[Patch net] ip6mr: avoid double unregister of pim6reg device

[Cong Wang <xiyou.wangcong@gmail.com>]

If we unregister the pim6reg device via default_device_exit_batch(),
we will receive a notification and ip6mr_device_event() will
unregister it again. This causes a kernel BUG at net/core/dev.c:6813.

Like commit 7dc00c82cbb0 ("ipv4: Fix ipmr unregister device oops")
we should avoid double-unregister in netdevice notifier.

Reported-by: Andrey Konovalov <andreyknvl@google.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
---
 net/ipv6/ip6mr.c | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/net/ipv6/ip6mr.c b/net/ipv6/ip6mr.c
index 6ba6c90..72bee6d 100644
--- a/net/ipv6/ip6mr.c
+++ b/net/ipv6/ip6mr.c
@@ -774,7 +774,8 @@ static struct net_device *ip6mr_reg_vif(struct net *net, struct mr6_table *mrt)
  *	Delete a VIF entry
  */
 
-static int mif6_delete(struct mr6_table *mrt, int vifi, struct list_head *head)
+static int mif6_delete(struct mr6_table *mrt, int vifi, struct list_head *head,
+		       bool unreg)
 {
 	struct mif_device *v;
 	struct net_device *dev;
@@ -820,7 +821,7 @@ static int mif6_delete(struct mr6_table *mrt, int vifi, struct list_head *head)
 					     dev->ifindex, &in6_dev->cnf);
 	}
 
-	if (v->flags & MIFF_REGISTER)
+	if ((v->flags & MIFF_REGISTER) && unreg)
 		unregister_netdevice_queue(dev, head);
 
 	dev_put(dev);
@@ -1340,7 +1341,7 @@ static int ip6mr_device_event(struct notifier_block *this,
 		v = &mrt->vif6_table[0];
 		for (ct = 0; ct < mrt->maxvif; ct++, v++) {
 			if (v->dev == dev)
-				mif6_delete(mrt, ct, &list);
+				mif6_delete(mrt, ct, &list, false);
 		}
 	}
 	unregister_netdevice_many(&list);
@@ -1552,7 +1553,7 @@ static void mroute_clean_tables(struct mr6_table *mrt, bool all)
 	for (i = 0; i < mrt->maxvif; i++) {
 		if (!all && (mrt->vif6_table[i].flags & VIFF_STATIC))
 			continue;
-		mif6_delete(mrt, i, &list);
+		mif6_delete(mrt, i, &list, true);
 	}
 	unregister_netdevice_many(&list);
 
@@ -1707,7 +1708,7 @@ int ip6_mroute_setsockopt(struct sock *sk, int optname, char __user *optval, uns
 		if (copy_from_user(&mifi, optval, sizeof(mifi_t)))
 			return -EFAULT;
 		rtnl_lock();
-		ret = mif6_delete(mrt, mifi, NULL);
+		ret = mif6_delete(mrt, mifi, NULL, true);
 		rtnl_unlock();
 		return ret;
 
-- 
2.5.5