packet *)skb->data;
+	packet = (struct batadv_frag_packet *)skb->data;
 
-		batadv_inc_counter(bat_priv, BATADV_CNT_FRAG_FWD);
-		batadv_add_counter(bat_priv, BATADV_CNT_FRAG_FWD_BYTES,
-				   skb->len + ETH_HLEN);
+	if (packet->ttl < 2)
+		goto free_skb;
 
-		packet->ttl--;
-		batadv_send_unicast_skb(skb, neigh_node);
-		*rx_result = NET_RX_SUCCESS;
-		ret = true;
-	}
+	if (skb_cow(skb, ETH_HLEN) < 0)
+		goto free_skb;
 
-out:
-	batadv_neigh_node_put(neigh_node);
-	return ret;
+	packet = (struct batadv_frag_packet *)skb->data;
+
+	batadv_inc_counter(bat_priv, BATADV_CNT_FRAG_FWD);
+	batadv_add_counter(bat_priv, BATADV_CNT_FRAG_FWD_BYTES,
+			   skb->len + ETH_HLEN);
+
+	packet->ttl--;
+	batadv_send_unicast_skb(skb, neigh_node);
+
+	return NET_RX_SUCCESS;
+
+free_skb:
+	kfree_skb(skb);
+	return NET_RX_DROP;
 }
 
 /**
diff --git a/net/batman-adv/fragmentation.h b/net/batman-adv/fragmentation.h
index 51e281027ab63..3c98a4f82286e 100644
--- a/net/batman-adv/fragmentation.h
+++ b/net/batman-adv/fragmentation.h
@@ -17,10 +17,11 @@
 
 void batadv_frag_purge_orig(struct batadv_orig_node *orig,
 			    bool (*check_cb)(struct batadv_frag_table_entry *));
-bool batadv_frag_skb_fwd(struct sk_buff *skb,
-			 struct batadv_hard_iface *recv_if,
-			 struct batadv_orig_node *orig_node_src,
-			 int *rx_result);
+struct batadv_neigh_node * __must_check
+batadv_frag_fwd_neigh_get(const struct sk_buff *skb,
+			  struct batadv_hard_iface *recv_if);
+int batadv_frag_skb_fwd(struct batadv_priv *bat_priv, struct sk_buff *skb,
+			struct batadv_neigh_node *neigh_node);
 bool batadv_frag_skb_buffer(struct sk_buff **skb,
 			    struct batadv_orig_node *orig_node);
 int batadv_frag_send_packet(struct sk_buff *skb,
diff --git a/net/batman-adv/routing.c b/net/batman-adv/routing.c
index ca71e29a9ad33..d5772429535e9 100644
--- a/net/batman-adv/routing.c
+++ b/net/batman-adv/routing.c
@@ -1206,6 +1206,7 @@ int batadv_recv_frag_packet(struct sk_buff *skb,
 	struct batadv_priv *bat_priv = netdev_priv(recv_if->mesh_iface);
 	struct batadv_orig_node *orig_node_src = NULL;
 	struct batadv_frag_packet *frag_packet;
+	struct batadv_neigh_node *neigh_node;
 	int ret = NET_RX_DROP;
 
 	if (batadv_check_unicast_packet(bat_priv, skb,
@@ -1220,11 +1221,15 @@ int batadv_recv_frag_packet(struct sk_buff *skb,
 	skb->priority = frag_packet->priority + 256;
 
 	/* Route the fragment if it is not for us and too big to be merged. */
-	if (!batadv_is_my_mac(bat_priv, frag_packet->dest) &&
-	    batadv_frag_skb_fwd(skb, recv_if, orig_node_src, &ret)) {
-		/* skb was consumed */
-		skb = NULL;
-		goto put_orig_node;
+	if (!batadv_is_my_mac(bat_priv, frag_packet->dest)) {
+		neigh_node = batadv_frag_fwd_neigh_get(skb, recv_if);
+		if (neigh_node) {
+			ret = batadv_frag_skb_fwd(bat_priv, skb, neigh_node);
+			batadv_neigh_node_put(neigh_node);
+			/* skb was consumed */
+			skb = NULL;
+			goto put_orig_node;
+		}
 	}
 
 	batadv_inc_counter(bat_priv, BATADV_CNT_FRAG_RX);
-- 
2.47.3