[B.A.T.M.A.N.] [PATCHv2 3/7] batman-adv: prevent duplication of ARP replies when DAT is used

[B.A.T.M.A.N.] [PATCHv2 3/7] batman-adv: prevent duplication of ARP replies when DAT is used

[Andreas Pape]

If none of the backbone gateways in a bla setup has already knowledge of
the mac address searched for in an incoming ARP request from the backbone
it must be prevented that multiple ARP replies are generated and returned
to the backbone by the dat address resolution mechanism of other dat
enabled nodes of the mesh.

Signed-off-by: Andreas Pape <apape@phoenixcontact.com>
---
 net/batman-adv/distributed-arp-table.c |   65 +++++++++++++++++++++++++++++++-
 1 files changed, 64 insertions(+), 1 deletions(-)

diff --git a/net/batman-adv/distributed-arp-table.c b/net/batman-adv/distributed-arp-table.c
index 0f899b9..f60fccb 100644
--- a/net/batman-adv/distributed-arp-table.c
+++ b/net/batman-adv/distributed-arp-table.c
@@ -1081,6 +1081,8 @@ bool batadv_dat_snoop_incoming_arp_request(struct batadv_priv *bat_priv,
 	u8 *hw_src;
 	struct sk_buff *skb_new;
 	struct batadv_dat_entry *dat_entry = NULL;
+	struct batadv_unicast_4addr_packet *unicast_4addr_packet;
+	struct batadv_orig_node *orig_node = NULL;
 	bool ret = false;
 	unsigned short vid;
 	int err;
@@ -1104,8 +1106,38 @@ bool batadv_dat_snoop_incoming_arp_request(struct batadv_priv *bat_priv,
 	batadv_dat_entry_add(bat_priv, ip_src, hw_src, vid);

 	dat_entry = batadv_dat_entry_hash_find(bat_priv, ip_dst, vid);
-	if (!dat_entry)
+	if (!dat_entry) {
+		/* Check if this is a 4addr unicast DAT_DHT_GET frame from
+		 * another backbone gw of the same backbone. If yes, drop
+		 * it as this leads to multiplication of arp requests in bla
+		 * setups as long as there is no dat_entry fo this answer.
+		 * In this case better drop the DHT_GET. Normal bla code
+		 * doesn't take care of these packets as they are tunneled
+		 * via unicast.
+		 */
+		unicast_4addr_packet =
+				(struct batadv_unicast_4addr_packet *)skb->data;
+		orig_node =
+			batadv_orig_hash_find(bat_priv,
+					      unicast_4addr_packet->src);
+		if (orig_node) {
+			if ((unicast_4addr_packet->u.packet_type ==
+			     BATADV_UNICAST_4ADDR) &&
+			     (unicast_4addr_packet->subtype ==
+			      BATADV_P_DAT_DHT_GET) &&
+			     (batadv_bla_is_backbone_gw(skb, orig_node,
+							hdr_size))) {
+				batadv_dbg(BATADV_DBG_DAT, bat_priv, "Doubled ARP request removed: ARP MSG = [src: %pM-%pI4 dst: %pM-%pI4]; originator: %pM\n",
+					   hw_src, &ip_src,
+					   batadv_arp_hw_dst(skb, hdr_size),
+					   &ip_dst, unicast_4addr_packet->src);
+				ret = true;
+			}
+			batadv_orig_node_put(orig_node);
+		}
+
 		goto out;
+	}

 	skb_new = arp_create(ARPOP_REPLY, ETH_P_ARP, ip_src,
 			     bat_priv->soft_iface, ip_dst, hw_src,
@@ -1204,6 +1236,7 @@ bool batadv_dat_snoop_incoming_arp_reply(struct batadv_priv *bat_priv,
 	__be32 ip_src, ip_dst;
 	u8 *hw_src, *hw_dst;
 	bool dropped = false;
+	struct batadv_dat_entry *dat_entry = NULL;
 	unsigned short vid;

 	if (!atomic_read(&bat_priv->distributed_arp_table))
@@ -1223,12 +1256,40 @@ bool batadv_dat_snoop_incoming_arp_reply(struct batadv_priv *bat_priv,
 	hw_dst = batadv_arp_hw_dst(skb, hdr_size);
 	ip_dst = batadv_arp_ip_dst(skb, hdr_size);

