ipv4: reset rt_iif for recirculated mcast/bcast out pkts

Multicast or broadcast egress packets have rt_iif set to the oif. These
packets might be recirculated back as input and lookup to the raw
sockets may fail because they are bound to the incoming interface
(skb_iif). If rt_iif is not zero, during the lookup, inet_iif() function
returns rt_iif instead of skb_iif. Hence, the lookup fails.

v2: Make it non vrf specific (David Ahern). Reword the changelog to
    reflect it.
Signed-off-by: Stephen Suryaputra <ssuryaextr@gmail.com>
Reviewed-by: David Ahern <dsahern@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 12 insertions, 0 deletions

diff --git a/net/ipv4/ip_output.c b/net/ipv4/ip_output.c
index 16f9159234a2..8c2ec35b6512 100644
--- a/net/ipv4/ip_output.c
+++ b/net/ipv4/ip_output.c
@@ -318,6 +318,7 @@ static int ip_finish_output(struct net *net, struct sock *sk, struct sk_buff *sk
 static int ip_mc_finish_output(struct net *net, struct sock *sk,
                                struct sk_buff *skb)
 {
+        struct rtable *new_rt;
         int ret;
 
         ret = BPF_CGROUP_RUN_PROG_INET_EGRESS(sk, skb);
@@ -326,6 +327,17 @@ static int ip_mc_finish_output(struct net *net, struct sock *sk,
                 return ret;
         }
 
+        /* Reset rt_iif so that inet_iif() will return skb->skb_iif. Setting
+         * this to non-zero causes ipi_ifindex in in_pktinfo to be overwritten,
+         * see ipv4_pktinfo_prepare().
+         */
+        new_rt = rt_dst_clone(net->loopback_dev, skb_rtable(skb));
+        if (new_rt) {
+                new_rt->rt_iif = 0;
+                skb_dst_drop(skb);
+                skb_dst_set(skb, &new_rt->dst);
+        }
+
         return dev_loopback_xmit(net, sk, skb);
 }