ipv6: If neigh lookup fails during icmp6 dst allocation, propagate error.

Don't just succeed with a route that has a NULL neighbour attached.
This follows the behavior of addrconf_dst_alloc().

Allowing this kind of route to end up with a NULL neigh attached will
result in packet drops on output until the route is somehow
invalidated, since nothing will meanwhile try to lookup the neigh
again.

A statistic is bumped for the case where we see a neigh-less route on
output, but the resulting packet drop is otherwise silent in nature,
and frankly it's a hard error for this to happen and ipv6 should do
what ipv4 does which is say something in the kernel logs.

Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 4 insertions, 2 deletions

diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index d98cf41edf2a..4bf362baa97a 100644
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -1089,8 +1089,10 @@ struct dst_entry *icmp6_dst_alloc(struct net_device *dev,
                 neigh_hold(neigh);
         else {
                 neigh = __neigh_lookup_errno(&nd_tbl, &fl6->daddr, dev);
-                if (IS_ERR(neigh))
-                        neigh = NULL;
+                if (IS_ERR(neigh)) {
+                        dst_free(&rt->dst);
+                        return ERR_CAST(neigh);
+                }
         }
 
         rt->dst.flags |= DST_HOST;