Subject: [PATCH 02/30] ipv6: avoid unregistering inet6_dev for loopback

From: WANG Cong <[email-masked]>
Date: Wed, 21 Jun 2017 14:34:58 -0700

[ Upstream commit 60abc0be96e00ca71bac083215ac91ad2e575096 ]

The per netns loopback_dev->ip6_ptr is unregistered and set to
NULL when its mtu is set to smaller than IPV6_MIN_MTU, this
leads to that we could set rt->rt6i_idev NULL after a
rt6_uncached_list_flush_dev() and then crash after another
call.

In this case we should just bring its inet6_dev down, rather
than unregistering it, at least prior to commit 176c39af29bc
("netns: fix addrconf_ifdown kernel panic") we always
override the case for loopback.

Thanks a lot to Andrey for finding a reliable reproducer.

Fixes: 176c39af29bc ("netns: fix addrconf_ifdown kernel panic")
Reported-by: Andrey Konovalov <[email-masked]>
Cc: Andrey Konovalov <[email-masked]>
Cc: Daniel Lezcano <[email-masked]>
Cc: David Ahern <[email-masked]>
Signed-off-by: Cong Wang <[email-masked]>
Acked-by: David Ahern <[email-masked]>
Tested-by: Andrey Konovalov <[email-masked]>
Signed-off-by: David S. Miller <[email-masked]>
---
 net/ipv6/addrconf.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
index 9725e8faf56d..177eee060027 100644
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c
@@ -3334,6 +3334,7 @@ static int addrconf_notify(struct notifier_block *this, unsigned long event,
 	struct net_device *dev = netdev_notifier_info_to_dev(ptr);
 	struct netdev_notifier_changeupper_info *info;
 	struct inet6_dev *idev = __in6_dev_get(dev);
+	struct net *net = dev_net(dev);
 	int run_pending = 0;
 	int err;
 
@@ -3349,7 +3350,7 @@ static int addrconf_notify(struct notifier_block *this, unsigned long event,
 	case NETDEV_CHANGEMTU:
 		/* if MTU under IPV6_MIN_MTU stop IPv6 on this interface. */
 		if (dev->mtu < IPV6_MIN_MTU) {
-			addrconf_ifdown(dev, 1);
+			addrconf_ifdown(dev, dev != net->loopback_dev);
 			break;
 		}
 
@@ -3465,7 +3466,7 @@ static int addrconf_notify(struct notifier_block *this, unsigned long event,
 			 * IPV6_MIN_MTU stop IPv6 on this interface.
 			 */
 			if (dev->mtu < IPV6_MIN_MTU)
-				addrconf_ifdown(dev, 1);
+				addrconf_ifdown(dev, dev != net->loopback_dev);
 		}
 		break;
 
-- 
2.13.0