Merge branch 'ipv4-fix-bugs-when-enable-route_localnet'

Shijie Luo says:

====================
ipv4: fix bugs when enable route_localnet

When enable route_localnet, route of the 127/8 address is enabled.
But in some situations like arp_announce=2, ARP requests or reply
work abnormally.

This patchset fix some bugs when enable route_localnet.

Change History:
V2:
- Change a single patch to a patchset.
- Add bug fix for arp_ignore = 3.
- Add a couple of test for enabling route_localnet in selftests.
====================
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/devinet.c

@@ -1287,6 +1287,7 @@ __be32 inet_select_addr(const struct net_device *dev, __be32 dst, int scope)
 {
 	const struct in_ifaddr *ifa;
 	__be32 addr = 0;
+	unsigned char localnet_scope = RT_SCOPE_HOST;
 	struct in_device *in_dev;
 	struct net *net = dev_net(dev);
 	int master_idx;
@@ -1296,10 +1297,13 @@ __be32 inet_select_addr(const struct net_device *dev, __be32 dst, int scope)
 	if (!in_dev)
 		goto no_in_dev;
 
+	if (unlikely(IN_DEV_ROUTE_LOCALNET(in_dev)))
+		localnet_scope = RT_SCOPE_LINK;
+
 	in_dev_for_each_ifa_rcu(ifa, in_dev) {
 		if (ifa->ifa_flags & IFA_F_SECONDARY)
 			continue;
-		if (ifa->ifa_scope > scope)
+		if (min(ifa->ifa_scope, localnet_scope) > scope)
 			continue;
 		if (!dst || inet_ifa_match(dst, ifa)) {
 			addr = ifa->ifa_local;
@@ -1352,14 +1356,20 @@ EXPORT_SYMBOL(inet_select_addr);
 static __be32 confirm_addr_indev(struct in_device *in_dev, __be32 dst,
 			      __be32 local, int scope)
 {
+	unsigned char localnet_scope = RT_SCOPE_HOST;
 	const struct in_ifaddr *ifa;
 	__be32 addr = 0;
 	int same = 0;
 
+	if (unlikely(IN_DEV_ROUTE_LOCALNET(in_dev)))
+		localnet_scope = RT_SCOPE_LINK;
+
 	in_dev_for_each_ifa_rcu(ifa, in_dev) {
+		unsigned char min_scope = min(ifa->ifa_scope, localnet_scope);
+
 		if (!addr &&
 		    (local == ifa->ifa_local || !local) &&
-		    ifa->ifa_scope <= scope) {
+		    min_scope <= scope) {
 			addr = ifa->ifa_local;
 			if (same)
 				break;
@@ -1374,7 +1384,7 @@ static __be32 confirm_addr_indev(struct in_device *in_dev, __be32 dst,
 				if (inet_ifa_match(addr, ifa))
 					break;
 				/* No, then can we use new local src? */
-				if (ifa->ifa_scope <= scope) {
+				if (min_scope <= scope) {
 					addr = ifa->ifa_local;
 					break;
 				}

tools/testing/selftests/net/route_localnet.sh

+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0
+#
+# Run a couple of tests when route_localnet = 1.
+
+readonly PEER_NS="ns-peer-$(mktemp -u XXXXXX)"
+
+setup() {
+    ip netns add "${PEER_NS}"
+    ip -netns "${PEER_NS}" link set dev lo up
+    ip link add name veth0 type veth peer name veth1
+    ip link set dev veth0 up
+    ip link set dev veth1 netns "${PEER_NS}"
+
+    # Enable route_localnet and delete useless route 127.0.0.0/8.
+    sysctl -w net.ipv4.conf.veth0.route_localnet=1
+    ip netns exec "${PEER_NS}" sysctl -w net.ipv4.conf.veth1.route_localnet=1
+    ip route del 127.0.0.0/8 dev lo table local
+    ip netns exec "${PEER_NS}" ip route del 127.0.0.0/8 dev lo table local
+
+    ifconfig veth0 127.25.3.4/24 up
+    ip netns exec "${PEER_NS}" ifconfig veth1 127.25.3.14/24 up
+
+    ip route flush cache
+    ip netns exec "${PEER_NS}" ip route flush cache
+}
+
+cleanup() {
+    ip link del veth0
+    ip route add local 127.0.0.0/8 dev lo proto kernel scope host src 127.0.0.1
+    local -r ns="$(ip netns list|grep $PEER_NS)"
+    [ -n "$ns" ] && ip netns del $ns 2>/dev/null
+}
+
+# Run test when arp_announce = 2.
+run_arp_announce_test() {
+    echo "run arp_announce test"
+    setup
+
+    sysctl -w net.ipv4.conf.veth0.arp_announce=2
+    ip netns exec "${PEER_NS}" sysctl -w net.ipv4.conf.veth1.arp_announce=2
+    ping -c5 -I veth0 127.25.3.14
+    if [ $? -ne 0 ];then
+        echo "failed"
+    else
+        echo "ok"
+    fi
+
+    cleanup
+}
+
+# Run test when arp_ignore = 3.
+run_arp_ignore_test() {
+    echo "run arp_ignore test"
+    setup
+
+    sysctl -w net.ipv4.conf.veth0.arp_ignore=3
+    ip netns exec "${PEER_NS}" sysctl -w net.ipv4.conf.veth1.arp_ignore=3
+    ping -c5 -I veth0 127.25.3.14
+    if [ $? -ne 0 ];then
+        echo "failed"
+    else
+        echo "ok"
+    fi
+
+    cleanup
+}
+
+run_all_tests() {
+    run_arp_announce_test
+    run_arp_ignore_test
+}
+
+run_all_tests