[maint,v2] batman-adv: fix packet loss for broadcasted DHCP packets to a server
Commit Message
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 v1:
- now really fixing orig_dst_node initialization
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 | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)
Comments
On Donnerstag, 22. März 2018 00:21:32 CET Linus Lüssing wrote:
> 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
[...]
> ---
> net/batman-adv/gateway_client.c | 5 ++++-
> 1 file changed, 4 insertions(+), 1 deletion(-)
Applied as 49b2132f0fe2 [1].
Thanks,
Sven
[1] https://git.open-mesh.org/batman-adv.git/commit/49b2132f0fe2753a3b46103db9719898c5cd44aa
@@ -746,7 +746,7 @@ bool batadv_gw_out_of_range(struct batadv_priv *bat_priv,
{
struct batadv_neigh_node *neigh_curr = NULL;
struct batadv_neigh_node *neigh_old = NULL;
- struct batadv_orig_node *orig_dst_node;
+ struct batadv_orig_node *orig_dst_node = NULL;
struct batadv_gw_node *gw_node = NULL;
struct batadv_gw_node *curr_gw = NULL;
struct batadv_neigh_ifinfo *curr_ifinfo, *old_ifinfo;
@@ -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)