Merge branch 'net-ipv4-fix-circular-list-infinite-loop'

Florian Westphal says:

====================
net: ipv4: fix circular-list infinite loop

Tariq and Ran reported a regression caused by net-next commit
2638eb8b ("net: ipv4: provide __rcu annotation for ifa_list").

This happens when net.ipv4.conf.$dev.promote_secondaries sysctl is
enabled -- we can arrange for ifa->next to point at ifa, so next
process that tries to walk the list loops forever.

Fix this and extend rtnetlink.sh with a small test case for this.
====================
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/devinet.c

@@ -428,8 +428,9 @@ static void __inet_del_ifa(struct in_device *in_dev,
 		if (prev_prom) {
 			struct in_ifaddr *last_sec;
 
-			last_sec = rtnl_dereference(last_prim->ifa_next);
 			rcu_assign_pointer(prev_prom->ifa_next, next_sec);
+
+			last_sec = rtnl_dereference(last_prim->ifa_next);
 			rcu_assign_pointer(promote->ifa_next, last_sec);
 			rcu_assign_pointer(last_prim->ifa_next, promote);
 		}

tools/testing/selftests/net/rtnetlink.sh

@@ -269,6 +269,25 @@ kci_test_addrlft()
 	echo "PASS: preferred_lft addresses have expired"
 }
 
+kci_test_promote_secondaries()
+{
+	promote=$(sysctl -n net.ipv4.conf.$devdummy.promote_secondaries)
+
+	sysctl -q net.ipv4.conf.$devdummy.promote_secondaries=1
+
+	for i in $(seq 2 254);do
+		IP="10.23.11.$i"
+		ip -f inet addr add $IP/16 brd + dev "$devdummy"
+		ifconfig "$devdummy" $IP netmask 255.255.0.0
+	done
+
+	ip addr flush dev "$devdummy"
+
+	[ $promote -eq 0 ] && sysctl -q net.ipv4.conf.$devdummy.promote_secondaries=0
+
+	echo "PASS: promote_secondaries complete"
+}
+
 kci_test_addrlabel()
 {
 	ret=0
@@ -1161,6 +1180,7 @@ kci_test_rtnl()
 	kci_test_polrouting
 	kci_test_route_get
 	kci_test_addrlft
+	kci_test_promote_secondaries
 	kci_test_tc
 	kci_test_gre
 	kci_test_gretap