[SRU][Trusty][PATCH 1/2] ipv6: reallocate addrconf router for ipv6 address when lo device up

[Joseph Salisbury]

From: Gao feng <gaofeng at cn.fujitsu.com>

BugLink: http://bugs.launchpad.net/bugs/1634545

commit 25fb6ca4ed9cad72f14f61629b68dc03c0d9713f
"net IPv6 : Fix broken IPv6 routing table after loopback down-up"
allocates addrconf router for ipv6 address when lo device up.
but commit a881ae1f625c599b460cc8f8a7fcb1c438f699ad
"ipv6:don't call addrconf_dst_alloc again when enable lo" breaks
this behavior.

Since the addrconf router is moved to the garbage list when
lo device down, we should release this router and rellocate
a new one for ipv6 address when lo device up.

This patch solves bug 67951 on bugzilla
https://bugzilla.kernel.org/show_bug.cgi?id=67951

change from v1:
use ip6_rt_put to repleace ip6_del_rt, thanks Hannes!
change code style, suggested by Sergei.

CC: Sabrina Dubroca <sd at queasysnail.net>
CC: Hannes Frederic Sowa <hannes at stressinduktion.org>
Reported-by: Weilong Chen <chenweilong at huawei.com>
Signed-off-by: Weilong Chen <chenweilong at huawei.com>
Signed-off-by: Gao feng <gaofeng at cn.fujitsu.com>
Acked-by: Hannes Frederic Sowa <hannes at stressinduktion.org>
Signed-off-by: David S. Miller <davem at davemloft.net>
(cherry picked from commit 33d99113b1102c2d2f8603b9ba72d89d915c13f5)
Signed-off-by: Joseph Salisbury <joseph.salisbury at canonical.com>
---
 net/ipv6/addrconf.c | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
index 9b00640..4aabb5f 100644
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c
@@ -2619,8 +2619,18 @@ static void init_loopback(struct net_device *dev)
 			if (sp_ifa->flags & (IFA_F_DADFAILED | IFA_F_TENTATIVE))
 				continue;
 
-			if (sp_ifa->rt)
-				continue;
+			if (sp_ifa->rt) {
+				/* This dst has been added to garbage list when
+				 * lo device down, release this obsolete dst and
+				 * reallocate a new router for ifa.
+				 */
+				if (sp_ifa->rt->dst.obsolete > 0) {
+					ip6_rt_put(sp_ifa->rt);
+					sp_ifa->rt = NULL;
+				} else {
+					continue;
+				}
+			}
 
 			sp_rt = addrconf_dst_alloc(idev, &sp_ifa->addr, false);
 
-- 
2.7.4