udp: fix bcast packet reception

commit 996b44fcef8f216ea0b6b6e74468c5a77b5e341f upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index 781be33a9c2ea9f5e16720efe6cb0feaeab6b40c..84861d71facea872d5310c9c984131b38ef61aa9 100644 (file)
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -2235,20 +2235,16 @@ 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);