[IPV6]: ipv6_fl_socklist is inadvertently shared.

The ipv6_fl_socklist from listening socket is inadvertently shared
with new socket created for connection.  This leads to a variety of
interesting, but fatal, bugs. For example, removing one of the
sockets may lead to the other socket's encountering a page fault
when the now freed list is referenced.

The fix is to not share the flow label list with the new socket.
Signed-off-by: Masayuki Nakagawa <nakagawa.msy@ncos.nec.co.jp>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv6/tcp_ipv6.c

@@ -1453,6 +1453,7 @@ static struct sock * tcp_v6_syn_recv_sock(struct sock *sk, struct sk_buff *skb,
 	   First: no IPv4 options.
 	 */
 	newinet->opt = NULL;
+	newnp->ipv6_fl_list = NULL;
 
 	/* Clone RX bits */
 	newnp->rxopt.all = np->rxopt.all;