IPv6 NAT: Do not drop DNATed 6to4/6rd packets

[ Upstream commit 7df37ff33dc122f7bd0614d707939fe84322d264 ]

When a router is doing DNAT for 6to4/6rd packets the latest
anti-spoofing commit 218774dc ("ipv6: add anti-spoofing checks for
6to4 and 6rd") will drop them because the IPv6 address embedded does
not match the IPv4 destination. This patch will allow them to pass by
testing if we have an address that matches on 6to4/6rd interface.  I
have been hit by this problem using Fedora and IPV6TO4_IPV4ADDR.
Also, log the dropped packets (with rate limit).

Signed-off-by: Catalin(ux) M. BOIE <catab@embedromix.ro>
Acked-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/include/net/addrconf.h b/include/net/addrconf.h
index c7b181cb47a6a9ae4b4e30ca2d94ce74f5f9ef40..2683730a6c6dafb9ad6e7f43c5aa6f773601983d 100644 (file)
--- a/include/net/addrconf.h
+++ b/include/net/addrconf.h
@@ -73,6 +73,10 @@ extern int                   ipv6_chk_home_addr(struct net *net,
                                                   const struct in6_addr *addr);
 #endif
 
+bool ipv6_chk_custom_prefix(const struct in6_addr *addr,
+                                  const unsigned int prefix_len,
+                                  struct net_device *dev);
+
 extern int                     ipv6_chk_prefix(const struct in6_addr *addr,
                                                struct net_device *dev);
 

diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
index 498ea99194af69eeaab39f05134e4eb646e22c8a..0f99f7b57a6f93794a2fdf021fa994d2e7555b8a 100644 (file)
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c
@@ -1533,6 +1533,33 @@ static bool ipv6_chk_same_addr(struct net *net, const struct in6_addr *addr,
        return false;
 }
 
+/* Compares an address/prefix_len with addresses on device @dev.
+ * If one is found it returns true.
+ */
+bool ipv6_chk_custom_prefix(const struct in6_addr *addr,
+       const unsigned int prefix_len, struct net_device *dev)
+{
+       struct inet6_dev *idev;
+       struct inet6_ifaddr *ifa;
+       bool ret = false;
+
+       rcu_read_lock();
+       idev = __in6_dev_get(dev);
+       if (idev) {
+               read_lock_bh(&idev->lock);
+               list_for_each_entry(ifa, &idev->addr_list, if_list) {
+                       ret = ipv6_prefix_equal(addr, &ifa->addr, prefix_len);
+                       if (ret)
+                               break;
+               }
+               read_unlock_bh(&idev->lock);
+       }
+       rcu_read_unlock();
+
+       return ret;
+}
+EXPORT_SYMBOL(ipv6_chk_custom_prefix);
+
 int ipv6_chk_prefix(const struct in6_addr *addr, struct net_device *dev)
 {
        struct inet6_dev *idev;

diff --git a/net/ipv6/sit.c b/net/ipv6/sit.c
index 21b25dd8466bc25b40d227ecf22d4d0674b7951f..9b32bba86bd35fa7b857c477a03e0e4bbb97f1a5 100644 (file)
--- a/net/ipv6/sit.c
+++ b/net/ipv6/sit.c
@@ -566,6 +566,70 @@ static inline bool is_spoofed_6rd(struct ip_tunnel *tunnel, const __be32 v4addr,
        return false;
 }
 
