IPv6: do not create temporary adresses with too short preferred lifetime

From RFC341:
A temporary address is created only if this calculated Preferred
Lifetime is greater than REGEN_ADVANCE time units.  In particular, an
implementation must not create a temporary address with a zero
Preferred Lifetime.
Signed-off-by: Benoit Boissinot <benoit.boissinot@ens-lyon.org>
Signed-off-by: YOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv6/addrconf.c

@@ -776,6 +776,7 @@ static int ipv6_create_tempaddr(struct inet6_ifaddr *ifp, struct inet6_ifaddr *i
 	struct inet6_dev *idev = ifp->idev;
 	struct in6_addr addr, *tmpaddr;
 	unsigned long tmp_prefered_lft, tmp_valid_lft, tmp_cstamp, tmp_tstamp;
+	unsigned long regen_advance;
 	int tmp_plen;
 	int ret = 0;
 	int max_addresses;
@@ -836,8 +837,23 @@ retry:
 	tmp_tstamp = ifp->tstamp;
 	spin_unlock_bh(&ifp->lock);
 
+	regen_advance = idev->cnf.regen_max_retry *
+	                idev->cnf.dad_transmits *
+	                idev->nd_parms->retrans_time / HZ;
 	write_unlock(&idev->lock);
 
+	/* A temporary address is created only if this calculated Preferred
+	 * Lifetime is greater than REGEN_ADVANCE time units.  In particular,
+	 * an implementation must not create a temporary address with a zero
+	 * Preferred Lifetime.
+	 */
+	if (tmp_prefered_lft <= regen_advance) {
+		in6_ifa_put(ifp);
+		in6_dev_put(idev);
+		ret = -1;
+		goto out;
+	}
+
 	addr_flags = IFA_F_TEMPORARY;
 	/* set in addrconf_prefix_rcv() */
 	if (ifp->flags & IFA_F_OPTIMISTIC)