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From: Andreas Pape <apape@phoenixcontact.com>
To: b.a.t.m.a.n@lists.open-mesh.org
Subject: [B.A.T.M.A.N.] [PATCH v5 6/6] batman-adv: handle race condition for claims between gateways
Date: Fri, 10 Jun 2016 13:11:04 +0200	[thread overview]
Message-ID: <1465557064-24406-7-git-send-email-apape@phoenixcontact.com> (raw)
In-Reply-To: <1465557064-24406-1-git-send-email-apape@phoenixcontact.com>

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.

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

diff --git a/net/batman-adv/bridge_loop_avoidance.c b/net/batman-adv/bridge_loop_avoidance.c
index 2ccce6e..4c3b294 100644
--- a/net/batman-adv/bridge_loop_avoidance.c
+++ b/net/batman-adv/bridge_loop_avoidance.c
@@ -1904,10 +1904,22 @@ bool 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 */
--
1.7.0.4



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  parent reply	other threads:[~2016-06-10 11:11 UTC|newest]

Thread overview: 23+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-06-10 11:10 [B.A.T.M.A.N.] [PATCH v5 0/6] Optimizations for setups running dat and bla Andreas Pape
2016-06-10 11:10 ` [B.A.T.M.A.N.] [PATCH v5 1/6] batman-adv: prevent multiple ARP replies sent by gateways if dat enbled Andreas Pape
2016-07-01 13:52   ` Simon Wunderlich
2016-06-10 11:11 ` [B.A.T.M.A.N.] [PATCH v5 2/6] batman-adv: speed up dat by snooping received ip traffic Andreas Pape
2016-06-25 10:04   ` Sven Eckelmann
2016-06-26  8:54     ` Ruben Wisniewski
2016-06-26  9:29       ` Sven Eckelmann
2016-07-01 13:49   ` Simon Wunderlich
2016-07-19  6:29     ` Linus Lüssing
2016-07-19  6:59       ` Sven Eckelmann
2016-07-19  7:06         ` Ruben Wisniewski
2016-07-19 16:15           ` Linus Lüssing
2016-07-19 16:13         ` Linus Lüssing
2016-06-10 11:11 ` [B.A.T.M.A.N.] [PATCH v5 3/6] batman-adv: prevent duplication of ARP replies when DAT is used Andreas Pape
2016-07-01 14:11   ` Simon Wunderlich
2016-06-10 11:11 ` [B.A.T.M.A.N.] [PATCH v5 4/6] batman-adv: drop unicast packets from other backbone gw Andreas Pape
2016-07-01 13:48   ` Simon Wunderlich
2016-06-10 11:11 ` [B.A.T.M.A.N.] [PATCH v5 5/6] batman-adv: changed debug messages for easier bla debugging Andreas Pape
2016-06-10 11:11 ` Andreas Pape [this message]
2016-06-10 11:51 ` [B.A.T.M.A.N.] [PATCH v5 0/6] Optimizations for setups running dat and bla Sven Eckelmann
2016-06-13  8:06   ` Andreas Pape
2016-06-13  9:01     ` Sven Eckelmann
2016-07-01 14:12       ` Simon Wunderlich

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