sysctl: ipv6: use correct net in ipv6_sysctl_rtcache_flush

Before this patch issuing these commands:

  fd = open("/proc/sys/net/ipv6/route/flush")
  unshare(CLONE_NEWNET)
  write(fd, "stuff")

would flush the newly created net, not the original one.

The equivalent ipv4 code is correct (stores the net inside ->extra1).
Acked-by: Daniel Lezcano <daniel.lezcano@free.fr>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv6/route.c

@@ -2557,14 +2557,16 @@ static
 int ipv6_sysctl_rtcache_flush(ctl_table *ctl, int write,
 			      void __user *buffer, size_t *lenp, loff_t *ppos)
 {
-	struct net *net = current->nsproxy->net_ns;
-	int delay = net->ipv6.sysctl.flush_delay;
-	if (write) {
-		proc_dointvec(ctl, write, buffer, lenp, ppos);
-		fib6_run_gc(delay <= 0 ? ~0UL : (unsigned long)delay, net);
-		return 0;
-	} else
+	struct net *net;
+	int delay;
+	if (!write)
 		return -EINVAL;
+
+	net = (struct net *)ctl->extra1;
+	delay = net->ipv6.sysctl.flush_delay;
+	proc_dointvec(ctl, write, buffer, lenp, ppos);
+	fib6_run_gc(delay <= 0 ? ~0UL : (unsigned long)delay, net);
+	return 0;
 }
 
 ctl_table ipv6_route_table_template[] = {
@@ -2651,6 +2653,7 @@ struct ctl_table * __net_init ipv6_route_sysctl_init(struct net *net)
 
 	if (table) {
 		table[0].data = &net->ipv6.sysctl.flush_delay;
+		table[0].extra1 = net;
 		table[1].data = &net->ipv6.ip6_dst_ops.gc_thresh;
 		table[2].data = &net->ipv6.sysctl.ip6_rt_max_size;
 		table[3].data = &net->ipv6.sysctl.ip6_rt_gc_min_interval;