+	/* If ip_dst is already in cache and has the right mac address,
+	 * drop this frame if this ARP reply is destined for us. We have
+	 * most probably received already a reply from someone else. Delivering
+	 * this frame would lead to doubled receive of an ARP reply.
+	 */
+	dat_entry = batadv_dat_entry_hash_find(bat_priv, ip_src, vid);
+	if ((dat_entry) && (batadv_compare_eth(hw_src, dat_entry->mac_addr))) {
+		batadv_dbg(BATADV_DBG_DAT, bat_priv, "Doubled ARP reply removed: ARP MSG = [src: %pM-%pI4 dst: %pM-%pI4]; dat_entry: %pM-%pI4\n",
+			   hw_src, &ip_src, hw_dst, &ip_dst,
+			   dat_entry->mac_addr,	&dat_entry->ip);
+		dropped = true;
+		goto out;
+	}
+
 	/* Update our internal cache with both the IP addresses the node got
 	 * within the ARP reply
 	 */
 	batadv_dat_entry_add(bat_priv, ip_src, hw_src, vid);
 	batadv_dat_entry_add(bat_priv, ip_dst, hw_dst, vid);

+	/* If BLA is enabled, only forward ARP replies if we have claimed the
+	 * source of the ARP reply or if no one else of the same backbone has
+	 * already claimed that client. This prevents that different gateways
+	 * to the same backbone all forward the ARP reply leading to multiple
+	 * replies in the backbone.
+	 */
+	if (!batadv_bla_handle_local_claim(bat_priv, hw_src, vid)) {
+		batadv_dbg(BATADV_DBG_DAT, bat_priv,
+			   "Device %pM claimed by another backbone gw. Drop ARP reply.\n",
+			   hw_src);
+		dropped = true;
+		goto out;
+	}
+
 	/* if this REPLY is directed to a client of mine, let's deliver the
 	 * packet to the interface
 	 */
@@ -1241,6 +1302,8 @@ bool batadv_dat_snoop_incoming_arp_reply(struct batadv_priv *bat_priv,
 out:
 	if (dropped)
 		kfree_skb(skb);
+	if (dat_entry)
+		batadv_dat_entry_put(dat_entry);
 	/* if dropped == false -> deliver to the interface */
 	return dropped;
 }
--
1.7.0.4



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Re: [B.A.T.M.A.N.] [PATCHv2 3/7] batman-adv: prevent duplication of ARP replies when DAT is used

[Sven Eckelmann]

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On Friday 26 February 2016 14:18:39 Andreas Pape wrote:
>  	dat_entry = batadv_dat_entry_hash_find(bat_priv, ip_dst, vid);
> -	if (!dat_entry)
> +	if (!dat_entry) {
> +		/* Check if this is a 4addr unicast DAT_DHT_GET frame from
> +		 * another backbone gw of the same backbone. If yes, drop
> +		 * it as this leads to multiplication of arp requests in bla
> +		 * setups as long as there is no dat_entry fo this answer.
> +		 * In this case better drop the DHT_GET. Normal bla code
> +		 * doesn't take care of these packets as they are tunneled
> +		 * via unicast.
> +		 */
> +		unicast_4addr_packet =
> +				(struct batadv_unicast_4addr_packet *)skb->data;
> +		orig_node =
> +			batadv_orig_hash_find(bat_priv,
> +					      unicast_4addr_packet->src);
> +		if (orig_node) {
> +			if ((unicast_4addr_packet->u.packet_type ==
> +			     BATADV_UNICAST_4ADDR) &&
> +			     (unicast_4addr_packet->subtype ==
> +			      BATADV_P_DAT_DHT_GET) &&
> +			     (batadv_bla_is_backbone_gw(skb, orig_node,
> +							hdr_size))) {
> +				batadv_dbg(BATADV_DBG_DAT, bat_priv, "Doubled ARP request removed: ARP MSG = [src: %pM-%pI4 dst: %pM-%pI4]; originator: %pM\n",
> +					   hw_src, &ip_src,
> +					   batadv_arp_hw_dst(skb, hdr_size),
> +					   &ip_dst, unicast_4addr_packet->src);
> +				ret = true;
> +			}
> +			batadv_orig_node_put(orig_node);
> +		}
> +
>  		goto out;
> +	}

This looks really squashed. Maybe this stuff can be moved in a separate
function.

Kind regards,
	Sven

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Re: [B.A.T.M.A.N.] [PATCHv2 3/7] batman-adv: prevent duplication of ARP replies when DAT is used

[Simon Wunderlich]

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On Friday 26 February 2016 14:18:39 Andreas Pape wrote:
> If none of the backbone gateways in a bla setup has already knowledge of
> the mac address searched for in an incoming ARP request from the backbone
> it must be prevented that multiple ARP replies are generated and returned
> to the backbone by the dat address resolution mechanism of other dat
> enabled nodes of the mesh.

Isn't this patch somewhat redundant due to the change in patch 4? In that 
patch we already drop unicast packets, and this patch just adds a check for a 
more specific unicast subtype ...?

Thanks,
     Simon

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