From: Paolo Abeni <pabeni@redhat.com>
Date: Mon, 9 Oct 2017 14:52:10 +0200
Subject: udp: fix bcast packet reception
Patch-mainline: v4.14-rc5
Git-commit: 996b44fcef8f216ea0b6b6e74468c5a77b5e341f
References: bsc#1076830

The commit bc044e8db796 ("udp: perform source validation for
mcast early demux") does not take into account that broadcast packets
lands in the same code path and they need different checks for the
source address - notably, zero source address are valid for bcast
and invalid for mcast.

As a result, 2nd and later broadcast packets with 0 source address
landing to the same socket are dropped. This breaks dhcp servers.

Since we don't have stringent performance requirements for ingress
broadcast traffic, fix it by disabling UDP early demux such traffic.

Reported-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Fixes: bc044e8db796 ("udp: perform source validation for mcast early demux")
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Acked-by: Michal Kubecek <mkubecek@suse.cz>

---
 net/ipv4/udp.c | 14 +++++---------
 1 file changed, 5 insertions(+), 9 deletions(-)

diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index 16fc46096c92..a86c0d84f7a1 100644
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -2176,20 +2176,16 @@ int udp_v4_early_demux(struct sk_buff *skb)
 	iph = ip_hdr(skb);
 	uh = udp_hdr(skb);
 
-	if (skb->pkt_type == PACKET_BROADCAST ||
-	    skb->pkt_type == PACKET_MULTICAST) {
+	if (skb->pkt_type == PACKET_MULTICAST) {
 		in_dev = __in_dev_get_rcu(skb->dev);
 
 		if (!in_dev)
 			return 0;
 
-		/* we are supposed to accept bcast packets */
-		if (skb->pkt_type == PACKET_MULTICAST) {
-			ours = ip_check_mc_rcu(in_dev, iph->daddr, iph->saddr,
-					       iph->protocol);
-			if (!ours)
-				return 0;
-		}
+		ours = ip_check_mc_rcu(in_dev, iph->daddr, iph->saddr,
+				       iph->protocol);
+		if (!ours)
+			return 0;
 
 		sk = __udp4_lib_mcast_demux_lookup(net, uh->dest, iph->daddr,
 						   uh->source, iph->saddr, dif);
-- 
2.16.0