udp: Increment UDP_MIB_IGNOREDMULTI for arriving unmatched multicasts

As NIC multicast filtering isn't perfect, and some platforms are
quite content to spew broadcasts, we should not trigger an event
for skb:kfree_skb when we do not have a match for such an incoming
datagram.  We do though want to avoid sweeping the matter under the
rug entirely, so increment a suitable statistic.

This incorporates feedback from David L. Stevens, Karl Neiss and Eric
Dumazet.

V3 - use bool per David Miller

Signed-off-by: Rick Jones <rick.jones2@hp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 9 insertions, 3 deletions

diff --git a/net/ipv6/proc.c b/net/ipv6/proc.c
index 1752cd0b4882..679253d0af84 100644
--- a/net/ipv6/proc.c
+++ b/net/ipv6/proc.c
@@ -136,6 +136,7 @@ static const struct snmp_mib snmp6_udp6_list[] = {
         SNMP_MIB_ITEM("Udp6RcvbufErrors", UDP_MIB_RCVBUFERRORS),
         SNMP_MIB_ITEM("Udp6SndbufErrors", UDP_MIB_SNDBUFERRORS),
         SNMP_MIB_ITEM("Udp6InCsumErrors", UDP_MIB_CSUMERRORS),
+        SNMP_MIB_ITEM("Udp6IgnoredMulti", UDP_MIB_IGNOREDMULTI),
         SNMP_MIB_SENTINEL
 };
 
diff --git a/net/ipv6/udp.c b/net/ipv6/udp.c
index 9b6809232b17..b756355e9739 100644
--- a/net/ipv6/udp.c
+++ b/net/ipv6/udp.c
@@ -771,7 +771,7 @@ static void udp6_csum_zero_error(struct sk_buff *skb)
  */
 static int __udp6_lib_mcast_deliver(struct net *net, struct sk_buff *skb,
                 const struct in6_addr *saddr, const struct in6_addr *daddr,
-                struct udp_table *udptable)
+                struct udp_table *udptable, int proto)
 {
         struct sock *sk, *stack[256 / sizeof(struct sock *)];
         const struct udphdr *uh = udp_hdr(skb);
@@ -781,6 +781,7 @@ static int __udp6_lib_mcast_deliver(struct net *net, struct sk_buff *skb,
         int dif = inet6_iif(skb);
         unsigned int count = 0, offset = offsetof(typeof(*sk), sk_nulls_node);
         unsigned int hash2 = 0, hash2_any = 0, use_hash2 = (hslot->count > 10);
+        bool inner_flushed = false;
 
         if (use_hash2) {
                 hash2_any = udp6_portaddr_hash(net, &in6addr_any, hnum) &
@@ -803,6 +804,7 @@ start_lookup:
                     (uh->check || udp_sk(sk)->no_check6_rx)) {
                         if (unlikely(count == ARRAY_SIZE(stack))) {
                                 flush_stack(stack, count, skb, ~0);
+                                inner_flushed = true;
                                 count = 0;
                         }
                         stack[count++] = sk;
@@ -821,7 +823,10 @@ start_lookup:
         if (count) {
                 flush_stack(stack, count, skb, count - 1);
         } else {
-                kfree_skb(skb);
+                if (!inner_flushed)
+                        UDP_INC_STATS_BH(net, UDP_MIB_IGNOREDMULTI,
+                                         proto == IPPROTO_UDPLITE);
+                consume_skb(skb);
         }
         return 0;
 }
@@ -873,7 +878,7 @@ int __udp6_lib_rcv(struct sk_buff *skb, struct udp_table *udptable,
          */
         if (ipv6_addr_is_multicast(daddr))
                 return __udp6_lib_mcast_deliver(net, skb,
-                                saddr, daddr, udptable);
+                                saddr, daddr, udptable, proto);
 
         /* Unicast */