[7/7] batman-adv: handle race condition for claims between gateways

Message ID 1456381870-29872-1-git-send-email-apape@phoenixcontact.com (mailing list archive)
State Superseded, archived
Delegated to: Marek Lindner

Commit Message

Andreas Pape Feb. 25, 2016, 6:31 a.m. UTC
  This patch is crucial for prevention of looping broadcast or multicast
packets in a bla setup. Consider the following situation: 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 multicast into the backbone as it is the responsible gw
and 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 multicast
forwarded by B (due to backbone topology or some delay in B) we get
a critical situation: in the current code A will immediately unclaim
C if the multicast is received due to the roaming client scenario
although the position of C has not changed in the mesh. If this
happens the broadcast will be sent back into the mesh and we have a
loop 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.

Signed-off-by: Andreas Pape <apape@phoenixcontact.com>
 net/batman-adv/bridge_loop_avoidance.c |   20 ++++++++++++++++----
 1 files changed, 16 insertions(+), 4 deletions(-)



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diff --git a/net/batman-adv/bridge_loop_avoidance.c b/net/batman-adv/bridge_loop_avoidance.c
index 6311ca2..7afddd9 100644
--- a/net/batman-adv/bridge_loop_avoidance.c
+++ b/net/batman-adv/bridge_loop_avoidance.c
@@ -1761,10 +1761,22 @@  int batadv_bla_tx(struct batadv_priv *bat_priv, struct sk_buff *skb,
 		/* 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 */