[PATCH] net: ipv6: Fix warning of freeing alive inet6 address

[Mike Manning <mmanning@brocade.com>]

While this is not reproducible manually, Andrey's syzkaller program hit
the warning "IPv6: Freeing alive inet6 address" with this part trace:

inet6_ifa_finish_destroy+0x12e/0x190 c:894
in6_ifa_put ./include/net/addrconf.h:330
addrconf_dad_work+0x4e9/0x1040 net/ipv6/addrconf.c:3963

The fix is to call in6_ifa_put() for the inet6_ifaddr before rather
than after calling addrconf_ifdown(), as the latter may remove it from
the address hash table.

Fixes: 85b51b12115c ("net: ipv6: Remove addresses for failures with strict DAD")
Reported-by: Andrey Konovalov <andreyknvl@google.com>
Signed-off-by: Mike Manning <mmanning@brocade.com>
---
 net/ipv6/addrconf.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
index 80ce478..361993a 100644
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c
@@ -3902,8 +3902,11 @@ static void addrconf_dad_work(struct work_struct *w)
 	} else if (action == DAD_ABORT) {
 		in6_ifa_hold(ifp);
 		addrconf_dad_stop(ifp, 1);
-		if (disable_ipv6)
+		if (disable_ipv6) {
+			in6_ifa_put(ifp);
 			addrconf_ifdown(idev->dev, 0);
+			goto unlock;
+		}
 		goto out;
 	}
 
@@ -3950,6 +3953,7 @@ static void addrconf_dad_work(struct work_struct *w)
 		      ifp->dad_nonce);
 out:
 	in6_ifa_put(ifp);
+unlock:
 	rtnl_unlock();
 }
 
-- 
2.1.4