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

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>

1 files changed, 27 insertions, 0 deletions

diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
index d6ff12617f36..a0c3abe72461 100644
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c
@@ -1499,6 +1499,33 @@ 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;