Patch "batman-adv: handle race condition for claims between gateways" has been added to the 4.4-stable tree

This is a note to let you know that I've just added the patch titled

batman-adv: handle race condition for claims between gateways

to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
batman-adv-handle-race-condition-for-claims-between-gateways.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Andreas Pape <[email protected]>
Date: Mon, 5 Sep 2016 13:20:29 +0200
Subject: batman-adv: handle race condition for claims between gateways

From: Andreas Pape <[email protected]>

[ Upstream commit a3a5129e122709306cfa6409781716c2933df99b ]

Consider the following situation which has been found in a test setup:
Gateway B has claimed client C and gateway A has the same backbone network as B. C sends a broad- or multicast to B and directly after this packet decides to send another packet to A due to a better TQ value. B will forward the broad-/multicast into the backbone as it is the responsible gw and after that A will claim C as it has been chosen by C as the best gateway. If it now happens that A claims C before it has received the broad-/multicast forwarded by B (due to backbone topology or due to some delay in B when forwarding the packet) we get a critical situation: in the current code A will immediately unclaim C when receiving the multicast due to the roaming client scenario although the position of C has not changed in the mesh. If this happens the multi-/broadcast forwarded by B will be sent back into the mesh by A and we have looping packets until one of the gateways claims C again.
In order to prevent this, unclaiming of a client due to the roaming client scenario is only done after a certain time is expired after the last claim of the client. 100 ms are used here, which should be slow enough for big backbones and slow gateways but fast enough not to break the roaming client use case.

---
 net/batman-adv/bridge_loop_avoidance.c |   20 ++++++++++++++++----
 1 file changed, 16 insertions(+), 4 deletions(-)

@@ -1603,10 +1603,22 @@ int batadv_bla_tx(struct batadv_priv *ba
 		/* if yes, the client has roamed and we have
 		 * to unclaim it.
 		 */
-		batadv_handle_unclaim(bat_priv, primary_if,
-				      primary_if->net_dev->dev_addr,
-				      ethhdr->h_source, vid);
-		goto allow;
+		if (batadv_has_timed_out(claim->lasttime, 100)) {
+			/* only unclaim if the last claim entry is
+			 * older than 100 ms to make sure we really
+			 * have a roaming client here.
+			 */
+			batadv_dbg(BATADV_DBG_BLA, bat_priv, "bla_tx(): Roaming client %pM detected. Unclaim it.\n",
+				   ethhdr->h_source);
+			batadv_handle_unclaim(bat_priv, primary_if,
+					      primary_if->net_dev->dev_addr,
+					      ethhdr->h_source, vid);
+			goto allow;
+		} else {
+			batadv_dbg(BATADV_DBG_BLA, bat_priv, "bla_tx(): Race for claim %pM detected. Drop packet.\n",
+				   ethhdr->h_source);
+			goto handled;
+		}
 	}
 
 	/* check if it is a multicast/broadcast frame */

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/batman-adv-handle-race-condition-for-claims-between-gateways.patch