ebtables dnat rule gets system frozen

ebtables dnat rule gets system frozen

[Tom Yan]

Kernel version being 5.3.8, after adding a dnat rule (to the OUTPUT
chain) with ebtables-nft in iptables 1.8.3, my system is frozen as
soon as I ping anything. I couldn't catch anything with dmesg -w. Can
anyone reproduce the same issue? I am on Arch Linux.

Re: ebtables dnat rule gets system frozen

[Florian Westphal]

Tom Yan <tom.ty89@gmail.com> wrote:
> Kernel version being 5.3.8, after adding a dnat rule (to the OUTPUT
> chain) with ebtables-nft in iptables 1.8.3, my system is frozen as
> soon as I ping anything. I couldn't catch anything with dmesg -w. Can
> anyone reproduce the same issue? I am on Arch Linux.

Yes, investigating.

[PATCH nf] bridge: ebtables: don't crash when using dnat target in output chains

[Florian Westphal]

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>
---
 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 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;
-- 
2.23.0

Re: [PATCH nf] bridge: ebtables: don't crash when using dnat target in output chains

[Pablo Neira Ayuso]

On Sun, Nov 03, 2019 at 08:54:28PM +0100, Florian Westphal wrote:
> xt_in() returns NULL in the output hook, skip the pkt_type change for
> that case, redirection only makes sense in broute/prerouting hooks.

Applied, thanks.