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

[ Upstream commit b23c0742c2ce7e33ed79d10e451f70fdb5ca85d1 ]

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>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/net/bridge/netfilter/ebt_dnat.c b/net/bridge/netfilter/ebt_dnat.c
index dfc86a0..1d8c834 100644 (file)
--- a/net/bridge/netfilter/ebt_dnat.c
+++ b/net/bridge/netfilter/ebt_dnat.c
@@ -19,7 +19,6 @@ 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_make_writable(skb, 0))
                return EBT_DROP;
@@ -32,10 +31,22 @@ 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;