sit: fix off-by-one in ipip6_tunnel_get_prl

When requesting all prl entries (kprl.addr == INADDR_ANY) and there are
more prl entries than there is space passed from userspace, the existing
code would always copy cmax+1 entries, which is more than can be handled.

This patch makes the kernel copy only exactly cmax entries.
Signed-off-by: Sascha Hlusiak <contact@saschahlusiak.de>
Acked-By: Fred L. Templin <Fred.L.Templin@boeing.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv6/sit.c

@@ -274,7 +274,7 @@ static int ipip6_tunnel_get_prl(struct ip_tunnel *t,
 
 	c = 0;
 	for (prl = t->prl; prl; prl = prl->next) {
-		if (c > cmax)
+		if (c >= cmax)
 			break;
 		if (kprl.addr != htonl(INADDR_ANY) && prl->addr != kprl.addr)
 			continue;