Commit 996b44fc authored Oct 09, 2017 by Paolo Abeni Committed by David S. Miller Oct 09, 2017

udp: fix bcast packet reception



The commit bc044e8d ("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: bc044e8d ("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>

parent 41c87425

net/ipv4/udp.c

+5 −9

Original line number	Diff line number	Diff line
		@@ -2240,20 +2240,16 @@ 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;
		}

		sk = __udp4_lib_mcast_demux_lookup(net, uh->dest, iph->daddr,
		uh->source, iph->saddr,

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