+/* Checks if an address matches an address on the tunnel interface.
+ * Used to detect the NAT of proto 41 packets and let them pass spoofing test.
+ * Long story:
+ * This function is called after we considered the packet as spoofed
+ * in is_spoofed_6rd.
+ * We may have a router that is doing NAT for proto 41 packets
+ * for an internal station. Destination a.a.a.a/PREFIX:bbbb:bbbb
+ * will be translated to n.n.n.n/PREFIX:bbbb:bbbb. And is_spoofed_6rd
+ * function will return true, dropping the packet.
+ * But, we can still check if is spoofed against the IP
+ * addresses associated with the interface.
+ */
+static bool only_dnatted(const struct ip_tunnel *tunnel,
+       const struct in6_addr *v6dst)
+{
+       int prefix_len;
+
+#ifdef CONFIG_IPV6_SIT_6RD
+       prefix_len = tunnel->ip6rd.prefixlen + 32
+               - tunnel->ip6rd.relay_prefixlen;
+#else
+       prefix_len = 48;
+#endif
+       return ipv6_chk_custom_prefix(v6dst, prefix_len, tunnel->dev);
+}
+
+/* Returns true if a packet is spoofed */
+static bool packet_is_spoofed(struct sk_buff *skb,
+                             const struct iphdr *iph,
+                             struct ip_tunnel *tunnel)
+{
+       const struct ipv6hdr *ipv6h;
+
+       if (tunnel->dev->priv_flags & IFF_ISATAP) {
+               if (!isatap_chksrc(skb, iph, tunnel))
+                       return true;
+
+               return false;
+       }
+
+       if (tunnel->dev->flags & IFF_POINTOPOINT)
+               return false;
+
+       ipv6h = ipv6_hdr(skb);
+
+       if (unlikely(is_spoofed_6rd(tunnel, iph->saddr, &ipv6h->saddr))) {
+               net_warn_ratelimited("Src spoofed %pI4/%pI6c -> %pI4/%pI6c\n",
+                                    &iph->saddr, &ipv6h->saddr,
+                                    &iph->daddr, &ipv6h->daddr);
+               return true;
+       }
+
+       if (likely(!is_spoofed_6rd(tunnel, iph->daddr, &ipv6h->daddr)))
+               return false;
+
+       if (only_dnatted(tunnel, &ipv6h->daddr))
+               return false;
+
+       net_warn_ratelimited("Dst spoofed %pI4/%pI6c -> %pI4/%pI6c\n",
+                            &iph->saddr, &ipv6h->saddr,
+                            &iph->daddr, &ipv6h->daddr);
+       return true;
+}
+
 static int ipip6_rcv(struct sk_buff *skb)
 {
        const struct iphdr *iph = ip_hdr(skb);
@@ -588,19 +652,9 @@ static int ipip6_rcv(struct sk_buff *skb)
                skb->protocol = htons(ETH_P_IPV6);
                skb->pkt_type = PACKET_HOST;
 
-               if (tunnel->dev->priv_flags & IFF_ISATAP) {
-                       if (!isatap_chksrc(skb, iph, tunnel)) {
-                               tunnel->dev->stats.rx_errors++;
-                               goto out;
-                       }
-               } else if (!(tunnel->dev->flags&IFF_POINTOPOINT)) {
-                       if (is_spoofed_6rd(tunnel, iph->saddr,
-                                          &ipv6_hdr(skb)->saddr) ||
-                           is_spoofed_6rd(tunnel, iph->daddr,
-                                          &ipv6_hdr(skb)->daddr)) {
-                               tunnel->dev->stats.rx_errors++;
-                               goto out;
-                       }
+               if (packet_is_spoofed(skb, iph, tunnel)) {
+                       tunnel->dev->stats.rx_errors++;
+                       goto out;
                }
 
                __skb_tunnel_rx(skb, tunnel->dev);
@@ -752,7 +806,7 @@ static netdev_tx_t ipip6_tunnel_xmit(struct sk_buff *skb,
                        neigh = dst_neigh_lookup(skb_dst(skb), &iph6->daddr);
 
                if (neigh == NULL) {
-                       net_dbg_ratelimited("sit: nexthop == NULL\n");
+                       net_dbg_ratelimited("nexthop == NULL\n");
                        goto tx_error;
                }
 
@@ -781,7 +835,7 @@ static netdev_tx_t ipip6_tunnel_xmit(struct sk_buff *skb,
                        neigh = dst_neigh_lookup(skb_dst(skb), &iph6->daddr);
 
                if (neigh == NULL) {
-                       net_dbg_ratelimited("sit: nexthop == NULL\n");
+                       net_dbg_ratelimited("nexthop == NULL\n");
                        goto tx_error;
                }