netfilter: fix looped (broad|multi)cast's MAC handling

By default, when broadcast or multicast packet are sent from a local
application, they are sent to the interface then looped by the kernel
to other local applications, going throught netfilter hooks in the
process.

These looped packet have their MAC header removed from the skb by the
kernel looping code. This confuse various netfilter's netlink queue,
netlink log and the legacy ip_queue, because they try to extract a
hardware address from these packets, but extracts a part of the IP
header instead.

This patch prevent NFQUEUE, NFLOG and ip_QUEUE to include a MAC header
if there is none in the packet.

Signed-off-by: Nicolas Cavallari <cavallar@lri.fr>
Signed-off-by: Patrick McHardy <kaber@trash.net>

1 files changed, 2 insertions, 1 deletions

diff --git a/net/ipv6/netfilter/ip6_queue.c b/net/ipv6/netfilter/ip6_queue.c
index 065fe405fb58..249394863284 100644
--- a/net/ipv6/netfilter/ip6_queue.c
+++ b/net/ipv6/netfilter/ip6_queue.c
@@ -204,7 +204,8 @@ ipq_build_packet_message(struct nf_queue_entry *entry, int *errp)
         else
                 pmsg->outdev_name[0] = '\0';
 
-        if (entry->indev && entry->skb->dev) {
+        if (entry->indev && entry->skb->dev &&
+            entry->skb->mac_header != entry->skb->network_header) {
                 pmsg->hw_type = entry->skb->dev->type;
                 pmsg->hw_addrlen = dev_parse_header(entry->skb, pmsg->hw_addr);
         }