batman-adv: add detection for complex bridge loops

There are network setups where the current bridge loop avoidance can't
detect bridge loops. The minimal setup affected would consist of two
LANs and two separate meshes, connected in a ring like that:

   A...(mesh1)...B
   |             |
 (LAN1)        (LAN2)
   |             |
   C...(mesh2)...D

Since both the meshes and backbones are separate, the bridge loop
avoidance has not enough information to detect and avoid the loop
in this case. Even if these scenarios can't be fixed easily,
these kind of loops can be detected.

This patch implements a periodic check (running every 60 seconds for
now) which sends a broadcast frame with a random MAC address on
each backbone VLAN. If a broadcast frame with the same MAC address
is received shortly after on the mesh, we know that there must be a
loop and report that incident as well as throw an uevent to let others
handle that problem.

Signed-off-by: Simon Wunderlich <simon.wunderlich@open-mesh.com>
[sven@narfation.org: fix conflicts with current version]
Signed-off-by: Sven Eckelmann <sven@narfation.org>
Signed-off-by: Marek Lindner <mareklindner@neomailbox.ch>
Signed-off-by: Antonio Quartulli <a@unstable.cc>

1 files changed, 139 insertions, 0 deletions

diff --git a/net/batman-adv/bridge_loop_avoidance.c b/net/batman-adv/bridge_loop_avoidance.c
index 2c9aa671a49b..5064ae5e9b34 100644
--- a/net/batman-adv/bridge_loop_avoidance.c
+++ b/net/batman-adv/bridge_loop_avoidance.c
@@ -50,6 +50,7 @@
 #include "hash.h"
 #include "originator.h"
 #include "packet.h"
+#include "sysfs.h"
 #include "translation-table.h"
 
 static const u8 batadv_announce_mac[4] = {0x43, 0x05, 0x43, 0x05};
@@ -407,6 +408,14 @@ static void batadv_bla_send_claim(struct batadv_priv *bat_priv, u8 *mac,
 			   ethhdr->h_source, ethhdr->h_dest,
 			   BATADV_PRINT_VID(vid));
 		break;
+	case BATADV_CLAIM_TYPE_LOOPDETECT:
+		ether_addr_copy(ethhdr->h_source, mac);
+		batadv_dbg(BATADV_DBG_BLA, bat_priv,
+			   "bla_send_claim(): LOOPDETECT of %pM to %pM on vid %d\n",
+			   ethhdr->h_source, ethhdr->h_dest,
+			   BATADV_PRINT_VID(vid));
+
+		break;
 	}
 
 	if (vid & BATADV_VLAN_HAS_TAG)
@@ -427,6 +436,36 @@ out:
 }
 
 /**
+ * batadv_bla_loopdetect_report - worker for reporting the loop
+ * @work: work queue item
+ *
+ * Throws an uevent, as the loopdetect check function can't do that itself
+ * since the kernel may sleep while throwing uevents.
+ */
+static void batadv_bla_loopdetect_report(struct work_struct *work)
+{
+	struct batadv_bla_backbone_gw *backbone_gw;
+	struct batadv_priv *bat_priv;
+	char vid_str[6] = { '\0' };
+
+	backbone_gw = container_of(work, struct batadv_bla_backbone_gw,
+				   report_work);
+	bat_priv = backbone_gw->bat_priv;
+
+	batadv_info(bat_priv->soft_iface,
+		    "Possible loop on VLAN %d detected which can't be handled by BLA - please check your network setup!\n",
+		    BATADV_PRINT_VID(backbone_gw->vid));
+	snprintf(vid_str, sizeof(vid_str), "%d",
+		 BATADV_PRINT_VID(backbone_gw->vid));
+	vid_str[sizeof(vid_str) - 1] = 0;
+
+	batadv_throw_uevent(bat_priv, BATADV_UEV_BLA, BATADV_UEV_LOOPDETECT,
+			    vid_str);
+
+	batadv_backbone_gw_put(backbone_gw);
+}
+
+/**
  * batadv_bla_get_backbone_gw - finds or creates a backbone gateway
  * @bat_priv: the bat priv with all the soft interface information
  * @orig: the mac address of the originator
@@ -464,6 +503,7 @@ batadv_bla_get_backbone_gw(struct batadv_priv *bat_priv, u8 *orig,
 	atomic_set(&entry->request_sent, 0);
 	atomic_set(&entry->wait_periods, 0);
 	ether_addr_copy(entry->orig, orig);
+	INIT_WORK(&entry->report_work, batadv_bla_loopdetect_report);
 
 	/* one for the hash, one for returning */
 	kref_init(&entry->refcount);
@@ -1060,6 +1100,10 @@ static int batadv_bla_process_claim(struct batadv_priv *bat_priv,
 	if (vlan_depth > 1)
 		return 1;
 
+	/* Let the loopdetect frames on the mesh in any case. */
+	if (bla_dst->type == BATADV_CLAIM_TYPE_LOOPDETECT)
+		return 0;
+
 	/* check if it is a claim frame. */
 	ret = batadv_check_claim_group(bat_priv, primary_if, hw_src, hw_dst,
 				       ethhdr);
@@ -1265,6 +1309,26 @@ void batadv_bla_update_orig_address(struct batadv_priv *bat_priv,
 }
 
