At first contact between two nodes, an endpoint might sometimes have
time to send out a LINK_PROTOCOL/STATE packet before it has received
the broadcast initialization packet from the peer, i.e., before it has
received a valid broadcast packet number to add to the 'bc_ack' field
of the protocol message.
This means that the peer endpoint will receive a protocol packet with a
broadcast acknowledge value of 0, without knowing that this value is
invalid and should be ignored. Under unlucky circumstances this may lead
to the original, already received acknowledge value being overwritten,
so that the whole broadcast link goes stale after a while.
We fix this by delaying the setting of the link field 'bc_peer_is_up'
until we know that the peer really has received our own broadcast
initialization message. The latter is always sent out as the first
unicast message on a link, and always with seqeunce number 1. Because
of this, we only need to look for a non-zero unicast acknowledge value
in the arriving STATE messages, and once that is confirmed we know we
are safe and can set the mentioned field. Before this moment, we must
ignore all broadcast acknowledges from the peer.
Signed-off-by: Jon Maloy <jon.ma...@ericsson.com>
---
net/tipc/link.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)
diff --git a/net/tipc/link.c b/net/tipc/link.c
index c1df33f..4cd76bb 100644
--- a/net/tipc/link.c
+++ b/net/tipc/link.c
@@ -1582,7 +1582,12 @@ void tipc_link_bc_sync_rcv(struct tipc_link *l, struct
tipc_msg *hdr,
if (!msg_peer_node_is_up(hdr))
return;
- l->bc_peer_is_up = true;
+ /* Open when peer ackowledges our bcast init msg (pkt #1) */
+ if (msg_ack(hdr))
+ l->bc_peer_is_up = true;
+
+ if (!l->bc_peer_is_up)
+ return;
/* Ignore if peers_snd_nxt goes beyond receive window */
if (more(peers_snd_nxt, l->rcv_nxt + l->window))
--
1.9.1
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