DHCP connectivity issues can currently occur if the following conditions are met:

1) A DHCP packet from a client to a server 2) This packet has a multicast destination 3) This destination has a matching entry in the translation table (FF:FF:FF:FF:FF:FF for IPv4, 33:33:00:01:00:02/33:33:00:01:00:03 for IPv6) 4) The orig-node determined by TT for the multicast destination does not match the orig-node determined by best-gateway-selection

In this case the DHCP packet will be dropped.

The "gateway-out-of-range" check is supposed to only be applied to unicasted DHCP packets to a specific DHCP server.

In that case dropping the the unicasted frame forces the client to retry via a broadcasted one, but now directed to the new best gateway.

A DHCP packet with broadcast/multicast destination is already ensured to always be delivered to the best gateway. Dropping a multicasted DHCP packet here will only prevent completing DHCP as there is no other fallback.

So far, it seems the unicast check was implicitly performed by expecting the batadv_transtable_search() to return NULL for multicast destinations. However, a multicast address could have always ended up in the translation table and in fact is now common.

To fix this potential loss of a DHCP client-to-server packet to a multicast address this patch adds an explicit multicast destination check to reliably bail out of the gateway-out-of-range check for such destinations.

The issue and fix were tested in the following three node setup:

- Line topology, A-B-C - A: gateway client, DHCP client - B: gateway server, hop-penalty increased: 30->60, DHCP server - C: gateway server, code modifications to announce FF:FF:FF:FF:FF:FF

Without this patch, A would never transmit its DHCP Discover packet due to an always "out-of-range" condition. With this patch, a full DHCP handshake between A and B was possible again.

Fixes: afae4e42aae6 ("batman-adv: refactoring gateway handling code") Signed-off-by: Linus Lüssing linus.luessing@c0d3.blue ---

Changes since RFC:

- fixed an uninitialized variable error for orig_dst_node by initializing it to NULL - Verified the issue and tested the fix in VMs, added the test setup description to the commit message --- net/batman-adv/gateway_client.c | 3 +++ 1 file changed, 3 insertions(+)

diff --git a/net/batman-adv/gateway_client.c b/net/batman-adv/gateway_client.c index c294f6fd..e7a245bd 100644 --- a/net/batman-adv/gateway_client.c +++ b/net/batman-adv/gateway_client.c @@ -757,6 +757,9 @@ bool batadv_gw_out_of_range(struct batadv_priv *bat_priv,

vid = batadv_get_vid(skb, 0);

+ if (is_multicast_ether_addr(ethhdr->h_dest)) + goto out; + orig_dst_node = batadv_transtable_search(bat_priv, ethhdr->h_source, ethhdr->h_dest, vid); if (!orig_dst_node)