From 8d64561dbc0542e7e1185591b8ecde3e56e1bfca Mon Sep 17 00:00:00 2001 From: Guus Sliepen Date: Tue, 6 May 2014 12:39:59 +0200 Subject: [PATCH] Nexthop calculation should always use the shortest path. When tinc runs the graph algorithms and updates the nexthop and via pointers, it uses a breadth-first search, but it can sometimes revisit nodes that have already been visited if the previous path is marked as being indirect, and there is a longer path that is "direct". The via pointer should be updated in this case, because this points to the closest hop to the destination that can be reached directly. However, the nexthop pointer should not be updated. This fixes a bug where there could potentially be a routing loop if a node in the graph has an edge with the indirect flag set, and some other edge without that flag, the indirect edge is part of the minimum spanning tree, and a broadcast packet is being sent. --- src/graph.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) diff --git a/src/graph.c b/src/graph.c index edea91b..9592f98 100644 --- a/src/graph.c +++ b/src/graph.c @@ -212,9 +212,13 @@ static void sssp_bfs(void) { && (!e->to->status.indirect || indirect)) continue; + // Only update nexthop the first time we visit this node. + + if(!e->to->status.visited) + e->to->nexthop = (n->nexthop == myself) ? e->to : n->nexthop; + e->to->status.visited = true; e->to->status.indirect = indirect; - e->to->nexthop = (n->nexthop == myself) ? e->to : n->nexthop; e->to->prevedge = e; e->to->via = indirect ? n->via : e->to; e->to->options = e->options; -- 2.25.1