[PATCH 4.19 025/321] bridge: ebtables: dont crash when using dnat target in output chains

Greg Kroah-Hartman
2019-12-03T22:46:20Z

From: Florian Westphal <fw@strlen.de>

[ 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>
---
net/bridge/netfilter/ebt_dnat.c | 19 +++++++++++++++----
1 file changed, 15 insertions(+), 4 deletions(-)

diff --git a/net/bridge/netfilter/ebt_dnat.c b/net/bridge/netfilter/ebt_dnat.c
index dfc86a0199dab..1d8c834d90189 100644
--- 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;
--
2.20.1