 /**
+ * batadv_bla_send_loopdetect - send a loopdetect frame
+ * @bat_priv: the bat priv with all the soft interface information
+ * @backbone_gw: the backbone gateway for which a loop should be detected
+ *
+ * To detect loops that the bridge loop avoidance can't handle, send a loop
+ * detection packet on the backbone. Unlike other BLA frames, this frame will
+ * be allowed on the mesh by other nodes. If it is received on the mesh, this
+ * indicates that there is a loop.
+ */
+static void
+batadv_bla_send_loopdetect(struct batadv_priv *bat_priv,
+			   struct batadv_bla_backbone_gw *backbone_gw)
+{
+	batadv_dbg(BATADV_DBG_BLA, bat_priv, "Send loopdetect frame for vid %d\n",
+		   backbone_gw->vid);
+	batadv_bla_send_claim(bat_priv, bat_priv->bla.loopdetect_addr,
+			      backbone_gw->vid, BATADV_CLAIM_TYPE_LOOPDETECT);
+}
+
+/**
  * batadv_bla_status_update - purge bla interfaces if necessary
  * @net_dev: the soft interface net device
  */
@@ -1301,6 +1365,7 @@ static void batadv_bla_periodic_work(struct work_struct *work)
 	struct batadv_bla_backbone_gw *backbone_gw;
 	struct batadv_hashtable *hash;
 	struct batadv_hard_iface *primary_if;
+	bool send_loopdetect = false;
 	int i;
 
 	delayed_work = to_delayed_work(work);
@@ -1316,6 +1381,22 @@ static void batadv_bla_periodic_work(struct work_struct *work)
 	if (!atomic_read(&bat_priv->bridge_loop_avoidance))
 		goto out;
 
+	if (atomic_dec_and_test(&bat_priv->bla.loopdetect_next)) {
+		/* set a new random mac address for the next bridge loop
+		 * detection frames. Set the locally administered bit to avoid
+		 * collisions with users mac addresses.
+		 */
+		random_ether_addr(bat_priv->bla.loopdetect_addr);
+		bat_priv->bla.loopdetect_addr[0] = 0xba;
+		bat_priv->bla.loopdetect_addr[1] = 0xbe;
+		bat_priv->bla.loopdetect_lasttime = jiffies;
+		atomic_set(&bat_priv->bla.loopdetect_next,
+			   BATADV_BLA_LOOPDETECT_PERIODS);
+
+		/* mark for sending loop detect on all VLANs */
+		send_loopdetect = true;
+	}
+
 	hash = bat_priv->bla.backbone_hash;
 	if (!hash)
 		goto out;
@@ -1332,6 +1413,9 @@ static void batadv_bla_periodic_work(struct work_struct *work)
 			backbone_gw->lasttime = jiffies;
 
 			batadv_bla_send_announce(bat_priv, backbone_gw);
+			if (send_loopdetect)
+				batadv_bla_send_loopdetect(bat_priv,
+							   backbone_gw);
 
 			/* request_sent is only set after creation to avoid
 			 * problems when we are not yet known as backbone gw
@@ -1405,6 +1489,9 @@ int batadv_bla_init(struct batadv_priv *bat_priv)
 		bat_priv->bla.bcast_duplist[i].entrytime = entrytime;
 	bat_priv->bla.bcast_duplist_curr = 0;
 
+	atomic_set(&bat_priv->bla.loopdetect_next,
+		   BATADV_BLA_LOOPDETECT_PERIODS);
+
 	if (bat_priv->bla.claim_hash)
 		return 0;
 
@@ -1602,6 +1689,55 @@ void batadv_bla_free(struct batadv_priv *bat_priv)
 }
 
 /**
+ * batadv_bla_loopdetect_check - check and handle a detected loop
+ * @bat_priv: the bat priv with all the soft interface information
+ * @skb: the packet to check
+ * @primary_if: interface where the request came on
+ * @vid: the VLAN ID of the frame
+ *
+ * Checks if this packet is a loop detect frame which has been sent by us,
+ * throw an uevent and log the event if that is the case.
+ *
+ * Return: true if it is a loop detect frame which is to be dropped, false
+ * otherwise.
+ */
+static bool
+batadv_bla_loopdetect_check(struct batadv_priv *bat_priv, struct sk_buff *skb,
+			    struct batadv_hard_iface *primary_if,
+			    unsigned short vid)
+{
+	struct batadv_bla_backbone_gw *backbone_gw;
+	struct ethhdr *ethhdr;
+
+	ethhdr = eth_hdr(skb);
+
+	/* Only check for the MAC address and skip more checks here for
+	 * performance reasons - this function is on the hotpath, after all.
+	 */
+	if (!batadv_compare_eth(ethhdr->h_source,
+				bat_priv->bla.loopdetect_addr))
+		return false;
+
+	/* If the packet came too late, don't forward it on the mesh
+	 * but don't consider that as loop. It might be a coincidence.
+	 */
+	if (batadv_has_timed_out(bat_priv->bla.loopdetect_lasttime,
+				 BATADV_BLA_LOOPDETECT_TIMEOUT))
+		return true;
+
+	backbone_gw = batadv_bla_get_backbone_gw(bat_priv,
+						 primary_if->net_dev->dev_addr,
+						 vid, true);
+	if (unlikely(!backbone_gw))
+		return true;
+
+	queue_work(batadv_event_workqueue, &backbone_gw->report_work);
+	/* backbone_gw is unreferenced in the report work function function */
+
+	return true;
+}
+
+/**
  * batadv_bla_rx - check packets coming from the mesh.
  * @bat_priv: the bat priv with all the soft interface information
  * @skb: the frame to be checked
@@ -1634,6 +1770,9 @@ int batadv_bla_rx(struct batadv_priv *bat_priv, struct sk_buff *skb,
 	if (!atomic_read(&bat_priv->bridge_loop_avoidance))
 		goto allow;
 
+	if (batadv_bla_loopdetect_check(bat_priv, skb, primary_if, vid))
+		goto handled;
+
 	if (unlikely(atomic_read(&bat_priv->bla.num_requests)))
 		/* don't allow broadcasts while requests are in flight */
 		if (is_multicast_ether_addr(ethhdr->h_dest) && is_bcast)