dccp: do not use ipv6 header for ipv4 flow

BugLink: https://bugs.launchpad.net/bugs/1826212

[ Upstream commit e0aa6770 ]

When a dual stack dccp listener accepts an ipv4 flow,
it should not attempt to use an ipv6 header or
inet6_iif() helper.

Fixes: 3df80d93 ("[DCCP]: Introduce DCCPv6")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

net/dccp/ipv6.c

@@ -427,8 +427,8 @@ static struct sock *dccp_v6_request_recv_sock(const struct sock *sk,
 		newnp->ipv6_mc_list = NULL;
 		newnp->ipv6_ac_list = NULL;
 		newnp->ipv6_fl_list = NULL;
-		newnp->mcast_oif   = inet6_iif(skb);
-		newnp->mcast_hops  = ipv6_hdr(skb)->hop_limit;
+		newnp->mcast_oif   = inet_iif(skb);
+		newnp->mcast_hops  = ip_hdr(skb)->ttl;
 
 		/*
 		 * No need to charge this sock to the relevant IPv6 refcnt debug socks count