Patch "udp: fix bcast packet reception" has been added to the 4.13-stable tree

Patch "udp: fix bcast packet reception" has been added to the 4.13-stable tree

[gregkh]

This is a note to let you know that I've just added the patch titled

    udp: fix bcast packet reception

to the 4.13-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     udp-fix-bcast-packet-reception.patch
and it can be found in the queue-4.13 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From 996b44fcef8f216ea0b6b6e74468c5a77b5e341f Mon Sep 17 00:00:00 2001
From: Paolo Abeni <pabeni@redhat.com>
Date: Mon, 9 Oct 2017 14:52:10 +0200
Subject: udp: fix bcast packet reception

From: Paolo Abeni <pabeni@redhat.com>

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>

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

--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -2235,20 +2235,16 @@ int udp_v4_early_demux(struct sk_buff *s
 	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);


Patches currently in stable-queue which might be from pabeni@redhat.com are

queue-4.13/udp-perform-source-validation-for-mcast-early-demux.patch
queue-4.13/ipv4-early-demux-can-return-an-error-code.patch
queue-4.13/udp-fix-bcast-packet-reception.patch