bridge: ebtables: don't crash when using dnat target in output chains

xt_in() returns NULL in the output hook, skip the pkt_type change for
that case, redirection only makes sense in broute/prerouting hooks.

Reported-by: Tom Yan <tom.ty89@gmail.com>
Cc: Linus Lüssing <linus.luessing@c0d3.blue>
Fixes: cf3cb246e277d ("bridge: ebtables: fix reception of frames DNAT-ed to bridge device/port")
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

1 files changed, 15 insertions, 4 deletions

diff --git a/net/bridge/netfilter/ebt_dnat.c b/net/bridge/netfilter/ebt_dnat.c
index ed91ea31978a..12a4f4d93681 100644
--- a/net/bridge/netfilter/ebt_dnat.c
+++ b/net/bridge/netfilter/ebt_dnat.c
@@ -20,7 +20,6 @@ static unsigned int
 ebt_dnat_tg(struct sk_buff *skb, const struct xt_action_param *par)
 {
         const struct ebt_nat_info *info = par->targinfo;
-        struct net_device *dev;
 
         if (skb_ensure_writable(skb, ETH_ALEN))
                 return EBT_DROP;
@@ -33,10 +32,22 @@ ebt_dnat_tg(struct sk_buff *skb, const struct xt_action_param *par)
                 else
                         skb->pkt_type = PACKET_MULTICAST;
         } else {
-                if (xt_hooknum(par) != NF_BR_BROUTING)
-                        dev = br_port_get_rcu(xt_in(par))->br->dev;
-                else
+                const struct net_device *dev;
+
+                switch (xt_hooknum(par)) {
+                case NF_BR_BROUTING:
                         dev = xt_in(par);
+                        break;
+                case NF_BR_PRE_ROUTING:
+                        dev = br_port_get_rcu(xt_in(par))->br->dev;
+                        break;
+                default:
+                        dev = NULL;
+                        break;
+                }
+
+                if (!dev) /* NF_BR_LOCAL_OUT */
+                        return info->target;
 
                 if (ether_addr_equal(info->mac, dev->dev_addr))
                         skb->pkt_type = PACKET_HOST;