Drop packets if their ttl/hl is too small for forwarding.

Fixes: d32de98ea70f ("netfilter: nft_fwd_netdev: allow to forward packets via neighbour layer")
Signed-off-by: Florian Westphal <fw@strlen.de>
---
 net/netfilter/nft_fwd_netdev.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/net/netfilter/nft_fwd_netdev.c b/net/netfilter/nft_fwd_netdev.c
index ad48dcd45abe..4bce36c3a6a0 100644
--- a/net/netfilter/nft_fwd_netdev.c
+++ b/net/netfilter/nft_fwd_netdev.c
@@ -116,6 +116,11 @@ static void nft_fwd_neigh_eval(const struct nft_expr *expr,
 			goto out;
 		}
 		iph = ip_hdr(skb);
+		if (iph->ttl <= 1) {
+			verdict = NF_DROP;
+			goto out;
+		}
+
 		ip_decrease_ttl(iph);
 		neigh_table = NEIGH_ARP_TABLE;
 		break;
@@ -132,6 +137,11 @@ static void nft_fwd_neigh_eval(const struct nft_expr *expr,
 			goto out;
 		}
 		ip6h = ipv6_hdr(skb);
+		if (ip6h->hop_limit <= 1) {
+			verdict = NF_DROP;
+			goto out;
+		}
+
 		ip6h->hop_limit--;
 		neigh_table = NEIGH_ND_TABLE;
 		break;
-- 
2.52.0