[NETFILTER]: bridge netfilter: deal with martians correctly

The attached patch resolves an issue where a IP DNATed packet with a
martian source is forwarded while it's better to drop it. It also
resolves messages complaining about ip forwarding being disabled while
it's actually enabled. Thanks to lepton <ytht.net@gmail.com> for
reporting this problem.

This is probably a candidate for the -stable release.

Signed-off-by: Bart De Schuymer <bdschuym@pandora.be>
Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 28 insertions, 8 deletions

diff --git a/net/bridge/br_netfilter.c b/net/bridge/br_netfilter.c
index ac47ba2ba028..bd221ad52eaf 100644
--- a/net/bridge/br_netfilter.c
+++ b/net/bridge/br_netfilter.c
@@ -34,6 +34,7 @@
 #include <linux/netfilter_ipv6.h>
 #include <linux/netfilter_arp.h>
 #include <linux/in_route.h>
+#include <linux/inetdevice.h>
 
 #include <net/ip.h>
 #include <net/ipv6.h>
@@ -221,10 +222,14 @@ static void __br_dnat_complain(void)
  *
  * Otherwise, the packet is considered to be routed and we just
  * change the destination MAC address so that the packet will
- * later be passed up to the IP stack to be routed.
+ * later be passed up to the IP stack to be routed. For a redirected
+ * packet, ip_route_input() will give back the localhost as output device,
+ * which differs from the bridge device.
  *
  * Let us now consider the case that ip_route_input() fails:
  *
+ * This can be because the destination address is martian, in which case
+ * the packet will be dropped.
  * After a "echo '0' > /proc/sys/net/ipv4/ip_forward" ip_route_input()
  * will fail, while __ip_route_output_key() will return success. The source
  * address for __ip_route_output_key() is set to zero, so __ip_route_output_key
@@ -237,7 +242,8 @@ static void __br_dnat_complain(void)
  *
  * --Lennert, 20020411
  * --Bart, 20020416 (updated)
- * --Bart, 20021007 (updated) */
+ * --Bart, 20021007 (updated)
+ * --Bart, 20062711 (updated) */
 static int br_nf_pre_routing_finish_bridge(struct sk_buff *skb)
 {
         if (skb->pkt_type == PACKET_OTHERHOST) {
@@ -264,15 +270,15 @@ static int br_nf_pre_routing_finish(struct sk_buff *skb)
         struct net_device *dev = skb->dev;
         struct iphdr *iph = skb->nh.iph;
         struct nf_bridge_info *nf_bridge = skb->nf_bridge;
+        int err;
 
         if (nf_bridge->mask & BRNF_PKT_TYPE) {
                 skb->pkt_type = PACKET_OTHERHOST;
                 nf_bridge->mask ^= BRNF_PKT_TYPE;
         }
         nf_bridge->mask ^= BRNF_NF_BRIDGE_PREROUTING;
-
         if (dnat_took_place(skb)) {
-                if (ip_route_input(skb, iph->daddr, iph->saddr, iph->tos, dev)) {
+                if ((err = ip_route_input(skb, iph->daddr, iph->saddr, iph->tos, dev))) {
                         struct rtable *rt;
                         struct flowi fl = {
                                 .nl_u = {
@@ -283,19 +289,33 @@ static int br_nf_pre_routing_finish(struct sk_buff *skb)
                                 },
                                 .proto = 0,
                         };
+                        struct in_device *in_dev = in_dev_get(dev);
+
+                        /* If err equals -EHOSTUNREACH the error is due to a
+                         * martian destination or due to the fact that
+                         * forwarding is disabled. For most martian packets,
+                         * ip_route_output_key() will fail. It won't fail for 2 types of
+                         * martian destinations: loopback destinations and destination
+                         * 0.0.0.0. In both cases the packet will be dropped because the
+                         * destination is the loopback device and not the bridge. */
+                        if (err != -EHOSTUNREACH || !in_dev || IN_DEV_FORWARD(in_dev))
+                                goto free_skb;
 
                         if (!ip_route_output_key(&rt, &fl)) {
                                 /* - Bridged-and-DNAT'ed traffic doesn't
-                                 *   require ip_forwarding.
-                                 * - Deal with redirected traffic. */
-                                if (((struct dst_entry *)rt)->dev == dev ||
-                                    rt->rt_type == RTN_LOCAL) {
+                                 *   require ip_forwarding. */
+                                if (((struct dst_entry *)rt)->dev == dev) {
                                         skb->dst = (struct dst_entry *)rt;
                                         goto bridged_dnat;
                                 }
+                                /* we are sure that forwarding is disabled, so printing
+                                 * this message is no problem. Note that the packet could
+                                 * still have a martian destination address, in which case
+                                 * the packet could be dropped even if forwarding were enabled */
                                 __br_dnat_complain();
                                 dst_release((struct dst_entry *)rt);
                         }
+free_skb:
                         kfree_skb(skb);
                         return 0;
                 } else {